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Head/deck question
Posted by: zarfnober ()
Date: June 15, 2022 09:06AM

I’ve got a pair of 140 heads, one chamber needs a weld at the gasket surface, but the heads were milled to eliminate quench. My question is what was the original height of gasket surface to deck surface? I’ve got a local welder that can do the repair needed, but am considering building up the chamber at the deck to use with milled pistons to keep compression low.

Thanks,

Rocco

Re: Head/deck question
Posted by: wittsend ()
Date: June 15, 2022 09:29AM

Hopefully others with this experience will chime in. Most of what I've heard indicates that a smaller quench regardless of the increased compression does more to decrease detonation (I'm presuming that is the goal) than just lowering the CR.

You say "building up the chamber." Are you saying you want to increase with weld (then machine) the head gasket area to effectively bring it back to its un-milled dimension thus lowering compression? Or are you saying you want to build up material on the flat portion of the chamber (quench area) but then compensate by milling the piston? If the latter it would seem you are trading quench on one side for the other and effectively making little or no change (other than to the wallet) and weakening the piston top in the process. No experience doing this with a Corvair myself but trying to apply general principles regarding the question.

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***'61 Lakewood, a "Freebie" in hibernation for 27 years - In the process of applying CPR.***

Re: Head/deck question
Posted by: zarfnober ()
Date: June 15, 2022 10:43AM

Heads are currently milled to match the deck, I got the heads years ago, and considering the cost of buying a different set of refurbished heads, I’d just assume rebuild these to use on a turbo application. So, build up gasket area and deck, and use a head gasket for the quench area as the former owner did for their high compression engine. Then mill heads opposite of chamber to bring compression down for said turbo, allowing probably stock length push rods and sheet metal fitting where the factory had it.

Re: Head/deck question
Posted by: KenHenry ()
Date: June 15, 2022 01:10PM

I'm not sure what you mean by deck surface? The quench pad of the combustion chamber? I was told that 0.060" was removed from my stock 140hp heads to remove the gasket step between the quench pad and the gasket seating surface. Ken

Ken Henry, Rochester, NY USA
1965 Corvair Corsa
140 hp, 4 speed



Edited 1 time(s). Last edit at 06/15/2022 01:12PM by KenHenry.

Re: Head/deck question
Posted by: Wagon Master ()
Date: June 15, 2022 03:11PM

zarfnober Wrote:
-------------------------------------------------------
Allowing probably stock length push rods and sheet metal fitting where the factory had it.

And that sheet metal fitment issue is a real pain in the tookus that you'll fight all the way to and including the air clear crossover.

Been aircooled since 1973
Northwest Ohio 45840

Re: Head/deck question
Posted by: v8vair ()
Date: June 15, 2022 03:37PM

Maybe just use a .052 head gasket ?
Clark’s offers a compression cut piston that keeps the squish too .
Many options

1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1998 Honda Prelude Dirt track car

Mike Levine

Re: Head/deck question
Posted by: zarfnober ()
Date: June 15, 2022 06:51PM

Quench /deck is the same for purpose of this discussion, sorry I got them mixed up. If he step/gasket surface is .060 from the “quench pad” then the .052 gasket should be fine. I was kinda hoping someone had a stock head laying around to measure, for some reason I seem to remember it being around .100”, just want to be sure and avoid potential headaches. Thanks!

Rocco

Re: Head/deck question
Posted by: Jonathan Knapp ()
Date: June 15, 2022 08:42PM

This seems like a reasonable approach to me. Here's how I would state it (if I am understanding correctly): weld up the step in the chamber to the old gasket surface dimension. Then use a 0.032 head gasket to reestablish a good quench area (with pistons at or even slightly above the cylinder tops). The welding would increase the chamber volume over the valves. Then mill the tops of the pistons that are adjacent to the valves (not adjacent to the welded up step) to adjust your compression ratio down for the turbo.

That way you get the compression ration you need for the turbo but still get a good quench area (which the stock turbo heads do not have). Best of both worlds!

Jonathan Knapp
Wheeling, WV
'66 Corsa Autocrosser

Re: Head/deck question
Posted by: zarfnober ()
Date: June 16, 2022 04:28AM

Jonathan Knapp Wrote:
-------------------------------------------------------
> This seems like a reasonable approach to me. Here's how I would state it (if I am understanding correctly): weld up the step in the chamber to the old gasket surface dimension. Then use a 0.032 head gasket to reestablish a good quench area (with pistons at or even slightly above the cylinder tops). The welding would increase the chamber volume over the valves. Then mill the tops of the pistons that are adjacent to the valves (not adjacent to the welded up step) to adjust your compression ratio down for the turbo.
>
> That way you get the compression ration you need for the turbo but still get a good quench area (which the stock turbo heads do not have). Best of both worlds!

Yes, you understood m correctly, thanks! PM sent

Rocco

Re: Head/deck question
Posted by: vairmech ()
Date: June 16, 2022 04:57AM

LOL, you don't want to quench anything, it is a squish area!

That squish area creates turbulence for better combustion. Spark knock starts in a lean area. Where is there a lean area? How about the .100+ clearance on a 110 engine? That is why you need premium on a 110.

Every 140 gasket step I have measured has been real close to .060. If you think about the combustion chamber design that is why it has the same compression ratio as the 110 engine.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

Re: Head/deck question
Posted by: zarfnober ()
Date: June 16, 2022 06:20AM

Well, the water/meth injection will quench the thirst for detonation reduction!

I had no idea I’d cause such confusion ????

And thanks for the number Ken, that’s exactly what I was looking for!

Now let me go find another way to entertain the troops, thanks for all the replies.

Rocco

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