Another smoking 390
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Another smoking 390
Yes, its another smoking 390. Ive searched the forums, but didnt find one with quite the problem i have. Gotta 74 f250, 4x4, 390 4sp. Only getting oily smoke in the cab when im goind down the road, although a faint blue trail has been noticed occasionally. I have recently noticed smoke puffing out the top side of the drivers side valve cover, and sometimes the breather while it is cranking to start. PCV valve is good, hose going to the carb. I got this truck about a month ago, and didnt have a smoking problem at first. Ive heard "rings" and it may be. This truck did sit for awhile, but I put probably 500 miles on it after it sat with no problem. Intake Manifold leak maybe? Cant really get it to smoke though in the driveway, gotta be going down the highway. I do have an exhaust leak, but its been that way since I got it
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Tuned
Joined: Aug 2003
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From: Eastern Virginia
How many miles are on it? How is the compression? Does it use oil? Could check your drain back holes in the head....and while the valve covers are off check the gaskets there too.
My 360 did the same thing. My cab smelled like oil all the time. And the truck burned/puked a quart every 100 miles. I pulled it down to find 2 cracked compression rings and the oil rings were toast. The truck had 116K and the oil had been changed every 3000. The inside of the motor was clean as a whistle. But it had sat for 10 years when it was new and 7 years before I got it last year. Mine would blowby so bad it would blow the crankcase breather out of the holder and spray oil into my air filter. Soon to be a 390...
My 360 did the same thing. My cab smelled like oil all the time. And the truck burned/puked a quart every 100 miles. I pulled it down to find 2 cracked compression rings and the oil rings were toast. The truck had 116K and the oil had been changed every 3000. The inside of the motor was clean as a whistle. But it had sat for 10 years when it was new and 7 years before I got it last year. Mine would blowby so bad it would blow the crankcase breather out of the holder and spray oil into my air filter. Soon to be a 390...
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Not sure of the actual miles on this motor. I noticed when I bought it that the motor still had fairly decent motor paint on it, and the silicone on the gaskets (Head, Valve cover, etc) still had bright color to it. I saw no oil leaks, etc., and the motor didint look freshly washed either. I pulled the valve covers here a little while ago. It doesnt look like oil's making it up to the rockers very well, and its a kinda burnt on oil look in there. Can I check the rings without pulling the motor completely out? Im gonna try and get my hands on a compression tester this weekend. Any advice before I commit to pulling all this stuff off?
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Sure sounds like blowby to me.
Do the compression test, and note the results on all cylinders. Then squirt some thick motor oil into all the cylinders, and do the tests again.
If the numbers rise appreciably after putting in the oil, it's rings. If not, it's valve stem guides and seals.
A badly worn valve guide can let enough oil into a cylinder to make some smoke. The seal won't last long, because the worn guide is letting the valve jump around and hog out the seal.
After sitting, rings can become seized, but after 500 miles, they should have loosened up.
Do the compression test, and note the results on all cylinders. Then squirt some thick motor oil into all the cylinders, and do the tests again.
If the numbers rise appreciably after putting in the oil, it's rings. If not, it's valve stem guides and seals.
A badly worn valve guide can let enough oil into a cylinder to make some smoke. The seal won't last long, because the worn guide is letting the valve jump around and hog out the seal.
After sitting, rings can become seized, but after 500 miles, they should have loosened up.
Last edited by scroob; Apr 17, 2004 at 03:25 AM.
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Thanks scroob....The more I mess with it the more Im thinking rings. Ill probably be changing the motor out. Anyone got opinions on if a 351m is better than a 390? Thats what I had in my 79, and was definately more impressed with its durability, or should I just look at a ring job?
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351M into 390 is a hard swap. Nothing matches. Tranny different, motor mounts different, exhaust different. Besides, you wouldn't want a 351M - you want a 400 with 49 free cubic inches and stump puller torque.
I've had several FEs, and durability never seemed to be in question with them.
I've had several FEs, and durability never seemed to be in question with them.
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