My buddy has gotten an Exedy chromoly flywheel for his '6 Mustang GT, and he's having trouble getting the clutch dowel pins into it. I suggested that he throw it in the oven, and throw the pins in the freezer. How hot can the flywheel get before the properties of the original heat-treating process are changed?
I would think that anything under 350F is okay, and that is being generously conservative. It probably sees a lot hotter when the clutch is slipping.
My gut feeling, however, is that he's just not using a hammer properly, or is too afraid of hitting his fingers to give the dowels a proper whackin'. But maybe he is and this is a wrong assumption.
Or put the the pins in the freezer overnight might be the only thing needed. Did this on a keyway, worked quite well.
Paul B
It ended up being a matter of preloading the pins with a C clamp, then tapping (somewhat vigorously) on the clamp to introduce enough vibration to allow things to move. Chalk it up to "beginner mechanic" problems. He was just afraid of berkeleying something up.
You might be able to go as high as 800 or so. Just to be on the safe side though, you probably want to keep it less than 500 or 600.
Edit: Nevermind, looks like it has been sorted out already.
Finished flywheels are unlikely to be in the annealed condition. I'd guess quench and tempered to somewhere in the 28-36Rc range, which puts the temper temperature as low as 900. The easy button for them would be to simply make it from 4140HT, which comes heat treated 28-32Rc. Meaning it was tempered in the 1000-1100 range. It's best to always stay at least 100 or so under the final temper temperature.
Not disagreeing, but with all the stresses of forging etc., why would a flywheel not be annealed for stress relief?
Dan
Dowel pins with an interference fit installed in a blind hole can “air lock” making them hard to get started into the hole. Key is to make sure the pin is straight before driving into the hole. Also some but not all hardened dowel pins have a radius on one end and a slight taper on other end. Tapered end should be end started into hole.
In reply to 914Driver :
In my experience, extremely few steel flywheels are actually be forged. Most will be machined from 'billet'...Which is typically just marketing speak for round bar. Either way, while it would have been normalized or annealed after forming, and can be delivered as such if desired, I doubt that would be the final condition desired for the parts. Quench and tempering it adds both strength and machinability, and the heat treated properties of 'chromoly' are the main reason people want to use it over 'lesser' (cheaper) steels.
914Driver said:Not disagreeing, but with all the stresses of forging etc., why would a flywheel not be annealed for stress relief?
Dan
Typically forgings and castings are annealed to remove stresses and soften prior to machining. They are rough machined leaving finish stock. They are then hardened by heating to a temperature less then the annealing temperature and quenched to harden. They are then tempered to the desired hardness by heating to a specific temperature for that hardness requirement. They are then finished machined removing the rough stock left during initial machining. Depending on the alloy and amount of material removed during rough machining a stress relieve heat treatment may be used prior to hardening.
In reply to pirate :
Good explanation, although modern machining practices can save both time and money by allowing most parts to be machined from start to finish in the final heat treated condition. Often times a light heat treatment even makes it machine better in general as well.
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