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Timing Belts


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9 replies to this topic

#1 popeye5

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Posted 04 December 2012 - 01:03 PM

I'm in the process of changing timing belts on my 2001 OB wagon, with 156K miles on it.
All has gone well up to this point, BUT:
While aliginging the new timing belt marks and marks on engine I inadvertently turned the left cam past it's mark and it did a "revolution" throwing the whole engine out of sync. I've wrenched for sometime , I'm 66, but I'm unsure as to how many more times I would need to turn the left cam clockwise to get it back in sync with the rest of the engine. And for that fact how do I tell if the crank, right cam, and left cam are all in sync?
Thanks in advance for any advice you can throw my way.

#2 porcupine73

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Posted 04 December 2012 - 01:31 PM

Hello and welcome. Provided you lined up all the hash marks (mainly the crank sprocket with the oil pump notch) then no cylinders are near TDC, so rotating the cams is not an issue on the sohc. Just rotate it (in normal direction of rotation is probably preferable) so that the hash mark lines up with the notch in the timing cover.

It doesn't matter how many times you rotate it. As long as all the notches are lined up properly it will be fine. The genuine belts are nice because the lines on them correspond exactly with the notches.

And it is the notches (___not___ the arrows).

Tensioner - must compress VERY slowly like taking 10 minutes slowly in a vise or you will kill it.

Idlers - Replace at the absolute minimum the geared/toothed idler, or at least replace the bearings.

#3 89Ru

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Posted 04 December 2012 - 01:34 PM

no worries about the cam snapping like that, happens all the time and it can be unnerving but since you're at TDC you won't get impacts between the piston and valves. just turn it back to line up the vertical hash mark on the outer rim of the cam to the mark on the plastic cover. do you have a procedure of how to line up the marks? search the board or http://techinfo.subaru.com/index.html.

http://www.ultimates...ad.php?t=116854

welcome to the board.

(sorry for redundant post!)

Edited by 89Ru, 04 December 2012 - 01:37 PM.
whoops too slow :)


#4 popeye5

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Posted 04 December 2012 - 01:53 PM

Thanks for speedy reply.
Correct me if I'm wrong but none of these, crank or cams should be rotated counter clockwise with or without belt?
So you're saying just turn the already once rotated cam sprocket ( from original setting that belt was removed at,with crank on mark and key pointing down) continue clockwise again till it's where it needsto be?
Won't that throw the whole engine out of sync

#5 The Dude

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Posted 04 December 2012 - 01:55 PM

no worries about the cam snapping like that, happens all the time and it can be unnerving but since you're at TDC you won't get impacts between the piston and valves. just turn it back to line up the vertical hash mark on the outer rim of the cam to the mark on the plastic cover. do you have a procedure of how to line up the marks? search the board or http://techinfo.subaru.com/index.html.

http://www.ultimates...ad.php?t=116854

welcome to the board.

(sorry for redundant post!)


Actually, when the crankshaft pulley is properly aligned for a timing belt replacement NONE of the pistons are at TDC. TDC means, "top dead center". When changing the timing belt, you want all four pistons positioned at half stroke in their respective cylinders.

TDC is what you want when you are adjusting the valves. TDC means that the piston is at the very top of its compression stroke. A piston at TDC would almost certainly bend valves if the camshaft "snapped" during a timing belt change.

Edited by The Dude, 04 December 2012 - 01:58 PM.


#6 porcupine73

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Posted 04 December 2012 - 02:08 PM

Thanks for speedy reply.
Correct me if I'm wrong but none of these, crank or cams should be rotated counter clockwise with or without belt?
So you're saying just turn the already once rotated cam sprocket ( from original setting that belt was removed at,with crank on mark and key pointing down) continue clockwise again till it's where it needsto be?
Won't that throw the whole engine out of sync


I always rotate only in the direction of normal engine rotation (though should this happen on a dohc you might not be able to do that). So that would be, when facing the engine with the hood up, clockwise.

Right, line up the notches on the cam sprockets with the notches in the timing belt covers (and the crank sprocket notch should have been lined up with the oil pump before you removed the old belt). Turning the crankshaft without the belt on could get you into trouble if it crashes too hard into any valves.

As long as the notches are aligned it will work fine, you can't be out of synch on the cams if everything is aligned. I understand why you're asking but it doesn't matter, what does matter is the timing marks line up perfectly, even one tooth off and you'll have issues.

#7 89Ru

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Posted 04 December 2012 - 02:16 PM

Actually, when the crankshaft pulley is properly aligned for a timing belt replacement NONE of the pistons are at TDC.


yes, you are absolutely correct.

#8 89Ru

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Posted 04 December 2012 - 02:24 PM

none of these, crank or cams should be rotated counter clockwise with or without belt?


ok to rotate cams, they will resist and give as you turn them
not ok to rotate crank unless you have a non-interference engine (which you don't)

So you're saying just turn the already once rotated cam sprocket ( from original setting that belt was removed at,with crank on mark and key pointing down) continue clockwise again till it's where it needs to be?


yes, CW or CCW doesn't matter

#9 popeye5

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Posted 04 December 2012 - 06:06 PM

Thanks one and all, tommorrow I may return to finish the job.

It did appear that the left cam was slightly off the marks when I dissassembled and removed the belt.

Another confusing issue was not only white marks, but red ones on the pulleys and the block, although the actual scribe appears to be in between the red and white on most of the markings.


The belts where changed once by the dealer at my expense when I had it in for warranty work on the head gasket issue.


Would the belt being off one tooth on either cam be very noticeable?
Thanks again

#10 porcupine73

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Posted 04 December 2012 - 06:23 PM

There are usually some splotches of paint colors on the cam sprockets. It's just the single hash mark you want, that has to line up with the notch in the back of the timing belt covers. And on the crank sprocket, the single notch to line up with the notch on the oil pump.

If the belt is off a tooth it is pretty easy to notice when you line up the belt. It might look a little off, like the cam on the right as you face the engine at the hood, it might look to be slightly cw of where it should be, but when you pull the tensioner pin it usually moves right to where it needs to be.

One tooth off and the engine will start and run but can be lacking in power and fuel economy.

The critical thing is actually the proper amount of teeth between each cam sprocket and the crank sprocket. The genuine belts the marks on them line up exactly.




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