Pressing together a motorcycle crankshaft? How?

Ask the folks over at reeky (rec.motorcycles) . Just my opinion , but I'd think a press would be a *much* better option . How ya gonna align/true it ? The outboard shafts (pinion and sprocket shafts on a H-D , dunno what the rest calls 'em) *must* be very precisely aligned ...

Set the crank in one half of the case. Tap the other end with a brass hammer until you get zero runout. The crank ends will be parallel but not necessarily in line.

--Andy Asberry recommends NewsGuy--

Some of the old British singles were like this, I have the instructions somewhere for it. Done by thumping with a lead hammer as I recall.

Is the crank tapered?

I used to build Italian go kart motors (Komets, Parillas, etc.) with

3-piece cranks. I think we used a big vise to assemble the crank, might have had to chill the crank pin first to shrink it. I don't think the cranks were tapered; it was just an interference fit.

The trick was tru>Pressing together a motorcycle crankshaft? How?

Was this after or before it was pressed together?

If after, why wouldn't it go out of true as soon as the engine started?

If before, would it stay true during the press operation?

This is done after pressing together. But _try_ to align it as good as you can while pressing / starting to press.

Depending on the size of crank, you need a copper hammer / mallet or a hydraulic press. I have seen 4 cyl cranks being pressed true on a special hydraulic bench. Nice tool, but it takes an expert to get all 5 bearings aligned. The one who operated it made it in a minute or two.

No, it will not as much as you would like to. But the better you align it before, the less work you will have after. I guess you have no special jig to align it while pressing. And telling the truth: If you think about making it in the vice, I'd bet you will fail aligning it.

Nick

Done 100's of these mainly Bultaco and some british singles.

I have an allignment rig which is just a pair of V shaped knife edges with a couple of dial gauges.

I use a big flypress, and partially press together after roughly alligning with nothing more than a engineers square.

Then the assembly goes on the knife edges to see which way the flywheels have to be hit! I usually try to get nearly zero runout at this stage.

Then finally press together and retrue as necessary. It's suprising how easy it is to move the flywheels on the crankpin, with such a tight press fit. I use a big Thor copper faced hammer.

Small 50cc cranks can be done in a reasonably sized bench vice.

Wayne....

Ah, no. If they cannot answer this at rcm, reeky has zero chance of getting any answer, much less the correct one...

Jim

I , ah , kinda had my tongue buried in my cheek when I said that ... Though sometimes a gem comes tumbling outta that morass . There are some very knowledgeable guys there , but ya gotta pick the gems out of the crap . I generally hang out in RMH (you probably figgered that out from my sig ...) , but tune in once in a while to see if the Harley boys are still stirrin' it up .

After.

Same thought occurred to me at the time, but they stayed true and ran reliably. That's how the factory assembled them initially. The tolerance of the press fit was important. On teardown, the cranks still were true. However, if the motor had been rebuilt too may times the crankshaft might start to behave like a wet noodle and then the crank pin would have to be replaced. I don't recall ever having to replace an entire crankshaft.