I have had a problem with my 87 IROC since it’s engine (L98) was rebuilt. I took it back to the rebuilder who said the intake gasket was installed incorrectly. He said he re-installed a new gasket, but the problem persisted. I gave up on him.

The problem is number 1 cylinder burns oil. In the past I would just change the plug when it got oil fouled about every 3-4 weeks. I’ve been doing this for about 3 years. It burns a quart every 1500 miles.

I’m looking for advice in troubleshooting the problem. Any number of things could be causing the problem, including but not limited to – bad valve seals, guides, or valves, bad rings, or bad intake gasket. Should I just start with replacing the valve seals? Would a compression test indicate bad rings if that were it? Is there anything else to do to isolate the cause of the problem? Remember, the problem has existed since the rebuild, so somebody made a mistake in the rebuild or a faulty component was used.

The guy that did the assembly was very young, probably not 20 years old. The machinist at the shop that did the rebuild were supposed to be competent, but a mistake could have been made in that process. The problem with the engine was a broken crankshaft. Wonder if the machinist could have bored 40 over on number 1 and the assembly guy used a 30 over kit? I’m just guessing at this point.

 

Compression and leak down test. What are you using for heads? How many miles? More info if you could.

 

Stock heads. 26k on stock rebuild. The rebuild included machining the deck and checking for flatness, knurl valve guides, new valves, seals, resurface seats. Existing springs and rocker arms were used. Engine is strong, number 1 does not misfire when accelerating or cruising, idles at 550, misfires some, plug eventually fouls, then it hunts 550-750. MPG typical 16/23. Does not smoke or leak.

 

I would do a compression check, and if its all good, id change the valve seals.

 

If you had a smaller piston in one of the holes, you'd hear it rattling.

 

And only #1 fouls? None of the others show anything? Probably gonna need to do the tests and come back with results. They decked the block, did they mill the heads as well? Any numbers for either?

 

I heard of a similar problem once.
The guy ended up tearing it down and found out that the piston ring gaps weren't aligned the right way. He realigned them... and bingo! the oil burning stopped.
Something else to consider is that possibly the cyls weren't honed correctly for the type of rings you're using, or maybe the rings were put in upside down, or in the wrong grooves, or maybe a ring was broken during installation.

 

Red - Only #1 fouls, all others show nice light gray or tan. The heads were milled. I didn't get a build sheet with it, no numbers.

Street - ring alignment is a common mistake with inexperienced assemblers, could be it.

I'm gonna do the compression test and replace the seals. Then do the intake if the seals don't fix it. If none of that solves, I'll drive it like I have been; I don't have the money to fix ring/piston/cylinder possibilities. Thanks for the input.

 

If you can do the leak down as well, you get a better picture that way, and you'd detect a crack or leak much easier.

 

Hey... At least it's the #1 cyl... it's easy to get to for changing the plug.
Ever seen those non fouling plug adapters in JC Whitney? Well, they actually do work. They're kinda mickey mouse, but as long as you're going to be running a motor that's impaired to begin with...

Good luck with the seal fix, hope that's it.

 

Another frequent cause of mystery plug fouling, especially an end cylinder, is the intake gasket.... don't forget, the bottom of the intake ports is right next to the crankcase; a leak there will suck oil in. You might want to just try tightening the intake blots along that side and see if it makes any difference.

 

Really doubt a small piston in a big hole is the problem.

However...

Back in '91, when I lived in San Diego (Lemon Grove, to be specific), I picked up a 350 long block from a guy that ran a small shop in Spring Valley. It was .030"-over/.010" under 4-bolt main. First thing I noticed is he put a metric nut on one of the rocker studs. Said he'd fix it. The engine also seemed pretty hard to turn over. He said he assembles them tight, it'll loosen up after it's broken in.

Then I noticed it was using quite a bit of oil. About a quart every 300 miles. Bring it in for a leak down, he said.

Before I got those taken care of, driving to work one day about a month after I got it running, I left a big stream of coolant in the parking lot. One head had cracked along the casting line on the outside. I immediately took it to his shop, but he wasn't there. There was a hand-printed sign taped to his door that said, "You have my money. I don't have an engine. See you in court." The guy in the business next door said he hadn't been there in two weeks.

Took the heads to another shop, who fixed up one he had around to replace the cracked one, checked the other one and fixed the stud that had the metric nut on it, put it back together. Compression test showed the cylinders were fine, but it still used oil.

6 months later the oil turned creamy - took the intake off, cracks in the block lifter valley.

Took the engine out and tore it apart. The rear main bearing was horribly distorted, the oil groove was almost closed over with displaced bearing material. Turned out to be a .020"-under bearing (the other 4 were fine).

Slipped the rings into the cylinder to check gap. The compression rings were fine, but the oil rings had a huge gap. Doing the math, it appears they were .020"-over oil rings. Small wonder it had good compression but liked oil.

How he mixed those bearings & rings, I'll never know (he was never seen again). He obviously built up the engine using scrap castings.

Dirt ball...

The intake manifold gasket is a possibility, but I'd guess you have either a head or a block that wasn't put together properly. A compression test would only show a problem if the cylinder wall is hurt. A missing or damaged valve seal is a good possibility.

 

Had my mechanic look at it. He's telling me No. 1 has no compression, so it's something more than the valve seals. I'll have him do the intake gasket, if that's not it I guess it's the rings. A bad head gasket wouldn't suck oil would it? Could valves not seating properly be the problem?

 

a bad intake, or even missing intake gasket won't result in zero compression. you can tell a bit more by adding oil to the dead hole and retesting it.

 

Man, all these horror stories of rebuild shops are giving me the heebie jeebies... I almost want to do my 383 rebuild myself now... (yep, REAL good option there, I've never had and engine apart in my life!) Tell me there are reputable shops around, please!

 

Yes there are. Make you feel better?

Now you have to figure out the where.

 

Now I get word the gauge gave a bad reading, compression was re-tested and has 130lbs. I have good oil pressure so it did surprise me when he said 0 compression. I'm getting my car outta there.

One other detail that may or may not contribute to the diagnosis - the exhaust does not smoke, at startup or any other time. It's general consensus that bad valve seals will cause smoke at startup.

 

I had a similar problem on a LT1 engine in a 93 Firebird the #2 cyl spark plug would always fowl out in about 500 -1000 miles. I changed the valves seals same problem. It never smoked while driving but once and a while at startup. I had an oil leak at the rear of the intake so I replaced the intake gaskets cause my drive way was getting trashed. After I replaced the gaskets the fowling problem went away. So the gasket was leaking internally through the #2 intake port. It was kinda nice to fix two problems at the same time.

 

how hard is it to replace valve guide seals? what is involed in doing it (what parts are removed?)

 

I have not done it, but I understand this is what is involved. Remove valve covers, apply compression to cylinder (through plug hole) to prevent valve from dropping, remove rockers, retainers (spring is compressed), replace seals, reassemble. What did I leave out?