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Head Gasket Surface Cutting
Posted by: wittsend ()
Date: June 02, 2020 08:39PM

Disclaimer: Before some say, "You're not suppose to do THAT!" Please understand this is a free Lakewood someone gave me 25 years ago. If I'll be driving it 100 miles a year that will be a lot. And that is no wild estimate. I have numerous collector cars that see similar mileage each year. I'll be the first to admit that I'm cheap, but I'm not lazy. So, this is where I'm at.

One of my heads had significant damage from..., rat wiz. It caused the head to "become one" with the cylinder ( http://corvaircenter.com/phorum/read.php?1,909647,page=2 third post down) . Since I was going to use the bottom surface of the head as a reference I needed to restore some degree of flatness to the area. I cleaned my table saw surface and then put a sheet of plate glass on top. I put an old X-Ray film on the glass. Then I applied JB Weld to the area the rat wiz had damage. I placed the head on the X-Ray film and put weight on top for 24 hours.

I removed the film and mounted 240 wet & dry paper to the glass. Holding the head at the center (and periodically switching sides) I moved it across the paper to clean the surfaces. It actually didn't take much effort or time to get a clean surface. I'd guess I removed a few thousandths at the most.

Having seen what I recall was a Lisle Corvair head cutter I had my son machine me a two piece cutter. The reason I went two piece is that I could put material (X-Ray film again) between the pieces and increase the cut depth. Initially I was contemplating a dual cutter but in the end only opted to use a single cutting edge. The handle was from an old lathe, free parts my son got in vocational school.

Long story slightly shorter I was able to get the surfaces clean. Until you get near a common surface it chatters somewhat and quick back cut and short strokes worked better than full rotations (until the end). At that point a socket on the center bolt with a ratchet helped to keep the pressure centered. In the end I was typically within .002 of the reference surface, at times .003.

It took roughly .016 to get the surface clean. My original measurements were not the nominal .571 I found listed here at Corvair Center. They were (1-6) .585, .583, .580, .575, .577, .579 respectively at the start. Currently they are all centered around .588. Given the "generous" 8:1 compression ratio of the 80 HP engine and with my minimal driving Premium fuel is doable and I'm hoping the .016 cut won't affect the compression ratio much especially since I've already bought .032 gaskets. I've cleaned the sharp edges of the combustion chamber and depending upon any input given I can CC the chambers if it is worth the bother. Thanks for looking and any input that might be given.



Edited 2 time(s). Last edit at 06/02/2020 08:42PM by wittsend.

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Re: Head Gasket Surface Cutting
Posted by: MattNall ()
Date: June 02, 2020 08:45PM

Good enough for that 80hp head..go for it!

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Re: Head Gasket Surface Cutting
Posted by: joelsplace ()
Date: June 02, 2020 08:59PM

CC the chambers. I would have used the thinnest possible gaskets to help the quench or squish area. Be sure to thoughly deflash the heads too. You can probably get away with regular. Did you read Ken's post on combustion chamber and head work?

[corvaircenter.com]

Joel
Northlake, TX
5 Ultravans, 114 Corvairs and counting...




Edited 1 time(s). Last edit at 06/02/2020 09:01PM by joelsplace.

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Re: Head Gasket Surface Cutting
Posted by: jjohnsonjo ()
Date: June 03, 2020 05:43AM

I've gone cheaper than that myself. Had a set with minor water damage on the registers. I used valve grinding compound with a old jug. I rotated it back and forth, counting how many turns on each surface, keeping them all the same. I stopped when the worst surface was clean. then I did the rest to that depth. It worked well for many years until the heads were removed for other reasons.

J.O.

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Re: Head Gasket Surface Cutting
Posted by: wittsend ()
Date: June 03, 2020 10:55AM

Matt, thanks for the encouragement.

Joel, thanks for the link. I had read that before and yesterday searched..., and never found it. All I can say is to get to a .040 quench it looks like I'd be removing a fair amount of the lower spark plug threads. Even after I finished my .016 cutting the quench was still .085 and that doesn't account for the .032 gasket or anything the piston may be in the hole.

J.O., as a 'finish' to the surface I used a gasket punch to pop out three dots of 280 Wet N' Dry. With the cutting edge out of the equation I spaced the dots 120 degrees apart and glued then to my tool. Rotating it makes for a light honing on the surface and cleans up any roughness. I check with the depth mic in four areas to keep things consistent but really little to nothing gets removed.

My son has a modified "Little Machine Shop" mill but the travel is too short to do the head and he was apprehensive anyway. The tool he made at the trade school he attended. He was an assistant there and has a 'sure come in if you need to do something' relationship with the Instructor. He said it was easier to do on a manual lathe/mill then the set up time on a Haas.



Edited 2 time(s). Last edit at 06/03/2020 10:56AM by wittsend.

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Re: Head Gasket Surface Cutting
Posted by: wittsend ()
Date: June 03, 2020 11:17AM

I wanted to add to the above. When I checked out Ken Hand's numbers they are very consistent with these heads even though his are 110HP and mine are 80HP.

He pulled out .085 and got .015 to the quench and I pulled out .016 and got .085 to the quench. Singh grooves..., I've studied them but hear conflicting information. I assume they are intended to burn the marginal mixture in the quench. I doubt my cutter would ever be sufficient for a .085 cut and then you have the push rod length issue.

Which, by the way, does my .015-.020 surface cut necessitate shortening the push rod tubes?



Edited 1 time(s). Last edit at 06/03/2020 11:18AM by wittsend.

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Re: Head Gasket Surface Cutting
Posted by: MattNall ()
Date: June 03, 2020 11:31AM

No need to shorten P-rods..

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Click HERE for My Website...Click HERE for My TechPages!
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