Locked motor - 01 YZ426F

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.

Thanks. We looked at that, but it wasn't lean...normal coloration on last piston, head, valves, plug and nothing changed to exhaust or carb. Wiseco engineer determined it was an oiling problem. We also made sure the lines were clean.

I'd like to find a high volume oil pump, but apparently that's only a hotrod car kinda thing to do.

I'm curious to see how this turns out...I had a very similar issue with my bike, that I'm trying to fix now....big-end rod bearing is bad, so I'm replacing it with 426 stuff, but I'm still at a loss as to WHY the bearing went bad....

good luck!

I'm curious to see how this turns out...I had a very similar issue with my bike, that I'm trying to fix now....big-end rod bearing is bad, so I'm replacing it with 426 stuff, but I'm still at a loss as to WHY the bearing went bad....

good luck!

JJ,

New piston and oil pump to be installed this week. More to follow soon, hopefully.

Thanks

Chris

Hey I caught this thread and I thought I would throw out some basic info. The most likely reason lower rod bearing are failing are due to inefficient (worn out) oil pumps and/or lack of maitanence (regular oil changes ect.). The oil is one of the main ways heat is taken away from critical internal components of the engine. Besides lubricating the engine the oil and pump are serving double duty now that they also help in cooling the engine. Also remember that these engine are producing close to 2 hp per cubic inch which is phenominal for a production engine. When you think about it these types of engines are utilizing approximately 25% of the heat energy generated as mechanical energy, the rest, 75% of the heat has to be dumped to the surrounding environment through the engines coolant, exhaust, oil, and etc. What I am getting at is this, these aren't the trail 90s and xr 600s of the past that made 1 hp per cubic inch. When you look at how much of a race engine these are and then you looked at what people considered to be proper maintanence you be astounded that 99% of people would never think that they should check their oil pump clearances to make sure it was still in spec for proper operating condtion. Hence most likely the reason why there have been many bottom end siezures. Get a shop manual and look through it, highlight anything that is a wearable part that has service clearance limits and check those parts as part of your maintanence. That is the only way to stay ahead of failures and even then you will still have parts that fail with out warning but those will be very islolated and uncommon events.

JJ,

New piston and oil pump to be installed this week. More to follow soon, hopefully.

Thanks

Chris

Okay, so the saga continues...after the second attempt, the shop got the bike back together...they failed to secure the upper engine mount to the frame, put three head gaskets on it, and failed to properly torq many bolts. They suck.

Then...

At the end of July, I found a piece of a gear tooth on the accessory drive side of my motor after hearing it ping around among the gears near the clutch basket, primary drive gear, oil pump gear. It was a good thing I heard it and shut the motor down immediately.

After a complete teardown, I learned that piece of gear tooth did not come from my engine.

What that means is the last person to work on my motor, which was a shop, D&T Motorsports in Lancaster, CA, either knowingly or accidentally left trash in my engine. They suck!

Now that I've been completely thru the motor, I'll never let anyone touch my bike again.

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. :crazy:

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.

Very important when rebuilding these motors: Before you start the bike for the first time, make sure you have the proper amount of oil in the bike and pull the spark plug and just kick the bike over a good 20-30 times. This will pump oil up to your top end and prime the oil lines. Even better if you kick it over with the valve cover off so you can see the oil pumping to the top end. I have seen a couple motors with seized cam journals because this wasn't done after a rebuild. It also helps to use lots of oil on assembly.

very good tip ther todds924

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now