| Moderated by: Greg Fletcher | ||
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BILLBEN Member
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74 J-H WAS RUNNING GREAT SINCE VALVE JOB 3 YEARS AGO. ON LAST A.M STARTUP FROM COLD, REVED TO ABOUT 6K- THROTTLE STUCK- I SHUT IT DOWN AT ONCE, BUT HEARD A SCARY RATTLE THAT SEEMS TO BE COMING FROM THE INTAKE SIDE-I CAN'T BE SURE.COMPRESSION IS EVEN AND WITHIN SPEC- DOES THIS RULE OUT THE VALVES?AND IF IT DOES, AND YOU WERE ME, WHERE WOULD YOU START??? MANY THANKS FOR ANY "LONG RANGE" CLUES! BILL |
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Greg Fletcher Administrator 
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A "scary rattle" is something to be very concerned about. I would classify this under Mystery Noise and assume the worst. If the compression is up to par, then we can assume the valves and rings are sealing, but that's about all. If you can't get a proper reading, then you have nothing to go on. First, be sure your throttle sticking problem is fixed, that's rather dangerous. If this were my car, I'd start by ruling out for certain any external source for the noise, such as pulleys or the alternator or whatever. You'd be surprised how one thing can sound like another with everything whirling around down there. Checking the valve clearances on each side as a matter of course before you remove the cam towers would be in order. If the noise is really coming from the valve train area, I would expect to find a broken part, such as a spring or even a valve guide. I've never seen this happen, but you never know. A broken ring in one of the cylinders can make some scary noise also. I once had a machine screw unknowingly get sucked into a carb on a Rover P6 where it ended up getting pounded in the combustion chamber. It made an interesting indentation in the piston and head and made a horrible racket that sounded like it was a valve problem. Almost like ball bearings in a blender. I just popped it out with a cold chisel and put everything back together and it was fine. |
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Gary Martin JH 15371 Member
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Another posibility would be a cracked piston or piston skirt. When cold the pistons have not expanded to proper tolerances. Older cars need to be warmed up before running at high RPM's. Newer cars have much better piston designs and materials that lessen this problem. If the noise is quite while at idle, but then becomes apparent when the engine is reved up, or when returning to idle, I would suspect a piston. The noise would be simiar to that of a bad rod bearing. If the noise is always there regardless of engine speed, then it could just be something in the valve train. Gary |
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smcmanus Member 
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When you revved to 6K under no load you possibly floated the valves. It is possible that one or more of the shims popped loose and I'm not sure where it would end up. There is the chance that this could happen so I think you should pull the cam towers and have a look. This would be happy news but don't rule out the other suggestions. But not to worry, you need to pull the cam towers to tear it down anyway. Good Luck Steve |
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Jensen Healey Super Moderator 
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These cars will make some crazy noises if the cam belt is too tight. I replaced my pulleys and overtightened the belt. There was a loud knocking noise and I thought the worst. After correcting the tension I have put about 1000 miles on the car with no problems, and fewer scary noises. |
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