1883cc problem on one cylinder/ JE piston

[GregVandenbussche]

Hi,

Since the first start of my engine (1883 shasta with coated JE piston, twin plug (10-25), oil squirters, carrillo rods, scatt crank, equilibrated to 0.1gr ) i had what i though was an exhaust leak (similar sound), i tried numerous times to find where it came from and unsuccessfully managed to fix it, sound has always been the same, a little less present when hot. after 3200miles I finally decided to get the engine out as i thought it might be a head/cylinder leak since the compression is 10.5:1
It turns out that cylinder/piston #2 looks like this on top and bottom:

Piston top

Bottom of piston

Ring pitting

Oil pressure gauge (calibrated) never shows under 3 bars at idle, 4 bars at higher RPM), temperature center gauge max (calibrated too)
as anyone experienced this? obviously looks like over heating, but on one cylinder? inspecting the cylinder it seems like it is oval. top ring show tiny pitting (picture bellow) my guess is from cylinder scratch friction, oil rings an oil scrapper rings are smooth, other cylinder/pistons are fine.

Cylinder scratches

[Ashley James]

Are the piston cylinder clearances correct because it looks like a straight forward seizure to me that greater running clearance would solve. Albeit with more noise.

[C J Murray]

Post a picture of the underside of the piston crown...pictures of all pistons top and bottom if you have them available.

Were the P&Cs a set and from whom?

What ignition timing were you using and did you have any issues with the #2 carb such as clogged jets?

[Cliff Hanson]

Your first photo shows some distress to the piston edge above the top ring. I am wondering if there was some detonation in this one cylinder that heated up the piston, reducing the clearance which resulted in the skirt scuffing. The skirt is between the pin bosses and there is much less thermal mass there, resulting in greater expansion. Could this cylinder have been running leaner than the rest? What did the spark plug(s) look like? I assume the engine was running on premium fuel. What was the max timing advance? Some accurate measurements of the piston skirt, mid way up the piston and cylinder bore diameters might tell something.

[Tim Berardelli]

One of your pictures shows misaligned oil ring rails, the gaps should be 180 degrees apart. Are the others the same? In a new engine with rings that are not broken in this condition would allow excess oil to enter the combustion chamber, lowering the octane number of the fuel and causing extra heat in that cylinder. If your calculated C/R was "on the edge" that may have been a significant factor in the issue.

[Ron LaDow]

Greg,
Using CA-legal "premium" gas, I've found the CR limit on a 1720cc twin-plug right at 10.0:1, and that with quench between .028" and .032", 25* all-in advance. 10.5:1 is getting greedy, particularly with the increased bore.
What quench did you establish and what is the timing? When things start banging around inside, I tend to look at detonation first, especially if you are pushing the CR limit.
(oops, just noticed Cliff H's comment; +1)
Oh, and have you taken a look at the rod bearings?

[Craig Richter]

Greg, I hate to admit it, but I suffered a few of your type failures in the past. I'm not sure I could always pin-point the reason for some of the odd failures, other than eating wrist pin clips or other rather obvious broken parts. Reassembly paid much attention to the heads, combustion chambers, cylinder lengths, carbs, so forth; and it didn't happen again, at least on that particular motor. So sometimes poo just happens.
I have no experience with the big-big bore Nicky's you must be using, although I am looking forward to trying a set in a dual-plug motor that Jack and I are (slowly=old guys) assembling. Bunch of left-over drag racing parts. Previous failures were 86mm Jahns, Arias, MC, etc. Not particular to brand. Keep checking stuff, Good Luck.

[Ashley James]

Are the pistons forged and what skirt clearance are you running? That type of seizure is usually inadequate running clearance, assuming it’s not lack of oil.

[Neil Bardsley]

One of your pictures shows misaligned oil ring rails, the gaps should be 180 degrees apart. Are the others the same? In a new engine with rings that are not broken in this condition would allow excess oil to enter the combustion chamber, lowering the octane number of the fuel and causing extra heat in that cylinder. If your calculated C/R was "on the edge" that may have been a significant factor in the issue.

In complete ignorance I've looked all all three pictures twice and I can't see the oil ring rail gaps that are too close?

[C J Murray]

Post a picture of the underside of the piston crown...pictures of all pistons top and bottom if you have them available.

Detonation should leave it's mark under the crowns and pictures of the other crowns tops might show your mixture whereas the failed piston just shows oil and a lack of compression.

Were the P&Cs a set and from whom?

I would expect that LN and Shasta would have the correct clearance however other companies sometimes use JE pistons but may or may not hold correct clearances during manufacturer.

What ignition timing were you using and did you have any issues with the #2 carb such as clogged jets?

Too much advance causes detonation. Too little fuel causes detonation.

Some answers to the questions above may yield a more specific diagnosis.

[Martin Benade]

The other crowns should also show signs of detonation, or are you saying that possibly only this cylinder had a detonation problem?

[C J Murray]

If the detonation was due to the general state of tune then all the pistons will have excessive color under the crown. If only #2 was out of tune(clogged jet?) then it would be the only darkly colored piston. If no significant color exists under any of the pistons then maybe piston cylinder clearance caused the problem.

[Cliff Hanson]

One of your pictures shows misaligned oil ring rails, the gaps should be 180 degrees apart. Are the others the same? In a new engine with rings that are not broken in this condition would allow excess oil to enter the combustion chamber, lowering the octane number of the fuel and causing extra heat in that cylinder. If your calculated C/R was "on the edge" that may have been a significant factor in the issue.

In complete ignorance I've looked all all three pictures twice and I can't see the oil ring rail gaps that are too close?

I don't see any ring gaps either. Maybe the light reflection in the first photo makes it look like there is a gao but I think it's just the glare from the light that makes the ring disappear.

[Vic Skirmants]

First photo; right at the bottom. Both oil rails perfectly lined up.

[Kevin Wills]

One of your pictures shows misaligned oil ring rails, the gaps should be 180 degrees apart. Are the others the same? In a new engine with rings that are not broken in this condition would allow excess oil to enter the combustion chamber, lowering the octane number of the fuel and causing extra heat in that cylinder. If your calculated C/R was "on the edge" that may have been a significant factor in the issue.

In complete ignorance I've looked all all three pictures twice and I can't see the oil ring rail gaps that are too close?

I don't see any ring gaps either. Maybe the light reflection in the first photo makes it look like there is a gao but I think it's just the glare from the light that makes the ring disappear.

I blew it up a bit and it does look like the oil ring gaps are aligned.