Piston Ring Failure Diagnosis

[Rick Finsta]

Well, let me pose this question; how much should I have seen the top ring gap open up? To me if it has opened up from 0.018" to 0.029" that indicates a lot more wear than I'd expect to see, but I suppose I have to pull another piston and check it out for comparison.

The intake valves are filthy from E85 goo (it's slowly coming clean as I feed it methylal in the fuel tank, obviously now that it is apart I'll clean them up) but the exhaust valves are clean. Could have been a valve, I suppose. With the leakdown I couldn't get a really good read on where the air was coming out - it wasn't in the coolant, wasn't the intake, and wasn't the exhaust, but it didn't seem to be a huge volume coming out the breather or oil fill neck, either.

All that said, how does my crosshatch look? I can fix it if it needs it:

[machinedave]

That seems to be a high leak down to be rings. Check the rings and make sure they rotate and with the the heads still off of the engine you could do a vacuum test or a solvent leak test of the valves.

[Rick Finsta]

Leakdown was done at 80psig, second gauge showed 46psig the first time and then 47psig the second time. With the heads off the valves are on the seats but I am going to pull them apart to clean everything up so I can look and see if something needs to be cut or a lapping or something.

[DaveMcLain]

Leakdown was done at 80psig, second gauge showed 46psig the first time and then 47psig the second time. With the heads off the valves are on the seats but I am going to pull them apart to clean everything up so I can look and see if something needs to be cut or a lapping or something.

The number one thing to remember is that the numbers from a leakdown test are 99.99% total nonsense and can be very misleading. Think about it, what does the number mean? Was it done hot or cold? How does a test done at zero rpm have any validity at all? When do you ever run the engine at zero rpm?

[Rick Finsta]

Engine was hot for testing (coolant at 180*F).

I understand what you're saying, but I think that it tells me that relative to the other cylinders, this one is putting combustion gas into the crankcase and causing the crankcase pressure issues I've seen. But I agree that is potentially confirmation bias at work...

I generally hate to just throw parts at a problem, but in this case I had:

1) Excessive crankcase pressure
2) Leakdown in normal range for an engine of this use and age, excepting one cylinder
3) No air in the radiator, intake, or exhaust during testing
4) Oil visible in the cylinder that is not visible in other cylinders using a boroscope
5) A top ring that has worn to open the end gap by over 50% - not sure if that's normal but it is different than the second ring.
6) A second ring with a normal wear pattern and a gap within 0.001" of where I set it over a decade ago

It's obviously too late now to go back and repeat testing with other variables (add oil, etc.) but I'm wondering what else those symptoms could have indicated? Can I check the ring itself for signs of flutter or anything?

[Xnke]

Put a new top ring on it, and put the piston back in the bore. I don't think it's your piston.

I think it's time to look at valve guide wear on that intake valve...or the valve stem seal. You're saying you have a 40+% leakdown in that cylinder, oil on top of the piston, and gunky valves, but the bore looks good and the piston seems to be OK...so look above the piston.

[Newold1]

Last time I looked, valve guide wear and valve stem seals tend to work on the suction side which can contribute to oil in the cylinder but unless the intake is not seating the leak down is on the compression side, not the suction side.

[Rick Finsta]

Valve guides are good I found one bad valve seal and replaced it when I was swapping cams this summer. The gunk is all from the E85 - trust me this shit is awesome at $1.69 for race gas but can be a nightmare also. I was using Speedway for a year and it was junk. The Kwik Trip stuff is good to go so far.

Maybe I'm looking at the wrong ring if I'm having an oiling issue? Oil ring problem?

Maybe the "oil" on the piston was actually fuel drying up with the brown gunk in it? Now that I think of it my oil is green now not amber colored... shit. THAT should have been obvious to me. Fucking Brad Penn why do they have to be different? Green = coolant leak you bastards get with the program LOL.

[fdicrasto]

OK,if the rings are responsible for the 47% leakage in that cylinder, you would not see clean piston surfaces between the rings.I would think there would be some ugly, dark burnt deposits there unless the issue was recently in effect. The picture of the piston looks very clean between but can't see 360 degrees. Combustion pressure creates blowby. If it is getting past rings,there should be some evidence.

[modok]

I might have missed the gaps, or misunderstood.

gap opening .010 is possibly OK for a cast ring.
That's a bit excessive for moly rings. I think yours are probably moly face top rings. Guys love moly rings in old fashioned engines but IMO they aren't the best for a lot of things. They can do strange things like chip if they twist too much.

I understand we aren't looking for best here, but just fix-er-up, but what rings would be best is an interesting question, that I don't know the answer! I'd guess chrome, but, for de-glaze and re-ring job, you probably want plain cast.
Looks a bit rough for moly, should be 280 grit or finer according to hastings, and a lot of people think that's too rough.

[MadBill]

Leakdown was done at 80psig, second gauge showed 46psig the first time and then 47psig the second time. With the heads off the valves are on the seats but I am going to pull them apart to clean everything up so I can look and see if something needs to be cut or a lapping or something.

Before you take them apart, you can just pour some solvent in the ports and see if it leaks by the valves, or put some in the chamber and give the port a blast with an air nozzle and watch for bubbles.

[Rick Finsta]

Modok- rings were plasma moly, getting replaced with the same. 240 grit was the "if you're not sure, use that" recommendation in some of Total Seal's literature for brush hones but I can't find it again now. All the tech info on their site is for proper honing machines.

MadBill, thanks I might just do that. I kinda want to clean the valves up anyways and get the E85 goo off them because it isn't helping flow to have it caked all over the reduced diameter area of the stem and my nice back cut valve heads...

Times like this I really wouldn't mind one of those valve train organizer trays!

[ozmuscleowner]

make sure you clean that crank off(and the rest of it down there) good and proper, looks like there is now grit from the hone......
It does look like its been ground with and angle grinder, I think my plasma moly hone is like 600 grit? 240 is way too coarse

[Belgian1979]

Was the block honed with a plate ?

[OILEAKY]

X2 with the angle grinder !