1883cc problem on one cylinder/ JE piston

[Neil Bardsley]

Thank you.

[GregVandenbussche]

Hi!

I'm running 10 degree initial advance and 25 max at full advance, one MSD firing the coils.
The ring gap is there because i rotated the rings to check that not a piece was missing. (and none was)
I have been in contact with Leonard and he is helping me get the new piston/cylinder to get the car running again as i will be (hopefully) at the Luftgekult show in LA in less 2 weeks
sorry for the delayed answer, the "good news" is that the other 3 pistons/cylinder are fine
Here are the pictures of the top of the problematic piston #2 and under:

Top of problematic piston #2

Under skirt of the problematic piston picture 1

Under skirt of the problematic piston picture 2

Other pistons top looks like I'm getting some oil in the chambers even though the bore and skirt are not damaged like the other one.

other side pistons

piston #1 (same oily top)

[GregVandenbussche]

Cliff,

The darker area on top of piston of picture n1 (previous page) is a bit of carbon deposit, the pistons have literally no scratch no chips (except N2 skirt)

[C J Murray]

Sometimes pictures are misleading but the carbon on the good pistons looks excessive and a bit wet, as in oily. If that is the case then the oil could be causing detonation. OR, the 10.5:1 compression with too short a duration cam can be causing detonation which leads to ring flutter which leads to poor ring seal and that leads to wet carbon which leads to more detonation. Sometimes it's hard to tell what happened first.

Was the engine using oil?

Was it running quite rich?

What cam specs are you using and is it in "straight up" or advanced?

[Dick Weiss]

Also noticed 1/2 of the top edge of the cylinder shows blow-by; What does the cylinder seat face-depth (in the head) look like?
Also, when torqueing the heads to the the cylinders, use the practice of alternating both heads by 7, 15, 22, and 28 ft.pds. which stresses
the case evenly--old racer findings; If you don't, 1-head will be tight but the 2nd won't be correct. Yes, you hafta flip over the engine
each time and final re-check twice more!
Also, make sure the cyl. seat depths match each other w/in .0004" in both planes!

[Dick Weiss]

Nothing wrong w/the multi-piece ring gaps being together; As long as they're near the top, they don't get involved w/compression much, but kinda retains oil for the skirt-clearance. The ring lands are slightly smaller than the skirt diameters.

There was an early bulletin for the 912 Mahle pistons being modified for extra 4-oil holes in the oil ring groove. (instead of just 4)

[Vic Skirmants]

Dick; I think the photo to which you're referring shows only the piston, not the piston in the cylinder. Those pistons have a large flat area along the outside. I don't see any photos of the cylinder tops.

[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.

Another possibility is that the detonation is so aggressive that the rings start to flutter and lose seal so early in the rpm range that the temperatures don't reach high enough to show "black death" under the piston crowns but did quickly cause #2 piston to almost seize.

Serious answer...I'm not sure what happened.

[Jacques Lefriant]

Hi Shasta "durabar"cylinders may have varying bore sizes and wrong taper since i believe they are made in a job shop. can you give us the sizes? also "durabar" is more like steel and may not oil as well as regular cast iron or "Nicasil".
j

[Jacques Lefriant]

Hi
i think Durabar is an excellent product but like any it has to be developed for the application. I believe the problem was clearance driven. Builders like Wilhoit have expended a lot of effort to select all the pieces to make them compatible. Now usually we can get away with not paying attention to: the alloy of the piston, the type of rings, the hone finish, and type of cylinder but sometimes you get bit.
j

[Dick Weiss]

Vic,

Look @ photo #5--it's under the oil cooler's mounting pad.

Dick

[Martin Benade]

Is that not a piston? I see no cylinder.

[Ron LaDow]

Serious answer...I'm not sure what happened.

Me neither, but asking 10.5:1 to live on CA pump gas is asking a lot even with very well-prepped chambers and twin plugs, and detonation would explain all of it.
So absent any other explanation, I'm positing it's a half-point too greedy on CR.

[Neil Bardsley]

Vic,

Look @ photo #5--it's under the oil cooler's mounting pad.

Dick

Is that a crack in the case?

[Mervyn Hyde]

Or 3?