How to be sure about a crank ?!

Hi,

I am building a J engine and bought a crankshaft from Kip Kawa in the U.K. (I live in Denmark). It's a used crank he said was good, he index and welded it, or so he said! When I got the crank it was welded but way out of true, did not spin when placed in the crankcase. He took the crank back and when I got it back I could tell he have had it apart. Laying in the crankcase and with the main bearing cap tightened it does turn freely but with the case tightened it has a tight spot. I tried sticking a straight rod through the small ends, I do not have a 17mm rod but with piston pins in the con rods I tried fitting a 12mm rod through the pins (fit nice and snug in the pins) but con rod number 4 does not seem to align perfectly with the rest. Can the crank be tightened up crooked in the case or is this evidence enough of the work done to the crank not being good enough?

Simon

the crank tightens up the same way in the cases every time.
i'm sure it doesn't matter if the crank is out on a table or tightend up in the cases if you can't get a straight snug rod through the wrist pins something is amiss.
something is wrong with the crank.

leon

Dont use it.
It needs to be right. This is the very foundation of any engine so why start with a problem
Since you gave the seller a chance to make it right and its still not right I personally would be looking in a different direction
for a good crank
Dave

Kip Kawas website say they've gone out of business

There are crank specialists that can straighten it if you wanted to dump more money into it. You have to ask around race shops and high end machine shops. Not Ma & Pa's motorcycle joints.

"J" cranks are a touchy subject.....it is very difficult and expensive to get a good crank to build a high performance engine on, but it is the first and most important part of putting an engine together!

The crank (and rods) has to be right - would you build a new house on a crumbling old foundation??????? Same idea. The crank must turn freely when installed in the cases, and the rods must be indexed properly or the engine will never run right.

So I urge you or anyone else building a J engine to spend the money and get a perfect crank built to suit the engine you want.

Many well known reputable pro shops offer the work - my trust is in the ones that supply to professional racers - Falicon, Fast by Gast, etc...

Also, it might be best to have them supply the core crank rather than shipping your own used crank (which might prove to be useless when inspected after disassembly, like two of my own cranks were). Shipping a KZ crank across the country is not cheap! Overseas is absolutely ridiculous!!!!!

if in need i have 1 brand new NOS 'J" crank to sell.

What I learned from Pearson is that once a crank has been welded once.....it's done. You cannot straighten and re-weld it, the steel will be way too brittle......so that I am thinkig the crank from Kip Kawa is toast.

I asked Jay at APE about cranks and he said they won't weld a crank that's been twisted, I interpret as he doesn't straighten cranks. Here's how he said to check the crank to make sure it's straight:

"If you have a degree wheel and a TDC tool. Find TDC on cylinder #1, Then move over to cylinder #4 and TDC should be at the same reading on the degree wheel. If it is, the crank is not twisted."

There is more to it than just welding a stock straight crank......

The crank has to be disassembled and inspected for wear and tolerances of the side play, etc....All bearings, journals, rods, and gears, and sprockets must be in top notch condition before they can be used on a welded crank. That goes for the tapered end were the rotor mounts too,

The thrust washers Kawasaki used on all the crank are extremely prone to failure, so those should certainly be replaced with a Torrington roller bearing assembly when the crank is re-assembled.

An aside - All the bearings and stock rods should be replaced with "aircraft" grade parts if the engine is going to make power equal to or exceeding Pro-Stock levels - i.e. over 250 HP or more than 11,000 rpm. At that point, it might be better to buy a custom billet crank or a completely custom engineered and built roller or plain bearing bottom end for their engine. Not likely ever the situation for myself or anyone seeking advice from KZR!

The crank has to be indexed and straightened while it is being assembled. Then it should be welded in a fixture, carefully and in a manner as to keep it straight (enough) during welding.

Spot welding in a few (at least three) points is ok for most any engine short of a top fuel drag racer. Welds do not have to be full circular beads.

And BTW - when we used to magna-flux or dye test car racing steel cranks - the racers would get very alarmed when they saw their expensive race cranks full of tiny (microscopic) cracks! All was well, though - all cranks have cracks and "dislocations" - it is the nature of metals in general. What we are looking for is large / deep cracks that extend longer distances from stress risers towards even higher stress areas.....

What about if the crank has been welded? Does that mean my 750 crank is toast?
Steve

Steve - your KZ750 has a built up crank????????????? Looks like a 1000 to me......