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 Posted: 03-22-2005 04:38 pm
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Rory Clark
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OK Lets Visit the "By the numbers" of Timing.  (73-JH without emissions no-Vac. advance)

Please advise if I am Wrong

Cam Sprockets: Intake 110 Exhaust 110, @ 0^ TDC  Static Time: 8-12^ BTDC 

On My car the strobe shows at idle 850 RPM 10^ BTDC (@ 2000 rpm 20^ BTDC)

Engine runs like dog dodo. Knowing my carbs require attention. just want to confirm above.  Idles fine (no Choke) back fires Badly through frt Stromberg @ 3000 rpm.

Rory

 

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 Posted: 03-22-2005 08:29 pm
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Mark Rosenbaum
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Cam timing is okay, static timing is okay, advance is a tiny bit less than spec but not something I'd be at all concerned about.

Other things I'd check, just to be CERTAIN:

1.  What is your points gap?  Should be 0.014" to 0.016".  If it gets much beyond these limits the engine will run poorly.  Did you lubricate the fiber arm on the points recently?  These can wear down very quickly if not lubricated -- 0.001" per 100 miles perhaps.

2.  Are all spark plugs in good shape, with good wires, installed tightly, and on correct plugs?  A common error is to wire up the dist. cap backwards which has the same effect as swapping the plug wires for cyls 2 and 3; engine will usually run, poorly, on 2 cyls.

3.  Observe the vacuum valves (pistons) inside carbs while working the throttle.  Do both pistons go up and down the same amount and at the same rate, every single time the throttle is blipped?  If not, either the carbs are out of balance, need rebuild, or there is something wrong (burrs, rust, etc.) inside.  With the engine off, does each piston give about the same resistance when being lifted by a finger, and does it return all the way down when released?

4.  How about air flow balance between the two carbs?  Do you have a Unisyn or something similar to check this?  

5.  Are both carb mixture needles the same?  Are the needles adjusted to give the right fuel/air mix?  If in doubt, pull the vacuum valves out and set the needles to the 'datum' point, which is where the little washer at the top of the needle is precisely flush with the bottom of the vacuum valve.  Put the carb back together and rotate the mixture adjuster 1/6 turn CLOCKwise, this will normally give you a very slightly rich mixture.  You do need the special adjuster tool to do this.

6.  Is the compression decent and roughly the same on each cylinder?

 

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 Posted: 03-23-2005 02:15 am
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Judson Manning
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Rory,

Do follow Mark's advice, but I'd like to add one of my favorite techniques:

Pull off all 4 plug wires and lay them on the intake manifold then attach 4 old spark plugs where you can see them.  With the key in the 'on' position, rotate the engine by hand.  Watch each plug fire (hopefully in 1-3-4-2 order!).  As Mark suggests, you could simply have 2 plug wires flip-flopped.

good luck...


 

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 Posted: 03-23-2005 02:23 am
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Mark Rosenbaum
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Judson,

love that trick but hardly ever think to mention it as I've been lucky and haven't screwed things up recently.  Of course, one doesn't want any fuel sloshing about when one tries it.  Engine bay fires are SO embarrassing....

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 Posted: 05-24-2005 02:50 pm
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kneff
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I'm confused about what I SHOULD be seeing on my cam sprockets. I have a 1974 J-H, and each cam sprocket has two markings: 110 In and 115 Ex. For both, 115 Ex is clockwise in relation to 110 In.

On my car, at TDC, the 110 In hash mark on the intake sprocket lines up with the 115 Ex hash mark on the exhaust sprocket. This exactly matches the picture in the service manual, but I have no idea whether this is correct for a 1974 model or not.

Any wisdom and/or guidance will be HUGELY appreciated!


Ken

Last edited on 05-24-2005 02:51 pm by kneff

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 Posted: 05-24-2005 04:01 pm
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Brett Gibson JH5 20497
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Ken, on my 75 JH I was told by Jim Medland at Delta to lign up the 110's with each other at TDC and that would give the best performance, any other alignment I would assume would not be.

Brett.

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 Posted: 05-24-2005 04:42 pm
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Mark Rosenbaum
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I suspect everybody has been confused about cam timing at one time or another, due in part to the fact that the drawing in the shop manual is wrong and the associated text is somewhat unclear.  The JH factory service bulletin numbered JH003K.PNG at http://www.paulnorton.org is one of many factory sources for the correct cam timing specs that I quote below.  In brief, these are:

115 IN / 115 EX -- Vehicles made in 1973 (and presumably 1972 as well)

110 IN / 110 EX -- Vehicles made in 1974

100 IN / 110 EX -- Vehicles made in 1975 and 1976 (both JH and GT)

IIRC the federal emissions standards were based on model year for high-volume cars and actual date of production for low-volume ones, while the California standards were based solely on production date.  This results in a complex regulatory muddle that only a bureaucrat could love.  In any event, the 100/110 setting really should be used only on engines with catalytic converters and air pumps, and not all cars notionally belonging to the 1975 model year were so equipped.

