Burning oil

[Guest HALLOWEEN Z]

I'm having problems with all the plugs on one side of the motor all black and oily and on the other side they are burning perfectly. Is there any way to tell if its the valve guides or piston by doing a compression test? I've been getting what I thought was carbon build up from possibly running rich on that side of the carb since I put the motor in the car. After a long road trip I noticed the oil on the plugs a lot more. Since its only one side is it most likely the valve guides in that head? I don't know much about replacing valve guides but when someone rebuilt these do they "bore" them out like a cylinder and use different size valves or are they always replaced with the same size?

[dr_hunt]

If you have a dual plane manifold with a split plenum then the carb could possibly be the culprit.

 

Heads are usually drilled out and a replacement guide is installed followed by doing a valve job and resurfacing the valve faces in some configuration. There are valve guide inserts that some people use, but the sure way to tell is to do a compression test, one dry and then squirt some oil in the cylinder crank it a few times and do it again, if the second reading is higher then the valves aren't seating well and the guides are likely worn out. On stock chevy heads, there is an o ring of sorts that keeps oil from running down the valve stem, if they are old heads then these are heat cracked and leaking, but if they are that old then likely they need rebuilding anyway. They make umbrella seals, perfect circle style seals and the o ring type. You can use one or a combination of PC style and o ring or umbrella style and o ring.

 

It is not worth doing just one head, and IMO it's not worth doing two heads without doing the whole engine rebuild if it's an old engine, but that's my opinion. If it's a new engine or relatively new then possibly somebody didn't do the heads right, and they need to be redone. This will offer you an occassion to change cams while your at it if you so desire. Good luck.

[John Scott]

Could also be a leaky manifold gasket pulling oil from the valley. One whole side of seals or guides usually doesn't fail all at once. Depending on manifold type and with carburetor removed, you can sometimes see if there is an oil trail from the manifold to head mating surface towards the valves. Also if heads or manifold have been machined without regard to eachother, angles don't match creating a problem like you describe. Just another thought.

John

[dr_hunt]

Yeah, but if it was leaking that much, it would hardly run or at best, be so rough you couldn't stand it and it wouldn't idle for squat.

[John Scott]

Hardly run? A gross machine mismatch yes, but personal experience, leaky gasket no. No misses, idled fine except for eventually fouling the 2,4,6,8 bank with oil. In my case a poorly sealing manifold to head gasket right at the base of the valley. Just as somewhat worn valve seals or guides won't create a vacuum related miss, but still draw oil into the chamber. I've also heard of this when using silicone for a gasket seal which eventually is broken down by the fuel, causing the seal to fail.