Insert for turning hard steel /Harley crankpin?

[john.k]

Can someone suggest a budget (ie Chinese) insert for turning a HD crankpin,likely Rc 60-63........I gather it will likely require CBN,but there is a bewildering array of these inserts for various things..........so ,firstly can a coated carbide turn such a hardness ?,and second if CBN is required ,what should I get ?...I havent yet looked into my holder sizes,whether any of them is suitable....I wish my grinders were operational,but no chance of that ,they have been sitting out in a field since the GFC.

 

[e189552]

If you can locate C7 grade carbide it will cut the 60 or so hardness steel.
There are not many coated inserts that can cut that hardness steels.

 

[jcp]

I have used ceramic inserts with success. Depends somewhat on the holders you have available.

 

[rgray]

Definitely a job for a grinder.
Might want to find someone with one to do that job.

 

[pontiac428]

I doubt the crank snout is that hard. Cranks need to be tough, not brittle. I promise you it's not as hard as tool steel.

 

[rgray]

I doubt the crank snout is that hard. Cranks need to be tough, not brittle. I promise you it's not as hard as tool steel.

But he said "crankpin" Not familiar with Harlys much, but for any other motorcycle that would tell me he's talking about a bearing surface.
Just thinking ground would be the normal process for bearing surfaces.
Ground and polished usually.
Tedious to duplicate with lathe turning and polishing.
I asked my crank grinder if polishing to a .001 or .002 undersize could work (automotive).
He claims it will end up being an hourglass shape and advised against it.

 

[cjtoombs]

Automotive crankpins using plain bearings are not normally hardened (they don't need to be). Some performance treatments surface harden the crankshaft, which I think is a waste of time and money, but hey to each their own. Lots of motorcycles use roller bearings, which need hardened crankpins. I would recommend having the pin ground at an automotive machine shop. The charge is usually not that high, as the specialized crank grinders are much quicker to set up for crank grinding than a general purpose machine. Besides the insert to cut the hardened pin, your machine stiffness will play a factor in surface finish, which is critical for bearing surfaces.

 

[benmychree]

I quite agree with the statement that the pin should be ground, and perhaps even lapped. The pins are quite hard as they have rollers running on them, and they run in hardened bushings in the rods, that are ground and lapped to fit, I think I remember that they run with only a few tenths of clearance. I had a 1928 Harley JDH back in the '70s.

 

[Cadillac]

Ive built two evo style s&s engines a 113” and a 120. Both had the majority of aftermarket Jim’s internals. Forged crank and rods everything was a ground finish and if I remember correctly clearances were tight. With the rod design how they interlock their isn’t much surface area so tolerance and finish need to be top notch. Unless you feel like doing it twice. It will self destruct.

 

[matthewsx]

Don't know nuthin' bout Harleys.

But, as a former race engine builder I'd say if you're asking the question here you're probably out of your depth. Of course, if you're an expert harley engine builder I apologize profusely for my lack of confidence in your abilities.

On to the advice....

Send it to someone who knows what they're doing and has the tools to make it happen. Even though I built some national championship engines, and some outlaws that dominate the track I still sent stuff out when I didn't have the tools or the expertise to make it happen. Unless you have extra cranks to use up trying to do this in a home shop is asking to be ordering new parts.

JMHO,

John