Blown rod bearing!

steell wrote:

And here's the original original thread

:pinch: :whistle:

OK, the diagnosis is in. There was nothing left of the #3 rod bearing other than chips in the oil pan and pump screen. Looks like the crankshaft took it pretty rough, there is a .030" difference from TDC to 90* turn and there is a .030" difference in the same positions on the inside of the rod, not to mention the rod is chipped and grooved.

Here is a nice view of the damage

The groove and chip are clearly visible here

another angle

Sorry I don't have pics of the case today, I forgot my camera's memory card in the PC. The chip was only a crack, I peeled it out with my thumb.
Can anyone tell me if these casting marks can direct me to their corrosponding bearings? (A,B,C?)

Now for the good news, I have a much less used crankshaft with 4 rods and bearings for a great deal on ebay. As for the cause of the blown bearing... oil flow looks good so far, maybe primary chain slack? Any comments?

otakar wrote:

Hi Marty
I have some bad news for you and some good news for you. I did find out that the stock pistons for that bike are not available any more NEW. They are also NOT exactly the same as the 1300 pistons, but the 1300 pistons WILL work. The 1300 pistons have a lower dome on them because of the longer stroke of the 1300. This will mean that the 1300 pistons will have lower compression in your bike by about 3/4 of a point. The other good news is that I should have enough pistons in exilent shape to provide you with all four. All I would have to do is clean up the other three. O your other choice is that you might be able to pick up this set for a song.
cgi.ebay.com/ebaymotors/Kawasaki-KZ650-K...dZ1QQsspagenameZWDVW

Sounds pretty good for compression, well with all we were talking about. I do believe I'll stay with the 650, just let me know how those pistons come along. Thanks again.

i just tore a 81 650 apart and was going to scrap the pistons.
pm me if you want them. ( free but you need to pay shipping )
i still have the crank also.
basically, i have everything but the upper case and the head.
those were the only things i wanted.


sorry for the bad picture, it was in the trunk and it was snowing.

Post edited by: kawsakiman, at: 2008/03/02 23:58

Post edited by: kawsakiman, at: 2008/03/03 00:03

Don't know why, but it seems to me that the #3 rod bearing is the weak spot. A couple of years ago, I killed the crank on my 84 750Turbo and when I posted on the 750 turbo website, someone piped in (before I said which bearing) and suggested I had spun the #3 bearing. He was right, of course and scatdrat's crank has gone the same way. I would be inerested to know, is this just me, or is it normally the #3 that dies first? Maybe there's an oiling problem.

Anyone else out there who has killed a 650/750 crank who would like to weigh in?

i blew #3 also on the first 650 motor but my oil cooler line blew off first.
blew line, repaired line then locked up motor 2 weeks later.
now this has me thinking.
i wonder if there is a oiling issue with these motors?
seems to common for it to always be #3

Got my "new" crankshaft in today. As you can see, she came with rods and rod bushings. Also got a new primary chain. The crank looks good and clean with no visible signs of wear or damage. I'll get the micrometer on it in the morning. One thing is the rods are all held in tight except for a little horizontal play. Is that normal?