71 750 right crank bearing

U

Used Piston

New member
My right crank bearing, not the rod bearing took a shit. I don't know when or why as I purchased the bike like this but hope one of you bright gentleman can give me an idea as to why. My engine number is 7361 which puts it in the late 71 production also before the left bearing upgrade.
Didn't seem to cause any damage other than throwng the crank slightly out of true and all the pieces remained in that section of the case.
I'll try to upload photos
Thanks, John
 
I can't help you but my Canadian registered '72 model did the same. The bearing is easy to replace if you don't mind pulling the motor apart. As far as I know .... this happened to a lot of them and a new bearing will give it a full continued life.
 
The earlier 750's used a ball bearing (pre No 10500 ish) on the primary drive side - Not sure what side you mean by "Right side" - they aren't (IMHO) the correct type for a drive side bearing due to the way the forces are applied when the clutch is dropped etc. The later roller can be fitted - but needs a locating device to stop it moving done a few myself and my own early proddy racing motor has been modded as well.  Regards - Phil
 
There is an oilway to the RHS main, which drains oil from the front right side of the head (valve gear) down the stud and through the cases. Mainly to get oil to the starter clutch freewheel but also oils that main bearing. Some gaskets don?t have the cutout for the oil, and sometimes some crap can block the oilway.
I have used special 12 ball bearings on both ends of my SFC crank for 80000km road and 14 seasons of classic racing and they are still perfectly serviceable. The later SF motors had a roller on LH end (located as Phil says) and a ball on the RHS. They as not known for regular failure. The earlier SF with 8 ball left hand main bearing were known to fail.
 
Usually the cage that gives up and splits, depends on how long you keep the stuff in there as to how much further damage results.  While not unknown, not exactly common either, just happens now and then.

piet
 
I have it all apart, and thoroughly cleaned. The crank has been done and I am readey to reassemble as soon as I can get the bearings from Wolfgang or? The bike only had 14K on it when the incident happened. Last registered in 82 and traded hands at least three times before I got it.I just want to get it back to life and ebjoy it.
 
Also rebuilt an SF1 motor that didn't even have the oilway drilled down from the base of the stud to the bearing journal. No damage had been caused in all the km that motor had travelled - amazingly! But I retro drilled it to be safe. Have also used 8-ball right (dynamo) side and 11-ball primary for many 1000's of km.

If your bike had only done 14000m in 47 years it probably lunched a bearing from sittin-idle seizure!! Ride tem and they seem to keep going ... bearings don't like to sit  around festering in old oil.
 
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