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Flywheel Resurfacing (The Real Way) sorta long
Posted by: vairmech ()
Date: February 06, 2022 06:40AM

The other thread promted me to write this as a lot of people try to treat the Corvair flywheel like a solid flywheel and they are NOT! You can't mount it in the center as that is just spring steel and will flex giving an uneven job. Even if you use a magnetic base the rivet heads are not all the same thickness and if it rests on the steel weight ring those are not flat either.

The only way to resurface a Corvair flywheel is when it is apart. I do it on my lathe but when it is apart it could be done on a Blanchard grinder also. What you will see in the following pictures you might not believe but nothing is staged. While this is only one flywheel they are ALL the same way, it's even a wonder they work as well as they do.

Starting with this first picture is the back side of the flywheel face. This is a factory machined surface so it should be flat and square, RIGHT?



I start by making the backide of the flywheel as true to the front as I can. In the picture you can see how off the backside is with just a quick run across the area. Look at the cut marks, they are not even nor all the way around.



In this picture it may be more evident that the backside that was machined is not flat by any means and this is not warpage. Yes I even do the mount ledge and the outer part and you can see how uneven they are. I don't remember how much I took off but it was something like .005" to true up the backside and the front side with the worst case scenario cleans up with .008-.010".



Now you want to talk about warpage, here it is! I did not stop the cut and take the picture, the face is warped that much.



Ignore the hard spots and look at the outer edge where the PP bolts to, even that is not flat. I didn't take a picture of how far out it was to begin with but it was probably .002" of not flat. Add all of these .002, .003 and more and how far out of plane can you get?



The hard spots are also high spots and I do take them off. The one thing I am looking for is an industrial oven so I can heat the faces to normalize the hard spots. I've had no complaints so far with how I have been doing flywheels.



The assembly is a whole other story. IF you take one apart DO NOT use the OD of the face to center! Per the blueprints these are Bolt Circle Centered. I made my own jig using the blueprints.





Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: v8vair ()
Date: February 06, 2022 06:41AM

Nice

1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1998 Honda Prelude Dirt track car
1967 Crown V8 under construction
Mike Levine
Cumming Georgia
North of Atlanta

Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: Wagon Master ()
Date: February 06, 2022 06:59AM

Not knowing what "Industrial" entails, what temperature oven do you need?

Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: vairmech ()
Date: February 06, 2022 01:03PM

Wagon Master Wrote:
-------------------------------------------------------
> Not knowing what "Industrial" entails, what temperature oven do you need?
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Probably something that will go to about 1,000 degrees. I think it takes 800 degrees for 12 hrs to normalize the hard spots.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: idiyaught ()
Date: February 06, 2022 02:33PM

the video referred to in the other thread had 1040 deg for 1/2 hr then left in the oven to cool over night.

John Oostdyk
Thornhill, Ont
63 Rampy
65 Greenbrier
64 Convertible

Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: vairsUPnorth ()
Date: February 06, 2022 05:51PM

vairmech Wrote:
-------------------------------------------------------
> Wagon Master Wrote:
> -------------------------------------------------------
> > Not knowing what "Industrial" entails, what temperature oven do you need?
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>
> Probably something that will go to about 1,000 degrees. I think it takes 800 degrees for 12 hrs to normalize the hard spots.


Technically this is not "normalizing" because the temperature applied is not above the austenite transition and you are not refining the microstructure (producing a particular pearlite fraction). What you are describing is a subcritical temperature stress relief. This is actually a very good idea considering the initial [likely] non-uniform cooling of the original casting, subsequent use, and now re-machining.

Dale K Dewald, PhD
Engineer/Scientist - Foundry Operations
Michigan Technological University
Houghton, Mi 49931

Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: jjohnsonjo ()
Date: February 06, 2022 06:26PM

Hard to believe but when I was having some machine shop work done locally the owner was working on a three piece flex flywheel. It was from a modern diesel import pickup truck. Forget what it was, but I guess engineers never learn. Sorry for the hijack.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: gbullman ()
Date: February 06, 2022 06:37PM

Great information! Hopefully skills like this keep getting passed down to keep these cars on the road.


Gary
1966 Corsa Convertible
Northern New Jersey


Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: Early Guy ()
Date: February 06, 2022 08:49PM

Nice work Ken on the bolt centering jig. That is no doubt the best way. As I stated in the video I've done hundreds of these using the outer edge with zero complaints. As far as the hard spots I feel the heat treating (normalizing) is essential, as the modern non asbestos clutch materials are non forgiving and don't like the hard/high spots. After much experimentation including consulting with a metallurgist friend, The temperature I set my furnace to is 1040 degrees F. It doesn't have to remain at that temp long about 1/2 hour then slowly cool in the closed turned off oven till it reaches a temp which can be handled usually overnight for me. Before we started heat treating about 20 years ago we did have some complaints about clutch chatter. The normalizing process has eliminated that.


Ray Johnson Villa Park IL 63 Spyder Conv. 140 EFI

Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: vairmech ()
Date: February 07, 2022 05:14AM

I read the tech article that Dale Langslather did way back when he started doing flywheels and even posted about how he made his jig. Even back then he posted about everything being bolt-circle centered and I have always remembered that. Even before I had my jig I did a crude bolt-circle centering using calipers.

Now I have the info that Dale probably got way back then and that is how I made my jig. In the print section below there is no mention of the OD centering, just bolt holes! The only reference to the OD is that the rivets must be within .010 concentric of the OD.



Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: isucorvair ()
Date: February 07, 2022 08:14AM

.
>
>
> Technically this is not "normalizing" because the temperature applied is not above the austenite transition and you are not refining the microstructure (producing a particular pearlite fraction). What you are describing is a subcritical temperature stress relief. This is actually a very good idea considering the initial [likely] non-uniform cooling of the original casting, subsequent use, and now re-machining.
>
> Dale K Dewald, PhD
> Engineer/Scientist - Foundry Operations
> Michigan Technological University
> Houghton, Mi 49931


I was 100% waiting for Dale to jump in on the 'normalizing' discussion. Its best to hear it from someone that understands the metallurgy!


Eric P.
DeWitt, IA

Re: Flywheel Resurfacing (The Real Way) sorta long
Posted by: Max Roeder ()
Date: February 14, 2022 12:24PM

Ah, a subject I love to see discussed and cussed. Without looking at the print I believe the tensile specification for the ductile iron flywheel was 60Kpsi. Many of you recognized the gentleman, Dale K Dewald as an excellent resource for understanding the behavior of ductile iron as it responds to localized hard spots caused by heat input from the clutch plate. I would like to know a little more about the subject of localized hard spots, normalizing, stress-relieving, and the influence on the wheel being serviced. Is there a better process to bring the wheel back to a stable condition? Would a full anneal, subcritical anneal or other heat treat process provide the best results. Is normalizing or stress-relieving adequate or are these processes providing a temporary cure to the issue of "hard spots"? If the hard spots are rendered "soft" for machining purposes are the "spot" fully gone? Are the hard spots more likely to reappear if the time/ temperature/ transformation aren't fully achieved? I'm always interested in the behavior of metals.

One more thing while I have your attention. All the bolt center alignment procedures are correct, great, and necessary. However, until you spin the flywheel up to the specified speed (I believe GM used 1000rpm) you don't know how the flywheel responds dynamically. If I remember GM wanted 1/2inch/ounce at the 1000rpm speed. Once the flywheel is stuck up inside the driveline with all of the other things that go round and round you are assuming you are good to go. I hate taking the drivelines out of corvairs!

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