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new top end blow up

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Hello, Can some one please explain this to me? I am lost as to how this happened. New ring and piston. Happened at only about 1 hour. Honed cylinder, measured at 54.07mm. No movement in crank bearing, and no movement in piston bearing.standard plug not fouled. 32;1 mix 1 1/2 out on air scew. cylinder not out of round but its like its hitting in the top 1/4 of the stroke. Should I just have it bored to next largest with new piston and ring? But dont want it to happen again.

DSC01890.jpg

DSC01891.jpg

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i was thinking a cold seize as well. How were you running the bike when it blew up?

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did you relieve the exhaust bridge, looks like thats where it hit...

Looks like it. There's a deep mark in the top corner of the right port.

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I dont have a pic of thetop of the piston right now but i can get one. Although I can assure you it is clean, no discoloration no nothing. I dont know what cold siez is. Can someone explain? The damage is to the left side of the piston which correspondes with the piston damage(oiler holes face to the front). My brother was riding it pretty hard. Maybe testing my wrenching abilities? But the plug didnt look lean and appeared to be what I think is normal to rich. If it is the impeller how do I test its operation? Thank you for all the help!!!

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Cold seize. When you start a cold motor the piston and cylinder have to expand (thermal expansion). The piston will expand faster than the cylinder because the piston has less mass than the cylinder does.

I personally DO NOT rev my motor(s) any higher than it takes to keep them running for the first few minutes. The first few minutes of ride time I take it easy with it to help prevent a cold seized piston.

Just a rule I personally go by is, with my riding glove on I put my hand on the exhaust pipe, when I can feel a good amount of warmth (this takes about 2 seconds to feel the heat). Then its hammer time.........

1 other thing is that a cold seize usually happens within the first few minutes, you said it took about a hr of ride time. I suppose its possible that you had a air pocket in the cooling system?

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Can someone expand upon the "exhaust bridge relief" process that was mentioned?

Just had my cylinder re-plated and a new piston installed and I don't wanna see my engine wind up like this one

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That bridge relief would be taken care of before your cylinder was replated.

On the older borable (or sleeved) bikes, you ground down the bridge after boring. If you did not do this, the hot, narrow bridge would expand right into the new piston and screw things up.

There are some good pictures here: http://www.smellofdeath.com/lloydy/piston_diag_guide.htm

Scroll down and read the section on "four corner seizure"

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The damage is to the left side of the piston which correspondes with the piston damage(oiler holes face to the front).

someone correct me if im wrong but every piston ive gotten through wiseco have said for the oiler holes to face the rear (intake side)...is it possible the piston was in backwards

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the last few top ends ive done the piston has a mark/ arrow on it for a reference. Im sure if the piston id put in backwords your going to see ill effects, like a very pitted jug/head/piston

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I was wondering if maybe it was the power valve that hit rather than the exhaust bridge. I hear that when you bore/hone/resleeve/replate a cylinder you need to ensure that the power valve doesn't hit the piston when you reassemble the top end.

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someone correct me if im wrong but every piston ive gotten through wiseco have said for the oiler holes to face the rear
\

OK I'll bite. That would be incorrect. The oil holes are for the exhaust bridge. The intake side will have an intake "window" or cut out.

Looking at the picture it does not look like a cold siezure. The cold sieze usually shows up with scrape marks at regular intervals from top to bottom of piston all the way around the piston, Ie four corner sieze. Yours looks burnt on the top and exhaust side.

It also does not look like the exhaust bridge expanded into the piston. If this were the case you would expect to see a scrape from top to bottom of the piston the same width as the exhaust bridge.

My guess would be overheating, probably due to a lean condition on the main jet or an air leak overlooked during re-assembly. The piston looks cooked on the exhaust side only, with some melting of the aluminum and the cylinder looks overheated/burnt as well.

Like previously mentioned make sure the water cooling system is working correctly. You can check this by starting the bike and while it is cold open the radiator and look to see if the coolant is moving.

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Thank you all for all the input. I have ordered a new ring. Also, I releaved the exhaust bridge and chamfered both exhaust ports, oh, and knocked down the power valves too.. It will be wednesday before I get the ring. I'll update then. In the mean time I'm going to check out the cooling system. I'll need to make sure proper break in is followed this time:banghead:

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You mean you didn't break it in first? Was that a Wiseco piston?

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If you were riding the piss out of it within an hour then you definitely didnt follow proper break in... Have to do heat cycles and also take extra care when the bike is cold since its a wiseco piston.

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