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post #1 of (permalink) Old 05-21-2000, 06:28 PM
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Intermittent blue smoke, 302 HO

Hey folks, new to this board, and I thought I would pick your brains. I have a 302 HO out of a mustang installed in my Bronco. I built the motor 10,000 miles ago (stock), and now once it's warm, and you let it sit for 10 minutes or more, and re- start, I get a minor puff of blue smoke for about 3-5 seconds. It doesn't happen all the time, only when the engine has been hot, and then sits, and you start it again. At first I thought it was the valve guides, and I replaced em, but it still does it. Where else can oil seep into the cylinders? I do not have any other performance problems. Any thoughts?

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post #2 of (permalink) Old 05-21-2000, 09:03 PM
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Re: Intermittent blue smoke, 302 HO

Perhaps it doesn't. I could just be the fumes/vapors that are vented to the crankcase and then sucked into the intake charge when you start up. The hot thingie leads me to believe that there's a fuel perculation event involved. Since you didn't say what year 302 you have it's hard to say what vapor control you have on it (gas tank, carb, etc.) ........not that I'd necessarily know....but one of the BlueOval veterans here will have a little more to work with.


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post #3 of (permalink) Old 05-22-2000, 01:14 AM
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Re: Intermittent blue smoke, 302 HO

Sorry about that [img]/wwwthreads_images/icons/smile.gif[/img], It's an 86 302, in an 88 Bronco, MPFI, with the late 80's emissions. I tried to re- torque the intake bolts with no results. I pulled the plugs to have a look see, and #2 and 4 plugs were fouled with ash, and the rest were super.

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post #4 of (permalink) Old 05-22-2000, 08:38 AM
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Re: Intermittent blue smoke, 302 HO

It sounds like valve guides, or seals. You say you replaced the guides, how did you do it? The guides are pressed into the head with an interference fit. If you press out the guide, you should reinstall an oversize (on the OD) replacement. The deformation to the cast iron head is large enough to allow for a tight guide, but still allow for a small amount of oil to leak down into the combustion chamber. Whenever we rework a head, we install a guide .0015" larger on the OD. This is for Aluminum. You could probably get away with a guide in the .0005" - .001" range. You should also check your tolerances for the guide ID as well. If it's a little sloppy you could be getting oil to seep by the valve stem. A typical clearance for the stem should be .0015" - .002". If you had the guides knurled, they may be worn out again. Knurling works short term on bronze, and isn't too good for cast iron guides.
Also check your seals. I don't know if you have the traditional seal, or the newer boot style. If either was installed scew to the guide, you'll get oil to blow by.
How is your compression? Check it out to find the suspect cylinder. You may want to investigate your rings as well. You could have a sticking, or cracked oil ring, or mis staggered gap on one of your pistons.
Keep us posted.

post #5 of (permalink) Old 05-22-2000, 11:00 AM
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Re: Intermittent blue smoke, 302 HO

Thanks, I'll have to start doing a little detective work, as I had a shop do the heads for me. I'm not sure how they did the guides, but the seals are the traditional type. Thanks again for the ideas to look into.

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