Spun a rod bearing

Well I finally got my motor torn apart after it locked up on me recently. It spun a rod bearing on #4. Luckily I got it torn down just in time to find and win this bad boy, cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll...em=380000315644&rd=1


Heres the bearings.

Post edited by: kxhonda, at: 2008/03/03 20:01

The nasty rod.

And prob my favorite part of this whole rebuild.
650 cylinders on the left, 750 clylinders on right.

Any ideas on what caused the problem to occur?

650ed wrote:

Any ideas on what caused the problem to occur?

Caution -- unsolicited opinion follows :lol:

Perhaps not the underlying cause in this instance, but am thinking one reason for rod bearing failure could be from gasoline intrusion into the crankcase oil. There have been several recent forum discussions regarding excessive fuel in the float bowl (for whatever reason the excess incoming fuel is not all being discharged by the overflow system) which excess fuel rises up into the carb bore and flows both ways, forward into the combustion chamber (then down around the pistons into the crankcase) and backward into the airbox (then down through the crankcase vent hose into the crankcase. This condition of fuel intrusion into the crankcase oil may occur while the bike is parked or during normal riding. So anytime a floatbowl overflow is noticed, it is usually a good idea to sniff-check the crankcase oil for any gasoline odor, and if so, change the oil and filter (plus correct the overflow problem). Another indication is an unexpected increase in oil level when viewed through the sight glass. And the fuel-contaminated oil will also likely be thin and watery.

This gets particularly critical with Mikuni smoothbore carbs which have no floatbowl overflow provision. I think it's the primary reason smoothie users run the crankcase vent tube to directly underneath the bike or anywhere besides into the airbox.

I just checked and I have been a member here for 1 month shy of 4 years,
and up until last week I don't recall any post on any 650 spinning
a rod bearing, and now there's two separate threads. I certainly
hope this doesn't indicate a trend

I think Patton has a point, I always turn off
the petcock when I shut off the motor. I'm
glad the 750B's have on/off/reserve petcocks
and not vacuum operated.

Post edited by: steell, at: 2008/03/03 21:23

I'm not real sure why it happened. I started to hear the rod knock mid summer. I put 2500 miles on it after that until it locked up. I changed the oil when I started hearing it knock. There wasn't any noticable amount of gas in the oil. I always turn my petcock to off.

Just bought a stud extractor to so I can get the top case to work so I can bore it out for the 750 cyclinders. Just about ready to order the 810 kit. Will I still be able to run pump gas running the 650 head without pinging and overheating? I am also putting a oil cooler on it. Anybody got a gpz750 oil pan they would like to get rid of? :whistle:

anytime I have seen a bearing failure due to fuel in the oil, all the bearings show signs of heat and the one that fails has a lot of gaulding on the bearing surface, this is due to lack of lubrication properties of the oil.
most of the time you see a bearing failure like that its caused by oil pumps going bad, and not keeping up with the demand of the motor.
On a small block chevy, rod bearings 5 and 6 will be the first to go when they loose oil pressure,
I would be rebuilding or replacing the oil pump for sure

Took the oil pump apart tonight. Clearances all checked out good. No scratches inside. I'd say its good.

hey kx, i live in pierceton really close to you, goodluck on your motor work!!!

hey kx, i live in pierceton really close to you, goodluck on your motor work!!!