thebruce

I finally got tired of stinking up the garage, and just as tired of my oil consumption going up, so I decided to pull the plugs and have a look. Four are definitely oily, four are clean, in a fairly random order.

What's next in the process of tracking down where the leak is?

From what I can tell, when some are oily and some aren't, it rules out a bad PCV valve, and I would imagine that it rules out a leaky manifold gasket too. So-- is there something other than valve seals that would cause this? Would poorly sealed manifold bolts do this? The engine was rebuilt about 20k miles ago, so I'm pretty sure the rings are fine.

The engine is a 350 with a CompCams XE268, Trick Flow 23 deg heads, RPM AirGap intake, and a Performer 600 carb.

Thanks for any suggestions.

-the Bruce :cheers:

rob75383

If you had the motor decked, and then put brand new heads and manifold on, you might have a slight leak by the ports between the head and the intake.
Although, I didn't have my heads or intake machined to correct the angles, I did eventually use the thick fel-pro gaskets, which probably have more leeway, and can seal that better than the cheep gaskets.
I had the same as you are describing, except that it was all of the plugs. No PCV, just 2 breathers. I had a fresh 383 shortblock that I assembled with one of those cheepo $40 full engine gasket sets.
A year or two later, I pulled the heads, had them machined for the teflon valve seals, bought some premium ARP bolts and studs, bought the felpro head gaskets for $30 each, and swapped my performer with an RPM air-gap, and again, used the premium felpro intake gaskets.
I can't say which fixed my oil consumption problem, but between all of those, I haven't had oily plugs since.

thebruce

No machine work done to the surfaces that I'm aware of. I'm going to be taking the AirGap off and putting the orginal L82 manifold back on pretty soon, so I guess I will be able to tell if the oil was coming through the manifold gasket.

I remember reading a post a few years ago that said you could figure out if the valve seals were leaking by having someone follow your car and look to see when it smoked more. Based on whether it was when you accelerated or decelerated you would know if it was the intake or exhaust valves. Anyone have an idea?

rob75383

Oil consumption gremlins suck!
I wonder why no one else is chiming in???

I was losing about a quart every 200 miles, and there was no visible smoke coming out of the tailpipe while cruising. I had my mechanic buddy follow me, and he didn't see a thing. There was a puff at startup, but he told me that was probably due to the mismatched parts that came on my world heads- (great castings 4 the $$$, but the stock umbrella seals had an OD that was equal to the damper spring's ID, which equalled chewed up umbrella seals). He guessed that the oil that was under the valve covers was seeping into the combustion chamber while the motor was off, hence the puff at startup.

What plugs are you using, and what heads do you have?
There's bound to be someone more qualified than me that can help you...
All I know is from what I've experienced, and I only had about 6 weeks experience working in a machine shop.

Larry B.

Actually .....It sounds like worn valve guides. SB chevy's are notorious for this. They really don't have valve guides per say but rathe an "O" riing at the top of the valve stem which doesn't do much at best. You can replace them with "umbrella" type seals ..IF the bosses are machined... some are..... some aren't...That's kind of a band aid untill you can do the heads with new vvalve guides.

thebruce

I've got Trick Flow Aluminum heads on the motor now, and they're pretty new (less than 2000 miles).

Larry B, I hope that worn valve guides isn't the problem. I will probably go ahead an put the umbrella seals on to see if that helps. From what I understand it's a pretty easy process and only requires the compressed air spark plug thread adapter, and a spring compressor. '75 383, any experience doing this in your shop? How big is the PITA factor?

Thanks. :flag

SpyderD

I have my own oily plugs, but only along the threads, and no noticable oil loss. After some research this is what I learned although I am not sure if it is accurate - oil on the actual plugs may mean leaky valve guides, oil on the threads may mean oil coming up through the piston rings and getting pushed out the threads.

Larry B.

+I've done it on the car, but I perfer the rope in the cylinder method over air. No chance of anything goin wrong. Just use new clean nylon rope.

rob75383

Since the heads are new, I doubt it is your valve guides. When I removed my heads to chase down the oil consumption, there was oil coked to the underside of the valve head, and on the stem right above- especially on the exhaust valves. Since I got the teflon seals put on, there is no more chunky burnt oil (like dried black cottage cheese) on the backs of the valves.
At my short-lived job at the machine shop, we did all of our work on disassembled pieces. At home, I always just pulled my heads to work on 'em. If you're going this route, before you disassemble everything, do a compression test, and a leakdown test, to look for major discrepancies between the cylinders. I have never personally tried the compressed air method of removing the springs. I do not reccomend it, my experience with using a spring compressor that I bought from summit, was that the valve has a tendancy to be pushed down as well as the spring. This was okay for me since the head was off the block. I think some of the cheeper spring compressors are poorly designed, and put too much lateral force, versus only downward force, on the valve-tip, to compress the spring. The nice pnuematic spring compressors we used at the shop were all for off-the-motor work, and waaay to pricey for me to buy. If you do decide to do the work with the heads on the engine, I think the rope method has less chance of error. I don't know what kind of seals come on the TFS heads, but if you're gonna change 'em, I'd recommend that you go with a seal that mounts to the guide, like the teflon or rubber seals, instead of the umbrella's.