Bad crank?

Well I thought I just had a bad rod but after pulling the crank it's obviously out of phase. I suppose that would explain broken valve on #1 and bent wrist pin on #4. 81' KZ 1000 J motor, are those cranks known to twist or spin out of phase? 

Do you have any damage on #1 cylinder on the head? Looks like the piston came in hard contact with a valve or the head. When you say broken valve does that mean its sheared in half?

I can't attest to the J model, but all the big fours are basically the same and its not a very common issue as far as I have ever heard. Mechanical collision at high RPM is always a problem no matter what. Count your blessing that the rod did not escape the cases.

From what I have heard they can go out of phase like that if hit very hard. It also happens if you try to drag race using either a slick or a air shifter without having welded the pins.

There are more knowledgeable members on here that may be able to shed more light on your issue. I mostly deal with 650/750 engines where crank failures are never a issue.

Definitely looks like a shopping trip is on the horizon

wrote:

 81' KZ 1000 J motor, are those cranks known to twist or spin out of phase? 

I have read reports here from knowledgeable folks who say that the early J motors did have a problem with twisting cranks.

www.kzrider.com/forum/2-engine/615717-welded-crank#846594

kzrider.com/forum/2-engine/216384-truein...ing-the-crank#216446

Also, from this 1982 Cycle World article:
issues.cycleworld.com/article/1982/2/1/w...-new-for-82-kawasaki

"There’s also been a change in crankshaft construction, with closer tolerances on the press fits, avoiding the problems the 1981 version had with cranks twisting with the first seriously-missed shift."

So it sounds like it may have been a particular issue with the 1981 J motor, which is exactly what you have.

The J model crank pictured below was removed from a 84 GPZ-ZX1100, with 18mm wrist pins.



It now serves as the heart of my 82 KZ1100A Shaft road bike with a renovated 84 ZN1100B LTD engine.

I believe this crank was professionally balanced, and welded as it was reassembled with a new set of rods.

😊

Wookie58 wrote:

Definitely looks like a shopping trip is on the horizon
I am purchasing a complete 2000 J model Police crank. It looks the same as the 81' to me. Should fit ,right?
 

Formula264 wrote:

I am purchasing a complete 2000 J model Police crank. It looks the same as the 81' to me. Should fit ,right?

Did you compare the part numbers?  

#1 exhaust valve head was laying on top of the piston on disassembly. Very little damage to anything, I don't think it was a high rpm issue. But who knows

DOHC wrote:

wrote:

 81' KZ 1000 J motor, are those cranks known to twist or spin out of phase? 

I have read reports here from knowledgeable folks who say that the early J motors did have a problem with twisting cranks.

www.kzrider.com/forum/2-engine/615717-welded-crank#846594

kzrider.com/forum/2-engine/216384-truein...ing-the-crank#216446

Also, from this 1982 Cycle World article:
issues.cycleworld.com/article/1982/2/1/w...-new-for-82-kawasaki

"There’s also been a change in crankshaft construction, with closer tolerances on the press fits, avoiding the problems the 1981 version had with cranks twisting with the first seriously-missed shift."

So it sounds like it may have been a particular issue with the 1981 J motor, which is exactly what you have.
 

I wonder if these later engines have decreased piston to valve clearance over the earlier engines?

I do know the '82 and later GPZ750 engines have reduced piston to valve clearance due to using a higher compression piston design over the KZ version engines. It is very easy to bend a valve on those engines but at least they have a one piece crank.

wrote:

#1 exhaust valve head was laying on top of the piston on disassembly. Very little damage to anything, I don't think it was a high rpm issue. But who knows
 

A sheared off valve head seems like a very hard hit!

Kawasaki valves especially the exhaust side are known to be extremely tough so that is a surprise. Kawasaki parts in general are overbuilt from the factory.