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Joenpate56
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I am replacing the old belt as it is several years
(10+) old.
The car runs. Can i just remove the old one and put the new one on without moving any of the gears. then set the tension.

Thanks

answerman
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Here. I have a very detailed explanation of how I did it (because I don't trust the gears to not turn). Probably overkill, but way less margin for error.

The approach I used (got the idea from a friend who's a Lotus afficianado) was to set the engine at TDC with the 110 marks lined up, then take a bottle of WhiteOut and mark each gear (both cams, crank, and ignition) with a mark on one slot, and mark the old belt with a corresponding mark on the tooth in that slot. Once I had done that, it was a simple matter to remove the belt, line it up with the new one, mark the corresponding teeth on the new belt (counting the teeth between the marks to be sure) and then pop the new belt on in the appropriate location. Worked just fine, the whole process took maybe 3 hours from start to finish... I was in no hurry and I am sure it would go faster the next time since I now know exactly what has to be removed to get at it.

For posterity, here's the order I did things (I used Greg's guide as a, well, guide, but there was more to be done than he had outlined:

1. Disconnect battery and coil wires, just because.

2. Remove top half of belt guard (I have the two piece guard)

3. Attempt to remove bottom half of guard. Grumble because it won't come out at this point, too much stuff in the way.

4. Loosen alternator, remove belt. Remove fan and pulley. Skin knuckles a bunch because of proximity to radiator.

5. Look down and realize that the lower guard still isn't going to come off.

6. Remove crank pulley. This went way better than I had expected... put a 19mm socket on my ratchet, put a pipe on the handle, and had Mrs. Answerman stand on the brake pedal (since I've never had a functioning hand brake) while I first hit my knuckle with a rubber mallet (ouch!) and then the pipe a few times to break it loose. Moved engine BACK to TDC since of course it moved during this process.

7. Now I can remove the lower belt guard. Did so.

8. Got my bottle of WhiteOut and marked one tooth/slot combination on each of the 4 gears.

9. Loosened tensioner and pulled belt off the gears. Loosened upper radiator hose clamp at top of engine, pulled hose off the fitting, and snuck the belt through there. Old belt is off!

10. Removed tensioner (that actually came out fairly easily).

11. Took tensioner to bench, followed Greg's process at http://www.jensenhealey.com/tech/bearing/bearing.html to disassemble tensioner and replace the bearings. The old ones seemed fine, but since I went this far I didn't see a compelling reason to NOT replace them.

12. Put newly assembled tensioner in place, loosely.

13. Take new belt, count teeth and make new WhiteOut marks corresponding with marks on old belt.

14. Put new belt on. Take belt off, put on again because I was one tooth off on the crank gear. Triple check all marks and deem it good.

15. Tighten tensioner till the belt tension seemed about like it was on the old one (was able to twist it about 45 degrees between the oil pump/distributor gear and the intake gear).

16. Think about it for a while and decide that I am going to be one of the 12 JH owners that still has the belt guard in place. Put the lower section back on.

17. Reinstall crank pulley and fan/pulley.

18. Reinstall alternator belt and tighten.

19. Reinstall top half of belt guard.

20. Reconnect coil wire and battery cables.

21. Say a little prayer, get in, and turn key. Starts right up and seems to run as well as she ever did. Whew.

Joenpate56
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Thanks Answerman: I really appreciate the detail. My belt should arrive today so maybe I can attack the project over the weekend.

Brett Gibson JH5 20497
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I heard that one approach is to cut the belt on the engine in half, length wise, then slide the new belt onto the pulleys, once on cut the old belt off then slide the new one the remainder, have not used this method myself but maybe at some point I will give it a try.

dwalls1
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I am going to salt this one away for the future. It sounds so simple and reasonable, there must be something wrong with it.

Joenpate56
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What would you use to cut the belt. Its pretty tough stuff.\?

Brett Gibson JH5 20497
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I cut one up just to see how tuff they are with an "OLFA" Knife box cutter, takes a little time but slices's it up. http://www.olfaproducts.com/ProductDetail.jsp?LISTID=370000-1137370779

Joenpate56
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i may try the cutting proceedure but i will mark everything up as Answerman detailed.
thanks for all the suggestions

JPJH
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Any advice on which tension gauge to use in setting the new cam belt tension?

Esprit2
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Brett Gibson JH5 20497 wrote:
(Snip)... cut the belt on the engine in half, length wise, then slide the new belt onto the pulleys (Snip)...dwalls1 wrote:
(Snip)... It sounds so simple and reasonable, there must be something wrong with it.That method, and using paint marks, etc-etc, are all ways of preserving the existing cam timing; however, neither makes sure the resulting timing is correct. If the timing was previously off a tooth, or more, all these methods do is preserve what was, even if it was wrong.

