Crank failure modes
 

Ok so tried out my new carb yesterday. Everything going peachy for 10-15 minutes and then it stalled at the top of a hill. Almost felt like it nipped up.

Little hard to push on lever maybe. . But started right up went for a while seemed ok but sometimes felt like it was dragging. Stalled down a hill, then again, got over small creek and it didn't sound right so I stopped it. Took rad cap off and a bit of water spurt like it was real hot.

Got a lift back.

Hmm, so took stator off, no dragging, water pump, clutch, no signs of mechanical distress.
Barrel off, top end not nipped up, piston and head the right colour.

Rod has no axial play and no perceptible rock in the mains. Spinning it over with the small end is seems to run smooth but, well maybe sounds a little whiney.

On my road race bikes I've blown a lot of cranks in 27 years, especially at the start using 2nd hand bits until I learnt to use quality parts, but it was always obvious if it were mains or bigend. And usually at 12,000 RPM.

There was a reasonable amount of oily mix when you spin it, but then it was loaded on its side on the way back and there is always residue.

So has anyone seen a slow failure where the bearings start to seize up when hot? I think one side bearing is not std roller type.
Just bizarre, always thought the violence of an engine would just create havoc every time.

I feel I'm missing something.

Had a similar situation on my EC300. Felt like it tightened for just a second, bike stalled coming into a corner. Restarted it about 1 minute later, rode another 15 minutes trying to make it back to the truck, then it seized completely, locking the rear wheel. For those fifteen minutes I felt the same "dragging" sensation you describe and thinking back it was vibrating more than usual (I've always found the 300s vibrate quite a bit to begin with).

When it finally went there was a death rattle and then a dead stop. Crank bearing. Fortunately I had a spare bottom end, have not had time to tear into the other as of yet, other than to take off the top and confirm it was the crank.

Having roadraced two-strokes for many years, I know exactly what you mean about taking a crank out at full revs, max speed. Not fun, or pretty, I used to run the banking at Daytona with two fingers over the clutch for precisely that reason.

I had something similar with my XC 200. I was on a trail ride with friends in another state. We came to this steep hill on the trail, the kind that everyone waits at the top to make sure everyone after you makes it up.

I hit it hard with the 200 and made it up just fine. After we got the last guy up, I went to fire up the bike and kick lever was locked solid. (Bike had been running fine all day.) I put the bike in top gear and rocked it back & forth , engine finally freed up and i was able to start it. It sounded like the crankshaft wanted to fly out of the cases, but I had no choice but to ride it out of the woods.

I just held a fast idle and using a lot of clutching, managed to ride about 5 trail miles back to the truck.

Upon disassembly , I found that the mag side crank bearing had lost the cage that holds the ball bearings in place. It must have wedged it's self between the crank & the cases and I freed it up by rocking it back & forth.

The crank, including the big end bearing was fine as were the cases, they did have some gouges but were still usable.

New crank bearings, gaskets, seals, new piston kit ,etc and it was good as new.

The 200 has ball bearings on both sides, unlike the 250/300.

RB

How many hours were on each of these crank bearings before they took the big dirt nap?

I'm the third owner so I have no idea of the hours of service. They may well have been original, for all I know. Sorry.

RB

I purchased the bike used in 2016 (2004 model) and then put over 300 hours on it myself (125 of those were racing hours) and had actually sank the poor thing past the gas tank in a river the week prior, so it really owed me nothing!

I am pretty sure that the submarine action is what sank your bearing.

Ok thanks guys, just needed that little push. Heck it's an 07 so the crank could do with a birthday irrespective. All original bits.

That is pretty good life and it does not owe you anything. I ran my 2000 until 3 years ago with the original bottom end under my 327 big bore. It still ran fine but upon the last topend rebuild I decided the bearings sounded a little gritty so I swapped out bottom ends with a spare I had hanging around. I think the early bikes had ball bearings on both sides of the crank and at some point before 2003 they switched to one roller on the ignition side and a ball on the clutch side.

Yeah maybe a bit of cage was dragging and stuck from time to time, dislodged repeat. Maybe. At least nothing got jammed up the transfers and trenched the bore 1/2 way out. Guess I stopped it in time.

Well enough risk to warrant full pull down. Found Woosner rod kit locally cheaper than I can import one and a mate had bought a bearing and gasket set for his 07 which he promptly upgraded to a 15.