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Old 06-19-2019, 05:50 AM   #21
Jacksonlll
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Default Re: Mystery Missfire

I come back to an intake leak. A cracked intake manifold can be hard to find. Good luck and let us know what you find.
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Old 06-19-2019, 01:32 PM   #22
john charlton
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Default Re: Mystery Missfire

1001H prompted a train of thought and I removed no4 plug and started the engine and let it idle on 3 cylinders . Took a compression with the running engine and got a steady 40 PSI VOILA !!! Problem revealed my guess that tight valve clearance on the inlet valve . Checked the PSI on cranking and got 75 PSI . The earlier 65 PSI I got I forgot to open the throttle fully . So here is hoping that the engine has adjustable lifters I have never had the cover off but knowing my luck I guess it is a head off job . I will keep you all informed ,stay tuned !!!

John in heavy rain Suffolk County England/
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Old 06-19-2019, 03:00 PM   #23
Ernie Vitucci
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Good Luck, John...Ernie in Arizona
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Old 06-19-2019, 11:40 PM   #24
Tom Wesenberg
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Default Re: Mystery Missfire

If you have a sticky valve, then I'd add a can of Sea Foam to the gas, and another can to the oil.
In less than 5 miles a can of Sea Foam in the oil made my clicking Olds engine sound like new. This was back in the 80's on a Cutlass with a sticking hydraulic lifter.
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Old 06-20-2019, 02:31 PM   #25
100IH
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Default Re: Mystery Missfire

The needle bouncing steadily leans toward tight lash. Erratic bounce, sticking guide, weak or broken spring. Sloppy stem clearance and washed out cam lobe might be a steady but low reading. Compression test-wet&dry, vacuum test readings, cylinder leakage test and lastly this vacuum gauge sans check valve if needed is about as much help as a fella can get. Good luck. One thing we do know, valves won't stick closed over night. They can bounce, leak, wobble and dance or stay open. Then there are rings but that ought to be consistently low, not intermittant. Sorta like herding cats.

Last edited by 100IH; 06-20-2019 at 03:02 PM.
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Old 06-21-2019, 12:49 PM   #26
john charlton
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Default Re: Mystery Missfire

Problem revealed no clearance on the exhaust valve not the inlet which I suspected . The inlet valve spring I can rotate by hand so I do have a clearance on that . I really dont want to pull the head just to fix one valve . Right now my 80 yr old brain is thinking that if I could compress the spring I could get a fine flat file and dress the valve foot to suit ( dont shudder ) I would of course use rags and powerful fridge magnet to catch any swarf . Has this been done before ??? Just thinking thinking thinking . DRAT no adjustable lifters

John in partly cloudy high pressure on the way Suffolk County England .
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Old 06-22-2019, 01:08 PM   #27
100IH
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Default Re: Mystery Missfire

This is a model A. There isn't anything that hasen't been done. Obviously it did not have adjustable lifters. Think I might try the same. File might not touch it due to hardness, got nothing to loose XX.
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Old 06-22-2019, 01:29 PM   #28
nick c
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Default Re: Mystery Missfire

John, I've done this, take a small rag like a piece of an athletic sock or towel, soak in motor oil, rap around lifter base, it will catch and hold the filings. Buy a new file it will cut with no problem.
carry on nick c
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