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Can a steel flywheel be machined?

General engine tech -- Drag Racing to Circle Track

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RT Machine
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Re: Can a steel flywheel be machined?

Post by RT Machine »

Let me clear up some myths about machining flywheels here.
I make steel flywheels for custom applications etc, they are made from 1010 or 1020 steel plate.
It does,nt matter how much heat and abuse a steel flywheel receives - it is still easy to re - machine on a lathe, even if you use HSS cutting tools !
This is because 1010 and 1020 steel does not have enough carbon content to be hardened by heat treatment [ apart from case hardening ]
Now cast iron flywheels, are a different story, they are affected by heat because the carbon content is between aprox 2.5 and 4.0 %
They can still be machined on a lathe, but if they contain hard spots , then you can use ceramic or diamond tooling.
This is why its easier to grind cast iron flywheels, and on that note :- cast iron flywheels have no place on a performance engine, but almost everyone on here would know that.
Dan Timberlake
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Re: Can a steel flywheel be machined?

Post by Dan Timberlake »

Is the 15# (cast) ductile iron L-88 flywheel SFI approved ?

https://sdparts.com/i-19932898-chevrole ... gJ7S_D_BwE
rebelrouser
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Re: Can a steel flywheel be machined?

Post by rebelrouser »

Just for my info, years ago I ran an aluminum flywheel with a steel insert, about once a season the clutch would start to chatter, steel insert was warped, replaced with rivets, used the rivet machine for big truck brakes. Those inserts I assumed were steel, and they got hot spots and eventually warped. What material do they use in aluminum flywheels for the inserts?
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Re: Can a steel flywheel be machined?

Post by benno318 »

i dont have a dedicated flywheel grinder however i have a horizontal surface grinder and a rotary table i attach when i want to grind a flywheel.
this only does flat or downwards stepped flywheels though, so for anything in-stepped i do on my big lathe - over the years i have found the best way is a super slow rpm, this will ride best over the hot spots to the point they dont protrude as they do if you spin the flywheel faster.

they also tell me the subaru ones that are bolted together should be unbolted, machined, then re-assembled - however i see this as a potential for runout. i would have done 50+ of these and never once had a shudder complaint, in fact for close customers i have even taken a dial gauge around to their shop to confirm no runout when re-assembled.

some local shops will flip a flywheel in their grinder, face off the rear, flip it again and grind the friction face - not once machining anything relative to the hub! one of these i measured 20 thou runout as fitted to a crank!
AC sports
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Re: Can a steel flywheel be machined?

Post by AC sports »

I'm still sitting on this waiting to see what I'm going to do as far as clutch is concerned.
So to those that grind on a dedicated machine, how do you machine the step afterwards? Do you take it out of the grinder and into the lathe to cut the peripheral step? You must be indicating off the newly machined surface right?
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Re: Can a steel flywheel be machined?

Post by modok »

A flywheel grinder can make steps no problem.
The location of the step is usually not tight tolerance, just needs to be somewhere between where the disk ends and the PP bolts on.
it does FORCE you to center the flywheel on the rotating table. Sometimes i wonder why they even have a step.
Sometimes it serves a clear purpose sometimes not, other than to possibly just to um..."encourage" the flywheel to be properly centered and ground on a decent machine.
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Re: Can a steel flywheel be machined?

Post by modok »

Or possibly just because the step costs nothing when the flywheel is produced so they use it as some kind of adjustment to match the pressure plate and disk thickness.
but speaking of that, if you want to overthink it... you might look into that aspect.

You buy a pressure plate and disk from some company and it's just supposed to be right, but they aren't always.
Making the step height match OE spec is a safe decision, but it may actually need to be more or less....to get the pressure plate in it's happy range.
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Re: Can a steel flywheel be machined?

Post by Schurkey »

Dan Timberlake wrote: Tue Sep 14, 2021 4:15 pm Is the 15# (cast) ductile iron L-88 flywheel SFI approved ?
No.

Neither were the GM ductile damper units.

Far as I know, both parts come from a time when SFI approval wasn't required for big-name racing.

Ever tried driving a street-car engine (mild tune) with a 15-lb flywheel? I knew a guy... Either the tires burned at every stop-light, or the engine bogged. It was like the throttle was digital (on, or off.)
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