need help, smoking 390.....
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Senior User
Joined: Jan 2006
Posts: 217
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From: Dillon, Colorado
need help, smoking 390.....
I have a 1972 f-250 camper special with a 390. The guy i bought it off of said it needed different heads because the current heads (c8aeh) did'nt have hardened valve seats, and that's why it smokes. That's all fine, but upon reading some thread here, I wondered if we was right. The motor runs great, and dosen't smoke at all until it's hot. Does that fit the description of soft valve seats?
Lead Driver
Joined: Oct 2004
Posts: 8,062
Likes: 35
From: Central Oregon
The c8, I think would make those heads from 1968, and they would not have the hard seats. But you smoking sounds more along the lines of worn valve guides and or seals. If the engine is running great, I don't think your valve seats are worn though. I have been running a 67 390 with out the harden seats with no problems, I got the engine in 1971 with 40k on it and I put rings and bearings in it in 1981 and put it in my 66 F-100 4x4 and it's been running great all along.
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
Likes: 423
From: Long Island USA
If it were rings, it would smoke on startup and clear up as it warms up.
If it were the valve guides, it would do it on startup and clear up pretty quick, usually.
I wonder ...
Next time it's smoking, the more the better, pull the PCV valve out of the valve cover, and see if you see oil pooling in the head.
Sounds like the heads are filling with oil and running down the valve guides. Worn rocker arms and shafts will cause this...
If it were the valve guides, it would do it on startup and clear up pretty quick, usually.
I wonder ...
Next time it's smoking, the more the better, pull the PCV valve out of the valve cover, and see if you see oil pooling in the head.
Sounds like the heads are filling with oil and running down the valve guides. Worn rocker arms and shafts will cause this...
Cargo Master
Joined: Apr 2004
Posts: 2,574
Likes: 4
From: Golden, CO
Stick with the lighter oil for the winter. Heavier oil takes longer to distribute through the motor, which puts more wear on all those dry bearings.
Trivia: One dry start wears bearings the equivilant of 500 highway miles.
I agree with Art; if it works, don't fix it quite yet. The valve stems came with rubber seals on the top. The rubber hardens, breaks up and clogs the drainback holes at the corners of the head. The oil pools till it's level reaches the intake, then drains down the valley under the intake. This puts the valve stems under oil.
You may have to pull the valve covers to check the lower drains. I seem to remember my covers having baffles under the openings.
Trivia: One dry start wears bearings the equivilant of 500 highway miles.
I agree with Art; if it works, don't fix it quite yet. The valve stems came with rubber seals on the top. The rubber hardens, breaks up and clogs the drainback holes at the corners of the head. The oil pools till it's level reaches the intake, then drains down the valley under the intake. This puts the valve stems under oil.
You may have to pull the valve covers to check the lower drains. I seem to remember my covers having baffles under the openings.
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Elder User
Joined: Jul 2002
Posts: 510
Likes: 0
From: Charlotte
Along with all mentioned above, I recently went through worn valves due to non-hardened seats. Compression test found low on 3 cylinders but I had NO smoke. I did have a miss at idle and cruise that was hard to diagnose. 66 390 heads.
A compression test will let you know if the seats are heading south.
A compression test will let you know if the seats are heading south.
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