Turbo Cam timing problem(s)

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mintus
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Turbo Cam timing problem(s)

Post by mintus »

Hi; this is open for discussion, as I have spoken to a number of people that have different and some very complicated procedures. This is how I would like to start and again I am open for contrary points of view before I complete this job on my car. I would first say my car is a 1986 E24 m30b34 with a turbo cam and a extra 0.012" thick head gasket. I have removed all the goodies in front of the cam gear, the spark plugs removed and the valve head cover removed and every thing in between. OK the first step was to rotate cw the engine until the crank gear wheel mark meets with the engine mark T!0 center. Once this is set I have to check for TDC of the number one cylinder. This is confirmed with the piston in the TDC position, the cam gear has 4 bolts and the 3 and 9 bolts should be in the same plane as the head, plus the dewl hole is on the bottom left side approx..7 o'clock. My engine is one tooth off and that accounts for the car fall off at 4500 rpm so it need to be retarted one tooth point one and the turbo cam has a lobe angle of 110 degree for intake and 120 degree for exhaust, that is 10 degrees in advance difference. With the one tooth off and the 10 degree advancement with the exhaust on the cam also with the extra thick head gasket being 0,012" which is 1 degree advancement so that is a total of 10 + 10 + 1 = 21 degree in advance timing. One tooth on the cam gear is 30 teeth / 360 degrees = 1 tooth for each 10 degrees. I would now have the job of retarting my cam 2 teeth. To do this I will slacken the tensioner to zero and mark the chain and mark the cam gear wheel in 3 places with 3 different colours. I have now come to a problem, if I move the cam so that the cam lobes are vertical zero degree for the TDC of cylinder one. This is cylinder in the fully closed position, I still have to retard the cam chain two teeth, but I do not want to move the crank off it's mark, so how do I move the cam gear retard two teeth and have no movement on the crank and the cam gear fitting on the same plane as the cam head??????????? Your help is greatly appreciated. Cheers.
I have two cars. One is a bastard 1979 633 CSI m30b34 transformed into a 1987 635 csi five speed m30b35
ron
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Re: Turbo Cam timing problem(s)

Post by ron »

LOCATION in your profile needed!
They are ALWAYS rustier than you thought!!!!!!
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Brucey
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Re: Turbo Cam timing problem(s)

Post by Brucey »

A. you can't. If you want to revise the cam timing as you desire, the cam WILL have to be in a different place when the crank is at TDC, by definition. The mantra about the cam support bolt holes only applies to normal camshafts.

BTW that the cams have the LCA figures you quote does not mean that the cam timing should be moved as you suggest; your suggestion appears to make the assumption that the lift on overlap (LOA) should be about equal; this is a fairly safe assumption for NA cams (within a certain bhp/litre range) and is a useful sanity check to see if you are one tooth out with a standard setup.

However in this case I would suggest that it is a bad assumption to make. You should enquire with the cam manufacturer what the approximate cam timing should be; with a turbo cam the LOA is often nothing like equal.

I'd also note that if you are using a non-standard head gasket thickness, the cam may not be ground to allow for that and permit you to use standard cam sprockets, i.e. you may need to have an adjustable cam sprocket to make it all work properly.

The conventional method of getting the timing exact (without spending a fortune on it) is to slot the sprocket bolt holes and to use a staggered dowel (that has to be machined to fit once the exact sprocket position is known). The spendy solution is to buy a Vernier type adjustable cam sprocket mounting; I'm not sure if there is a good one that fits M30 engines easily.

If you are using a setup that is proven, you ought to be able to find out what cam timing works best, and just use that. But if the setup is at all different from know setups, the chances are that a lot of time on the dyno will be required to really optimise the cam timing. The good news is that you will typically only make small changes to many turbo engines by making small adjustments the cam timing, they are not like NA engines in this respect.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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jps635
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Re: Turbo Cam timing problem(s)

Post by jps635 »

Korman Autoworks sell an offset adjustable cam timing gear for the M30
'85 635csi JPS (RA2-66)
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