It's not difficult to time the engine from scratch, and doing so makes sure timing is correct.

Regards,
Tim Engel

Last edited on 11-12-2016 05:22 pm by Esprit2

Esprit2
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Joenpate56 wrote:
I am replacing the old belt as it is several years
(10+) old.
The black, trapezoidal tooth timing belt is supposed to be replaced every 24k miles or 24 months, whichever comes first. I hope the 10+ years was not running, in storage.(Snip)... Can i just remove the old one and put the new one on without moving any of the gears. then set the tension.You can, but if the timing is set to book-spec, then it's an emissions setting. You can pick-up 10 hp by setting both the intake and exhaust pulleys to 110 MOP timing. Doing that will require removing both pulleys, flipping them over, and setting the timing by using marks that may not be on your pulleys (some pulleys have dual 110/115 timing dots, and some just have one... 115 MOP). See the recent JHPS discussion, here:
http://www.jensenhealey.com/forums/view_topic.php?id=1293&forum_id=2&page=4
Pick-up the discussion on page 4, message 65... onward.

For detailed instructions on replacing the timing belt, go to the Jensen-Healey page on Facebook.com, click on FILES in the upper-left margin, and download the Word.doc on the how to replace the timing belt. Or just go here:
https://www.facebook.com/groups/102760143109766/files/

Or PM me with your email address, and I'll send to you as a file attachment.

Regards,
Tim Engel

qwerty
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Me again :)

You can also replace the standard belt with a gates racing belt for apparently 3x the life.
Gates Part # T104RB

I receieved mine, confirmed trapezoidal tooth shape.

Esprit2
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qwerty wrote:
You can also replace the standard belt with a gates racing belt for apparently 3x the life.
Gates Part # T104RB
The Gates Racing blue timing belts are a definite step up in durability. The other plus is that the blue belts are very stable, and it should not be necessary to re-tension the belt for a long time. Continue to check the tension on the normal schedule, but it should rarely be necessary to make a tension adjustment.

The only problem is that Lotus isn't doing any new parts development work on an engine that went out of production approx 36 years ago (907 with trapezoidal belt), and Gates Racing won't make decisions/ specs for another company's product (a Lotus engine). As a result, there is no official tension spec, and no corporate effort to establish one.

There has been a Gates Racing blue belt for the round-tooth HTD belt for several years, and a pretty strong grassroots effort to zero in on a correct tension (mostly on the TurboEsprit list on YahooGroups). At the Lotus tension spec, the blue belt has a pronounced whine, which indicates it is too tight. With a lot of users reporting results, it now appears that 82-84 on a Burroughs gauge is about right for the HTD. But, the Burroughs gauge is thickness sensitive, and the blue HTD is thicker than the old black belts. So while a 'reading' of 82-84 works, I can't say exactly what the actual tension in the belt is. I suspect that it's something in the 90 range, but can't say for certain.

If you really want longer belt life, then the best solution is to convert to HTD pulleys, then go with the Gates Racing blue belt. Still hold the mileage limit down to about 50k miles, but ten years should be reasonable for a time limit.

Short of converting to HTD, the Gates Racing #T104RB blue belt is the best trapezoidal-tooth belt option available, but it's going to take another grassroots effort to zero-in on a consensus tension for it.

Somebody needs to go first. Looks like that's you. I highly recommend that you tension it using a Burroughs gauge so that the data is easier to correlate back to accepted numbers.

Set the tension as tight as possible, short of causing a whine. The belt may not whine on cold start-up, but the tension increases as the engine comes up to temperature. (A OEM black belt set to 90 Burroughs cold will end up at about 125 when the engine is hot.) Since the tension is to be set cold, it's necessary to let the engine cool down over night, then try setting the tension a few pounds lower, and let it warm up again. Repeat as necessary, one tension adjustment per heat cycle.

As I mentioned above, the blue HTD is thicker than the older black HTD belts. The basic web, not the depth of the teeth. Use a vernier to measure the web thickness between two teeth, and report the thickness here. That will be helpful in trying to correlate blue vs black Burroughs readings.

Once the Burroughs tension is determined, it's then possible to correlate a Krikit KR-1 tension reading. On a cold engine, take a fresh reading with a Burroughs. Then take a reading with a Krikit. If you feel energetic, change the Burroughs tension in increments of 5, from around 75 to 100, taking a corresponding Krikit reading as you go. Create a conversion scale.

There's no published math formula that relates Burroughs to Krikit, so empirical measurements is the only way to go. Neither gauge actually measures the tension in the belt. They measure some other attribute, and correlate that back to tension through some formula they're not sharing. Unfortunately, each gauge measures a different attribute, so back to back measurements of the same belt tension is the only way I know of to correlate readings.

