chromoly flywheel

[havok91]

I'm designing a chromoly flywheel and I was going to have a shrink fit for the ring gear. The diametral interference fit is .013." I've run the numbers and this fit is acceptable, actually it leaves half the original fit at max speed which is 8000rpm. I've never seen steel flywheels with welded or bolt retained flywheels. Those with whom I've consulted indicate that I don't need anything other than the shrink fit.

Ideas

 

[patprimmer]

I have seen shrink fit only.

I have seen shrink fit and spot welds.

I have seen cast iron, aluminium and steel flywheels. I have never been aware of any need for special high strength steel.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[IceStationZebra]

I agree with Pat. Probably 99% of the flywheels in service have shrink fit ring gears. I have also seen one or two ring gears that were shrink fit and spot welded - more as insurance if I remember correctly. As far as material choice, the big concern would be if it is being used for a clutch surface. Make sure the friction material is compatible with the flywheel material.

ISZ

 

[patprimmer]

I have seen aluminium flywheels with steel inserts for the friction areas.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[evelrod]

I use an alloy steel flywheel on my Mini, ultra light weight, 6 lb., with the ring gear welded on.

I use an Al flywheel with a steel insert on the Lotus. Ring gear is shrink fit and drilled/tapped...the bolts that fit the clutch cover/pressure plate also hold the ring gear in place. I have had ring gears move on Al flywheels without such effort to secure them. I have seen gears knocked off by the starter drive on iron wheels. For a street car, OEM type, I see no need for any other method than shrink fit. For racing, it makes sense to go that extra mile.

I have, in the past, used Al flywheels with a 'sprayed on' surface. While that makes for a cheap, light weight unit, life expectancy is limited.

If you are curious about what I use as a steel insert, on one of my sprayed on units I "saved" it by installing an insert made from a Skill saw blade!

Rod

 

[havok91]

Thanks for the input guys. The flywheel will weigh 15 lbs with the ring gear and mate to a twin disk clutch (the assembly can actually accomodate a triple, just with thinner floaters and friction disks). The car will be street driven, but, I live close to the Bonneville Salt Flats and I plan to venture out there and run in some of the club runs.

evelrod, care to expound on the sprayed on units?

 

[RossABQ]

Porsche uses ring gears that just bolt on, on some of their water cooled engines.

 

[evelrod]

Not sure I can add much. Lee Mueller, a friend, fellow competitor and founder of Lee Mueller Racing started his business in the 60's by building Al flywheels and exhaust headers for SCCA production racing. His first flywheels had a coating on the contact surface...some type of plasma spray...that worked well enough with organic clutches. Not knowing this little fact, I used a Tilton button clutch on it and it failed soon after. I installed the steel insert...the aforementioned Skillsaw blade.

Ancient history... We were not close friends, but I liked Lee. He could be an arrogant a-hole sometimes, but I liked him anyway. He was at Ceders-Sinai getting a heart transplant the same week as Carrol Shelby. Where Shelby is alive and doing well, Lee died shortly afterward.

Rod

 

[Bribyk]

It could be a carbide coating of some type, that's what we used on our aluminum brake rotors for FSAE and it worked well for the application.

 

[havok91]

"It could be a carbide coating of some type, that's what we used on our aluminum brake rotors for FSAE and it worked well for the application"

Interesting. How was the coating applied? We do HVOF at our facility.

 

[Bribyk]

It was likely HVOF, the finished appearance was a matte grey color and they resisted wear well. Unfortunately, I don't remember the details so you'll have to talk to your coatings guys.

 

[lawayosh]

Back in the 60's we used both Schiefer clutch/flywheel assemblies that were aluminum with copper/iron spray applied surfaces and Weber aluminum flywheels that had a steel friction insert. This was for our drag strip only stuff and everyday driver street rods.

Keep in mind that some of us were driving (barely) street legal race cars to our day jobs. Stock clutches did not last and cast iron flywheels and pressure plates were just waiting to come apart, especially with small block Chevies turning over 7000 RPM. We ran the aluminum stuff for safety if nothing else.

