465 cracked case

[drummer-on-a-EX]

I've had the motor about 8 months and it pulls VERY strong, I hit the dunes about 2 or 3 times a month and ride full open throttle so it does take its fair share of abuse.

There was no vibration coming from the motor and after the motor was taken apart the case was cracked length wise front to rear centered on the bearings, the bearings were not chafed and the 4mil. stroked crank was balanced when the motor was built.

I'm looking for answers/advice from some of you that have similar motors to keep this from happening again, I want to keep the bike, I've got too much invested in it to sell it, by the same token I can't afford to rebuild it every 8 months.

[chad502ex]

any pictures available?




chad502ex.com

[drummer-on-a-EX]

Sorry no picures, cracked the camera (unrelated) as well.

[duke416ex]

Ain't you just a cracker, anything else look out of place in the motor, did anything hit the outside of the case very hard? It could just be that you had a weak casing.

[drummer-on-a-EX]

I'm thinking it was just a weak case, the bike is 4 years old and been ridden very hard and those aluminum cases are garbage, I've heard of a few other cases breaking but they were in bikes with unbalanced cranks.
The crack appears right at the bearings leading me to believe the extra pressure from the crank is at fault.
Chad seems to have a long history with these bigger motors as well as some others on here, I've seen posts on here from FDO as well, hoping someone had some thoughts (not half wit) on the subject.
Thanx

[MIKE400EX]

I've only seen one cracked 400 case before and it was through the right side bearing bore. It was a stroker that was also run hard for extended periods. Probably just from metal fatigue. I'm sure they weren't designed for almost double the stock output. Three things you might look into would be to get the rotating/reciprocating assembly as light as possible and/or go up a tooth up front to reduce the RPM some. Remember balancing doesn't eliminate loading, but does reduce and sometimes cancels the different forces/harmonics. Also, was the crank welded, and could it have twisted?

[chad502ex]

Originally posted by drummer-on-a-EX
I'm thinking it was just a weak case, the bike is 4 years old and been ridden very hard and those aluminum cases are garbage, I've heard of a few other cases breaking but they were in bikes with unbalanced cranks.
The crack appears right at the bearings leading me to believe the extra pressure from the crank is at fault.
Chad seems to have a long history with these bigger motors as well as some others on here, I've seen posts on here from FDO as well, hoping someone had some thoughts (not half wit) on the subject.
Thanx

well, the first thing that i looked for on your setup was compression ratio, but since it was 11:1 i asked for pictures. I doubt that your setup develops more tq to crack the cases then my 11:1 502 develops so engine flex would not be concern. What type of fuel were you using- don't say pump gas. Pump gas you have to extra be sure that there is no detonation (pre-ignition) cause all that force goes to the crank bearings if there is detonation. It's ok to run pump gas on 11:1 if your dialed in perfectly, but if your running lean on pump then ouch on crank bearings until failure. Say you didn't run pump! ??

[drummer-on-a-EX]

Thanks for the input, The crank was not welded, it is now, As far as fuel I'm running a 50/50 mix of vp red and pump, no pre-ignition and the top of the piston looks good.

[chad502ex]

:confused:

i'd have to see pics to investigate further. I tell ya what: send me the motor and i'll look into it ;)