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Odd deck height results
Posted by: KenHenry ()
Date: September 16, 2021 10:36AM

Hi everyone, I'm assembling a 140 motor and am getting some unusual deck height measurements

Cylinder
1 0.017"
3 0.013"
5 0.022"

2 0.022"
4 0.021"
6 0.022"

I get the same results done a few different ways. One, by snugging the cylinder down with the cross bar shown and using a depth probe. Two, by leaving the cylinder loose but tilting the engine so the weight of the cylinder pushes it towards the crank. I don't think I am completely compressing the cylinder base gasket either way because I can see a thin gap between the gasket and cylinder base (maybe a few thousandths max).

At first I thought variance in the piston machining or modified aftermarket rods might be responsible. But putting a straight edge over the top of cylinder 5, I can measure with a feeler gauge that the top cylinder 3 is 0.009" lower, closer to the block. Cylinder 3's top is also down from the top of cylinder 1 by a few thousands. The good news is the cylinder tops all appear to be parallel with each other. So, the different deck heights seems to be due to some oddity of the block or maybe a shorter cylinder (unlikely?), resulting in different cylinder top heights on the 1/3/5 bank.

How should I correct this? A difference of 0.009" seems large enough that it could compromise sealing of the head gasket especially on cylinder 3. This is especially a concern because the full fin cylinders are bored 0.105" over for this 2.85L build, so have less sealing area than normal. Some options coming to mind are 0.042 head gaskets on 1 and maybe 3 or maybe some kind of shim under the base gasket?? Or maybe this is not enough of a difference to worry about.

Heads are 140 with the steps milled out, and I had planned to use 0.032" head gaskets. Another question is whether the squish will be tight enough at ~0.050" (head gasket plus deck height)? I was expecting deck height of ~0.010" for 0.040" squish. Compression ratio will be around 10:1...

Thanks for any input! Ken

332D12B6-BC08-422C-90FB-D2FE1D12735B by kenhenry_06268, on Flickr

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

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Re: Odd deck height results
Posted by: cnicol ()
Date: September 16, 2021 11:03AM

I wonder if some of your cylinders have had the head gasket surface machined? That would account for the lower deck height on some of them.

Also, there were two different base gaskets; thicker ones for some A/C cars. Are all of you base gaskets the same? As I recall, the thicker ones were copper colored.

You definitely want all three to be the same distance from the block. Maybe an extra base gasket on the low ones?

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
65 Canadian Monza 4dr 110/PG 40k
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: Odd deck height results
Posted by: joelsplace ()
Date: September 16, 2021 11:30AM

"I don't think I am completely compressing the cylinder base gasket either way because I can see a thin gap between the gasket and cylinder base (maybe a few thousandths max)."
This is a problem. No way to get accurate measurements without resolving this issue. I would torque the hold down bar to 30lbs. If you still have a gap investigate to figure out the problem and fix it. The measure your deck height.

Joel
Northlake, TX
5 Ultravans, 129 Corvairs and counting...

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Re: Odd deck height results
Posted by: KenHenry ()
Date: September 16, 2021 11:47AM

The cylinders are new full fin so I would not expect some of them to be machined differently than others, but I will check that out. The base gaskets are new Clark's standard base gaskets which they list as ~0.015". They also offer a thicker 0.020" base gasket which is copper and listed for 140 powerglide. Mine are all the standard steel ones.

These base gaskets have a little ridge in the center which I positioned toward the cylinder. Theoretically it should squish down under torque but I didn't get anywhere close to 30 ft pounds. I'll try torquing down the bar and maybe even the other two studs to see if the gap collapses down. Oddly I don't see any evidence of of a ridge on the old base gaskets I took out, but maybe they're permanently flattened by being squished in there for decades...

Thanks! Ken

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

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Re: Odd deck height results
Posted by: Wagon Master ()
Date: September 16, 2021 12:01PM

Seem like your tolerances are stacked up in a perfect storm.