Relatively short life was expected on the race cars and they didn't last all that long on the street either. Without the weight of an iron clutch/flywheel, on the street our high end tuned, big cam and over-carbureted, motors would bog as soon as you started to engage the clutch. But, slipping the clutch was not much of an option.

The Schiefer surfaces did not like the slippage needed to get a '56 or '57 Chevy moving on the street and would progressively gall or smear. This made the clutch grab, making you get in and out of the clutch to get underway.

Weber flywheels, their pressure plates were steel, had their own problems because of the splippage as the inserts would warp, reducing clutch adjustment to where you might not be able to fully disengage the clutch.

We all got real good at changing a clutch and flywheel in less than 30 minutes after dinner so we could drive to work the next day. Needless to say, our parts supplier loved us.

First post so must apologize for not figuring out how to provide a link to Paul Schiefer on the SEMA (Specialty Equipment Market Association) web site.

 

[evelrod]

In the 50's I was drag racing a much modded 8BA Merc with a cut down iron flywheel...revs were, maybe, 6000 tops, if that. I do recall several Chebbys grenading their flywheels and clutches on a rather alarming basis at the NHRA strips that I frequented. One chunk came from a C Altered right through the windscreen of a 41 Willys and into my pit...damn close as I recall. Scatter shields were 'recommended' but not yet mandatory in many classes.

Rod

 

[lawayosh]

Rod -

The ability to disintegrate cast iron was one reason that small block Chevy guys ran them. Nothing else would turn that many revs and live. By the time I got into street rods and drag racing around '61 scattershields were required.

There was another problem with frangible cast iron bellhousings that sometimes were where the rear motor mounts attached. A flywheel would come apart, taking the bellhousing with it, the back of the motor would drop, the trans would do a nose dive and, with luck, the scattershield would catch it by the input shaft.

By the way, as you knew Lee Mueller, do you remember Kas Kastner, who was fielding cars in the same SCCA classes in the '60's and '70's with Don Devendorf driving?

Yosh

 

[evelrod]

I never met Kastner, but he is still around, alive and kicking as I hear. I've met Don on several occasions back in the early 80's. I did not know him very well, his shop was just two doors down the street from a good friend that owned AVO in El Segundo (I drove one of AVO's cars once). I also had a very close encounter with him at T4 at RIR...He had rolled his car at the end of the Esses and stirred up a big dust cloud...As I came out of the cloud in a Lotus Cortina, Don's car passed in front and above me upside down and airborne, passing from right to left. Next lap, I could see the car with the driver's window smashed down to about a foot...with Don (who is a big guy) coming out through it!!!

Rod

 

[lawayosh]

Kas was sort of like British Leyland West running as Kastner-Brophy out a shop east of Sepulveda in El Segundo. At the time, I was considering having them build me a Spitfire to play with on squiggle tracks. A spit was pretty cheap to build in comparison with our dragsters and Don said they were easy to drive.

Dave Kent, who later did Toyota and Mazda racing, was doing the metal and paint for Kas. Dave had a shop in ES where Penske would park his CanAm Porsches when in town. They would have two stalls tarped over so no one could see what was going on or get a look at the (Mark Donohue's term) "unobtanium" pieces.

 

[evelrod]

It's been a rainy weekend at Buttonwillow...Lost the electronics in the Lotus on Sat. morning...Switched Robert to a "Celebrity Toyota" from Danny McKeever's Fast Lane School for the rest of the weekend. (Danny is the greatest and if your in the mood, taking one of the road courses offered by Fast Lane at Willow Springs is certainly money well spent. I'm not affiliated with Fast Lane, Dan is just a friend for over 40 years).

To the point: Jerry Barker and I run in the same VARA class, me in my Mini Cooper and Jerry in a beautifully restored Herald...I'll see him at the Moss Motors British Extravaganza at BRP in May...I'll try to remember and ask about Kastner...If I can remember!!! If your in the area, that first weekend in May is well worth the trip up to Buttonwillow, especially for fans of British cars.

Rod

 

[lawayosh]

Losing the electrics on a Lotus sounds like the prince of darkness struck again.

I might be out of town around that time but it sounds like it would be fun. Will try to make it if I can.

Yosh