weird locked engine problem ...

[Z0RR0]

Hi all,

I have the weirdest problem of all ... I'm usually pretty good at repairing my bike, but this leaves me stumped.

My bike is a 2000 CR250.

Yesterday I went riding (snow ride! woot) and as I was taking off, the engine stalled and the kicker wouldn't budge. Felt pretty bummed (oh noes! seized the engine!), trailered back home and started disassembly.

Piston has a bit of pinging on top (will get better gas and new piston before re-assembling), but no other damage, definitely no melting or scratches, the cylinder wall is absolutely pristine. Kinda relieved. Removed the cylinder (confirming the piston is not seized) ... and crank still won't turn over, be it by hand or by kicker. :think:.
Remove the side case, everything looks fine, no broken gears, oil is a bit gray, but that's it. Put a ratchet on the crankshaft output gear and try to turn it over clockwise ... no dice. Counter-clockwise ... and it's free, turns over smoothly. Back to clockwise again, works fine ... until after a random amount of turns, it locks again. No grinding noise, just as if a rag was being caught between gears.
Remove clutch and kicker mechanism, they look just fine, no broken gears, no crap lodged anywhere.
Back to turning the crank over ... and it turns over free, there's a wee bit of resistance, that I assume comes from the stator (the only thing still on (powervalve command thingie is removed as well) ... and that's it.

So there I am ... all disassembled, looks to be fixed, and I have no clue whatsoever on what went wrong. I'd think it's the kickstart mechanism, but I really did not see anything wrong.

Can't put it back together like this, it locked as I was taking off (2mph and idle) ... if it locks again as I'm about to take off on a 40ft tabletop, it ain't gonna be pretty!

Any help appreciated. :)

 

[whenfoxforks-ruled]

Is the kickstarter gear and shaft in the proper orientation? You should have been able to see the kickstarter gear engaging if that is what is out of place. Does sound like that though, does it in the drive direction and the opposite runs free. The crank should turn pretty free, no drag with the clutch removed, it don't touch anything on the rotor side.

 

[BSWIFT]

Did you remove the clutch and eliminate the tranny?

 

[76GMC1500]

I've seen bearings that only allow rotation in 1 direction after failure, but the allowed rotation was never smooth.

 

[MX Junkie]

Time for a crank rebuild I would think

 

[Z0RR0]

Kickstarter is fine, I guess ... I mean, I've been riding problem free for 2 years. So if it was the wrong way around, I would've probably figured it out earlier ...

Removed clutch, yes.

76GMC, by a not smooth rotation, do you mean you could feel some grinding, or just a smooth rotation with a spot that require a wee bit more effort? I have the latter.

The crank bearings have been changed 2 years ago, I run a good 50:1 (probably closer to 40:1) ... would think they'd last longer.



After a second good look around, I found a nice deep scratch in the case, right next to where the powervalve actuator gear is. That would indicate I have a rather large piece of steel floating around ... but I did not find it! Nothing in the old oil, nothing on the floor. Have not seen a single damaged tooth on clutch/powervalve actuator/kickstarter mechanism/crank output gears ...

 

[76GMC1500]

Well, you could not turn it in one direction and you could barely turn it in the other.

A piece of debris in the case would certainly explain your problem. Rotate it one way and the debris wedges between the crank and case. Rotate it the other way and the debris unwedges itself and everything turns freely. Split the cases, I doubt there is anything but superficial damage to the crank or case, but getting the power valve back in order may require some new parts.

 

[rmc_olderthandirt]

This bike is water cooled, correct?
You went on a snow ride....

Could your cooling system have froze?

It does sound like something is loose down in the crankcase. Is it possible that the cooling system froze and the expanding ice broke something internal, causing broken pieces to fall into the case?

It seems odd that it would break down like that right at the beginning of a ride.

 

[zaneyzrex]

sounds to me your crank bearings/rod bearing is toast. you leaned it out during your SNOW ride.

 

[Z0RR0]

Frozen cooling system = very unlikely. I run 40% anti-freeze, the bike sits in the basement (garage is too cold :laugh: ) and I warmed it up right as I pulled it out.

As for the jetting the plug is cocoa coloured ... and I can't figure out how/why a lean jetting would damage the crank bearings. Too lean of a jetting would overheat, and melt the piston ... but as long as I have not forgotten premix oil, it's not gonna damage anything with the crank bearings (unless the piston broke to pieces, which did not happen).

 

[1BAD250]

weird happend to my bike the other day to me & a buddy was riding the other day it was between -8 to -12 below 0 i let the engine worm up as you should took off it ran just fine no inictions of any problems after about an hour we went in to worm up went back out to ride agin & the engine would not crank, its not locked up cuz if i put it in gear the piston & rod will go back & forth but stops on the down stroke, ive never had stis type of thing happen before, im thinking the piston may have cooled to fast & cracked or worped one of the skirts, well right now im just waiting till wormer wether so i can power wash it cuz its dirty cant take it apart as dirty as it is, but weird huh.. :whoa:

 

[Z0RR0]

ah! That's exactly what happened to me ... ran for an hour, had a blast, bike ran perfect. Stopped for 5 mins, and then no way to crank it.

 

[Z0RR0]

Kinda running out of ideas ...

Can the pinging/detonation have ruined the crank bearings?

I never noticed detonation when riding during summer, so I assume it all happened within an hour of winter riding.

Can detonation that leaves small marks on the exhaust side on top of the piston destroy crank bearings within an hour?

 

[76GMC1500]

Kinda running out of ideas ...

Can the pinging/detonation have ruined the crank bearings?

I never noticed detonation when riding during summer, so I assume it all happened within an hour of winter riding.

Can detonation that leaves small marks on the exhaust side on top of the piston destroy crank bearings within an hour?

Detonation can destroy bearings, but the marks on the crown of the piston may be the result of destroyed bearings and not related to the cause of the bearing failure.

 

[rmc_olderthandirt]

How much of the engine have you disassembled?

I would start taking off everything that you can without splitting the case and see if you find something. Perhaps something got into the water pump? Could the governor have messed up? Take the clutch completely out. Take the carburetor & reed box off (if it isn't already).

There has to be something broken in there somewhere.

Rod

 

[Z0RR0]

Ok, after some more fiddling around, it's definitely the crank bearings going. Case splitting time. :(

 

[Z0RR0]

To all those who said crank bearings ... you get a cookie!!!

 

[Z0RR0]

Crank bearings ... is OEM the best?

Well, my crank bearings are gone, and I need to get a new set ... is OEM the best most durable thing available? Or anything better?

 

[whenfoxforks-ruled]

Has anyone tried ceramic bearings in mx applications?

 

[76GMC1500]

No, OEM are not the best or most durable... but, they are durable enough. Honda buys their bearings from another manufacturer like IKO. The bearings they buy are usually the cheapest that will do the job, engineering 101. They use no special coatings or no special alloys because the bearings do not need them to survive for an acceptable amoutn of time. Their tolerances are only average. Ceramic bearings seem to be better for crank applications. For chassis applications, I have seen that Timken makes a whole line of bearings designed for service in an environment where abrasive contamination is an issue. There are better bearings out there, good luck cross referencing them and good luck finding a supplier.

You can also buy kits from companies like Pivot Works, All Balls, and Boss. These bearings meet all of the requirements of OEM bearings (so long as you don't get the Chinese ones) and will perform the same. In some instances, they are even made by the same manufacturer.