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Cam Timing Off After Timing Belt Replacement?

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  • digger
    replied
    The belt has teeth you don't even really need much tension to rotate it slowly provided its sitting on the gears correctly it'll stay in phase. Just don't go backwards

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  • zaq123
    replied
    Originally posted by digger View Post
    It's fine if you unbolt after rotating a couple times and relighted but If you do it that way you need to tighten the tensioner loosen it then tighten it again. Why not tighten it once only....



    You don't crank the engine with tensioner loose you hand rotate it. If you rotate the crank the correct way the belt is skways under tension so the only p to v issue is if you put on wrong tooth and then it doesn't matter what you do.


    I agree that the belt is always under tension but with loose tensioner, it痴 just the tensioner spring agains all that cam resistance. I知 sure that the spring will hold since that痴 how you guys are doing it....probably just paranoia on my part..haha


    Sent from my iPhone using Tapatalk

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  • digger
    replied
    Originally posted by zaq123 View Post
    I知 not really questioning this...IMO if the belt is installed correctly, the tensioner spring will take all the needed slack from the get go. Belt teeth are going into sprockets and stay there. Rotate the engine a few times, that unbolt and rebolt the tensioner bolt to equalize the belt. Basically the same concept but different approach. I知 concern with P to V contact when cranking the engine with loose tensioner. The resistance of the aggressive cam can compress that tensioner spring IMO.
    As it is, belt already has a normal stretch that nets 2 degrees


    Sent from my iPhone using Tapatalkb
    It's fine if you unbolt after rotating a couple times and relighted but If you do it that way you need to tighten the tensioner loosen it then tighten it again. Why not tighten it once only....

    You don't crank the engine with tensioner loose you hand rotate it. If you rotate the crank the correct way the belt is skways under tension so the only p to v issue is if you put on wrong tooth and then it doesn't matter what you do.

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  • zaq123
    replied
    Cam Timing Off After Timing Belt Replacement?

    Sorry. Double post

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  • zaq123
    replied
    Cam Timing Off After Timing Belt Replacement?

    Originally posted by jeffnhiscars View Post
    When first wrapped around the gears the belt is typically tighter on one side than the other which can effect valve timing so Its SOP to rotate the engine and then tighten the tensioner. I'm surprised you questioned this.


    I知 not really questioning this...IMO if the belt is installed correctly, the tensioner spring will take all the needed slack from the get go. Belt teeth are going into sprockets and stay there. Rotate the engine a few times, that unbolt and rebolt the tensioner bolt to equalize the belt. Basically the same concept but different approach. I知 concern with P to V contact when cranking the engine with loose tensioner. The resistance of the aggressive cam can compress that tensioner spring IMO.
    As it is, belt already has a normal stretch that nets 2 degrees





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    Last edited by zaq123; 07-09-2019, 10:41 AM.

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  • jeffnhiscars
    replied
    Originally posted by zaq123 View Post
    what is the point of that? If marks aligned, tensioner is tightened and it's as good as it gets. Spinning it with the tensioner loose can compress the tensioner spring delaying the cam with the belt slack and risking P to V contact.
    When first wrapped around the gears the belt is typically tighter on one side than the other which can effect valve timing so Its SOP to rotate the engine and then tighten the tensioner. I'm surprised you questioned this.

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  • digger
    replied
    Originally posted by zaq123 View Post
    Isn't that what that spring is doing, picking up any belt slack? I just trying to imagine how the tensioner will be steel loose with the spring applying all that pressure on the belt.
    Only on the slack side. On a frictionless system it does both sides. there's enough friction in the crank and cam that means you can get some trapped on the other side.
    You also need to rotate to 100% confirm you got the right tooth.

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  • zaq123
    replied
    Originally posted by ForcedFirebird View Post

    To remedy this, I actually start by bolting the tensioner in the full "loose belt" position (spring completely compressed). Then back the crank up one tooth, wrap the belt starting at the crank, then cam, then pull the tension towards the tensioner and rotate the crank as I slip the belt on the tensioner. Then leave the tensioner spring fully compressed, rotate the engine two full times to be sure the marks repeat. Then loosen the tensioner bolt, let the spring do then tensioning, then re-tighten the tensioner bolt.
    I do something similar as well, install the belt with marks aligned, spring fully compressed and its bolt locked; Release the spring and lock it, recheck marks; Rotate a couple of time a check them marks again; Put the dial gauge on the valve, gear on the crank and find the exact cam timing.

