Why did this happen, 440 rods.

Long story below, short version here, I tore into the bottom end of my 440 when it locked up on me. I discovered that one of the rod bearings had pretty much exploded. I know what the problem is, now I am just looking to learn what could have caused it?

Long Story

I picked up a kz440 several months ago. The PO couldn't get it running, so I picked it up for next to nothing.

That day I got it running, he had installed a float bowl upside down. :S
(the essentially shut off carb was on the cylinder that went to shit)

I went through the standard routine, new plugs, fresh gas, oil and filter, and the valves adjusted. The bike ran great for a couple hundred miles. Then it went kaput.

I'm guessing that it was a preexisting problem and I just pushed it over the edge. What do you guys think?

The good news is that I already have a new set of rods and they look much better.

Because I can't at photos in a new post?

What does the crank look like?
Steve

That sucks. Did you feel it coming at all (knocking noises, anything?) or did it just happen in an instant?

Most likely the PO either run it very low on oil, or put it down the road -this can result in unseen damage and bearing failure shortly after. The marking on the back face of the bearing suggests overheating due to lack of oil. Was the oil pump and strainer etc ok?

Not sure about the 440, but most of the forged cranks come in three sizes, and the rods do too. You then select a shell insert which come in three size. Selective assembly allows then to build to precise tolerances whilst allowing for some machining dimension variance.

The bolts that hold the crank, just laughed at my impact driver. But it seems to look alright.

Tyrell thanks for that info, I will have to do a bit more research I guess.

I am amazed that the crank looks ok, considering the bearings are absolute toast.

Will advice you to measure up the crank before considering putting it back together again.

I manage to kill two cranks racing :whistle: :whistle: , one due to overheating, one due loss of oil pressure but they really looked like crap when I opened up the crankcase.

To spin the big end bearing on a rod it has to seize to the crank, usually that's from lack of oil. The other cause is incorrect bearing clearance, but that's probably not the case here...

You caught it before the bearing got completely tore up, and you may have saved the crank. You have to use some plasiguage when you put that together, and I would do it twice. Once with the crank at TDC and then again with the crank rotated 90° to make damn sure the journal is round and the clearance is ok all the way around.


IS that the rod on the right hand side? May have been from idling on the kick stand with low oil.

Tyler wrote: To spin the big end bearing on a rod it has to seize to the crank, usually that's from lack of oil. The other cause is incorrect bearing clearance, but that's probably not the case here...

You caught it before the bearing got completely tore up, and you may have saved the crank. You have to use some plasiguage when you put that together, and I would do it twice. Once with the crank at TDC and then again with the crank rotated 90° to make damn sure the journal is round and the clearance is ok all the way around.


IS that the rod on the right hand side? May have been from idling on the kick stand with low oil.

When I first got the bike I did an oil and filter change. I noticed some metal flakes when I drained the oil. Ran it a few hundred miles, then put seafoam in the crankcase, rode around the block a few times and then did another oil change. Still noticed flakes of metal, but thought it was just gunk getting cleared out.

I was passing a semi on the highway when it finally craped out. I limped a few miles home, no idea how it managed to no get completely mangled.

Once with the crank at TDC and then again with the crank rotated 90° to make damn sure the journal is round and the clearance is ok all the way around.


Good tip, measure twice in two positions if in doubt

How much sea foam did you put in...... wonder if you could a thined the oil out to much......I had a so called mechanic tell me once to put a quart of kerosine or trans fluid (I forget which) in my beater Ford pinto and let it idle for a while to clean the motor out before an oil change........ it sure did had a rod knocking after wards and ended up junking it after a year or two.

It wasn't much at all. I was having issues before I added it. Kinda hoped it would help get the junk out.