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Replacing Cam/timing belt  Rating:  Rating
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 Posted: 07-22-2005 07:05 pm
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Joel
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Ok, I'm starting to consider changing the timing belt. I bought the car a few weeks ago and have no idea when it was last changed. I screwed up the head on my 325BMW a few years ago (bent valves) when the belt broke. Now, I'm paranoid. Belts are a lot cheaper than heads. . .

I can't seem to find any good info on changing the belt. Even my 'manual' doesn't seem to give a very good idea of how to change it - except for telling me how to tension it properly. I searched this forum and there doesn't seem to be any info.

Can someone point me in the right direction?

And - any recommendations on a tool to check the belt tension?

I'll post elsewhere about my carburation travails when I decide to tackle that. I posted before - i think I'm running way rich but should probably check timing, plugs, etc before I jump into friggin around with the carbs.

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 Posted: 07-22-2005 07:30 pm
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Ron Earp
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Changing the belt, the short version as I know it from my simple car, which isn't as complex as some models with smog pumps etc.
 
1) Get beer and buddy. Drink beer. Talk to buddy.
2) Drain radiator. Remove upper and lower radiator bolts, remove radiator, hoses and fan from water pump pulley.
3) Remove the timing cover shroud. Cuss about the tiny bolts and cheap lock nuts.
4) Take timing cover, put into your right hand, go to your back yard, and throw it as far as you can.  Remove studs the cover was mounting on, vowing to never put that plastic POS back on there.  From now own you'll take it like a man and lose a finger if you stick in it in the cam gear while the engine is running.
5) Drink. Talk to buddy.
6) Use a wrench to turn the engine over to TDC. Make sure timing pulley marks are aligned.  If they are not aligned, turn it over once more to the other TDC.
7) Untension the alternator and remove the alternator/water pump drive belt.
8) Drink. Talk to buddy.
9) Use pulley puller to pull front crank pulley.
10) Using two wrenches on the tensioner bolt/assembly, release tension on the cam drive belt. Remove belt whilst not disturbing the cam gear positioning.  Do not disturb the distributor/oil pump gear positioning, but you'll have to re time the motor anyhow.
11) Drink. Evaluate chances of getting done with the job in time to please The Minister of Domestic Affairs (i.e., Wife).
12) Inspect all driven gears for problems - chipped teeth, missing teeth, rocks in cracks that might cause problems later, etc.
13) Put new belt on, trying it different ways until you get the slack in the right place - right where the tensioner is so that it can be taken out.
14) Tighten tensioner. Tighten it enough so that you can just twist the belt 45 degrees. Once you are sure everything is good, timing is good, marks are all aligned, then turn the engine though a couple of revolutions and re-check timing and tension.  Make sure all is good, if not, repeat.
15) Drink. Talk to buddy.
16) Now, re-install all the stuff you took off and you'll be good to go. If you have a leaking front seal on your motor, now is the time to replace it.

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 Posted: 07-22-2005 11:17 pm
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Panini
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dumb question on tdc. Everyone refers to alighning pulley marks. Where should the marks be?

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 Posted: 07-22-2005 11:46 pm
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Ron Earp
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Four marks on the engine, one on the crank. Crank mark should be aligned with the right most mark when viewed from the front of the engine. Each mark is 10 before TDC, so, first mark to the left of the most right one is 10 degrees before TDC, next is 20, and so on.

Ron

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 Posted: 07-23-2005 01:05 am
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Joel
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i appreciate the input. i have the most important points down - have buddy and beer. the rest should be easy.

mucho appreciated.

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 Posted: 07-23-2005 04:58 am
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Judson Manning
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Ron,

Very good for a neophite!  and I'm glad I'm not the only one who hates the timing cover!

Just one little thing...

Don't change the belt at TDC.  Instead, position the engine at 90^BTDC.  That way, if something does move, the pistons are far enough down to eliminate damage. 