Regards,
Tim Engel

qwerty
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Happy to be a guinnea pig,

Tim are there any specs on the HTD belt (which i was looking for but can't find the crank pulley, otherwise i would have gone down that road) with regards to Hertz tuning? At work we tune all our belts using Hz or "frequency vibration" to tune belts.

Thanks for the heads up on whine = too tight (<--EDITED). I will report back, also with a Hz frequecy.

There are apps for the iPhone out there for frequency tuning ( i used a continental app to compare), you place the microphone over the longest part of the belt and tap the belt with the handle of a screwdriver or simply your finger. The iPhone will record and display the frequency it vibrates at, indicating tenision. I was suprised at how accurate and repeatable it is.

Last edited on 10-16-2016 02:28 am by qwerty

Esprit2
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qwerty wrote:
Tim are there any specs on the HTD belt (which i was looking for but can't find the crank pulley, otherwise i would have gone down that roadAny of the Lotus parts specialists should be able to provide you with the crank sprocket (JAE, Dave Bean Engineering, SJ Sportscars). Failing that, contact Mike Taylor at Lotusbits in the UK. He can probably set you up with a serviceable used part.
Lotusbits Ltd,
lotusbits@hotmail.com (Mike's a good guy, but terrible at answering email)
07866 255 614 Cell, Mike TaylorTim are there any specs on the HTD belt(snip)with regards to Hertz tuning?Lotus issued a frequency spec for the B-prefix, HSN HTD belt. It does NOT apply to the earlier A-Prefix, HCR HTD belt, and definitely not to the trapezoidal belt. The spec changes the basic procedure from tensioning at TDC, to tensioning at 30° BTDC. The correct frequency response is 100-110 Hz.

The belt tension varies quite a lot as the crank is rotated, so crank position is critical when checking the tension. The original tension specs (both J-H & Lotus) call for checking tension at TDC; and the later frequency spec (circa 2000) calls for checking at 30° BTDC. Watch what you're doing, and don't mix them up!!Thanks for the heads up on whine = too loose. I will report back, also with a Hz frequecy.Nope! Read it again... whine = too tight. A belt that whines is too tight, so back off a bit.There are apps for the iPhone out there for frequency tuning (Snip)...I use TuneIt! on a laptop (they have versions for several smart phones as well), with a slender boom mic (stick mic?... Harry Potter's wand). The mic is easier to snake in to the timing belt, while the typical phone is too bulky (more of an issue on a Turbo Esprit... not so much on a J-H).

Most of the frequency apps are musical instrument tuners, and pick up the entire spectrum... meaning a lot of 'noise' outside the 100-110 Hz range. If your app has a 'set-up' option, narrow the band to little more than the target range. Something like 75-135 Hz. That will provide a much cleaner reading.

Regards,
Tim Engel

qwerty
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Thanks for the correction Tim,

I'll edit the post to keep correct information.

qwerty
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Esprit2 wrote: qwerty wrote:
You can also replace the standard belt with a gates racing belt for apparently 3x the life.
Gates Part # T104RB
The Gates Racing blue timing belts are a definite step up in durability. The other plus is that the blue belts are very stable, and it should not be necessary to re-tension the belt for a long time. Continue to check the tension on the normal schedule, but it should rarely be necessary to make a tension adjustment.

The only problem is that Lotus isn't doing any new parts development work on an engine that went out of production approx 36 years ago (907 with trapezoidal belt), and Gates Racing won't make decisions/ specs for another company's product (a Lotus engine). As a result, there is no official tension spec, and no corporate effort to establish one.

There has been a Gates Racing blue belt for the round-tooth HTD belt for several years, and a pretty strong grassroots effort to zero in on a correct tension (mostly on the TurboEsprit list on YahooGroups). At the Lotus tension spec, the blue belt has a pronounced whine, which indicates it is too tight. With a lot of users reporting results, it now appears that 82-84 on a Burroughs gauge is about right for the HTD. But, the Burroughs gauge is thickness sensitive, and the blue HTD is thicker than the old black belts. So while a 'reading' of 82-84 works, I can't say exactly what the actual tension in the belt is. I suspect that it's something in the 90 range, but can't say for certain.

If you really want longer belt life, then the best solution is to convert to HTD pulleys, then go with the Gates Racing blue belt. Still hold the mileage limit down to about 50k miles, but ten years should be reasonable for a time limit.

Short of converting to HTD, the Gates Racing #T104RB blue belt is the best trapezoidal-tooth belt option available, but it's going to take another grassroots effort to zero-in on a consensus tension for it.

Somebody needs to go first. Looks like that's you. I highly recommend that you tension it using a Burroughs gauge so that the data is easier to correlate back to accepted numbers.

