Locked motor - 01 YZ426F

[whyzee426F]

Well, after about 4 months of great riding, my new used bike left me stranded 9 miles out in the desert...but that's another story.

Any idea why the engine would lock up? Neither the oil nor the coolant was hot after 3 hours riding in 75 degree weather, and the bike had been running great all day. Never sounded bad either. Kick starter won't budge, and neither will the engine if I try to push start it.

What do you think - bad oil pump/water pump? I'm skilled mechanically, but don't have lots of time to devote to a rebuild...any idea how long it'll take? Is it as hard as the Clymer manual makes it sound? I saw some conflicting info: one statement said the jug couldn't be bored, then it recommended "reconditioning" if out of specs?

Thanks in advance...really appreciate all the great info from y'all on this site!

[642MX]

Rebuilding the YZF motor is actually pretty easy. My best advice is to start tearing it down and find out why it broke.

[whyzee426F]

Rebuilding the YZF motor is actually pretty easy. My best advice is to start tearing it down and find out why it broke.

Roger. I'll start Sat morning.

Notice your signature says 13.5 wiseco...would you recommend that or do you have the imfamous wiseco piston slap? Noticeable power gain?

Thanks

[sirthumpalot]

It seems that some of the desert guys (and other guys who run sustained high RPMs) have had some rod bearing failures. Let us know what you find about your bike.

[Raven1911]

That sucks!! Sorry to hear about that man! Good luck in the rebuild! ?

[glasseye]

Broken vavle? Did it clatter a bit prior to locking up?

[642MX]

Roger. I'll start Sat morning.

Notice your signature says 13.5 wiseco...would you recommend that or do you have the imfamous wiseco piston slap? Noticeable power gain?

Thanks

Yes, I have the Wiseco 13.5 piston. I would recommend it. It makes the bike pull alot harder from idle to about 9500 rpm. Its noisey, but you'll get used to it. ?

[chris288]

Mine was a siezed rod bearing..

[jrcgaf364]

my 400 was caused by oil pump failier

[tom nolan]

My 400 locked up because of a third gear failure. It sent shrapnel all through the engine and even some parts hitting the bottom of the piston. I figured it would take major bucks to fix but it really wasn't that bad. The engine is not that hard to figure out if you have some mechanical ability and follow the manual. I mostly ride out in the desert like you so make sure you use a good oil and change it regularly due to the sustained WFO riding. Good luck

[roy8762]

me and my mate we both got 426s his locked up last year, no reason, coolant ok, oil just been changed, it was striped down by a very reputable mx shop here in the uk, no fault wwas found and the only advice that was given was while the engine was in bits to change the cam chain, once it was reassembled it has run fine till this day! pewrhaps its the yzf form of arthrithus!!!

[whyzee426F]

Broken vavle? Did it clatter a bit prior to locking up?

Negative. No clatter, just a sputter (sounded like a misfire) and then nothing.

[yz426em]

Your motor lock up sounds the same and mine, and my problem turned out being the rod bearing seized, which was already mentioned. After tearing it apart I also found a few other bearing starting to go bad and the oil pump had some groves in it.

[whyzee426F]

Your motor lock up sounds the same and mine, and my problem turned out being the rod bearing seized, which was already mentioned. After tearing it apart I also found a few other bearing starting to go bad and the oil pump had some groves in it.

Turns out you're right. The rod bearing was shot, and the crank was heated up enough to turn one of the counterbalance lobes on the crank blue. Wrist pin to piston surface started to gall also. The piston skirts looked a bit rough, so I'll be measuring the jug to see if it's out of spec.

Is there anything that can be done to the YZ motor to prevent the rod bearing from going out? I heard of an "oil mod" but can't seem to find out exactly what that means.

I normallhy ride this bike on a Mx track till I can't stand anymore, then hit the desert for a couple hours and stretch it out in a few spots running it in top gear/5th at mid to high RPM. Should I replace the rod with a WR rod? Anything else?

Please advise -- and thanks!

[whyzee426F]

So I go thru and rebuild the motor and during break in, after heat cycling, and after 3 1/2 hours total on the motor I open it up a little bit it, sputters, I pull the clutch in and it stops running. It now has no compression.

The bore was honed and a B or C piston was used by the engine builder. Could it have been too tight?

I'm frustrated, so if anyone has any suggestions on how I can keep this thing together, I'm all ears.

Thanks.

[642MX]

3.5 hours and it has no compression? I would bring it back to your "engine builder".

[whyzee426F]

Melted piston after 3.5 hours on rebuild appears to have been the result of poor oiling, according to the engineer at Wiseco Piston. Anyone ever encounter that?

The shop said the oil pump was fine/within specs.

What's the fix, a high volume oil pump? Can you recommend one?

Thanks...from a very frustrated 426 owner.

[MotoGoalie]

I"ve never had any luck with Wisecos when I tried to use them in my 2 strokes.

[Pincushion]

That sucks! I'm kinda in the same predicament now. Rebuilt my 426 last summer and ran it last weekend without coolant (not on purpose!) so my jug/piston are now trashed.

Anyways.... it's possible the oil feed lines weren't properly cleaned when reassembled or some new contamination clogged one of them causing oil starvation. It also could have been the oil pump not doing its job. That's why my motor went AWOL last year out at Dove Springs. Not a fun tow back to camp!!!

I have (make that had) a Wiseco in my YZ and never had one issue with it. None of the infamous piston slap I hear so much of either. I'll be buying another one when I reassemble. BTW... I'm no certified mechanic, but I rebuilt my motor (including trans) without too much hassle. The owners manual is a great resource for these bikes.

[642MX]

Melted piston after 3.5 hours on rebuild appears to have been the result of poor oiling, according to the engineer at Wiseco Piston. Anyone ever encounter that?

The shop said the oil pump was fine/within specs.

What's the fix, a high volume oil pump? Can you recommend one?

Thanks...from a very frustrated 426 owner.

I would say that if it melted from the top down then oil has nothing to do with it. IMO detonation and being way too lean may have caused a melt down.