Piston seizure pics. 4 corner seize? Causes?

[t30mg]

I recently rebuilt a sled with the MCB fix kit, forged pistons, replated cylinder, and factory reman crank

Knowing that the forged pistons need a better warm up than cast, I always started it and let it idle to a minimum 95 F before driving.

I had it out several times myself and never had an issue with the over 100 miles i logged on the new engine.

I sold the sled and new owner put less than a mile on it and it died. He said it had a long warm up period, 10-15 minutes, before he hit the trail. He did not notice what the temp was when he hit the trail though. Made it less than 1/2 mile and the DET went off. He then noticed it was at 208*F. He put snow on the tunnel and fired it up and died again. He towed it back to the rig and trailered it to my house.

I turned it over by hand to verify compression in both cylinders. It seemed fine, so I started it and I warmed it up to pulled it in my shop last night. I elevated the rear and ran it for a bit using a garden hose to cool it. I would let it warm up to 135 and then spray the water on it and it would cool back down to 127. Did this several times and no issues. Okay, the water pump is working and it's definitely cooling the sled.

I let it cool down a bit and do a compression check, 144psi both sides. Good, he didn't hurt the engine with the overheat(i thought)

I go riding with him this morning to help him learn about pro's cooling needs. Warm up to 100, scratchers down, hit the trail. 1 mile it DET's. Restarts, sounds good, 127F, hit the trail. Another mile and it shuts down. Said it stopped dead and now won't start. Tow it back and bring it home.

No compression on the mag side, crap!
I tear it apart and the piston appears to have a 4 corner seizure. Both plugs had a nice chocolate brown burn. There is oil inside the crankcase, sitting on the reed flange, and in the underside of the piston. Doesn't look like a lube issue.
I read up on 4 corner seizure and the 2 most common causes are improper warm up or overheat. Definitely had a proper warm up today.

Could his overheat above 200F the previous ride started damage that didn't show up on compression test but continued running caused galling of the aluminum and lead to failure?

Also, the lower rod appears to have gotten hot on this side as well. Could an overheat cause this as well? The bearing feels smooth and has no vertical play.

Check out these pictures and help me understand what happened and if this new crank is toast.

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[sled_guy]

Crank is fine. That discoloration is from the casting and machining of the rods.

4 corner seize can also happen if the midrange is too lean and you pull wide open and then back off to part throttle. It can also happen if the clearances are too tight, piston to cylinder wall.

When was the fuel filter changed last?

The DET hitting is interesting... I've seen DET come on when the filter was restricted, that is why I ask about the fuel filter.

sled_guy

 

[geo]

Holy big pictures lol.

Just some thoughts. You never said year (I think). '13 is the most prone ('cause of fuel map) to this without a controller.
This is not a cold sieze to me unless the pistons were designed wrong. Know nothing about MCB.

144 psi? How did you not get det when you rode it?
I know gauges are different and like to think my old Snap On gauge is half close but at 1100',where I build, I found about 130 psi the limit for the fuel we have up here at the pump. 137 at home, 20% AV gas is required for me to ride 5000' to 6500' but a few add ons.

Det will heat the top of a piston faster than anything and barrel will take time to catch up (still tight) and continued det creates combustion temps that the cooling system can't keep up to (208F in 1/2 mile?). Too-hot-a-top 'causes the oil underneath to burn into carbon crusty's (your pic?).
I've see forged pistons expand quick enough and big enough from just light det to crack the barrel straight down from the back boost port to the base. Have a good look there.

Imo. I know I have enough oil when the puddle in the case is big enough to deposit oil on the crank webs as the engine is rotated. This is all "splash" lubricated in this area and above.
If one rod is different in color find out why. I check each line by removing the "intake end" off the pump, inserting the bandjo bolt with both washers and a 6 mm nut to tighten, then squirt to confirm flow with and ol' oil squirt can with two stroke oil though the bolt's hole.
Bleeding the oil is important if you take a tank off because bubbles can get stuck if you don't force them through in the beginning. Best in the shop on a stand Imo.
Good time to change the filter. Start with the tank installed and throttle bodies off. Use the bleed screw on the pump until no more bubbles (doesn't take long) (have you replaced the cap yet?) come out. Use a rag lol.
After the rest is installed, take a bit of wire, hook the pump lever, pull it up to full open and secure to the frame some place. Fire the sled up and let it idle while you put it on a track stand and get a fan pointed out the shop door. Then,,, throttle it up to 4 or 4500 rpm and run it until a neighbor comes over and asks whether they should call the fire dept. Should be bled by then and the motor will be so happy. If you live in the country, I wouldn't wait for the neighbor.

If I use forged pistons that are not OEM (like when I installed the MNTK kit on my Pro) I do this smoke show (without waiting for the neighbor) in my shop, before loading, for 5 rides just 'cause I've used stuff like Wiesco's in the past.
Kinda anal I know but zero failures using "kit" pistons since.