Engine: Minimum safe quench?

[Matthew Wendt]

A lot of talk recently on quench. Searched old posts, didn't see exactly what I was looking for. I have a stock R2 (.030" overbore) that I just rebuilt. New flat pistons. .026 deck to piston on one side, .016 deck to piston on the other side. One of the middle pistons on the .016 side is only .010" Heads were also surfaced just a few thousands to ensure flatness.

In hindsight I should have evened the sides out during the decking of the block and figured out why the one piston is .006" taller. To late now as it is in the car. I put it together with .040-.045" thick Best Gaskets.

Seams to me like any composite gasket will eliminate proper quench. My question is can the engine be safe with only .025" head to piston clearance assuming a I change to the .015" steel head gasket?

I want what will be safe for the motor while optimizing the performance. Thoughts?

Thanks,
Matt

[PackardV8]

Yes, .025" net piston-to-head is too tight. Most consider .035" the minimum and .050" maximum. Having said this, I'm running .025" on the Packard V8 in my E12 pickup. I won't be turning it much over 4,000 RPMs. It's rod stretch at higher RPMs which cause the problems.

One of the middle pistons on the .016 side is only .010" . . . In hindsight I should have . . . figured out why the one piston is .006" taller.

Yes, you shoulda, but you're not much further out than most standard rebuilds. One possibility is the rods on shorter holes are rebuilt, having had the mating surfaces cut down and the bores honed round, thus a shorter rod. The long hole might have a new rod.

A mis-machined piston is also a possibility. If it's the piston, there is usually enough stock to cut the top to match the others, but it's not an operation most engine shops are equipped to do. Holding a piston on a mill table requires a special vise. Holding them in a lathe again requires a special setup.

Bottom line - go with the composition gaskets.

FWIW, I spend a lot time explaining to prospective customers why I no longer do CASO-builds and why a precision rebuild costs so much. Shop time is expensive. Measuring all the pistons and rods beforehand, boring and honing to exact size, cleaning, doing a trial assembly, measuring everything, disassembling and machining where needed, cleaning and reassembly is labor-intensive and has to be done by a tech with years of experience. How precise can you afford to be? That extra $500 - $1000 buys a much better running, more durable engine, but it's your money, your build, your decision.

jack vines

[Mike Van Veghten]

Yep...what Jack said.

And on the same note for when I port cylinder heads. It's just not worth cheap out...for me OR the customer.
Back when I had my Pro Gas Anglia, and before I started using Total Seal piston rings, I ran a tighter thAn recommended ring gap...why, because it worked.
BUT, would I do the same when building an engine for someone else...NO I never did, nor will I now. It sorta ok if I hurt something of my own while experimenting (that's how you learn), but never worth it on a customer engine. Just normal dimensions for everyone else.

Mike

[Matthew Wendt]

Thanks for the feedback. This is my first complete rebuild and lesson learned. I am doing another 289 for a 61 Hawk now and will take what I learned and apply it.

Thanks,
Matt

[Paul Keller]

Just finishing (?) my '63 rebuild w/ mild warming. The decks were .015" mismatched - Yours are quite close.
The steel (shim) Fel-Pro gaskets used were '018" at the flat surfaces - A used set measured at '022" at the compressed raised embossed area.
Paul TK