Set the tension as tight as possible, short of causing a whine. The belt may not whine on cold start-up, but the tension increases as the engine comes up to temperature. (A OEM black belt set to 90 Burroughs cold will end up at about 125 when the engine is hot.) Since the tension is to be set cold, it's necessary to let the engine cool down over night, then try setting the tension a few pounds lower, and let it warm up again. Repeat as necessary, one tension adjustment per heat cycle.

As I mentioned above, the blue HTD is thicker than the older black HTD belts. The basic web, not the depth of the teeth. Use a vernier to measure the web thickness between two teeth, and report the thickness here. That will be helpful in trying to correlate blue vs black Burroughs readings.

Once the Burroughs tension is determined, it's then possible to correlate a Krikit KR-1 tension reading. On a cold engine, take a fresh reading with a Burroughs. Then take a reading with a Krikit. If you feel energetic, change the Burroughs tension in increments of 5, from around 75 to 100, taking a corresponding Krikit reading as you go. Create a conversion scale.

There's no published math formula that relates Burroughs to Krikit, so empirical measurements is the only way to go. Neither gauge actually measures the tension in the belt. They measure some other attribute, and correlate that back to tension through some formula they're not sharing. Unfortunately, each gauge measures a different attribute, so back to back measurements of the same belt tension is the only way I know of to correlate readings.

Regards,
Tim Engel


Tim,

Thickness of the Gates Blue T104RB excluding tooth height is averaging 2.35 - 2.40mm measuread at various points around the belt and on both sides. I will be able to measure a Gates HSN and JHPS belt tomorrow.

Ordered a Krikit 1, now to find a Burroughs.

Are you aware of anyone making HTD Red dot sprockets for the stock JH Cam without adjustability. IE non vernier. I found green dots but no red.

Last edited on 10-16-2016 08:32 am by qwerty

qwerty
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Brett Gibson JH5 20497 wrote: I cut one up just to see how tuff they are with an "OLFA" Knife box cutter, takes a little time but slices's it up. http://www.olfaproducts.com/ProductDetail.jsp?LISTID=370000-1137370779

I also tried this on an old belt an noticed the belt construction on this particular belt (BANDO) brand is spiralled so if you do go down this track make sure to pull it in the direction that the belt will get wider as you tear it away rather than smaller.

Esprit2
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qwerty wrote:
Thickness of the Gates Blue T104RB excluding tooth height is averaging 2.35 - 2.40mm measuread at various points around the belt and on both sides. I will be able to measure a Gates HSN and JHPS belt tomorrow.Did you ever measure the Gates HSN & JPS belts? I just measured a new Flennor 24513311 black belt, and two other used belts I couldn't identify, and the readings were all 0.088-0.089 inch (2.235-2.261 mm). That's about 0.004" / 0.1mm difference between the blue & black belts. Not as much as between the blue & black HTD belts.

Stretching my memory, but for the HTD belts, I think the difference was more like 0.016-0.015"), and that made about a 3-5 lb difference in Burroughs readings.

Last edited on 11-02-2016 12:52 am by Esprit2

Esprit2
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Brett Gibson JH5 20497 wrote:
I cut one up just to see how tuff they are with an "OLFA" Knife box cutter, takes a little time but slices's it up. http://www.olfaproducts.com/ProductDetail.jsp?LISTID=370000-1137370779A friend's Esprit had the timing belt jump a few teeth, and took out the valves. When we got the belt out, we found it had been rubbing on something, and was worn down to half it's normal width. He was going to trash it, but I saved it.

I then bought a large strap wrench from Harbor Freight, and replaced the strap with the narrow timing belt. Now when I want to securely hold a pulley while tightening or loosening the retaining bolt, I have a strap wrench that will actually engage the pulley teeth. It has a very secure grip.

Regards,
Tim Engel

Last edited on 11-02-2016 12:42 am by Esprit2

qwerty
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Esprit2 wrote: qwerty wrote:
Thickness of the Gates Blue T104RB excluding tooth height is averaging 2.35 - 2.40mm measuread at various points around the belt and on both sides. I will be able to measure a Gates HSN and JHPS belt tomorrow.Did you ever measure the Gates HSN & JPS belts? I just measured a new Flennor 24513311 black belt, and two other used belts I couldn't identify, and the readings were all 0.088-0.089 inch (2.235-2.261 mm). That's about 0.004" / 0.1mm difference between the blue & black belts. Not as much as between the blue & black HTD belts.

Stretching my memory, but for the HTD belts, I think the difference was more like 0.016-0.015"), and that made about a 3-5 lb difference in Burroughs readings.

JHPS Belt Gates T104 White writing - 2.40mm - 2.45mm
Gates Green T104 HTN Belt - 2.50mm +0.00 -0.00
Gates Green T104 HTN Belt - 2.40mm - 2.45mm
Gates T104RB Blue Belt 2.20 - 2.30mm (I ordered two belts this is the second one, the first is measured above with different verniers).

