Broken Cranks on Jackpiners – 1973?

[Ernie Phillips]

In the last two weeks I have looked to buy Jackpiner project bikes and found both engines had broken cranks.  In both cases, the break occurred on the ignition side at the junction of the crank web (flywheel) and spindle.  Were (are) crank failures common on early black engine 175's?  On a rebuild, how do you prevent reoccurrence?  Anybody got a spare crank in good condition or a good bottom end?  Thanks  -EP


Ernie P.
Chattanooga, TN

[slvrbrdfxr]

Ernie,
I'm not sure when the changeover occured but the early black 175 engines had a smaller shaft on the ignition side than the later engines. The early engines were 20mm shaft and the later models were a 25mm shaft. I can't say for certain but it's a good bet the 20mm shafts were not holding up and thus a reason for the increase in the size. Hopefully someone else will jump in with some more info.
Dave McCullough

[G Ellis]

Give me a call 217 260 0237  Later Gary

[Kip Kern]

Both the 175 and 250 black engines had crank problems, thus the change on the silver engines.  I have not heard of any these days but have heard of them when produced (early 70's).  I have had to disassemble various cranks to get enough parts to make one good one for rebuilds, I am sure others have ran into this?

[Dwight Rudder]

I had kickstart and 3rd gear problems on my 1972 model.  I had heard of crank breakage on the 1972 models also.  I have not heard of these problems on 1973 models.
Dwight

[Ernie Phillips]

Thanks for the info guys.  Looks like I've got lots to learn about these KTM engines.

Gary, I'll call you tonight.  -EP

Ernie P.
Chattanooga, TN

[Rocket]

I had a new 73 175 and it broke the crank on the mag side.  The first 175's had a 20mm crank pin and it must have been too weak.  My dealer sent the crank back to Ohio and it got replaced with an upgraded 25mm crank pin.  No more problems.
Rocket

[Mike Lenz]

If you a PVL internal rotor ign you wont have to worry about it. Not enough flywheel weight to break it...at least mine has lasted.

[brian kirby]

I was thinking the same thing, the smaller internal rotors would not stress the crank as much.

Brian

'73 Berkshire