valve seal vs leaky ring

[Chris6050]

My car burns oil. I have to add a quart every 500-700 miles. The car USUALLY doesn't smoke under normal acceleration. It sometimes smokes at start up and when I'm getting on it. Last night though it started misfiring and there was a lot of smoke coming out at idle and and while driving. I found out that the #8 cylinder plug had oil on it. I changed the plug and now it's back to running ok.

It's been burning oil since I bought the car a year ago and has been getting slightly worse ever since. It has 75k miles on it when I bought it and had about 2k miles put on it the year before I bought it. I've heard that the seals tend the go bad if the car isn't used that much. I use it as a daily driver so going from 2k miles in a year to a daily driver is a pretty big change.

I know the best way to check would be a leak down check, but I figured I'd ask first before I buy the tool needed. The compression is consistant in the other 7 cylinders but is lower in the #8 one. Anyone have any ideas which could be causing the oil burning? Thanks.

-Chris

 

[dastang2]

heads need to be rebuilt, i had a tbird that would smoke on startup, but it would scoot down the road quick. one day i was going probably 115 for 5 minutes and i looked and smoke was everywhere but it was running fine. i started driving normal and it stopped.

 

[Chris6050]

I think its the valves too. The only thing I'm concerned about is the oil on the plug. When the smoke was pouring out it wasn't running fine, it was missing.

 

[88stangmangt]

fouled plug...............since you changed it things are fine................the cylinders should all be within 10% of each other if they are you need to put in new seals and that means it is time for those bigger heads you always wanted.

 

[Chris6050]

I have a set of Trick Flows waiting to go in. I'm just trying to figure out if I need to do a cheap rebuild or just install the H/C/I and save for that 331 stroker I've always wanted.

 

[Chris6050]

Anyone else?

 

[HISSIN50]

how where the wet vs dry compression numbers?

 

[battyice]

Faulty valve seals won't cause low compression, but they will allow oil to leak down around the valve stem into the combustion chamber; hence the smoke when the engine is started. It is possible that one of your valve seals/guides is totally shot and has allowed enough oil to leak into the cylinder to burn dirty and form deposites on your valve seats, the result would be low compression due to poor valve sealing.

An old trick to help determine the cause of low compression is to do a compression check normally, then squirt a small amount of motor oil into the cylinder through the spark plug hole and do the compression check again. If your compression in that cylinder is higher once the oil was added, you probably have worn compression rings (the oil added will help seal the rings and raise the compression reading).

Either way, if you're going to go through the trouble to tear down the engine for a new set of heads I would recommend pulling the motor and freshing it up. You'll save yourself a lot of headaches down the road by doing it right the first time. Assuming your engine isn't totally shot, you can clean up the cylinders with a quick hone, replace the rings, crankshaft bearings, timing set & oil pump, and then button it up with fresh gaskets. Get the flywheel resurfaced and throw in a fresh clutch and you'll be ready for action. (obviously this is just a quick overview and omits some parts/steps but you get the idea).

Rebuilding a mild motor isn't nearly as difficult as some people make it out to be, as long as you're just looking for 300hp or so spend your money in other areas. Personally I'd rather have a 302 with a fresh re-ring kit in my car and spend some money on upgraded brakes, new shocks, and all the other things that could stand to be replaced on a 15 yr old foxbody.

You should consult with some of the other members on this board to see what kind of fuel system upgrades (if any?) will be necessary to support those new heads.

Just my $.02, good luck.

 

[Chris6050]

HISSIN50 what do you mean by dry vs wet #'s?

battyice, I agree with you, I would like to refreshen my engine up, but I really want to save and stroke it to a 331. If it's just the seals, I can swap the heads and then save up the money I'll need for the 331.

 

[jerry beach]

HISSIN50 what do you mean by dry vs wet #'s?

He is talking about a dry comp. test, then a wet one with some oil in the cylinders. If the #'s go way up, the rings are shot, if not the bottom end is prolly ok. Do this FIRST to make sure the bottom end is good. You can buy a compression tester for $20 or so a the parts store. Read the directions, it will tell you exactly how to do the wet and dry test.

Pull the valve covers off it and see if there are puddles of oil on top of the heads. Some folks never change the oil and the drain holes in the heads get clogged with sludge. This can cause the condition you describe, and its the cheapest, easiest thing to check on and fix if that is your problem. You just run a length of coat hanger down the holes to clear them and you problem is solved. Wouldnt hurt to change the valve seals while you are there.