The above all measured with the same verniers in the same way, so could account for the discrepancy. The blue belt was +- 0.05 around the belt with tolerance whereas the black belts were pretty uniform. Interestingly the two green HTN Belts measured differently with ~0.1mm difference.

qwerty
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Made a cam Lock today out of an old belt... Temporarily held together with a superglue bond. Definitely wait for it to dry before installing on cam sprockets.

Attachment: Cam Lock1.JPG (Downloaded 199 times)

Last edited on 11-06-2016 09:33 am by qwerty

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and now filled with Sikaflex. The back end if blocked off with a cut out of another length of timing belt on it's side with the teeth facing in.

Will clean it up a bit on a surfacer once it's set.


Attachment: CamLock Filled.JPG (Downloaded 194 times)

Last edited on 11-04-2016 08:43 am by qwerty

dwalls1
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Does the Sikaflex set up hard like epoxy, or softer like silicone?

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dwalls1 wrote: Does the Sikaflex set up hard like epoxy, or softer like silicone?
No, definitely not a hard epoxy. A Flexible silicone.

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Finshed tool, sweet.

Attachment: Finished.JPG (Downloaded 180 times)

Screenplay
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Nice work; we could all use something like that.

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This little thingy has become an invaluable tool while troubleshooting the timing belt so i'll elaborate. It looks like lot of steps but it's really not, just being clear.
  • Cut a length of used belt to 215mm cut on an angle (Pic Attached) I started from the inside of one tooth to the outer of two teeth over. The pic will explain (Blue Line)
  • Turn inside out and Temporarily super glue with the teeth aligned, the teeth need to be pretty accurately aligned.
  • Align cam gears to exactly TDC, we need to get this spot on as installing the tool and additionally while it's in place installing a belt will be a lot easier later on
  • After glue has completely dried push into cam gears, you should have two empty circles at either end
  • Insert top and bottom hard circular fillers (Aluminium) in my case, anything hard can be used, we just want to stop rotation. Mine was 15.3mm and 18.0mm yet an average will most likely work of 16.65mm each. Just as long as they are snug and all the teeth sit nicely.
  • Once the hard circular fillers are in there, partially fill with Sikaflex to bond the shape, make sure you get a fix on both the top and bottom surfaces as we want to keep it's shape when we remove it. Leave overnight but don't let it seep out the back of the belt and on to the cam sprockets.
  • Once dry Remove it, then reinsert making sure it fits and it's kept it's shape. If it doesn't reinsert and fill a bit more making sure not to soil the cam sprockets.
  • Once you have a nice fit take it to a dry flat surface and fill all of it, i cut an additional piece of belt as a backing, traced it and pushed it in and filled it solid, we don't any want rotation.
  • I then ground a lead in with a linisher to make it easier to insert and also marked the center TDC tooth for reference.

In use it takes a good thumb push to get it in there but once it's in it instils confidence.

Attachment: Length and cut angle.JPG (Downloaded 150 times)

Last edited on 11-12-2016 04:13 pm by qwerty

Steve Johnson
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Does anyone have the gates part number for the htd blue racing timing belt?

I just got the t104rb and it is the trapezoid one.
Thanks,
Steve

Esprit2
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The trapezoidal tooth belt is standard for the JH 907. If your engine has the round-tooth HTD pulleys, then that was a very worthwhile upgrade you or some prior owner made to the engine.

A bunch of years ago, JAE worked with Gates Racing to have the blue HTD belt produced in the Lotus size. Since JAE paid for the development, it's an exclusive to them and Gates does not sell it over-the-counter. In turn, JAE sells it to other Lotus specialists, and to Lotus Cars itself. So while you might find blue HTD belts at several Lotus specialists, ultimately they all come from JAE. There is no standard Gates part number that will get you a blue HTD belt at your local auto parts store or motor factor.

In the USA, contact JAE, Dave Bean Engineering, rdEnterprises. In the UK, contact SJ Sports Cars, Kemp Performance Engines, PNM Engineering, etc. Specifically ask for the blue HTD belt. It's very expensive compared to the standard black belt, but it's worth it.

(805) 967-5767 - JAE (Near you in Goleta, CA)
(209) 754-5802 - Dave Bean
(215) 538-9323 - rdEnterprises

The blue HTD belt needs to be set to a different tension than the black belt. With a Burroughs BT-33-86J gauge (or BT-33-73F), set it to 83-84.

