Cam timing
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Tourer
Joined: Apr 2018
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From: SE Mass
Cam timing
I'm helping a buddy this weekend do the cam chain tensioners on his TC88. I'm quite sure I read somewhere that when the alignment marks on the pinion and cam gears are lined up, then one of the pistons is at TDC and when the marks are completely opposite each other, the other piston is at TDC. Please confirm if that is true and if so, which piston is it in each scenario. Thanks.
Road Master
Joined: Mar 2012
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From: Ohio
Just line up the two marks as pointing towards each other. Every rotation of the crank is one half rotation of the cam. So every other rotation the cam timing marks are 180° out. One more rotation and they're aligned again. There's no way to screw that up as long as the timing marks are towards each other when putting the chain and sprockets on.
Keep in mind the pushrods need to be out so that you are not trying to overcome the valve spring pressure.
Keep in mind the pushrods need to be out so that you are not trying to overcome the valve spring pressure.
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Tourer
Joined: Apr 2018
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From: SE Mass
Just line up the two marks as pointing towards each other. Every rotation of the crank is one half rotation of the cam. So every other rotation the cam timing marks are 180° out. One more rotation and they're aligned again. There's no way to screw that up as long as the timing marks are towards each other when putting the chain and sprockets on.
Keep in mind the pushrods need to be out so that you are not trying to overcome the valve spring pressure.
Keep in mind the pushrods need to be out so that you are not trying to overcome the valve spring pressure.
HDF Community Team
Joined: Jan 2022
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From: B.C.
I'm helping a buddy this weekend do the cam chain tensioners on his TC88. I'm quite sure I read somewhere that when the alignment marks on the pinion and cam gears are lined up, then one of the pistons is at TDC and when the marks are completely opposite each other, the other piston is at TDC. Please confirm if that is true and if so, which piston is it in each scenario. Thanks.
Line the marks up properly or get someone who can.
END OF STORY.
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Tourer
Joined: Apr 2018
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From: SE Mass
I never said I was using that reference for the actual procedure. Just asking a question. END OF STORY.
Stellar HDF Member
Joined: Sep 2007
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From: Vancouver Island B.C.
I'm helping a buddy this weekend do the cam chain tensioners on his TC88. I'm quite sure I read somewhere that when the alignment marks on the pinion and cam gears are lined up, then one of the pistons is at TDC and when the marks are completely opposite each other, the other piston is at TDC. Please confirm if that is true and if so, which piston is it in each scenario. Thanks.
HDF Community Team
Joined: Jun 2006
Posts: 12,791
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From: san antonio
I'm helping a buddy this weekend do the cam chain tensioners on his TC88. I'm quite sure I read somewhere that when the alignment marks on the pinion and cam gears are lined up, then one of the pistons is at TDC and when the marks are completely opposite each other, the other piston is at TDC. Please confirm if that is true and if so, which piston is it in each scenario. Thanks.
I don't speak for Ohio but I think what he was tellling you was that if the timing marks on the inner cam sprockets are properly aligne, the timing marks on the pinion and rear cam sprockets have to be aligned; fool proof.
Last edited by djl; Apr 15, 2024 at 02:29 PM.
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Tourer
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From: SE Mass
Thank you for an actual answer.
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Thread Starter
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Tourer
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From: SE Mass
I think you're right but I don't have any concerns with how that works. Was just trying to remember if there was a relationship between the marks on the sprockets of a properly timed engine to the relative position of the pistons. The question has been answered. Moving on.
Road Master
Joined: Mar 2012
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From: Ohio
Not sure I understand the question; are you looking for TDC or verification of cam timing? Take a look at the attached images of the relationship between pinion and rear cam sprockets at TDC for each cylinder. The first image is TDC front cylinder #2, the second image is TDC rear cylinder #1.
I don't speak for Ohio but I think what he was tellling you was that if the timing makrs on the inner cam sprockets are properly aligne, the timing marks on the pinion and rear cam sprockets have to be aligned; fool proof.
I don't speak for Ohio but I think what he was tellling you was that if the timing makrs on the inner cam sprockets are properly aligne, the timing marks on the pinion and rear cam sprockets have to be aligned; fool proof.
Common knowledge is that the two cylinders are 45° apart. So turning the crank another 360° will put the rear piston on TDC again. You have to turn the crank 45° from rear TDC to get front TDC.
Last edited by Ohio HD; Apr 15, 2024 at 02:10 PM.