aluminium flywheel / ring gear fit and materials
aluminium flywheel / ring gear fit and materials
(OP)
In constructing an aluminium flywheel with a steel ring gear, what should be taken into account to determine the inteference fit between the 2 components? I notice that many aluminium flywheels use bolts or pins to ensure the ring gear remains a good fit - is this really necessary (and wouldn't the pins be placed under unnecessary shear, likely to fail)?
The proposed ID of the ring gear is 285mm, the temperatures it will endure are typical environmental temperatures for a passenger car - i.e. from -35 degC (on a very cold day?) to around 80 degC (I'm guessing) but of course the surface temperature of the friction surface could be very much higher......
If assembled with a mild inteference fit, say 3 thou at a temperature difference of 220 degC, then, according to my simple calculations, the inteference fit is still an order of magnitude bigger than the differential diameter change due to cooling at -35 degC. Does that sound right? So why do people pin them?
Should the expansion due to centrifugal force be taken into account? (Up to 8, perhaps 9000 rpm). Seems trivial.
And what are the most suitable materials for the aluminium flywheel and the steel friction surface?
Thanks for advice and suggestions.
The proposed ID of the ring gear is 285mm, the temperatures it will endure are typical environmental temperatures for a passenger car - i.e. from -35 degC (on a very cold day?) to around 80 degC (I'm guessing) but of course the surface temperature of the friction surface could be very much higher......
If assembled with a mild inteference fit, say 3 thou at a temperature difference of 220 degC, then, according to my simple calculations, the inteference fit is still an order of magnitude bigger than the differential diameter change due to cooling at -35 degC. Does that sound right? So why do people pin them?
Should the expansion due to centrifugal force be taken into account? (Up to 8, perhaps 9000 rpm). Seems trivial.
And what are the most suitable materials for the aluminium flywheel and the steel friction surface?
Thanks for advice and suggestions.





RE: aluminium flywheel / ring gear fit and materials
Rod
RE: aluminium flywheel / ring gear fit and materials
Rod
RE: aluminium flywheel / ring gear fit and materials
For some cars positively securing the ring gears in place is a necessity. On more than a few of my TR6s, the ring gears have worked themselves sufficiently loose that the starter would no longer engage... man it sucks to pull the gearbox just to correct the ring gear's position.
RE: aluminium flywheel / ring gear fit and materials
If it's a temperature / expansion issue, it should be at really cold temperatures that the problem occurs. But like I say, according to my calculations, the change in inteference due to differential Al/Fe contraction is about a tenth of the magnitude of the designed inteference fit......... So it shouldn't move - designing a lip on the oouter edges of the flywheel (or a lip and a taper) could help keep its position if it's a centrifugal expansion issue (higher density of the steel ring gear - it will experience a greater expansion than the flywheel at high rpm) - but do you think that this is the issue?
Or is the issue to do with how these aftermarket flywheels are assembled? - I'll be using a heated press which certainly gives a greater control over assembley than heating and then quickly transerring a hot ring gear and positioning it in the cold press.
From your experiences it sounds like bolts / pins are needed but I don't see why. Is it really centrifugal expansion ? Any more ideas about the design criteria?
I had a look at Fidanza's site but it didn't tell me very much...... http://www.aluminumflywheels.com/flywheels.html
I notice some of the flywheels are anodised though. Do you think that's a good idea for preventing corrosion?
RE: aluminium flywheel / ring gear fit and materials
Rod
RE: aluminium flywheel / ring gear fit and materials
Other considerations, with the TR6 at least, is that the flywheel deviates from its at-rest plane by as much as 1/2" when running above 7500RPM. The crankshaft flex is horrible, and I can only imagine what that does to a flywheel when combined with the help of the Lucas starters in loosening the ring gear.
RE: aluminium flywheel / ring gear fit and materials
At that loading, at that speed, low cycle fatigue of the interface could be an issue.
Also, a 3 thou press fit might be enough to locally yield the aluminium, so you don't have the interference you thought you had. What is the push-off load?
Cheers
Greg Locock
RE: aluminium flywheel / ring gear fit and materials
It appears to fit against a shoulder in the aluminium, so the ring gear is pressed towards the shoulder as the starter engages.
Also, being a boat, there is no clutch on the flywheel, and as it has not corroded, I presume it is marine grade alloy.
I expect that problems can arrise if there is no supporting shoulder to resist end loads from the starter engagement. I also expect that clutch heat will expand the flywheel a lot more than the ring gear, causing yeilding by the increased interference, exasivated by the heat reducing the compressive strength of the aluminium.
Also, I believe that unless very well heat treated, the silicone in aluminium continues to dissolve into the aluminium during thermal cycling, causing the aluminium to shrink. At least that is how a metalurgist once explained it to me when I had a project that required aluminium parts with exceptional dimensional stability, while undergoing repeated thermal cycling.