Regards,
Tim Engel

Last edited on 07-10-2017 08:29 pm by Esprit2

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I was PM'd and asked for a similar Burroughs/ Krikit spec for the black trapezoidal tooth belt. I thought others might find the info useful, so here's what I replied:

*~*~*~*

With the Burroughs BT-33-86J or the BT-33-73F, set a new black trapezoidal tooth belt's tension a little high, at 100 (55 Krikit KR-1), to allow for initial stretch. After 500-1000 miles, the belt will have taken an initial stretch, and the tension will end up about where it's supposed to be for normal running... around 95

Then for routine checking and re-tensioning of a used belt, set the tension to the normal running spec of 95 Burroughs (52.25 Krikit). Lotus experimented through the years, started at 90 (too low), went as high as 105 (too high), and eventually settled at 95. It's a good tension value with a proven track record.

Neither gauge has great resolution, so the two-place decimal is just a matter of doing the math. Don't worry about trying to get anything closer than a round number... plus or minus. Personally, I'd rather err a little on the plus side. Anything over 105 Burroughs (58 Krikit) will cause a black belt to whine, and any belt that whines is too tight.

When you do a routine tension check, anything down to 90 Burroughs (49.5 Krikit KR-1) is acceptable. 90 is not "good", and 95 is better... but it's not "bad". Any lower than 90, and you should re-tension the belt as soon as possible.

At 80 Burroughs (44 Krikit KR-1), count your lucky stars and don't even put the keys in the ignition. That's scary loose.

*~*~*~*

The values given above apply to both the black HTD round tooth belt and the black trapezoidal tooth belt. The trapezoidal belt is supposed to run with more tension than the HTD belt. However, the Burroughs gauge is thickness sensitive, and the HTD belt is thicker than the trapezoidal belt. The end result is that the trapezoidal belt ends up tensioned as the Burroughs gauge says it is (95), and the HTD belt ends up a few pounds lower... where it should be. It works without the need to calibrate another gauge, and it's easier to remember one tension spec for both black belts.

The blue Gates Racing belts are another story. The tension for the blue HTD belt was discussed previously, and that's been worked out through owner experience over on the TurboEsprit list on YahooGroups. There is no offical factory tension spec for the blue HTD from either Gates or Lotus. This is all grassroots.

The blue trapezoidal belt is relatively new on the market, and I'm not aware of an established tension yet. Expect it to be a few pounds lower than the standard black trapezoidal belt tension. For starters, we're setting the tension just below (~comfortably below) the "whine threshhold". Sorry, I don't have an established number for you yet. If you use a blue trapezoidal belt, report your results so we can all learn from your experience. We'll add it to the collective experience/ knowledge base.

*~*~*~*

IMHO, the tension spec given in the JH Workshop Manual is too low. Finding a Kent-Moore KM-128 gauge might be difficult enough to keep anyone from using that tension spec, but the tension that results is too low. I won't recommend using it.

Regards,
Tim Engel

Last edited on 03-11-2017 02:21 am by Esprit2

Rick in Miami
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Using the Burroughs/Krikit comparison data I found either on this forum or perhaps a Lotus forum for the Gates T104 and also the recommended Burroughs values for the T104RB I calculated an approx 55% difference between the two gauges (cold) and installed my blue belt last week at 47 lbs cold. Belt deflections are in accordance with a Judson Manning post from 2006
(http://www.jensenhealey.com/forums/view_topic.php?id=528&forum_id=2&jump_to=3319
So far so good but I’ll be keeping my eye on it.

Gates T104
Burroughs Gauge 90-95# cold 120-125# hot
Krikit 50-52# cold 60-69# hot

Gate T104RB
Burroughs Gauge 82-84# cold 112-114# hot
Krikit 45-47# cold 56-62# hot

Esprit2
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Rick,
Save yourself some grief, and don't set the tension hot. Always check or set the belt tension on a cold engine, before the engine has been started for the first time that day.

And don't use a twist test or belt deflections if you have access to a good gauge. Deflection tests are especially un-reliable since the different evolutions of the belt have different thicknesses and strength/ stiffness. They don't all react the same to a deflection load.

Regards,
Tim Engel

Last edited on 03-15-2017 06:56 am by Esprit2

Rick in Miami
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I did set the tension cold @ 47# with a Krikit. I included calculated hot specs only because they had been included in the T104 tension specs. The twisting & deflection test comparisons were done to reinforce that I was in the ballpark. I am open to more hands-on experience and recommendations but since none had been offered to this point I wanted to share mine.

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Rick in Miami wrote:
I did set the tension cold @ 47# with a Krikit.
Okay, good. I'm with you there.

Rick in Miami wrote:
I included calculated hot specs only because they had been included in the T104 tension specs.
My concern was that it sounds to me like you're giving the hot tension too much credibility as a "Spec". It's not. There is no hot spec in terms of something with real value/ worth. If you properly set the tension cold, then allow the engine to warm up fully and measure the tension again, the hot tension you get is the result of your good procedure. In a cause and effect relation ship, hot tension is the effect, not the cause. Doing the correct procedure well, then gaining confidence in your work because it produced the "correct" hot result is bogus thinking. You're giving credibility to the hot result like it's the god given end goal. It's not. And it's not reliable. Purge if from your thinking as "something to attain".

