Bad Crank Bearing Cause

[waveblasta001]

hey guys,

blaster took a dump on me over the week. Just had a chance to tear into it and found some detonation on the pto side. When i opened the hood i noticed oil above the exhaust port on the same side. Mods are an ada girdled head, factory b mod pipe and trd waterbox. The crank bearing let go on the pto side which was the cause of the detonation. Just was wondering if it may have just been its time to go or if there was a cause that i should be looking into. The gasket on the head was not ripped but maybe it got pinched on the install causing the oil to cover the head pipe? This motor has had 2 seasons on it with no issues since the build. Here are some pics of the damage. Also does anyone know if its okay to run a dome that has mild detonation around the edges?

 

[Quinc]

Dome is fine to run. Looks like it didn't get oil to the bearing and it seized up. Or maybe you ingested some water?

 

[Jr.]

What looks to be deto is not. Its debris from the lower rod cage that pelted the piston and dome.
That is a very common crank failure. On non-rebuilt cranks, its generally due to age. The output side of the motor takes the greater wear. Its also seen on rebuilt cranks as when rebuilt, they are either pressed to tight, or slightly out of phase. Its your choice on how you Budget repair? Rebuild your crank? Rebuilt exchange? New OEM, or New Aftermarket? Its probably advisable to run a fresh bore and hone? Dome looks to be ok? Run some emery paper over it and ck actual condition? Worse case, a new dome is about $40

Good Luck!


Ski Ya, Paul

 

[waveblasta001]

Thanks for the quick response guys. I appreciate it. Paul your right, I was mixing up my terms on the deto. Do you have any guidance on what direction i should go for the crank? budget is a little bit of a concern but i want it to last and dont want to cheap out. The cylinders do not have any gouges in them. I think just a quick hone to clean them up should be fine. I wouldnt mind boring them out and going with a little larger piston.

 

[Jr.]

Rebuilt cranks are ok by reputable rebuilders like Compition cranks or Crank worxs,
The WSM aftermarket crank is actually very good! And can be had for aprox $550.
New OEM cranks are best, but very pricy! If it was me? Ask yourself how hard your going to run it?
And at what compression? Stock comp as a weekend warrior? Rebuilt is fine.
Hardcore enthusiast? The WSM aftermarket or OEM.

Before you just hone cyl and throw in new pistons? Have your shop run a bore gauge thru it and make sure bore is still round? And within clearance spec ?

Ski ya, Paul

 

[waveblasta001]

i believe the compression on the domes i have is 180 i think. ( i still run pump gas) SBT sells a rebuilt crank for $199 any input on that one?