Four corner seizure: improper warm up or something more?

[JZ05220r]

Hey guys, on my 1991 kdx I found some markings in the cylinder. They turned about to be a four corner seizure resulting from piston expanding quicker than the cylinder. Ken O’Connor Racing informed me that the piston was still good. The thing that stumps me is that I have always warmed the bike up for 5 - 10 minutes with very slight throttle blips. Could just being too lean even while warming it up gently cause this? And should I have him order another piston or take his word on that? Thanks

[SS109]

If Ken says the piston is good I would tend to believe him. If the piston wasn't scored you are probably good to go.

On warm up, never blip your throttle until you can actually feel the radiators are getting warm and then only gently and low revs. Yes, a lean condition will make it run hotter but I doubt that would be the sole issue but could be a contributing factor.

I'm assuming Ken measured your cylinder and the piston is matched size wise, yes?

[JZ05220r]

If Ken says the piston is good I would tend to believe him. If the piston wasn't scored you are probably good to go.

On warm up, never blip your throttle until you can actually feel the radiators are getting warm and then only gently and low revs. Yes, a lean condition will make it run hotter but I doubt that would be the sole issue but could be a contributing factor.

I'm assuming Ken measured your cylinder and the piston is matched size wise, yes?

I didn’t even question whether or not it was sized properly, I sent the engine to him corroded and rusted to crap and he sent it back freshly rebuilt spic and span last year. I did just shoot him a message about double checking the sizing of the piston. I don’t like to ask that kind of stuff to someone with that type of experience as it can come as an insult but I’ll see what he says.

[John_S]

No offense SS of course. Everyone’s got their ways of doing it.
If you look at wiseco’s website (blog section), the instructions for a brand new piston have you “never letting it idle”. It has you lightly blipping the throttle the whole time during the first three start ups. Once just until the cylinder feels warm. Then a little hotter, then full operating temp with only a very slight cool down in between. Revving it higher each stage.

Ken O Conner also says to blip it up and down right away when you first start it with a new piston and throughout the break in. No idle. I saw him discussing that on a video years ago.

I doubt improper warm up caused it considering you don’t kick it and then launch off full throttle.

[JZ05220r]

No offense SS of course. Everyone’s got their ways of doing it.
If you look at wiseco’s website (blog section), the instructions for a brand new piston have you “never letting it idle”. It has you lightly blipping the throttle the whole time during the first three start ups. Once just until the cylinder feels warm. Then a little hotter, then full operating temp with only a very slight cool down in between. Revving it higher each stage.

Ken O Conner also says to blip it up and down right away when you first start it with a new piston and throughout the break in. No idle. I saw him discussing that on a video years ago.

I doubt improper warm up caused it considering you don’t kick it and then launch off full throttle.

I have heard and seen both those examples. Maybe it just got too hot for a very short period of time from being jetted on the leaner side. I just remember how crisp it was running and thought it was spot on. This video I took a week prior to finding out there was a problem. I know the video doesn’t mean much but it sounds very healthy. https://youtube.com/shorts/n4Vp5dqv_zc? ... nzs4i6StTg

[SS109]

No offense SS of course. Everyone’s got their ways of doing it.
If you look at wiseco’s website (blog section), the instructions for a brand new piston have you “never letting it idle”. It has you lightly blipping the throttle the whole time during the first three start ups. Once just until the cylinder feels warm. Then a little hotter, then full operating temp with only a very slight cool down in between. Revving it higher each stage.

Ken O Conner also says to blip it up and down right away when you first start it with a new piston and throughout the break in. No idle. I saw him discussing that on a video years ago.

I doubt improper warm up caused it considering you don’t kick it and then launch off full throttle.

None taken!

Yes, that procedure is for breaking in a brand new piston and rings. I was referring to a normal warm up after break in. Sorry I wasn't clear but I didn't read that it was a brand piston new.

I do sort of the same on new as what they recommend. My break in procedure is as follows... Light blips which are to help keep the cylinder from glazing while the rings are trying to wear in yet get some heat in to the piston. Once I get some warmth in the radiators I start riding it gently while constantly, yet gently, varying the throttle. Once fully warm I put it 2nd or 3rd gear and rev it hard from almost a lug to the upper rpm's, then chop throttle and slow down using engine braking only, and repeat those same steps again about ten times. After that the piston and rings are seated and it's time to rip! Been doing this procedure for years and I always get great ring seal right out of the gate.

[JZ05220r]

No offense SS of course. Everyone’s got their ways of doing it.
If you look at wiseco’s website (blog section), the instructions for a brand new piston have you “never letting it idle”. It has you lightly blipping the throttle the whole time during the first three start ups. Once just until the cylinder feels warm. Then a little hotter, then full operating temp with only a very slight cool down in between. Revving it higher each stage.

Ken O Conner also says to blip it up and down right away when you first start it with a new piston and throughout the break in. No idle. I saw him discussing that on a video years ago.

I doubt improper warm up caused it considering you don’t kick it and then launch off full throttle.

None taken!

Yes, that procedure is for breaking in a brand new piston and rings. I was referring to a normal warm up after break in. Sorry I wasn't clear but I didn't read that it was a brand piston new.

I do sort of the same on new as what they recommend. My break in procedure is as follows... Light blips which are to help keep the cylinder from glazing while the rings are trying to wear in yet get some heat in to the piston. Once I get some warmth in the radiators I start riding it gently while constantly, yet gently, varying the throttle. Once fully warm I put it 2nd or 3rd gear and rev it hard from almost a lug to the upper rpm's, then chop throttle and slow down using engine braking only, and repeat those same steps again about ten times. After that the piston and rings are seated and it's time to rip! Been doing this procedure for years and I always get great ring seal right out of the gate.

Hey SS109. Since you are pretty familiar with the e series kdx I had a question for you. I have all of the kips timed correctly by corresponding all of the dot with the shaft all of the way out. The center valve however is a little crooked and appear to be off like a half tooth. There are 12 teeth on the center valve gear so that’s 30 degrees and this seems off by less. Does this look normal?

[SS109]

Hmm, that looks a little odd. I would probably pull it apart and see if a burr and/or some carbon is causing a little binding. Plus, to make things easier, I always assemble the KIPS with the cylinder off the engine and test it at that time before reinstalling the cylinder.

[JZ05220r]

Hmm, that looks a little odd. I would probably pull it apart and see if a burr and/or some carbon is causing a little binding. Plus, to make things easier, I always assemble the KIPS with the cylinder off the engine and test it at that time before reinstalling the cylinder.

Yea, everything is completely clean/no binding. It’s not that it’s binding but like the main shaft can be pulled out alittle further after the center valve is lined up. and I know if I bring it another tooth back I can tell it will still not be centered. Based on a feature I have built into my iPhone i can tell it’s rotated past being centered by about 6-7 degrees and, if skip back a tooth (30 degrees) on the center valve it will be even more crooked just in the opposite direction. That would in turn based on my calculations be about 23-24 degrees of rotation off center.