The Official 356Talk Forum

C J Murray wrote: ↑Sun Nov 10, 2019 7:18 pm Perhaps the previous owner had a plan to use low compression pistons to compensate for heads that were cut too deep thus getting to a manageable CR.

Did You have to shim up the rocker stands to get the adjuster screws into the correct range?

The guy I bought it from made a big deal about how he had the engine blueprinted back in the day, so maybe you a onto something.

Yes I had to shim up the base of the stands. I used typical spindle shims, two on each side.

This is the piston kit that came with the car. The jugs have one spacer under them. Maybe I should try these?

I can’t tell how high the dome is but they look like late pistons machined to work with early heads. I have done that a couple of times with 912 pistons, worked fine. They are pretty thick in that area, I would not be concerned that they would be too thin. I do think you should swap your heads too.

OK,

I'll concede that the cylinder head's machining was just concentric to the chamber's diameter.
However, it would've been simpler to just face mill it to the proper relationship of the cylinder
seat depth per spec book--if the cylinder top ends are correct and equal in overall height to the
bottom shoulder.
This is the 1st time I've seen it done this way!

Dan; those pistons look like what Ray Litz used to do, 84.7mm is probably an industrial kit. Ray would add the angle to the pistons and cut ONE exhaust pocket deeper for clearance. I imagine that the cylinders were cut shorter for all that to work. Measure the height of the cylinders and compare to your other ones. Ray had to caution people to install the pistons so the deeper pockets were under the EXHAUST valves. Seems some brilliant minds thought the deeper pocket must go under the INTAKE valves! Which do not come into the combustion chamber at an angle.

Was the top ring land still wide enough? Or is this not such a great idea?

Vic Skirmants wrote: ↑Mon Nov 11, 2019 9:06 am Dan; those pistons look like what Ray Litz used to do, 84.7mm is probably an industrial kit. Ray would add the angle to the pistons and cut ONE exhaust pocket deeper for clearance. I imagine that the cylinders were cut shorter for all that to work. Measure the height of the cylinders and compare to your other ones. Ray had to caution people to install the pistons so the deeper pockets were under the EXHAUST valves. Seems some brilliant minds thought the deeper pocket must go under the INTAKE valves! Which do not come into the combustion chamber at an angle.

So if everything pencils out there's no reason to not try them I suppose? I'm going to assume like Cliff suggested that the heads may have been cut with those particular Ps and Cs in mind and I gummed up the works using the AA ones.

I would try them.

Dan Epperly wrote: ↑Mon Nov 11, 2019 12:21 pm

Vic Skirmants wrote: ↑Mon Nov 11, 2019 9:06 am Dan; those pistons look like what Ray Litz used to do, 84.7mm is probably an industrial kit. Ray would add the angle to the pistons and cut ONE exhaust pocket deeper for clearance. I imagine that the cylinders were cut shorter for all that to work. Measure the height of the cylinders and compare to your other ones. Ray had to caution people to install the pistons so the deeper pockets were under the EXHAUST valves. Seems some brilliant minds thought the deeper pocket must go under the INTAKE valves! Which do not come into the combustion chamber at an angle.

So if everything pencils out there's no reason to not try them I suppose? I'm going to assume like Cliff suggested that the heads may have been cut with those particular Ps and Cs in mind and I gummed up the works using the AA ones.

Dan, the AA piston, cylinders, have nothing to do with the issue you found, the poor heads, are the culprit. C.J.'s observations, on the heads, and valves contacting the opposing surfaces, IS, the issue.

I think that is all true but as a secondary problem. The melted piston on the other side is the biggest factor here. Unless the heads also caused very high compression and detonation.

Martin Benade wrote: ↑Tue Nov 12, 2019 12:07 am I think that is all true but as a secondary problem. The melted piston on the other side is the biggest factor here. Unless the heads also caused very high compression and detonation.

Agreed, Martin, and the obvious unintended high compression ratio, was causal to the detonation, coupled with the extra load in the heat, and... that long climb. I've seen that detonation damage on 2 Japanese 86mm pistons before, in others engines, both long ago.

I took everything to the machinist. He measured the AA cylinders and there was minimal difference in height, half a thou I think he said. Not enough in his opinion to cause number two to leak. I still don't know why my number two cylinder was leaking.
He didn't cut the heads, they were done back in the day, he will clean them up.
He agreed that number three melted down because of the high heat and the partially clogged oil cooler.
He did find it odd that though there is signs of the exhaust valves hitting that it didn't knock the carbon off.
He measured my 85mm Mahle jugs and said they were cut fairly substantially. I will mock them up when I get everything back and report back.
Everything else escaped unharmed, even my mains didn't look too bad considering what happened. Big sigh of relief there. If I am able to use the Mahles then I really got off cheap. I will replace the cooler with a new one though. All in all not too bad. Tough little engines aren't they?

You didn’t mention it but he will cc the chambers and measure the cylinder seating surfaces in the head to make sure they are in the same plane?

Dan Epperly wrote: ↑Tue Nov 12, 2019 11:03 am I took everything to the machinist. He measured the AA cylinders and there was minimal difference in height, half a thou I think he said. Not enough in his opinion to cause number two to leak. I still don't know why my number two cylinder was leaking.

Because detonation is more powerful than a jackhammer and the vibration and heat made both cylinders leak.

Dan Epperly wrote: ↑Tue Nov 12, 2019 11:03 am He agreed that number three melted down because of the high heat and the partially clogged oil cooler.

Disagree. Your gauge didn't pin to the right. Your bearings suffered little to no damage. Your problem was on top of the pistons, detonation.

Dan Epperly wrote: ↑Tue Nov 12, 2019 11:03 am He did find it odd that though there is signs of the exhaust valves hitting that it didn't knock the carbon off.

The length of a cylinder changes from cold to hot as do valves and pushrods and cases. Carbon collects when conditions are right and you stopped your engine when conditions were right, no contact. Just like the ones in my picture.

What cam do you have???

Clean your crank and case passages very thoroughly!

Martin Benade wrote: ↑Tue Nov 12, 2019 11:24 am You didn’t mention it but he will cc the chambers and measure the cylinder seating surfaces in the head to make sure they are in the same plane?

You should give him a barrel and piston and have him estimate the CR you had.

What did he think of the piston hitting the head?

C J Murray wrote: ↑Tue Nov 12, 2019 11:35 am

Dan Epperly wrote: ↑Tue Nov 12, 2019 11:03 am I took everything to the machinist. He measured the AA cylinders and there was minimal difference in height, half a thou I think he said. Not enough in his opinion to cause number two to leak. I still don't know why my number two cylinder was leaking.

Because detonation is more powerful than a jackhammer and the vibration and heat made both cylinders leak.

Dan Epperly wrote: ↑Tue Nov 12, 2019 11:03 am He agreed that number three melted down because of the high heat and the partially clogged oil cooler.

Disagree. Your gauge didn't pin to the right. Your bearings suffered little to no damage. Your problem was on top of the pistons, detonation.

Dan Epperly wrote: ↑Tue Nov 12, 2019 11:03 am He did find it odd that though there is signs of the exhaust valves hitting that it didn't knock the carbon off.

The length of a cylinder changes from cold to hot as do valves and pushrods and cases. Carbon collects when conditions are right and you stopped your engine when conditions were right, no contact. Just like the ones in my picture.

What cam do you have???

Clean your crank and case passages very thoroughly!

My gauge did pin to the right soon after we lost power.
I'll get back about the cam.