Smoke on deceleration
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Smoke on deceleration
I started getting smoke on deceleration yesterday, and I'm also getting some popping sounds at the same time, kind of like a small backfire but out of the carb. I'm colorblind but I think the smoke is light blue.
I'm guessing since it's happening and deceleration that it's the valve seals sucking oil. Does that sound right? I know the rings are pretty shot too because I'm getting blowby as well but that should cause smoke on acceleration, not deceleration?
How hard is it to change the valve seals without taking off the heads? Any help would be appreciated. I had no idea what I was getting into when I bought this thing! I sure am learning a lot though...
It's a 72 F250 Camper Special with a 390 BTW.
-Chris
I'm guessing since it's happening and deceleration that it's the valve seals sucking oil. Does that sound right? I know the rings are pretty shot too because I'm getting blowby as well but that should cause smoke on acceleration, not deceleration?
How hard is it to change the valve seals without taking off the heads? Any help would be appreciated. I had no idea what I was getting into when I bought this thing! I sure am learning a lot though...
It's a 72 F250 Camper Special with a 390 BTW.
-Chris
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There's some weird stuff going on though too, it will only run if the points are really tight and the timing marks indicate it's at about 50*
It dies before you can even get it down to 20*. I think it may have jumped a tooth on the timing gear. I just need to baby and keep her running until December when I can do my rebuild.
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Are you sure about that? I'm pretty sure that smoke on acceleration is worn rings and smoke on deceleration is valve seals. My reasoning is that it doesn't smoke until you completely let off the gas, the throttle plates close and the engine vacuum is higher, thus sucking oil past the seals into the combustion chamber but I could be wrong.
Fleet Mechanic
Joined: Oct 2005
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From: Gainesville, GA
Yes you can replace the seals with the heads on. Remove the rocker shafts, either put a piece of rope in the cylinders or use an air fitting to hold the valves from falling into the cylinders, remove the keepers and springs and replace the seals. You need a special tool to compress the springs.
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Posting Guru
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From: VA
Probably your rings causing the smoking. You can do the valve seals without removing the heads, but I wouldn't bother since that's likely not your main cause and you say you're planning a rebuild coming up in December.
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Senior User
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From: Georgia
I had that problem on a old Camaro I had. Turned out that the intake was warped on the new crate motor. New intake and gasket and I was good. Of course it only smoked when I let off at around 65-70 mph.
Hotshot
Joined: Mar 2013
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From: Phoenix, Az.
2x Area on the compression test. Do it both wet and dry. Dry is as normal. "Then" Wet is you put a few healthy squirts of engine oil in the spark plug hole. There-by temporarilly sealing the rings. If the test numbers DON'T jump doing it wet the problem is in the heads.
Last edited by JEFFFAFA; Sep 17, 2013 at 10:39 AM. Reason: info posted backwards
Posting Guru
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From: VA
I think you meant to say that a jump in pressure with the wet test should point to bad rings not heads.
Hotshot
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From: Phoenix, Az.
.All please note. I edited my Post above to reflect what info I meant.
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