Stumped with rod bearings?????

[puv]

Some of you may remember how Promethius helped me diagnose a noise in the lower end of my XJ11. Well, after determining that it was most likely a rod bearing I started digging in and I have cracked the cases and determined the problem. The bearing that is bad is not the rod bearing, but the first shaft bearing nearest to the alternator or #4 cylinder. Reading from the Yamaha book I have determined the proper bearings for the rods but the book tells me there is a number on the inside walls of each cylinder (where the crank rotates) that will help get the right bearing for the crank shaft. There is no number in the area that the book describes therefore I cannot determine what bearings are needed for the crank shaft itself. Does any of this make sence? I hope so because I am confused. Like I said it was easy to get the right bearings for the rods, but having trouble with the crank bearings themselves. Thanks for any help you can give.

[John]

The main bearing size is stamped on the outside of the case. Look in front, near the joint where the case halves meet. I think it is near the upper, front motor mount. I can't recall which side of the engine. There should be a series of 5 digits. When you are able to find it, post back and I can help you find the correct bearing size, if you should need the help.

[Hired_Goon]

My "baby" XJ has the numbers engraved, not stamped, on the outside of the case. These numbers and the numbers stamped on the crank are used to calculate the bearing size.

The numbers on the outside relate to crankcase outer bearing size and the crank numbers relate to internal bearing size.

I know the numbers on the outside are hard to find and I can't remember exactly where they are but I think they are close to one of the engine mounts.

[pggg]

Japanese motorbike manufacturers DON'T supply undersize bearing shells for their engines. If you grind the journals on the crank, you can't get shells to fit. The crankshaft specialists either make up shells to fit, or build up the crank journals then re-grind them back to stock specs. Labour intensive and expensive.

The different sized stock shells are in fact almost identical in specifications. In other words they're all effectively 'standard' size. They're 'plug and play'. Assuming that the crank journal is undamaged, you can simply replace your 'dodgy' shell with a spare with no problems.

[pggg]

P.S. if one bearing is stuffed and the motor's in bits, and you plan on keeping the bike, then slap in a whole new set. Why was only one stripped? Must of ran with no oil pressure. Nice and loose for more power There's people here who know where to get those shells.

[mro]

Hi puv

Started to type an answer but maybe this is better.






mro

[mro]

btw

pages are from the "Genuine Yamaha Manual"


mro

[John]

In the pic showing the location of the journal size

The arrows are pointing ONLY to the affected journal. The dot where the arrows begin is where the numbers are located. The info in the pic is very confusing. I had the same problem the first time I split my engine apart.

[puv]

Sorry it's taken so long to respond. I had a big pile of life to take care of. I finally located the numbers I was looking for. The stamps on the case were very hard to see but I think I got the right ones now. Bike Bandit will be the place to order. I'm looking at $120.00 for all of them. I have one more question. There was no gasket in between the two cases when I split them. Is there a gasket out there somewhere or do I need some funny goop or something?

To answer some earlier questions about how this happened, It started with the gear grind job. To make the story somewhat short, one of the "C" clips on the fork rod slipped off forcing the rod to slide and jam against the clutch gear which then shattered the fork gear and sent a shock wave to the oil pump cracking the pump. All this happened while driving down the road. The cracking of the oil pump forced a loss of oil pressure causing a case bearing to run dry. Moral of the story is...........? Make sure your little "C" clips are tight!!!!

puv

[mro]

puv

There was no gasket in between the two cases when I split them. Is there a gasket out there somewhere or do I need some funny goop or something?

yamabond 4 or equivalent


mro

[puv]

Thanks, I guess I can buy it at the local Wrench?!