What you're stating is like taking poison after the fact in order to bolster your confidence that you took the right blood pressure medicine this morning. There's something wrong with that.

Rick in Miami wrote:
The twisting & deflection test comparisons were done to reinforce that I was in the ballpark.
Again, that's backwards. The twist & deflection test are not foundational. They're grassroots tricks that 'might' give ball park results if performed by someone with a practiced feel; but for an untrained first timer, the results are unreliable. The gauge measurement reinforces that you might have developed a practiced feel for the twist test... and frankly, I discount the deflection test as stated. But neither the twist nor deflection tests should be considered standards of correctness for any gauge.

Also, the twist and deflection test results vary dramatically with the stiffness of the belt. And the Gates Racing blue T104RB is thicker, and significantly stiffer than the old, black, HCR trapezoidal tooth belt. Twist test results for the blue belt (once they're developed) will be considerably different from those for the black belt. Don't mix them up.


Rick in Miami wrote:
I am open to more hands-on experience and recommendations but since none had been offered to this point I wanted to share mine.
Thanks for sharing the results of what you're doing, and please don't get the feeling that I'm beating you about the head and shoulders. We do need to collect that sort of data to zero in on a good tension setting for the T104RB blue belt, and I appreciate your contribution. I'm just trying to curb the spread of some common mis-information along the way.

If you, or anyone, have the time and the inclination, it would also be helpful to know what happens as the tension is increased in small steps. At what initial cold tension does the belt begin to whine when the engine gets hot? And at what cold tension does the belt begin to whine right away... cold? Those are upper limits we need to avoid, but yet approach. Staying too low just out of fear of reaching an unknown whine threshhold isn't good... too low tension is hazardous. But how high can we go without provoking a whine. So far, I've not read of anyone sneaking up on those tension values for the T104RB. At least not in a statistically meaningful sample... more than one incidence. Much of that work has been done for the round-tooth HTD blue belt. And the recommended Burroughs tension for the blue HTD is in that 82-84 cold range (I use 83-84, but that's splitting hairs).

In your previous message, you wrote that you used the Burroughs/ Krikit conversion factor of 55%, and the recommended Burroughs values "FOR THE T104RB" to get to a target setting of 47 lbs cold. Where did you find the recommended Burroughs setting for the T104RB? The value you used matches what many are using for the round-tooth HTD blue belt. It would be convenient if the same value also turned out to be the best tension to use for the blue trapezoidal T104RB as well, but I haven't heard any definitive results that support that. I'm not contesting that tension for the T104RB. It's just that if there's more information on that posted somewhere, I'd really like to read it and learn. Point me to it.

The trapezoidal belt's shallow tooth engagement requires higher tension to maintain a secure bite on the pulley, and to not jump timing. The HTD belt's deeper tooth has a better mechanical bite, and can run with lower tension. I previously mentioned that the Burroughs gauge is thickness sensitive, and the round-tooth HTD belt is thicker than the trapezoidal tooth belt. With that in mind, Lotus recommends 95 on the Burroughs for both belts, and the thickness differences result is a lower actual tension in the HTD belt than in the trapezoidal belt.

Maybe that's what we'll confirm for the blue belts as well. If 82-84 Burroughs works well for the blue HTD, then perhaps it will also provide the adequately higher tension for the blue trapezoidal belt by virtue of it's thinner section producing a higher Burroughs reading.

The paranoid concern is that the tension is lower... 82-84 vs 95. And historically, low tension has not worked well for trapezoidal belts. The trapezoidal belt has a long, early history of jumped timing and bent valves. It has long been shown that the trapezoidal black belt needs all the tension it can get, short of provoking a whine, so there's some fear/ reluctance at work in the search for a new 'lower' tension for the blue T104RB. How low is too low?

Myself, I'd rather start high, discover the belt whines when hot, and work my way down to a lower setting that doesn't provoke a whine. I'm fearful of just blindly dialing in a quiet low tension, then waiting to see if it jumps timing down the road. Unfortunately, each trial requires letting the engine cool down over night, so only one trial per day will drag out any testing. And it would be nice to test a number of belts on a number of engines. One is not statistically meaningful.

Technically, the blue belt is a worthwhile improvement. We just need to learn how to use it without bending anyone's valves in the process. Hot tension, twist, and deflection tests are not safe ways to get there. 'Maybe' we back into blue belt versions of the hot, twist & deflection "specs" later, after we've first determined a viable cold tension by using good gauges.

