Crankshaft Conversion to Ball Bearing

450roo

450roo

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Nov 10, 2020
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Location
Adelaide, South Australia. Australia
The pics tell it all, but the bearing is an SKF 75x45x16, C3
I turned up a bush to slid over the crank journal and fit the inside of the bearing.
I'm toying with feeding a little extra oil to the ball bearing for cooling? But then my Yamaha 250 has smaller ball bearing mains and is lubricated by splash.
Any opinions or improvement suggestions welcome!IMG20251220114607.jpgIMG20251220120045.jpgIMG20251220114747.jpgIMG20251220114822.jpgIMG20251220114911.jpg
 
Since that's the primary drive side, I wonder about the load capability of the replacement. Just curious
 
450roo said:
A small improvement, a tube sealed at the end and a 1mm hole drilled at a right angle to increase lubrication and cooling.
Click to expand...
I re-read this yesterday and was relieved to see that the actual feed hole was only 1mm. The size of the copper tube initially made me gasp at how much oil could be leaving that central distribution area when the top end of these engines is well-known to be marginally oiled. Nice job.
 
1mm is slightly smaller than the oil feed hole in the original bearing.
Did another 60 miles this morning, including about 20 miles on the 70mph freeway, it was much cooler than the 40 degrees on the last ride. No problems so far! I think that if there was going to be a catastrophic failure it would have happened by now. So with any luck the question now is how will it ware.
It is impossible to know what the original roller bearing was rated at, but looking at rollers of similar size, it would be about 35 KN, and that would be more than sufficient to take anything the motor is capable of for the life of the bike. The ball bearing is rated at 22.1 KN, which considering the mild use the motor gets these days, it should last for many 1,000's of miles.
Thanks for your interest and comments.
 
Having done 1000 miles I removed the clutch cover to inspect the bearing. No sign of over heating or damage, but the bearing had moved inward about 3 mm. There is no sign of the outer race spinning in the case mounting but I will still have to find a better way of locking it in place than loctite 641.
Any suggestions will be welcome!
 
450roo said:
A small improvement, a tube sealed at the end and a 1mm hole drilled at a right angle to increase lubrication and cooling.View attachment 53720
Click to expand...
Since fitting this oil feed I have learned that while the idea is good, feeding oil at 90 degrees will cause the oil to become a mist and the higher the rotation speed the more this will happen decreasing lubrication . The oil must be fed into the groove of the outer race at about 30 degrees in the direction of rotation.
 
After discussing the oil flow to the bearing with an engineer who said directing the oil flow at 90 degrees the oil would turn to a mist from hitting the fast moving web and balls. A modified feed through a 1mm jet directing the oil into the corner of the groove at 20 degrees in the direction of rotation will give much better lubrication. He also thinks I should get 10,000+ miles life from the bearing.
An extra 10.000 miles for $35- is worthwhile, considering that the modifications were done without dismantling the head and pistons.IMG20260228100833.jpg
 
I have now done 3500 miles and it is running well, I am not baybying the motor in any way, just riding as normal mostly between 40 and 70 mph. I check the bearing with a stethoscope regularly and hear no alarming noises. Will pull the clutch cover at 5000 to inspect the bearing for signs of overheating.
So far so good.
 
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