Edited 2 time(s). Last edit at 09/16/2021 12:07PM by Wagon Master.

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Re: Odd deck height results
Posted by: LeeS ()
Date: September 16, 2021 12:25PM

The base gaskets are a variable as they will deform and thin when the heads are torqued. Have you measured and compared the heights without the base gaskets installed? Or with spacers of identical thickness?



Edited 1 time(s). Last edit at 09/16/2021 12:29PM by LeeS.

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Re: Odd deck height results
Posted by: KenHenry ()
Date: September 16, 2021 12:41PM

I have not done that. My first step will be to pull the cylinders out a little and try to measure their heights with calipers - base surface to head surface. Measuring without the base gaskets is a good thought since it removes a source of variability, though that will mean pulling the rods or sacrificing the gaskets. That might not be too bad as the copper non-ridged base gaskets are looking more appealing even though they're a little thicker (0.020") than I wanted

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



Edited 1 time(s). Last edit at 09/16/2021 12:43PM by KenHenry.

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Re: Odd deck height results
Posted by: LeeS ()
Date: September 16, 2021 01:27PM

Oops, didn't consider that.

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Re: Odd deck height results
Posted by: Wagon Master ()
Date: September 16, 2021 01:33PM

Pulling the big end of the rods apart to remove the assemblies, the gasket and remeasuring is no big deal. Any builder that has never forgotten the base gaskets or the cylinder baffles below the jugs, and had to disassemble, is either extremely unique or a liar.



Edited 1 time(s). Last edit at 09/16/2021 01:36PM by Wagon Master.

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Re: Odd deck height results
Posted by: KenHenry ()
Date: September 16, 2021 07:08PM

Mystery solved: the cylinder barrels are all the same height but the base gaskets have different thicknesses due to variation in how pronounced the stamped ridge is. Maybe they would all squish down to the same thickness when the head is torqued but I sort of doubt it. I have a full set of used GM ones, all 0.012-0.013”, that I’ll clean up and use instead.

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

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Re: Odd deck height results
Posted by: JimBrandberg ()
Date: September 16, 2021 07:56PM

So I can't help but wonder if someone is selling cylinder base gaskets with a .009 variation.

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: Odd deck height results
Posted by: KenHenry ()
Date: September 17, 2021 04:02AM

Good question Jim. Upon further reflection this one is entirely my fault. I now remember partially torquing one head down with 2 cylinders installed to check valve train geometry. I must have used those two base gaskets and flattened them when I went to 10 ft pounds. This was two months ago, totally forgot about it until now. Seems I have been chasing my tail again… thanks

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

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Re: Odd deck height results
Posted by: v8vair ()
Date: September 17, 2021 04:19AM

There is some piston rock in the bores , apply pressure to all the tops or bottoms of the pistons and recheck , if you think it’s the base gaskets check it without them , if the rods have been resized then I bet that’s where the issue is , not many machines shops left that can do rods correctly anymore

1965 Crown V8 Racer
1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1979 Mazda RX7

Mike Levine

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Re: Odd deck height results
Posted by: vairmech ()
Date: September 17, 2021 05:08AM

When you use the base gasket that little ridge is supposed to deform to take car of any irregularities and prevent leakage. Yes we hav all reused gaskets and it works.

As far as measuring the base gasket measure the edge of it and not the raised center. Clark's copper colored ones are just that, copper. I know many of you have used copper everywhere but I avoid it whenever possible.

The rods are aftermarket and the tolerances are better than factory ever thought of.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: Odd deck height results
Posted by: KenHenry ()
Date: September 17, 2021 06:21AM

Thanks Ken, they are all made out of the same thickness steel, so I think the difference I saw was caused by whether I had torqued it down before and pre-squashed it. Mike: these are the rods:
DBF114A1-1D23-4717-A2CC-0A60E93F852A by kenhenry_06268, on Flickr

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



Edited 1 time(s). Last edit at 09/17/2021 06:27AM by KenHenry.

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