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328 cambelt change... degree the cams?

Discussion in 'Technical Q&A' started by kiesan, Feb 10, 2004.

  1. kiesan

    kiesan Formula 3

    Nov 21, 2003
    1,140
    Seattle
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    Kie Robertson
    I'll be changing the cambelts, tensioner bearings, seals, waterpump, etc. on my 328 this Spring. Whats the consensus on whether or not to degree the cams during a belt change? I don't seem to hear folks talking about it too much in all the cambelt threads so I'm guessing it's in the "why bother?" category.
     
  2. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    6,972
    After doing all the work to remove and reinstall the belts,

    Do you want the car to run like before, or do you want the car to run as well as possible?
     
  3. kiesan

    kiesan Formula 3

    Nov 21, 2003
    1,140
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    Kie Robertson
    If it ran like it does right now I would be happy. Seems to run exactly as it should. Naturally, I would like it to run as well as possible so if that means hooking up a degree wheel and the whole works then thats what I'll do. I guess my commentary was me wondering aloud why with so much cambelt chatter that there doesn't seem to be much discussion on that aspect of the job.
     
  4. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    6,972
    In the Ferrari workshop manual they show using both a degree wheel and a mircometer to fully degree each Cam. The micrometer is used to measure the lift on the valve while the degree wheel shows the angle of the crankshaft. In the F355 manual there is a list of 5 valve lifts that can be correlated with the degree wheel to get the cams dead on. This method is better that the factory stampings on the cams and retainers on the cams themselves for setting the timing.

    Does it show up on the bottom line--only if you screw up.
     
  5. ferrarifixer

    ferrarifixer F1 Veteran
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    Jul 22, 2003
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    Phil Hughes
    Degreeing the cams is a job more specifically associated with checking and adjusting the valve clearances, as the valve covers need to be removed.

    For a "peace of mind" precautionary belt change, I'd recommend just changing the belts, but check your mileage to see when the valve clearances were last done as you can save a lot of labour to do the full job properly...... once. Valve clearances ONLY need to be done on mileage, whereas belts have a time schedule also, of course.

    On 328 and 308QV, there is (almost) no advantage in doing a precautionary water pump overhaul, as it can be removed easily at any time. On the 2 Valve cars the belt covers are in they way, so that's why many chose to do a pump at the same time. The QV/328 belt covers are completely out the way of the water pump.

    If your pump is healthy, you can change belts in one day easily and continue to drive your car and enjoy it.

    A full valve clearance, new cam seals, degree timing, belts and water pump service would take a competant mechanic about 40 hours to complete.......Still only one week of work, plus a bit of down time if all parts are not on the shelf. To skip the degreeing would save about 6-8 hours of labour.

    The scope for human error in a poorly executed attempt at degreeing is higher than the potential error in matching the factory marks up properly. Since 1987 I've degreed about 30% (of around 150 major service jobs) of cams in, through either curiosity or request, but never recommendation. The marks are NEVER more than the line width away from the factory marks. Just look at them from straight above with a good eye. Use a mirror for the 5-8 bank.

    On 348/355/360 a Crank TDC needs to be established. All other V8 models have it already.

    To degree the 355/360 cam you must use the lateral inlet valve. Many techs use the wrong valve and end up with a cam almost a whole belt tooth off. I just corrected a dealer serviced car for this reason.
     
  6. kiesan

    kiesan Formula 3

    Nov 21, 2003
    1,140
    Seattle
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    Kie Robertson



    Thanks ferrarifixer... that is great info. My car (20k miles presently) had a complete 30k service at 9k in 1995 so I was going to renew the belts and I thought I might as well check the valve clearances for piece if mind. All the seals were replaced during that service at 9k miles as well but do you reccomend replacing them since I'm in there?
     
  7. peajay

    peajay Formula Junior

    Apr 17, 2002
    454
    near Paris, France
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    Paul
    If you plan on checking the cam belt timing to the cam marks (and not the approximate sheet metal pointers on the outside of the cam covers) you will have the cam covers removed anyway, so to check the clearances is a quick job. Of course if you need to change shims it will take longer, but definitely worth doing. I had no changes to make, so it only took about 30 minutes with the cam covers removed. I didn't check the degrees, I would think that in the vast majority of cases you can set it as close as is normally required by using the cam to cap alignment marks. I think Ferrarifixer has the right approach.
     
  8. ferrarifixer

    ferrarifixer F1 Veteran
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    Jul 22, 2003
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    Yes, I'd recommend changing the seals as you're in there anyway.

    Be aware though, most cam seals (or the seal housing O rings) leak due to poor assembly technique, and not actual seal failure.

    The seals are fairly straight forward to fit, but the housing O rings must be siliconed into the head AND cam cover groove. This causes a problem as it all needs to be done quickly before the silicone vulcanises.

    So, check all your clearances, remove the cams, change the seals and housing o rings and tappet shims as necessary, then cut the gaskets to shape etc.

    Make sure all parts are clean and DRY, then assemble it a quick as reasonably possible. With practice, perfect dry cam seal/housing can be achieved. It's not easy though.

    Change the distributor seals too.

    The race against the vulcanising silicone can be avoided by using hylomar. But it's is not strictly the correct way to do it. Any escaped hylomar in the oil circuit is bad news.
     
  9. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    6,992
    Groton, MA
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    Verell Boaen
    The reason for the o-ring mounting of the seal housings is that they let the housing float into final alignment in order to perfectly center the seals on the cams.

    I've seen seal leaks/seal lip failures due to the seal ending up off-center when anything other than several drops of oil was used in the o-ring grooves. (Of course,a matchhead sized dab of RTV is needed at the gasket's end to seal the gap in the outside of the groove at the joint between the cover & the head.)

    The oil ensures that the o-ring slips into final position w/o bulging into the gap between the cover & the head & getting pinched/nicked as the gap is being closed by the cover being screwed down.

    The o-rings end up being compressed very tightly into the grooves. The top & bottoms of the groove squeeze very noticable (~2mm wide!) flats on the top & bottom of the o-rings. An o-ring squeezed this tightly shouldn't leak.

    Since RTV is very slippery before it starts to cure, I guess I can see how it could also lubricate the o-ring, but it would have to be used very carefully & very sparingly to avoid problems.

    The problems I've seen w/RTV have been to fairly large quantities being gooped on:

    1) It cured w/the o-ring off-center & unevenly compressed, thus cocking the seal housing at a slight angle & unevenly compressing.

    2) It actually pushed the gasket out of the groove between the head & cam cover, leaving a gap that oil could ooze out of.


    Hmm, This is the 1st I've heard of hylomar causing problems in the oil stream. I can see how a drop of it could close up a very small passageway tho.

    One that comes to mind is the oil drain hold in the head that drains oil from behind the cam seal housing. I've seen it plugged sediment deposits & also RTV from a sloppy ass'y, so I can see how a big drop of hylomar could clog it.

    Is this the kind of problem you're referring to?
     
  10. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    10,163
    San Carlos, CA
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    Mitchell Le
    i have always thought (rightly or wrongly) that the reason to use Hylomar is that it gets dissolved by the oil if it gets in the oil, no?
     
  11. Verell

    Verell F1 Veteran
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    May 5, 2001
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    Verell Boaen
    NO!!!
    I've never assumed that, figured that if it's to do it's job as a gasket dressing it couldn't dissolve., but since you raised the question, I went to the permatex web site & looked at the Tech Data Sheet:

    http://www.permatex.com/MSDS_data/tds_files/25249.pdf

    Bottom line:"resists fuels, lubricants, water, water/glycol and related engine fluids."
     

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