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328 Camshaft Alignment

Discussion in 'Technical Q&A' started by carlrose, Apr 17, 2004.

  1. carlrose

    carlrose Formula Junior

    Nov 25, 2003
    295
    #1 carlrose, Apr 17, 2004
    Last edited by a moderator: Sep 7, 2017
    Quick question here. Have searched the archives with some success. Still tracking down my 328 (1988) irregular idle isse, intake plenum & runners off currently. Set intake cam 1-4 bank directly on marker on camshaft bearing cap (as seen through oil filler hole). Inspecting the *external* 5-8 bank camshaft alignment marks (on rear belt cover) the exhaust cam lines up exactly with pointer but (realizing these are external markings only) the intake cam seems a little off. Here's a poor picture:


    History: belts replaced 450mi previous excellent dealer, cams were set with degree wheel and valves adjusted as part of 30K. Ran perfectly for about 400 spontaneously developed irregular idle with "popping" sound in exhaust. Could I have a belt slipping one tooth causing my symptoms?

    Trying to decide if this merits rear cambelt cover removal to check bearing caps.

    Thanks for the help,

    :) Carl
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  3. Mark 328

    Mark 328 Formula Junior

    Nov 6, 2003
    510
    Orange, Ca
    Full Name:
    Mark Foley
    #2 Mark 328, Apr 17, 2004
    Last edited by a moderator: Sep 7, 2017
    Hi Carl:
    It is rainy and cold here so I went out and looked at my marks, on the rear bank, WRT to the pointers mine are off about as much as yours are, some of the cause may be parallax, but when the belt change was done the marks were off too. The picture is from the rear intake; did not get into the front. 0n my car, the pointers are not very accurate.
    It seems to me that if the belt were loose enough to jump one tooth it would probably jump another.
    Mark
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  4. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    6,992
    Groton, MA
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    Verell Boaen
    The external markers on the cam cover rear shields are really hard to read with any accuracy. With some luck you can tell if you're a belt tooth off, but don't try to use them to do any serious alignment.
     
  5. carlrose

    carlrose Formula Junior

    Nov 25, 2003
    295
    Thanks for the input Mr. Foley & Verell.

    Went out & put a tape measure on, shined flashlight along axis of camshaft, appears to be about 2-3mm off from pointer. What I was more concerned about when I noticed was why exhaust cam is "perfectly on" and intake is slightly off?

    Now if I get really determined & pull the cam cover, should I see the marks on the cams line up *exactly* with marks on the cam bearing covers?

    Thanks of course again,

    :) Carl
     
  6. Verell

    Verell F1 Veteran
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    May 5, 2001
    6,992
    Groton, MA
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    Verell Boaen
    #5 Verell, Apr 17, 2004
    Last edited by a moderator: Sep 7, 2017
    Yes, assuming your cams are properly aligned, the internal marks should line up.

    However, *exactly* is subject to subjective interpretation. As you can see from the attached photo, the mark on the cam cap is noticably wider than the mark on the cam itself. Ideally the mark on the cam s/b centered on the mark on the cap.

    Even with pulling the cam gear locking pin & iteratively trying various combinations of the holes in the cam & gear it seems to be very hard to get the marks to perfectly align on some engines.

    It sometimes ends up that the cam mark is within the cap mark, but slightly off-center when you look very very closely. This seems to be close enough for normal spirited street driving.

    There was a posted report of someone aligning his cams very precisely with a dial indicator & degree wheel and finding that when he was done the cam mark was slightly off-center of the cap mark. Best explanation is that the cam was imprecisely marked.

    Of course, there's one extreme case, documented in the archives, of a set of cams w/o any marks!!
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  8. carlrose

    carlrose Formula Junior

    Nov 25, 2003
    295
    Thanks Verell.

    Educate me - if the timing was off 1 tooth on one camshaft, would I necessarily see a difference in compression #s? I have between 185-190 on all cylinders/both banks.

    My initial response would be "not unless there such a timing overlap issue exists as to have insufficient stroke distance/time with valves closed to develop good compression". And thus cambelt 1 tooth off (12 degrees of rotation?) probably would not make a significant difference?

    Thanks again,

    :) Carl
     
  9. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    6,992
    Groton, MA
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    Verell Boaen
    You answered the question yourself. A cam can be pretty badly miss-timed & it won't affect a compression test.
     
  10. carlrose

    carlrose Formula Junior

    Nov 25, 2003
    295
    Thanks Verell. Next weekend fun now planned...!

    :) Carl
     

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