Broken crank

Patrick Hubbell · Posted: Mon Mar 22, 2004 11:46 pm Post subject: Broken crank

This is a first. My new Leopard with only 3 hrs of run time, had a PTO crankshaft failure this weekend. Mine was not the only failure. At Sundays IKF race at Stockton two Leopards had the same failure.

My other Leopard which was one of the early engines to be sold here, had over 50 hours on it and not one problem.

Has anyone else had a similar failure. I asked some of the engine builders who were at the track about this failure. They both said they haveseen quite a few brocken off PTO shafts in recent weeks.

Perhaps a bad batch of cranks?? It cost me valuable points in the Region 11 series. Last lap, last turn, wham! and I'm walking back to the scales.
_________________
Patrick Hubbell

Michael Brookes · Posted: Mon Mar 29, 2004 7:17 pm Post subject:

I also had a PTO side of a crank brake. It was a new crank half that was just put on, and it was the first hard lap after 3 break-in session.

Must have been a bad batch of cranks ( I Hope ).

After replacing the crank again, I raced the Jax Pro Moto and a local race without a problem.

Bob Ogden · Posted: Mon Mar 29, 2004 9:04 pm Post subject:

Pat,
You have a hell of a way of retiring Laughing

Have you contacted Russell to see if they have any info?

Patrick Hubbell · Posted: Thu Apr 01, 2004 4:23 pm Post subject:

Tom Hickey · Posted: Fri Apr 02, 2004 9:27 am Post subject:

I have heard the rumor that the Leopard when turned at excess RPM that the weight of the clutch wrecks havoc with the end of the crank. Is there any validity to this story?

Patrick Hubbell · Posted: Sun Apr 04, 2004 10:30 pm Post subject:

Bill Wharton · Posted: Thu Apr 08, 2004 10:45 am Post subject:

Crank PTO failure can becaused by many things.
Proper assembly will help to minimize potential problems.

When installing the clutch, always lap the clutch to the crank. This is very important to ensure that the fit is exact. Clean very well after lapping and before assembly. Ensure that the keyway fits the slot in the crank correctly and that it is not too tall. Sometimes you need to file the flat to ensure that the clutch will slide fully on to the crank taper. These steps only take a few minutes and it allows you to have perfectly matched componets as far as fit is concerned. These steps should always be followed when preparing your engine & clutch combination with new parts, but are especially important when no third bearing support is utilized. Verify that you use proper torque specs when you reassemble and try to ensure that during removal or assembly that you apply pressure at 90% to the crank while supporting the socket end of the wrench so that the end of the crank isn't stressed.

Another possiblity is the balance of the clutch. Although there are technically more accurate ways to balance the clutch, just do it like you would a wheel / tire assemble. Find the heavy spot and remove a little material, continue until balanced. Very there is no rules infraction if this is performed.

These steps cost little to nothing and should help to improve the life of your engines crank shaft.

Bill
Kartechracing.com