What caused this failure???

C

Compu-kart

Member
Rotax Max FR125. Leaded 110 octane/ 8 ounces of oil. 12,500 rpm/ temp 180 then jump to 200F before failure. Road race track. Failure of upper rod needle bearing.

Did piston seize then break the bearing? Did the bearing break first? Something else?
 

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Two possible things if the ring pin is in .
Cage failed allowing bearings too get displaced .
The bearing pin shattered which in turn broke the cage .
How is the piston pin ? Doubt the piston stuck , first .
 
Hard to see but looks like in picture #1 the piston split down through the ring land. Looks like some of my stuff in years gone by lol Chuck.
 
Looks like a simple bearing failure to me. How many hours did it have on it? Rotax's are pretty tough, but there is a limit.
Just for comparison, we do a top end on our X30 every 9-10 hours, and MAYBE a bottom end at the same time. Bottom and top at least every 15 hours. We let that up to our engine builder. I would THINK a Rotax could go 15-20 hours easily.
Clark Gaynor Sr.
 
Oil was Motul 2T synthetic. After further research Rotax recommends about 3 ounces of oil per gallon. We were running 8 ounces bc we didnt know any better. Could this have factored in to this failure? Seems doubtful.

No water leak, radiator is still full. Time on the engine is approximately 3 hours.

Chuck you are hilarious, I wish that was my hand! Water temp was steady at 180F before jumping to 200F
 

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We have one FR125 with over 45 hrs. They're virtually impossible to seize. A sudden jump in temp would make me suspect detonation, and the shock loading killing the bearing and piston. But that's pure speculation.
 
Extra oil did not cause this.

Most likely too much time on the URB.

This was fairly common with the KT-100 years back.

A couple other things that could trigger this failure are an over rev situation after loosing a chain. The pin bore in the piston can elongate or fracture causing a vibration that will knock the bearing out before the piston has a chance to fail.

Just pointing out the obvious as well, but your LRB (and rod and pin) will also need replaced.
 
Compu, I might be out of bounds not sure about the 125's but my 270 and 293 run best between 125-135 degrees on water temp. Anyway I'll give you a 9 on style later Chuck.
 
Ya Chuck. We were up on the temps at Daytona. The track was dirty and we had rubber, sand and gravel blocking the radiator. Normal water temp is about 160F

McCurry. Didnt lose the chain, max revs were 12500. Time on both bearing were about 3 hours. I'm splitting the case and doing a full rebuild. Damn.

Clark: I'm guessing it was jetted correctly, it ran perfectly on practice day and race day one.

What effect would too much oil have on this engine?
 
Compu-kart said:
Ya Chuck. We were up on the temps at Daytona. The track was dirty and we had rubber, sand and gravel blocking the radiator. Normal water temp is about 160F

McCurry. Didnt lose the chain, max revs were 12500. Time on both bearing were about 3 hours. I'm splitting the case and doing a full rebuild. Damn.

Clark: I'm guessing it was jetted correctly, it ran perfectly on practice day and race day one.

What effect would too much oil have on this engine?
Click to expand...
Foul a plug. And extra wear protection. lol
 
On oil two different theories some say more helps with friction others like less because they claim it fouls plugs I'm not getting in the middle of that lol. Where on the track did it blow? I ran there this year and it seemed most were faster on day one than the second day. The track was pretty clean on the laydown but that's like taking a bath lol later Chuck.
 
I've been told for years that more oil protected the bearings but won't stop a seizure.
8 oz/gl. of oil is the standard for most folks, especially road racers. And Motul is certainly a very good oil. We run it in all of our 2 stroke stuff at 8 oz. and NEVER had an issue with anything.
The outer edge of the top of the piston looks a little melted. If it wasn't for the bearing failure, I'd suspect detonation as mentioned above. But the side of the piston doesn't show any signs of melting. Likely NOT detonation. And besides you're running 110 octane leaded race gas, and it certainly doesn't need that much octane (like most other 2 strokes in road racing.....why we're still mandating 110 LEADED fuel is ridicules....but that's a discussion for another day!!!)
I suspect you had a simple, odd, unfortunate, very premature bearing failure. It sucks, but it does happen. We actually had a Stock Honda break a brand new piston in the first 5 minutes during break in. Stuff happens.
Clark Sr.
 
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