I don't mean to just stand on the sidelines and point. But I have an unheated garage, and for now it's still cold here in Minnesota. Plus, the engines I have access to right now have HTD belts & pulleys. I'll jump into the game as soon as I can.

Long winded again... sorry about the bandwidth.

Regards,
Tim Engel

Last edited on 03-16-2017 10:37 pm by Esprit2

Rick in Miami
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Thanks Tim – Advice well taken. I will try tightening further in increments (starting at the high end to introduce the whine) next week and share my findings. As for the Burroughs T104RB tension, I apparently misread a post on a Lotus forum discussing both the T104RB and the Blue HTD.

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I finally got to play with the belt tension yesterday. I started by tightening the tensioner counter-clockwise to a tension that caused a whine when hot. Then I backed it off until there was no whine. After turning the cold engine over by hand several times this AM I got consistent Krikit readings of just barely above & barely below 50. I continued to turn the engine to 6-7 different positions testing several times at each position and got the same readings.

Esprit2
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Good information, thanks for sharing. It's that kind of input that will help zero in on a preferred tension recommendation.

The tension varies with crank position. I've checked the tension in 10 degree increments for two full revolutions (ie, a 4-stroke cycle), and the graph of the results is a regular roller coaster ride. So it's important to check and set the tension at TDC. Explore if you wish, but set it using a tension gauge at TDC.

Around 1997 or so, Lotus issued a new procedure for the HTD round tooth belt only. It called for the use of a Clavis Frequency Meter to set the tension to 100-110 Hz at 30 BTDC. I find it much easier to set the crank to 30 BTDC than to TDC. The tension in the belt is higher at TDC, so it's more difficult to move it precisely, and it moves in jerks. If you're right next to the TDC mark trying to sneak up on it, pulling... pulling... then it jerks beyond TDC. Frustrating.

At 30 BTDC, it's easier to turn the crank, and you can roll right up to the TDC mark and stop, first time, every time. The only problem, there's no tension recommendation for the trapezoidal belt at 30 BTDC. That would be another grassroots effort.

So, out of curiosity, what tension are you zeroing in on at TDC? Then what is the corresponding tension at 30 BTDC? Curious minds want to know. Well, at least one does.

Thanks & Regards,
Tim Engel

Esprit2
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BTW, one of the nice things about the frequency method is that there are inexpensive/ free guitar tuning aps for smart phones, and even frequency analyzers. TuneIt! is one. With that installed, you can simply hold your phone or iPad down by the belt, and pluck it like a guitar string. The frequency appears on the screen.

Frank Schwartz
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Is there a product in the USA similar to Sikaflex??? Or where can I get some?

Have always had problem holding cams in place and this is what I need. Or perhaps regular silicone sealer which dries hard but rubbery is ok????

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Dumb me. I looked Sikaflex up and it is available for a few bucks at Home Depot. I had my mouth running before I had my brain in gear...

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Frank Schwartz wrote:
Have always had problem holding cams in place and this is what I need. Or perhaps regular silicone sealer which dries hard but rubbery is ok????Are you talking about the silicone sealant that is applied to the threads of the bolt that secures the pulley to the crank? Or something else? For that purpose, all you need is an automotive grade silicone sealant, like the Permatex Ultra series. Apply anti-seize to the bore of the pulley and the cam journal.

For the auxiliary pulley, use Loctite Retaining compound, or a red, high strength Threadlocker in the pulley bore and on the shaft. Wipe off any excess that gets squeezed out. Especially on the back side, since you don't want any to get into the rubber lip seal right behind the pulley.

Regards,
Tim Engel

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Yes, I know...I am referring to the white sealant he used in filling up that wedge gadget he used to hold the cam wheels in place and used a bit of old toothed belt.
Frank

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Frank Schwartz wrote:
Yes, I know...I am referring to the white sealant he used in filling up that wedge gadget he used to hold the cam wheels in place and used a bit of old toothed belt.
Frank
I didn't comment on Peter's pulley clamp earlier, because I thought it was a very clever design and use of available materials; however, I usually advise against using anything like that.

If you're using it to keep the pulleys from moving out of alignment between when the belt is removed and when a new one is installed, then all it does is preserve what was, without making certain what was, was correct. If the timing was off before you started, it will be off after you're done. That's not very reassuring.

It's very quick and easy to install and time a cam belt starting from scratch. It takes less time to do the task right without a pulley clamp that it does with one. Even if you spin the dials like a Rubic's Cube before starting, just follow the correct procedure from scratch and the engine will quickly end up correctly timed when you're done. And you know it's right.

Use a pulley clamp to keep the pulleys from moving, and the timing will be as screwed up after you're done as it was before you started. It might be right, it might not. I don't recommend that.

Regards,
Tim Engel

Last edited on 04-10-2017 03:13 am by Esprit2



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