crank bearing split

Message

500.FLETCH · #1 Post by **500.FLETCH** » Thu Oct 09, 2014 3:34 pm

can some please explain how this happed

many thanks

fletch

2smoke · #2 Post by **2smoke** » Thu Oct 09, 2014 4:09 pm

Never seen that before!
It may have cracked from the dowel hole.
Has it been rebuilt, what brand bearings are they?
If the dowel was under side force (pushing against the cases because it didn't fit in the groove) this might be the result.
What does the matching notch in the case look like?

500.FLETCH · #3 Post by **500.FLETCH** » Thu Oct 09, 2014 4:28 pm

all looks good only split engine to-do crank seals
and found this have two marks inside the crank case but nothing to write home about

Fletch

smokamoto · #4 Post by **smokamoto** » Thu Oct 09, 2014 5:19 pm

How many miles/kms on the crank??

Stinke · #5 Post by **Stinke** » Fri Oct 10, 2014 8:49 am

According to Stan Stephens in Classic Motorcycle Mechanics should this happen after 23000 miles / 36800 km

/ Stinke

Bengt Weil · #6 Post by **Bengt Weil** » Sat Oct 11, 2014 1:10 am

Double check but I think the bearing that Stan speaks of failing is an outer bearing (93306-20565 - upper crank/right side) that has a circlip groove, which is the reason for failure due to the location of the groove.

The failure in question here is an inner bearing, which does not have a circlip groove. I'd love to hear what did cause this catastrophic failure - sure looks ugly. Maybe Bill or Rick can share if they have seen anything like this...?

Stinke · #7 Post by **Stinke** » Sat Oct 11, 2014 8:19 am

Yep you are right, I was so happy that I found the article I didn't read it properly. But I think both type of bearings seems fragile.

/ Stinke

vma500 · #8 Post by **vma500** » Sun Oct 12, 2014 7:32 am

maybe the crankcase lube holes blocked ? and the dowel pin did do the rest

mine did over 50000 kms , but have never seen this before

500.FLETCH · #9 Post by **500.FLETCH** » Mon Oct 13, 2014 10:57 am

smokamoto wrote:How many miles/kms on the crank??

she's done 30000kms
all crankcase lube holes clear
koyo bearings are fitted I did not rebuild the engine

many thanks to all that replied

Fletch

Speed Freak · #10 Post by **Speed Freak** » Mon Oct 13, 2014 2:37 pm

Hmm, maybe i should think twice about my plan to not replace the crankshaft bearings in my 40000km RD...

theredbarron · #11 Post by **theredbarron** » Wed Oct 15, 2014 6:48 pm

Looks to me like a manufacturing fault, i have seen this on a number of bearings which have roll pins, dowels, grub screws etc set into the race. If the bearing has the slightest machining defect in this area known as a stress raiser the bearing will fail over time. Just to add, if you send the bearing to a metallurgist or company specialising in metallurgy they will tell you exactly where and why the bearing failed.

500 Two-Stroke Tech

crank bearing split

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