It is very easy for one (I can't remember which) cam to rotate clockwise at TDC while fine-tuning.  Getting either cam to rotate counter-clockwise is difficult as the bolt likes to come loose first.

Put the new belt on, tighten it, then rotate and watch the marks line up.  If they're off...it's easier and less risky to ajust at this point.

Keep up the good work Ron!

Judson

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 Posted: 07-23-2005 03:04 pm
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Mark Rosenbaum
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You can safely change the belt with the engine at TDC, provided you ensure that the cams do not rotate, but as Judson points out it is much safer to do it at 90^ BTDC.

And when the engine is at 90^ BTDC, I suggest that you mark the alignment point of the cam gears before loosening the belt tensioner.  This allows accidental movement of either gear to be quickly corrected, while avoiding the need to repeatedly go through the whole tedious installation process.  Naturally one would always make a final check at TDC.

From the engine bay photos I've seen, I'd guess that about 80% of all JH and GT owners strongly dislike the factory timing belt cover.  Nonetheless, since it is a safety feature, discarding it is a bit worrisome.  It occurs to me that one might fabricate a sensible alternative from expanded metal mesh, ideally with a folded metal strip or a thin wire secured to the edges for strength and stiffness.  This would allow visual and tactile examination of the timing belt and the front of the engine, yet would discourage or prevent the unintentional maiming of children, small animals, or incautious vehicle owners.

Come to think of it, this might even be a decent product for Greg Fletcher to add to the 'Jensport' line.

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 Posted: 07-24-2005 03:33 pm
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Ron Earp
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Good point Judson, it is actually how I did my own too, I left that out.  I would definitely turn the crank 90 degrees before pulling the old belt and putting the new on one - it'll possibly save you a bent valve.  Valves bend much easier than people think, much easier than I ever thought too, until I bent my first one (of a few) on a motorcycle with a cam chain R&R and then learned the hard way.

R

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 Posted: 11-03-2005 10:04 am
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quolypaduss
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Hello,

I have got a jensen healey from 72.

I would like to know where I can buy a belt/gear set as indicated in this article:

[ Adjustable Camshaft Gears
The newer style half moon tooth belt is a must have for any performance (or not) engine. A belt/gear set will set you back about US$300 but the piece of mind you get from that heavy duty belt is worth the extra cash. Positive grip prevents belt jumping and improves torque off the crankshaft (dyno tests indicate an extra two bhp). An added bonus, the belts last much longer (I change mine at 40,000 mile intervals) and replacements now only run about US$22 for the quality US made version. Forget that routine 18,000 mile timing belt change forever! ]

Thanks.

Attachment: RIMG0003.jpg (Downloaded 305 times)

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 Posted: 11-03-2005 01:14 pm
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Greg Fletcher
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These are getting harder to find, I'd try Dave Bean Engineering or JAE. When the cost was $285 for a set, it seemed like a good idea, however the cost now is more like $550-$600 and does not seem nearly as cost effective. It's a great upgrade, but changing your old belt every 18,000 miles is a lot cheaper.

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 Posted: 08-15-2006 04:24 am
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scout06
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dumb question, what is the distance between each of the marks on the engine?

How do i find 90^ BTDC? do i divide the cranks pully in 1/2 since one complete rotation = 180^

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 Posted: 12-15-2006 12:40 pm
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smcmanus
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The distance is 6 teeth on the cam gears and aux gear.  I marked it with a sharpie and turned the crank 90 degrees then, checked to see if the  spots were lined up.  I then marked the crank.  I then used a punch and made some permanent 90 degree marks.

The importance of using 90 degrees is that all the pistons are are half-mast so if/when you do turn a cam, the valves can't hit the pistons.  It seems the cams are prone to turning and are spring loaded when at TDC and also 90 degrees. This is also a good time to replace all the seals.  I found all of mine to be very hard crumbly worthless bits of old rubber. 

Good Luck

Steve

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