Engine failure - seizing - what happened?

[Bomberpilot]

I experienced an engine failure yesterday

I was going about 70 miles per hour when a strange sound appeared - like a scratching and I expected the piston rings to make this sound.
The sound began a few rides before - but only at the higher speeds. Even if the sound wasn't nice I was not too afraid because I just opened the engine and looked at the parts and measured the piston ring gap (it was 0.4mm-0.45mm) and everything looked good (the whole setup had about 1500-2000 miles on it and never made any problems and looked good as I said).
At the last inspection I mentioned I changed some parts:
I got now the Sudco PWK 41 pro Series with a 190 main jet and a 52 pilot jet and a DGK needle. Could that be too lean?
I added also a cylinder head with a raised compression and only little squish height but I couldn't hear any pinging...
The piston is a Wiseco (Seizeco?) 636M09050 4229E 90.50mm.

What the fuck happened here? I run 1/33 Motorex GP (very expensive Racing) oil.

Here are the pictures - what are your thoughts about all that?

[oggo69]

any over heating issues ?

[Bomberpilot]

not that I know... ok I got the (bigger) KTM radiators and the pressure relief valve openes from what I know at 1.2 bar (more than stock) but it didn't open - so I guess it wasn't that hot (also the wheater wasn't that hot - about 15°Celsius, 60°F).
The power of the bike at that day was very good before the engine broke down. I heated the bike up for about 4-5 miles and than I hit WOT. Not even one minute later the engine broke down (not all the time WOT).

[100hp honda]

its easy to see what happened but the question is why. i dont have a concrete answer. i can tell you i dont like the looks of that wristpin, sucker looks badly scorched. i would say the topend lost lubrication somehow and then the temp skyrocketed ? or maybe the temps were so high the oil just boiled off ? whats underneath the piston look like ?

have you considered a castor type oil ?

sorry man but i cant say exactly what happened

[Kuma]

My guess is a combonation of too much heat and not enough oiling.
what conditions where you riding? what gear were you in?

[100hp honda]

definatly looks that wristpin saw some heat

[AlisoBob]

...have you considered a castor type oil ?

x 2

[seanmx57]

Did you leak down test the motor after assembly?

[britincali]

definatly looks that wristpin saw some heat

All of mine come out like that.

[AlisoBob]

That thing is fudged up.....

[100hp honda]

am i the only one thats never leak tested a motor......ever ? i see the point behind it, but i dont see the point. if that makes sense

[Bomberpilot]

thanks for your answers!
so as I said I was in last gear and went about 70 miles/hour when that strange scratching sound came up. And this sound came up before but only at the high speeds when I had full load for a few more seconds.

I also sealed up the exhaust pipe at the flange but I don't think that this is bad...

I did not make a leak down test after assembling the engine

Yeah, really looks like high temp. and then the clearance went away - but really, the question is why as you all said. I never had overheating issues before.
Could that be that I make too much power now after all the changes and tuning I made and that the cooling system cannot cool that down? (the big point here I guess is the much higher compression!)

[oggo69]

i asked about cooling at the start becuase it looks like a heat seize to me , just wondering about clearances now , was there enough to allow for expansion ? ....

[craigf40]

looks like oil problem im sure if you check your bottom end you will find it got hot also from no oil ...whats your mix ratio and are you maybe not running to lean...main jet size

[hoofarted]

Just curious - how long were you holding it WFO?

IIRC Golden Rule with any 2T is never hold it WFO for too long. Always on/off, on/off. At least thats what I was taught - has worked well for me so far.

And x2 on the 927! 44:1 is all I run.

If you are planning on WFO for long periods of time, you may want to consider adding a powerjet.

[Bomberpilot]

my engine builder said that he did a clearance of 9/100mm or other 0.09mm or 0.0035".
as I already wrote - i used the Motorex Racing GP 2 Stroke Oil at 1/33.
My main jet in the PWK 41 Pro Series is 190, pilot jet is 52 and needle DGK - do you guys think that this is too lean?
I was on WOT for just about 3-5 seconds when the noise appeared. Then I let off the throttle and hit it again and let off and again... so I don't do WOT for too long, too.

so do you guys think that I can not just replace the cylinder and piston (got another set here)? do you think some of the other parts are damaged too? could I soo that without disassembling the bottum end?

[MojoScojo]

What does the plug look like?

[craigf40]

my engine builder said that he did a clearance of 9/100mm or other 0.09mm or 0.0035".
as I already wrote - i used the Motorex Racing GP 2 Stroke Oil at 1/33.
My main jet in the PWK 41 Pro Series is 190, pilot jet is 52 and needle DGK - do you guys think that this is too lean?
I was on WOT for just about 3-5 seconds when the noise appeared. Then I let off the throttle and hit it again and let off and again... so I don't do WOT for too long, too.

so do you guys think that I can not just replace the cylinder and piston (got another set here)? do you think some of the other parts are damaged too? could I soo that without disassembling the bottum end?

the plug will tell you if you to lean should be a coffee color any lighter and you too lean if you like full throttle ridding then make your main jet a lil richer than perfect color your main jet works mainly at WOT...well you could get away with the top end but make sure you find the cause ...if you were riding WOT then closing off and coasting meaning the motor spinning with the throttle shut off that could also cause it because the oil is fed with the fuel as you know and with the throttle shut off but the motor still spinning with the momentum of the wheel speed you could cause a seize. if you notice an increase in engine vibration then you know you have damaged you bottom end ...hopefully not

[hoofarted]

...if you were riding WOT then closing off and coasting meaning the motor spinning with the throttle shut off

I recall someone doing that on a dyno.

[Kuma]

If you have a 70 mph breeze going through the rads, that should be plenty of cooling for the coolant, what year is your motor, how is your water pump?

[Kuma]

Your engine builder wouldn't be GSS would it?

[2strokeforever]

If you have a 70 mph breeze going through the rads, that should be plenty of cooling for the coolant

thats more than enough airflow

[gregrobo]

loks like 70 mph then backed off to nothing no lube

[jarnott71]

i ride 1/2 mile ice race tracks all winter wfo then nothing lap after lap not a proplem more reliable than the 450 some times shit just brakes it lasted more than 15 miniutes it prolly just wore out 1500 2000 miles i would be happy with that unless i just putted around goin slow

[Gmbond]

Is there any dirt or water in the bottom of your carb that could have been sucked up to momentarily block off the main jet??