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  • zaq123
    replied
    Originally posted by digger View Post
    As you wind the engine over slowly the resistance of valvetrain ensures there's always tension so no harm is done by doing it loose. The purpose of doing it tensioner loose is it ensures the tension side is under some tension when the tensioner is locked off. If you had a bit of slack on the tension side and locked of the tensioner as soon as the crank rotates you'd get some slack.
    Isn't that what that spring is doing, picking up any belt slack? I just trying to imagine how the tensioner will be steel loose with the spring applying all that pressure on the belt.

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  • digger
    replied
    Originally posted by zaq123 View Post
    what is the point of that? If marks aligned, tensioner is tightened and it's as good as it gets. Spinning it with the tensioner loose can compress the tensioner spring delaying the cam with the belt slack and risking P to V contact.
    As you wind the engine over slowly the resistance of valvetrain ensures there's always tension so no harm is done by doing it loose. The purpose of doing it tensioner loose is it ensures the tension side is under some tension when the tensioner is locked off. If you had a bit of slack on the tension side and locked of the tensioner as soon as the crank rotates you'd get some slack.

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  • ForcedFirebird
    replied
    Originally posted by jb02 View Post
    engine is only pulling 15" vacuum
    The m20 does not pull a lot o vacuum in my experience. I came from the domestic car market before working on classic BMW's primarily. They really don't pull the typical 20" as most guides suggest (even stock cams have a lot of overlap compared to pushrod motors). I wouldn't use vacuum as a diagnostic on a BMW motor, in most cases anyways (~230ー vs ~250 stock cams - hence m20's not needing a PVC valve, or EGR to pass emissions). You can line up the crank using the reluctor wheel, and pull off the upper timing cover with just a few bolts and visually check timing (small mirror makes the job easier).


    Originally posted by zaq123 View Post
    what is the point of that? If marks aligned, tensioner is tightened and it's as good as it gets. Spinning it with the tensioner loose can compress the tensioner spring delaying the cam with the belt slack and risking P to V contact.

    It's actually easy to have the belt off one tooth (cam retarded) due to the belt design and oil pump drive. Cam timing can be off several teeth, car will still run and not have V to P contact - EDIT: on a stock cam/pistons design.



    To remedy this, I actually start by bolting the tensioner in the full "loose belt" position (spring completely compressed). Then back the crank up one tooth, wrap the belt starting at the crank, then cam, then pull the tension towards the tensioner and rotate the crank as I slip the belt on the tensioner. Then leave the tensioner spring fully compressed, rotate the engine two full times to be sure the marks repeat. Then loosen the tensioner bolt, let the spring do then tensioning, then re-tighten the tensioner bolt.
    Last edited by ForcedFirebird; 07-08-2019, 08:53 PM.

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  • zaq123
    replied
    Originally posted by jeffnhiscars View Post
    I think your heading may answer your question. Did you spin the engine 2x by hand and then tighten the tensioner ?
    what is the point of that? If marks aligned, tensioner is tightened and it's as good as it gets. Spinning it with the tensioner loose can compress the tensioner spring delaying the cam with the belt slack and risking P to V contact.

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  • jeffnhiscars
    replied
    I think your heading may answer your question. Did you spin the engine 2x by hand and then tighten the tensioner ?

    Are you sure the valves are not too tight ?

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  • zaq123
    replied
    vacuum leak somewhere?

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  • jb02
    started a topic Cam Timing Off After Timing Belt Replacement?

    Cam Timing Off After Timing Belt Replacement?

    I just finished replacing the timing belt, tensioner, and reset valve clearances. I was careful to double check that both the crank damper wheel and cam sprocket were aligned with their respective block and head markings. The engine starts but doesn't run well and will stall when put into gear. I put a vacuum gauge on the manifold port and the engine is only pulling 15" vacuum which suggests possible bad valve timing. Does this make sense given poor running symptoms?

    I am assuming that to correct this I need to drain down and remove the radiator and hoses again in order to completely disassemble the up and lower covers.
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