Bonneville America Forums Forums Technical Forums Performance Mods Cast or Forged?

Has anybody ever come across a reference or heard mention of whether or not the parallel-twin crankshafts are forged or cast? Just a curiosity, I'd look in the service manual if I actually had one

cheers!

Forged I think.
Went on the factory tour but when he was talking about cranks, I was nosing round some new bikes.

Typical, it's like being at school - as soon as you don'y listen to something, you get asked about it later

What good are you then? You've got insight into the super-duper incredible top secret manufacturing processes, and instead you're walking around like a kid in a candy store. You should be fired from your Job as the not-so-discrete bonnevilleamerica.com observer! Sorry, should have said Sacked! Off with your head!

Sounds to me like enough of an excuse to go again.

A few weeks ago, I emailed Falicon cranks to ask if they did a new stroker crank for Triumph twins. They replied no, but that they could do welded stroking on one's sent-in crank.

That tends to tell me the stock crank is forged, rather than cast, though a cast crank journal can be welded for repair.

I can say definitely that the Hinckley twins have cast pistons, which is a really good reason NOT to bump up against the rev limiter!!!!!!!!!!!!!

The Wiseco big bore kit comes with forged pistons, by the way. Rev 'em all you want.

From further investigation, I find this: http://www.stabbarps-auto.com/images/crank1.jpg

It's a crank pic of jojje's turbo engine project. It looks like a casting to me. Note the rounded "seam" on the con rod pin flanges. Were it a forging, that "seam" would show grinding marks from knocking down the forging flash.

One could drop ol' jojje a note here: http://www.stabbarps-auto.com/contact.html
I'm sure he would be happy to give you the propper answer.

There are further considerations about the crank. Casting is certainly cheaper than forging. Since the Speedy and America use the offset rod pins, as opposed to the standard 360* Bonny crank, it would make sense to cast that one, too.

It's even possible that the crank is cast steel, rather than cast iron. Pontiac used cast steel cranks in it's own V-8, for years. An other possibility is that the crank material is nodular iron, a stronger metal than "regular" iron. Ford used nodular cranks in their engines.

Again, ask jojje. I'm sure he knows.

The give away is the sandy texture on the unfinished parts. Forged cranks have a different texture because they are literally pounded into shape.

Just posed the question to Jojje on this forum. I'd read casual mention from an internet article that the cranks were forged, but who knows what that's worth. We'll see what the Fast Swede has to say eh? Adey, you're still not quite off the hook yet :-)

Here's what Jojje had to say:

"I also think it's cast. It looks like that and it rings out like a church bell when you hit it.
But it's strong enough for 160hp so it should not be a problem for most people"

Puts that one to rest, but it's good to hear that they're strong!