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#21
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https://forums.maxperformanceinc.com...=795907&page=2
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65 Tempest, 400, TH400 86 Fiero SE 2.8 |
#22
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Was the cylinder up on top dead center when he 'blew air in '? It needs to be to be an accurate test. In my past experience with these engines over 40+ years, a burnt exhaust valve is the most common cause of low compression. You may be in for a simple valve job. Not a big deal. An actual leak down tester with the gauge would be the right way to verify engine condition here.
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Jeff |
#23
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I’m not sure if it was top dead center or not. He’s a pretty old school mechanic locally. I assume he knows.
Believe me, I’m open to somebody testing it too as knowing it’s just a valve job might ease some stress. Out of curiosity if it’s just a valve job and I get the heads rebuilt, wouldn’t that put pressure on the bottom end too or it should be ok? |
#24
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Jeff |
#25
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Noise out the intake or exhaust, or bubbles in the cooling system are a dead giveaway of engine problems. Noise out the oil fill cap is not, without a gauge you have no idea how good/bad the rings are. I've tested engines that sounded horrible for noise at the oil fill cap, but the gauge said they were OK--and others that sounded OK but the gauge and engine performance verified that the rings were bad. "Most" compression tester hoses will need to have the valve core removed before using them with a leakdown tester, or plugging them in to "shop air". Quote:
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Pop the valve stems directly in-line with the valve guides with a soft hammer--or a hammer and brass punch--so the valve snaps open and closed. Doesn't take much. The valve doesn't need to open more than an eighth of an inch, if that. If there's carbon interfering with the valve seal, that'll break it up. More likely, it's a defective valve/seat/guide. Quote:
For $1100, he might as well double-up and invest in Edelbrock heads as flush money down the toilet on ancient iron castings that weren't all that great 40 years ago. Quote:
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I've seen a couple marginal engines get a valve job; all eight cylinders run for the first time in a long time. I found out that those pistons/rods/bearings were only quiet and smoke-free before because there was no cylinder pressure on 'em. Others overheated because with the engine making full power, the corroded/clogged radiator could no longer keep up with the heat load. "It never overheated before you worked on it!" Yeah, but it only made half or 2/3 the power it was supposed to, and you were driving it like my mother. Now that it runs right, you're burning rubber and smiling about it every day. You've got one cylinder (at least) that's had the rings and cylinder walls gas-washed for awhile. You'll know more when you get the heads off. |
#26
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You mind explaining how the cylinder got "gas-washed" when the intake valve wasn't opening any at all? Clay |
#27
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There's some evidence of poor valve-to-valve seat sealing. Last edited by Schurkey; 10-23-2020 at 03:30 PM. |
#28
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Until a bonafide leakdown test is performed, everything is speculation. Perform a leakdown test and go from there.
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Jeff |
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