The Official 356Talk Forum

Vic Skirmants wrote: ↑Wed Oct 16, 2019 8:12 am Mike Horton: Yes, I use AA P&Cs in our 65 coupe, as well as many street rebuilds (when I was still doing those). Never had a problem that I heard of.
For the race engines, I used stock cast iron cylinders, machined to 83.5mm by a local friend. He gave me the best, straightest, round cylinders I have ever seen, Unfortunately he passed away a few years ago, so now I use the Shasta iron cylinders with pistons made to my design by JE. No, I do not stock any street P&C sets.

I've never had the priveledge to meet Vic in person, but we've talked on the phone many times, and corresponded via e-mail, and one thing I've always admired about Vic, is that he offers straight, factual answers, in short order. Thanks, Vic, again.

(I still recall the wise council you gave me, on parts selection, and the BBBC Normal trans gear selection, for my old late '60 T5, many years ago, for a car I've owned, since '69 !)

Mike Horton wrote: ↑Wed Oct 16, 2019 8:30 am I've never had the priveledge to meet Vic in person,

He's shorter in person!

Finally had space in the garage to roll the B Coupe in and pull the engine. My friend Pascal came by today to lend a hand and extra set of eyes, so we tore the engine down to the small block.

Basically we found no obvious cause for the failure. It is clear that the cylinder was not sealing bri as for why we don't know. I will take th emess to the machinist Monday to see if he can figure it out.
What I know is that the had studs were torqued to specs because I checked them before pulling the head.
There are no visible cracks in the head or cylinders.
There is obvious indications of gasses and oil leaking from number two.
The engine was not running lean or overheated.

Here are some pictures of the heads, the cost is of theee four, which had as you can see different look in the combustion chambers from one two which are in the next two pictures.

If you look at the picture of number two cylinder you might notice a sort of gold or brassy sheen, all four cylinders have this. Could that be caused by the brass flakes in the oil? We found the source of that, the brass gear on the crank has a small chip in it. Not sure how that happened.never had any brass in the oil until the drive to and fro Flagstaff and the distributor was not pulled out.

Anyway, here's the pix. Any and all comments are welcomed.

I take it the head’s sealing surfaces were machined? It looks like it. I suspect they were not to exactly the same depth, unless one cylinder is a little short. One head on my car is like that, I had to cut a base shim from shim stock with scissors. That’s what can happen when you let your friend machine your heads.

Yes, the heads were machines.

C J Murray wrote: ↑Thu Oct 10, 2019 12:33 pm If it is popping compression out at the top of the cylinder you may have a head where the sealing surfaces of the two cylinders is not the same depth. I have also seen brand new p&c sets with cylinders not all the same height. If the case has been machined the sealing surface must be true.

My suggestion from October 10

Measure the cylinder lengths first. That is from seating surface to seating surface and it doesn't take much of a difference to result in a leak. .006" is too much.

This is not likely the cause of the problem, but your heads need some work, The arrow points to where the sealing surface should end and where the conical shap of the chamber should begin. The flat ring to the left of the arrow says you have a 3-4mm ledge hanging out over the cylinder wall: In worst cases, that ends up being a secondary, 'peripheral' combustion chamber and the local compression ratios can lead to detonation and the collapse of the top[ ring land, so:

Hi Dan, I see no contact info for you. I have a pair of unmolested complete B heads, cheap. Contact me if you are interested.

Ron LaDow wrote: ↑Fri Nov 08, 2019 12:07 pm This is not likely the cause of the problem, but your heads need some work, The arrow points to where the sealing surface should end and where the conical shap of the chamber should begin. The flat ring to the left of the arrow says you have a 3-4mm ledge hanging out over the cylinder wall:
1967283.jpg
In worst cases, that ends up being a secondary, 'peripheral' combustion chamber and the local compression ratios can lead to detonation and the collapse of the top[ ring land, so:
Peripheral chamber.jpg

Hi Ron,
why would the sealing surface be too wide? Is that the surface area for stock jugs and is exposed because I am using 86mm cylinders?
Martin thanks for the offer but I have a stack of B heads if this one turns out to be the problem.

That surface gets wider during resurfacing unless the angled portion is also cut.

Martin Benade wrote: ↑Fri Nov 08, 2019 4:12 pm That surface gets wider during resurfacing unless the angled portion is also cut.

Ah, makes sense.

Martin Benade wrote: ↑Fri Nov 08, 2019 4:12 pm That surface gets wider during resurfacing unless the angled portion is also cut.

+1
And whoever is standing on the server power cord? Please get off; you're blocking the electrons.

Yes it is running slow

Martin Benade wrote: ↑Fri Nov 08, 2019 8:01 pm Yes it is running slow

Not until the seal on number two let go.
Engine ran like a top and then bam, it didn't.