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Sun Apr 30, 2023 7:19 am

I've found oil in cylinder 4 and need some advice....

I rebuilt my engine about two years ago. It was a total rebuild (1600 dual port). It only has about 1,000 miles on it since the rebuild. It hasn't been started for the last six months. I have it on the bench to sort out some external oil leaks.

I pulled the plugs this afternoon. Three plugs were very sooty (I knew it had been running v rich), but #4 was also very wet. I checked deeper and could see fluid in the cylinder and the back of the inlet valve was wet. It didn't smell fuelly and the fluid was viscous, so must be oil.

Pulled the 3/4 head and there was maybe 1/4 teaspoon of oil in cylinder 4. Cylinder 3 is bone dry.

Pulled the #4 jug and checked the rings all round. They look pristine. I didn't think to check where the gaps had landed, so can't tell whether they'd come to rest lined up allowing oil to leak through, but I don't *think* they had.

There are some longitudinal marks on the lowest point of the bore on the crankcase side of the rings at BDC (outside of the combustion chamber).

Both 3 and 4 show some light longitudinal marks along their length all round.

I can't feel any of the longitudinal marks with my fingernail or the pad of my finger.

The only reasons I can think for the problem are fuel washing the cylinder walls leading to scoring, or that the ring gaps had aligned prior to shut down. Otherwise, I'm stumped.

And only #4 had oil in it. I'm running a single carb, so I'd expect fuel washing to affect all the cylinders the same?

I'm out of my depth at this point, so need some advice on what to do to diagnose and remedy the issue.

Do I need to re-hone the cylinders? If so, how and with what sort of hone?

Should I replace the rings? They were part of a matched set with the pistons and jugs (Kolbenschmidt).

So, what do I do next?

Sun Apr 30, 2023 11:13 am

Is it leaking past the valve guide? look in the intake port.

eQ

Sun Apr 30, 2023 11:39 am

earthquake wrote: Is it leaking past the valve guide? look in the intake port.

eQ

Back of the intake valve of #4 is wet and looks sooty.

Sun Apr 30, 2023 5:40 pm

The back of the intake valve being wet is a possible concern, but passing that much oil is not likely by a stem unless the guide is gone or has come loose.
Disassemble and check the heads in case you have a guide issue but I think it's rings, which lost their seal for an unknown reason, I've seen it several times. Cast or chrome rings? It seems more common with chrome as they seem fussier about wall surface. It could be carbon buildup on the piston ring lands but probably not.

I don't subscribe to the ring gap theories. I offset them when building, of course, but I've torn down engines I've built and the gaps have moved. IMO, the rings walk when running.

I'd pull it down, soda blast the pistons, ball hone the jugs and put in cast rings. Bead blast the heads and valves, lap them, check them with bluing and air test the cyls on assembly.

I had one not long ago with a similar concern- oil was actually dripping from the exhaust port (where it meets the heater box) it was passing so much oil. Full teardown, everything looked like new and ring gap was at new spec. A ball hone and cast rings fixed it.

Good Luck!

Sun Apr 30, 2023 6:08 pm

Are you sure the engine didn't get tipped over sometime during removal or transferring it to the work bench? Oil run down from the oil bath air cleaner, through the carb, down the intake and into the only open intake valve?

If the rings or intake valve guide were passing that much oil you would have seen a blue cloud following you for the last 1000 miles!

Mon May 01, 2023 2:39 am

I've read the above and had a chance to think. Seems there are three likely causes - 1/. rings, 2/. valve guides, 3/. Other/false-positive (i.e just a fluke)

Rings

For some reason I think they're less likely to be the cause than other options.

No trail of smoke and no burning oil smell while driving (my wife has followed in our daily driver a few times and said it smells fuelly, but not oily).

If I'd realised there might be a problem, I'd have done a compression test before pulling the engine, but that ship has sailed.

Any tips for checking further to see if they could be the culprits, bearing in mind that the head is off now?

Are the longitudinal marks an indicator of an issue, or normal for a flat four engine?

Valve guides

Once or twice (and literally just that) in the last couple of years, I've had a puff of blue smoke and a smell of burnt oil on startup after it sat for weeks between runs.

I will strip the head down to check the valve guides and valve stems as a precaution.

After the first comments about valve guides; I did some Googling.

It seems extreme that the guide would wear within 1000 miles unless a/. it was faulty or badly machined to start with, b/. I damaged it while reassembling the head after cleaning or c/. I screwed up the rocker geometry.

a/. is possible. They're Empi heads, but new stock from a supplier with high turnover. I've read have better quality control than recent past years, but I could have got a bad one.

b/. is also possible. I used a traditional long-reach valve spring compressor to reassemble after CCing and cleaning. The compressor was fiddly and slipped off the stem/spring on a couple of occasions. Could that have damaged a guide?

c/. again possible - this was my first build. That said; Empi heads come with stainless valves and need lash caps. The caps show circular witness marks about 3mm diameter, which I think indicates the adjusters are wiping correctly, given that they should also be spinning the valves/caps?

If a guide needs replacing...

Should I get them all replaced as a precaution? (I don't have the tools to do this myself)

If so, should I get the other head done as well?

If I have them replaced like-for-like, does the valve seat need re-cutting? I've read that it does, but I don't know if that's if you change from one type to another.

Other causes/false positives

I guess oil could have got in there while I was maneuvering the engine to fix the oil leaks, I've been tipping it back and forth to get better access.

I don't think could have come from the oil bath though. The engine is in a '56 truck and the bath mounts on a snorkel tube. And I removed it before pulling the engine.

I drained crankcase oil before pulling the engine, but some has leaked out while maneuvering it (I took the oil pump and push rod tubes out to reseal and I redid the main seal and flyweel o ring as a precaution as well).

The engine has been tipped back and forth while I've been working on fixing the leaks though, so maybe residual oil got in to the head via the pushrod tubes before I pulled them? I don't recall huge amounts gushing out when I removed either valve cover.

The #4 intake valve that is wet was partly open, so maybe oil in the head could have sloshed around and gone down the tube. The tube projects from the head casting though.
Could that much oil have got splashed up high enough to go down the tube?

Mon May 01, 2023 3:40 am

If a guide needs replacing, then yes, they should all be checked. Loose guides are also a cause of early dropped valves not just passing oil. Yes, if guides are replaced, valve face to seat needs to be checked

Mon May 01, 2023 5:04 am

Personally I think you are chasing a nonexistent problem. Engines removed and rolled around get oil in all kinds of places. Even just tipped up on one side for any length of time the oil will run into the cylinder and seep past the ring gaps eventually.

1000 miles in 3 years? Wow! I hope that wasn't multiple 10 minute trips. Not a good way to break in new rings if it was. I don't think I could stand having a new engine sit around like that. My enthusiasm would not let me! I bet I put 1000 miles on the fresh engine in my Street Buggy in the first 3 days just sorting out the mixture and timing.

A puff of blue smoke on a horizontally opposed engine on start up is perfectly normal. Again you have both cylinders and valve guides sitting level that oil can creep along and end up in the cylinder and exhaust ports. Go on YouTube and watch an radial aircraft engine on start up. They not only have horizontal cylinders but several hanging down too. Great clouds of blue smoke! Perfectly normal!

Yes check out the guides just to ease your mind.

As for the cylinders, I see nothing abnormal there. Too bad you disturbed the rings. They may or may not reseat if reused but my guess is that they have not yet fully seated with only 1000 miles on them.

You need to do something about that over rich condition. Cylinders that black with those few miles is not right. Also the smell of raw gas following you is not normal.

Just my observations from many miles away...