Quote:
Originally Posted by wl_walker
Oil consumption is high at least 1/2 quart in 300 miles. The rattle is heard while cruising with light throttle, I would expect, if it were pinging I hear, to get worse under greater load which I don't. It goes away. Since compression is 155-160 per cylinder including the suspect one it would seem to me that the valve seals and rings are doing their job. I agree that the initial thing would to do valve stem seals. Just that I always open the 'can of worms' lol
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If the advance mechanism vacuum source is drawn from the intake manifold as opposed to ported vacuum, at light loaded cruise the vacuum will be high and, depending on the vacuum advance "curve", could be at maximum advance.. Under greater load or accelerating, the vacuum will go lower, pulling out some of the timing --- pinging disappears..
Don't be fooled by your compression readings.. Quite often worn rings will indeed exhibit good compression. Have you conducted wet/dry compression tests??. At the rate of your oil consumption, valve seals will help some, but will not totally cure that.. I'm afraid you have a well worn engine. Do the seals and see what happens.. Another thing to consider is oil leaks.. If your engine "marks its territory" there's part of your problem.
{EDIT} The can of worms theory always applies when working on these old trucks. There's no getting around it..