Can you swap the big end and main bearings on the crank and connecting rods?

I have split my case to do a full restore on the bike. It has around 40K miles on the engine but runs well. Has a slight ping to it while running and the starter clutch was slipping so it seemed like a good idea to split the case and take a look.

Problems:
Starter chain guide had broke and left some small rubbery/plastic particles in the case (never a good start).
Found my connecting rods have a slight jiggle on the crankshaft and the crankshaft main bearings could stand to be replaced. I'm not sure if the rods are supposed to have that much play or if it is a bearing issue, so I said might as well replace them. Unfortunately after doing all the Yamaha bearing mathematics, discovered I need some bearing sizes(colours) that I cannot seem to find (brown, black, green). I have seen the yellow and blue sizes but didn't know if I could just swap them out.

The engine runs well aside from the pinging but I know as a small engines teacher "pinging is never a good thing". So I am looking for some advice, help, or ideas to correct the issue or if it is a lost cause.

 

You have to maintain the proper clearances. That's why there are different bearing colors (sizes).
Before giving up on her, get some plastiguage and measure what the current clearances are.
Worst case, you'll need to do some hunting to find the bearings that you need (if you need any).

 

Alright, plastiguage is on its way.

 

What year and model bike are you working on? We have most "size" (color) bearings available.

Main journal and rod bearings are definitely NOT interchangeable!

 

I have an 1982 XJ750RJ.

According to the Yamaha math:
BR-Brown
BL-Black
GR-Green

Crankshaft Main Bearing
1 2 3 4 5
BR BR BR BL GR

Big End Bearing
1 2 3 4
GR GR BR BR

Those are the bearings for the bike in NEW form. I am not sure what I would have to use now nor do I know the size differences between the different colors. You know come to think of it I'm not sure I knew what I was getting myself into. Its amazing how many specifications there are in such simple mechanics.

 

According to the plastiguage my clearances on the big end journals are hovering around .038mm. I know you do not want to go over .04mm which I am getting very close to.

 

ALLOWABLE MAIN BEARING OIL CLEARANCE 0.040 - 0.064mm (0.0016" - 0.0025")
ALLOWABLE ROD BEARING OIL CLEARANCE 0.030 - 0.090mm (0.0012" - 0.0035")
ALLOWABLE CRANKSHAFT JOURNAL (both main and rod journals) RUN-OUT LIMIT: 0.040mm (0.0016")

One version of the factory service manual actually gives the CRANKSHAFT bearing shell measurements...these same shells are used on all XJ650, XJ700, XJ750, and all XJ900RK, RL, N/FN, and F engines:

Blue: 1.5000 + 0.002 to + 0.006mm
Black: 1.5000 - 0.002 to + 0.002mm
Brown: 1.5000 - 0.002 to - 0.006mm
Green: 1.5000 - 0.006 to - 0.010mm
Yellow: 1.5000 - 0.010 to - 0.014mm


CON-ROD bearing dimensions for all XJ650 (except Turbo) and XJ750 air-cooled engines:

Blue: 1.5000 + 0.002 to + 0.006mm
Black: 1.5000 - 0.002 to + 0.002mm
Brown: 1.5000 - 0.002 to - 0.006mm
Green: 1.5000 - 0.006 to - 0.010mm

 

Hi, i have got same problem :/ need 2 brown bottom bearings and cant find it anywhere after i search propably entire web...
Have you got any ideas where to get them ??

 

What year/model bike are you servicing?

 

Xj750 seca 1982 11m

 

Hi Marcin, we do have the brown lower shells for your engine, please write to us at: info@xj4ever.com for pricing and shipping, etc. information.