atb

Here's the latest dilemna on the stroker front.
My most recent plan was to use used 968 pistons with the HPC coating. Overhoning by 7 ten thousandths to clear the coating created an interesting end gap issue with the factory rings. Filing down oversized rings would cure that, but create a potential ring backspace issue. I decided that running the used pistons was no longer an option.

Before making my next move, I went ahead and had the block sonic tested. I had measured the cylinders with calipers before I had the block bored, so I knew it was going to come out thin to begin with. I believe Reynolds has a .250" minimum thickness recommendation. I've heard (not verified) of some bored out blocks (not DEVEK motors) running close to .200". I know Marc T likes 'em thick, understandably so.

I've attached the results of my sonic test. I've got a deposit on a set of Mahle motorsport pistons, which is what I'll run if I run the block as is. Or, do I go ahead and have deck plates welded in to reinforce the cylinders and go with the JE/nikasil combo.

Curious to hear everyone's comments. Particularly if any has any info on a thin cylinder failing.

Oh, the top measurement was taken at 62mm from the top of the cylinder.

Adam C

I am also using an uncoated block with uncoated 968 pistons. Why do you need a coating with factory block / piston combo?

FWIW, I am going without a deck plate.

Shane

Adam after you get this up and running, do you think you are going to put any forced induction on it? Deck it!!

atb

Adam,

I was going to coat the 968 pistons because the set I had, had some scuffing.

-Adam

atb

Shane,

These rear mounted turbos that are going through development really have me interested. According to Corky Bell, it looks like 6.5 liters may be too much displacement for a single turbo. I wonder if there's room to fit two in place of the rear muffler?

Fastest928

Adam,
I have other options for you ... you need to call me.

Marc

Adam C

Marc, why not post it so we can all learn?

Fastest928

Adam,
I told you back when you first posted pics that it was too thin ...remember?

I have other borable blocks and also the tooling to ring this blocks, been doing it for years .. although yours maybe too thin to recover.

Tom. M

Just a couple of simpleton questions...

If you deck plate it..doesn't it just hold the upper portion of the bores in place reducing movement, ?...
wouldn't a thinner wall just be prone to cracking from either bore pressure and loading from the piston?

where is the piston to cylinder wall loading the greatest...sides ? fronts? at the bottom? or at the top?...if this is known then compare greatest possible loading positions to wall thickness'...maybe workable after all if the thin wall is on a non-heavy load face?..

Just some questions and thoughts..
later
Tom
midlman@rennlist.net
89GT

Barry Johnson

Deck it buddy

BC

I have sent a GTS block to motorsport to deck (hopefully). I think if its a possibility that its a better solution for long range planning.

Has anyone seen how thin those walls look when they are at 104mm on the bores? VERY THIN>

Lagavulin

Adam, I think it's too late to deck-plate the block. From several sources I've heard the 928 block is difficult to weld, let alone one with very thin cylinder walls. The optimum order of operation would have been to install the deck-plate first, deck it, then bore and lap it; you would have had some really nice straight cylinders that way.

If you proceed now and put the deck-plates in after you had it bored and lapped, more than likely your cylinders will not be straigtht afterwards, and that's if you don't crack anything during the process.

BC

Lags right. I have been told and told again that the block can't be decked *after* its been finish bored.

fst951

Hi there.

Lag is right that it needs to be welded first and then machined. However, the block is weldable when the right consumables are used with a skilled welder. Still, it can crack. Its cast rather than forged and makes for a little more difficult crack propogation problem.

Good luck

atb

B.C. wrote:

That's assuming you are trying to save the finish on the alusil bore. I'm assuming if I go to a deck plate that I would be nikasiling the cylinders after making them round (or uh, not round) after installation of the deck plate.