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What's with my timing belt TDC?

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Old 07-07-2012, 12:58 PM
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1987Porsche944WithRealLongName
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Default What's with my timing belt TDC?

Trying to get these belts tensioned and proper. I turn the engine clockwise a couple of times until I get to the tdc mark on the camshaft sprocket. Then I go under the car and check for the flywheel mark, only to see it's off a centimeter or two. Then I pull on my flywheel clockwise to get it lined up, only to get out and see that the tdc mark on the cam is spot on. Repeat this as many times as necessary, I can't even get it set because every time I try to things seem to go back to indicating proper timing.

This is getting very old very fast as it's almost 100 degrees here and I'm in direct sunlight working on this thing.
Old 07-07-2012, 02:47 PM
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Dave W.
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Take a break so you can think straight.
Always rotate the engine clockwise, if there's any slack in the belt the crank may move a little before pulling on the belt and moving the cam. If you have to turn the crank counter clockwise (anti clockwise), I recommend turning it a little farther than needed, then turning it back a little so there's always tension on the belt pulling the cam clockwise.
Old 07-07-2012, 04:08 PM
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1987Porsche944WithRealLongName
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I got it

Slipping the belt on the camshaft with the side going to the crank pulley tight with the side going to the tensioner more loose did it.
Old 07-07-2012, 09:33 PM
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drift a 944
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Where are you checking your flywheel mark at?

"going under the car" seems to be throwing me off, as I've always checked mine from the top through the timing inspection hole...
Old 07-08-2012, 10:49 AM
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Will Feather
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Elliot, there is 3 spots to check for TDC. The cam sproket, the top of the bellhousing, and also a spot on the bottom of the bellhousing. I never use that one on the bottom but I was at a timing belt party and remember seeing it.
Old 07-08-2012, 01:11 PM
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931guru
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Originally Posted by banana944
Elliot, there is 3 spots to check for TDC. The cam sproket, the top of the bellhousing, and also a spot on the bottom of the bellhousing.
Actually, there are four, if you count using a wooden chopstick to sense the top of the #1 piston.
Old 07-08-2012, 03:37 PM
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my84-944
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Originally Posted by 931guru
Actually, there are four, if you count using a wooden chopstick to sense the top of the #1 piston.
One of my favorites...good piece of mind.
Old 07-08-2012, 04:39 PM
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kwikt
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I use a home made mount with a dial indicator which screws into #1 cylinder to find tdc. Works great!!!
Old 07-08-2012, 06:24 PM
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Will Feather
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Yes anything in the #1 cylinder will indicate. I meant 3 spots you can check on the motor, unless there is more I am unaware of.
Old 07-08-2012, 07:31 PM
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968 GUY
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But the flywheel mark is a positive indicator. If the cam was not aligned correctly previously, then TDC is still off.
Old 07-08-2012, 08:27 PM
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kwikt
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You can't go wrong checking piston #1 at tdc, Everything else should line up accordingly.
Old 07-08-2012, 11:55 PM
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968 GUY
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kwikt that is true to a point, but there are several (not sure exactly how many) degrees of no piston movement as the crank rolls over center, but you are right, it is close enough for putting the belt on.

I remember reading in one of the hot rod mags that the best way to find exact top dead center is to put a positive stop for the piston that is a bit off of TDC , putting a degree wheel on the crank and rotating clockwise til it stops, mark the degree, rotate CCW til it stops, mark degrees, then find TDC by splitting the difference.
Old 07-09-2012, 04:25 AM
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spanky
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When you reach TDC with the flywheel, confirm this by centering thre flywheel notch within the window at the bottom (6 oclock) of the bellhousing. The cam sprocket may be off its TDC mark by a few degress but should be damm close to being correctly positioned, If this is the case , remove the timing belt from the cam sprocket and line up this sprocket mark to its TDC mark on the clam shell sprocket cover. This should req no more than 1/8" movment in either direction of the cam sprocket fot this to be exactly at TDC. Reinstall the timing belt onto the cam sprocket Good luck.
Old 07-09-2012, 01:32 PM
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my84-944
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Originally Posted by spanky
When you reach TDC with the flywheel, confirm this by centering thre flywheel notch within the window at the bottom (6 oclock) of the bellhousing. The cam sprocket may be off its TDC mark by a few degress but should be damm close to being correctly positioned, If this is the case , remove the timing belt from the cam sprocket and line up this sprocket mark to its TDC mark on the clam shell sprocket cover. This should req no more than 1/8" movment in either direction of the cam sprocket fot this to be exactly at TDC. Reinstall the timing belt onto the cam sprocket Good luck.
EXACTLY...... But you can also use the top flywheel indicator on the back of the bell housing. But this is the correct procedure that I use. Three T belts and perfect timing says so anyway.



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