If you closely examine the cam gears found on most JHs, you'll note that the markings on the two faces are somewhat different, as indicated in the attached photo.  If you place the gears side by side, a bit of experimentation will make it apparent that flipping each gear so one face or the other is upward, will give you four possible ways to align an 'IN' index line on the left gear, with an 'EX' index line on the right gear: 110/110, 115/115, 110/115, and 115/110.  These are the four cam timings possible with these gears. 

CAUTION:  The engine generally will not run, and may be damaged, if one uses an 'EX' index on an intake cam, or an 'IN' index on an exhaust cam, to set the timing.

A stock 907 engine should run with any of these four combinations, but if memory serves the 110 IN / 110 EX setup gives slightly better low-end torque at the cost of top end power, while the 115 IN / 115 EX combination gives slightly better top-end power at the cost of low-end torque.  (Or perhaps it's the other way around.)  In any event, since even the California smog nazis do not check cam timing (yet), I'd suggest using whichever setting works best for you.  Most folks (myself included) seem to be happy with the 110 IN / 110 EX setup.

I've found through experience that the cam gear markings are generally hard to read when the gears are installed on the engine, and consequently it is quite easy to repeatedly mis-set the cam timing.  This eventually becomes terribly embarrassing.  I strongly recommend marking the desired indexes with daubs of paint, permanent magic marker, or the like, so that proper alignment will be obvious.

Historical note:  There are three types of JH cam gear, plus additional types used only on Lotus cars.  Early JH gears were marked only IN and EX and had no numbers.  Mid-range JH gears were as described above.  Very late JH/GT gears were similar to the mid-range gears but permitted 100/110 timing instead.  Earlier Lotus cars may have used any of these.  Later Lotus cars may have used gears with a variety of colored pimples and/or dimples that indicated their timing.  And, as seems typical of Lotus products, there were various minor and generally undocumented variations.

 

Attachment: engine cam gears annotated.jpg (Downloaded 100 times)

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 Posted: 05-24-2005 05:16 pm
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kneff
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Mark,

I have a 1974 J-H. If I understand correctly, then, my exhaust cam gear is mounted backward, since it is marked with 110 In and 115 Ex. It is impossible, the way the gears are mounted, to match 110 In with 110 Ex, as there is no 110 Ex on the exhaust cam gear (or the intake cam gear, for that matter).

If I'm correct, then what I'll do is set crank gear to TDC, remove cam belt (NOT moving gears, of course), and flip the exhaust cam gear over. Then I'll match 110 In on the intake cam gear with 115 Ex on the exhaust cam gear. Hopefully, it lines up pretty closely to where the cams already are, since it's running OK now (not great, but OK).

Thanks,
Ken

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 Posted: 05-24-2005 05:53 pm
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Ron Earp
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Fellows,

Aren't the cams for intake and exhaust exactly the same?

If so, then just pull the intake cam off and put it on the exhaust, and visa versa. Here is a post on the Lotus forum I started and lots of people put some useful info in on:

http://www.pistonheads.com/gassing/topic.asp?t=166269&f=17&h=0

Ron

 

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 Posted: 05-24-2005 11:40 pm
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Mark Rosenbaum
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Ken:

Yes, that's exactly it though I'd think you'd want 110 IN / 110 EX timing.  All you need do, in essence, is flip over the exhaust cam gear so the other side is facing forward.  For very small timing changes this can usually be done safely with the engine at TDC.  When starting from scratch you want the pistons well away from the valves, so you set the crank 90^ BTDC and offset each cam gear by 45^ (5 teeth) COUNTER-clockwise.  When you reinstall the belt and move the crank clockwise to TDC, the cam gear indexes should line up; if not, move back to 90^ BTDC and move the gear or gears as necessary.

Ron:

Yes, normally the two gears are identical.  In Ken's case his exhaust cam gear just has the wrong side forward, the intake side is OK.  That linked discussion on cam timing is the clearest explanation I've come across to date.

Last edited on 05-25-2005 12:07 am by Mark Rosenbaum

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 Posted: 05-25-2005 02:42 pm
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Rory Clark
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Guys I went around and around on this issue. For my Early 73-JH at 110/110 the heat build up was BAD and it ran bad. Changed it to 110/115 (as shown in the manual) and it everything came back together Runs like a bat out of hell and stays cool.

I have changed the sproket settings so many times I probibly need to replace the tension bolt on the timing belt. 

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 Posted: 05-25-2005 03:58 pm
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Mark Rosenbaum
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Rory, the 110/115 cam timing sounds odd to me, but there are so many variables involved that the only honest conclusion has to be, 'if it works on your car, go for it!'

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 Posted: 05-25-2005 05:38 pm
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Rory Clark
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Mark,

Since the car is down right now for Master Cyl replacement and Servo Rebuild.  And Since I knew it was going to be down I ordered and received a new Delta Exhaust system to install.

The only setting I have not tried is 115/115. Think I will try it  Like I said earlier I have screwed with it so many times it is less then a 10 min job.

Rory 73-JH

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