Bottom line, machine the aluminium with a shoulder, carefully calculate the interference at room temp and at say 300 deg C (or whatever a clutch is likely to reach), consider the compressive strength at that temp for the alloy you use, and use a heat stable alloy that has been heat treated to the extent that it will shrink no further.
I might still have details of the grade I ended up useing successfully, but the info will be buried dep if i still have it. The bar stock i used was over twice the price of the normal T6 high strength grade.
Regards
pat
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: aluminium flywheel / ring gear fit and materials
Pat, your comments about the dimensional stability and compressive strength are well taken. If you trip over the material spec of the aluminium you used, please let me know. In the meantime I will have a look at the compressive strength of various alloys and see what theoretical yield there might be at the temperature cycle and dimensions I'm using. Can anybody tell me where data on shrinkage due to thermal cycling might be found? And how much heat treating improves this?
RE: aluminium flywheel / ring gear fit and materials
Flywheel ring gears are not perfectly concentric before they are shrunk on the flywheel.
For the dimension parameters you might call Design Products (714)892-1513 or McLeod industries in Anaheim, Ca USA.
it is a bitxx of a job....wheel in the freezer for 12 hours and CAREFUL heating of the ring gear with a rosebud tip. Too hot and there goes the ring gear. About .015"-.020"
Three or four button head screws with red loctite only serve to keep things in place just as you would safety wire,clip,and clamp everything used for other than driving to and from the supermarket.
RE: aluminium flywheel / ring gear fit and materials
Rod
RE: aluminium flywheel / ring gear fit and materials
Copy the "bolted the ring gear on"....kinda rewriting my last paragraph....
I always use screws when using a iron or alloy wheel for other than driving back and forth to the supermarket. (grin)
its just common race prep.....(not an option).
RE: aluminium flywheel / ring gear fit and materials
Jim
RE: aluminium flywheel / ring gear fit and materials
Lee developed heart problems after a trip to Japan and required a heart transplant (Carrol Shelby and Lee were at Cedar Sanai while I was doing some work there). I don't know the cause of death which was some years later but he survived the transplant for years. His son John was still racing with Cal Club last I looked.
Rod
RE: aluminium flywheel / ring gear fit and materials
the flywheel ring gear loosened to a point where when we
went to start it to make another test , the starter just spun the ring gear not the engine
we had to pop the engine off the dyno and drill / tap for
(8) 1/4 inch bolts where i tig'ed welded the ring gear to
bolts
then a few weeks ago with a steel flywheel ..same thing
i was testing a NHRA A/ND Nostaglia front engine SBC 393 cid engine to 9400 RPM , and ring gear loosened and walked
backwards ....started hitting the starter bendix gear / sparks at very end of test
what was pretty strange ..i expected the ring gear to be loose ?? ...but i had to heat up and drive it back in place with hammmer blows ...so we wound up tig-welding
8 spots ring gear to flywheel
these are acceleration tests and i guess theres enough ring gear inertia at 9300 to 9500 to loosen ring gear as i either snap the throttle back closed at that RPM limit or the SF901 grabs the engine and tries to bring it back to starting RPM
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3
RE: aluminium flywheel / ring gear fit and materials
that pic link shows starter ring gear spot tig welded to 1/4 NC button head bolt.
its not pretty, but a quick fix so we could resume dyno testing
the 1/4-NC button head bolt was installed after drilling and tapping for it in the aluminum flywheel
this was a Weber aluminum 8-Bolt Chrysler Hemi flywheel
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3
RE: aluminium flywheel / ring gear fit and materials
Just stumbled in here looking for information on aluminium flywheels. Some very useful posts so far. I'm building an aluminium flywheel (in 7075-T6) for a custom car project and am trying to finalise my ring gear attatchment method. I have a few queries I hope some of you may be able to help with.
1. I had intended to have the ring gear shrunk on and use the clutch bolts to hold it in place (as well as holding the clutch on of course). But looking at it closer, the clutch bolts are m8 (6 of them) and drilling/tapping such big holes into the ring gear will leave it quite thin around the holes. I haven't done any calcs but it seems possible the ring gear may want to fall apart at high speed being so weakened. What size bolts/pins do people use to bolt on a ring gear, and how many?
2. Is it necessary to have a shrink fit if you're going to bolt the ring gear, or would an exact/interference fit be ok?
3. I'm a bit unsure about the terminology used in this thread. When people mention a '0.015" shrink fit', for example, does it mean the flywheel shoulder OD is machined 0.015" larger than the ring gear ID at room temp? Or is this the difference in diameter when the ring gear is heated ready to be fitted? Or are we talking radiuses or something else entirely?
4. Bearing in mind I will be bolting the ring gear on too, would a sufficient shrink fit allow the heated ring gear to drop onto the flywheel and grip as it cools, or would you always need a press? Any idea what sort of difference between flywheel and ring gear diameter I would need to achieve such a fit?
Right, that should do for now. Thanks for your time guys.
Liam