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Plain bearing question(s)

  • Thread starter Thread starter gearhead13
  • Start date Start date
G

gearhead13

Guest
I am getting ready to order parts to rebuild my '82 GS750 over the winter.
I am somewhat confused about the plain bearings. Maybe a dumb question i dunno. BUT, to me its dumb to make all the main and rod journals and saddles different sizes.......?
The question:
If I order 1 part number of rod or main bearing do I get both halves? Seems that they should be matched pairs?
 
1 matched set for 1 rod 0r 1 main journal should be the way they do it but ? if you look at the parts diagram it shows 8 as the required # needed. PAY ATTENTION to the brg color they are selective fit
 
Last edited:
Nope, each part is one half.

Yeah, it sorta sucks, but that's how it is. :mad:
 
One half shell probably has an oil hole and the other does not. Also, each bearing is probably a different size to make up for the machining clearance deviations from bearing bore to bearing bore. The clearances in the crank and rod bearings are very small, so to keep them within acceptable limits, several different size bearings are necessary. You can't keep an engine together at 10,000rpm+ with bearing clearances of several thou, it would hammer itself to pieces in short order as it broke through the oil film and metal to metal contact resulted.
 
The rod bearings are the same part#, the mains arent all the same #.
Thats $10 for half a bearing, OUCH!
When I take it apart I am going to plasticgauge it.
The book says service limit is 0.0031, so thats 3.1 thousanths? Doesnt seem that tight.
 
Not as tight as I would have expected. I do know that the difference between the coloured bearings for my XJ650 motor differed in circumference by less than a thou.
 
gearhead13 said:
The rod bearings are the same part#, the mains arent all the same #.
Thats $10 for half a bearing, OUCH!
When I take it apart I am going to plasticgauge it.
The book says service limit is 0.0031, so thats 3.1 thousanths? Doesnt seem that tight.
Click to expand...

Part of the reason for the 40W oil...I'de be tempted to build it to half of that if possible.

Is that on the mains, the rods, or both. 3 thou. on the rods would scare me but hey, they built it to run so.....:cool:
 
Ya, it says 'standard' clearances are one to two thou, I am going to want it somewhere in that range. The mains and rods are the same spec.
 
gearhead13 said:
I am getting ready to order parts to rebuild my '82 GS750 over the winter...../quote]

Were there symptoms occurring leading you to plan to tear the engine down? Just asking, as my plain-bearing 650G is at 75,000 km and I thought the bottom end seemed OK. What should I look for?
Click to expand...
 
Flaggo60 said:
gearhead13 said:
I am getting ready to order parts to rebuild my '82 GS750 over the winter...../quote]

Were there symptoms occurring leading you to plan to tear the engine down? Just asking, as my plain-bearing 650G is at 75,000 km and I thought the bottom end seemed OK. What should I look for?
Click to expand...
There isnt really anything that leads me to believe my bottom end is gone, but, I am doing a ring and valve job along with some mods, and I want to be sure it will take the extra abuse that I'll be giving it. I might go with a wiseco overbore kit as well.
Click to expand...
 
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