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Old 06-24-2001, 10:35 AM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The cam doesn't push directly on the top of the valve. The rocker arm is a lever that is supported on one end by the ballstud (adjustable pivot point on your motor, the top of an hydraulic lifter on V8s after 76). The other end sits on top of the valve. When the cam lobe comes around it pushes on the wear surface of the rocker arm about 60% along the distance from the ball stud to the valve.

The compression check will give you a baseline for future reference. I would suggest dealing with the performance issues first and see where they take you. If I were testing your compression I could gauge the amount of carbon in your engine. That is only because I have a lot of experience with my gauge and that engine. On my gauge I would suspect carbon build-up on a motor with over 170psi compression.

Decarboning an engine is another chore that improves with experience. I really hate to describe my technique to anyone who hasn't done it before. The last time I did a S500 I was pretty scared that I had bent a rod when the misfire continued after I finally burned all the smoke out on a test drive. Thankfully I had only been a victim of misfire identification and cycling the ignition reset it.

Decarbonning requires harsh chemicals and/or mechanical shock. My first experience with it came at my first dealer job (as a Chevrolet technician while I was going to college). Being next to I-75, we used to get all these cars towed in from the interstate gas stations with rod bearing noise diagnosis. The old guys would take a motor (absolutely DO NOT do this) and run it to 3 grand and in the same moment start dumping a quart of water through the intake while flooring the throttle. The engine would stay at 3000 due to the combined effects of the throttle trying to raise the speed and the water drowning it out ( a very sensitive balance with engine damage being just a short distance from carbon removal). I never was able to get the nerve to do this with success. This is one of those things that you can't just do more of a smaller amount. In other words, what one must do is smash the carbon with the water; one can tap on it all day and nothing will happen. The force level required is very close to that which will ruin the motor.

Luckily there are various tools and chemicals that bring this activity to those not so daring. The tool Motovac or any of its generic buddies can do a good job by spraying a chemical through the cars injection system with the added benefit of cleaning the injector rail and injector. I have gathered the experience to do a harsher cheaper mechanism using the product X66 (AC Delco) and the directions on the can. This is a very strong chemical, be VERY careful!!

Even with experience though I was sweating that S500.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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