Would you ignore this?

[trx88]

Love threads like this

[rablack21]

Think about this.
If you have had over heating problems in the past, you know the hottest places in the cylinder bore will be around the exhaust. Since theres no bridge in the main exhaust port, the only part like a bridge, is the part of the sleeve between the main & aux exhaust ports.
With over heating, the higher heat will cause that small part of the bridge, in the exhaust area, to bulge out & take up piston to bore clearance & sometime result in piston seizure.
Note, that all these after market cylinders, Pro-x & ESR, tend to run hotter on the left front side & top of those cylinders & if you've noticed, most of the time when a inner o ring has blown, it will be in that left front corner that it happens on.
I would say sometime in the past, that area of the lite seizure must have got super hot for a real shot time & the small amount of damage was the result of it.
Now this might sound crazy from me & I'm a big boy if some of you want to laugh at me for this, but that small seize spot on the piston, the aluminum has melted & metal has been removed, so if you sand off that little spot, smooth out the ruffness, you know that part of the pistons not going to touch the bore any more.

Only things to think about afterwards, what was causing that one area in the cylinder to run hotter. Was it the fact, that side of the cylinder will run leaner than the right side & cause it to run hotter. Could it be an issue of port linking, on that side from the edge of the aux exhaust port window linking up with the machined area on the side of that old model piston.
Next thing, is all those up & down scars on the exhaust side of the piston ?. Could it be the pipes not sealed at every joint & raw air & maybe dust being sucked back in on the returning wave, or old burnt carbon inside the pipe flaking off & being pushed back in by the returning wave. Lot of scars on the exhaus side & hardly any on the intake side.
Every piece of an engine inside, when you look at it has a story to tell, like that black look to the piston between the top & second ring, its saying that top rings not sealing & letting burnt gas & oil blow by & collect on the piston in that area.

Even with all this going on, I would check the piston real close for cracks because of hours used & if none, smooth that spot out, put those new rings in & let it ride, but fatten up that main jet just a hair.
Neil

I think you may be on to something. I did take notice that there was some grayish oily residue just on the outside of the pipe right there in front of the exhaust flange area. When I removed the pipe, I noticed that one of my orings on my double oring exhaust flange was broken and was not sealing well. This could very well have played into the issue.

[JoePA]

Can't beat those answers from Neil and Jerry. So how does he keep it from getting hot like that again? Also does he switch oil or just go from say 32:1 to 28:1?

[fearlessfred]

I hope none of us forget the people who come on here and help us,with out trying to sell us something.they make this forum a true pleasure to come on and learn

[rablack21]

I don't think there is one specific cause of this issue. I think several things have factored in. The fact that this engine got up to engine temps of 220-225° several times last year I'm sure didn't help. I don't really know how many hours I put on this engine during last years racing season. I should have kept up with it better. The fact that there is noticeable piston slap indicates the rings are wore out at the very least which could have very easily caused excessive heat in the piston and cylinder wall, well above what is supposed to be normal. I don't know how long the front of my pipe has not been sealed. I never noticed it not being sealed last year, but it would have started recently. Unfortunately, all of these conditions are abnormal to the engine's typical operation.

I am kicking myself my not pulling the head off of it during the off season to inspect everything after the end of the racing season. This would have made it easier to determine when it occurred. This could have occurred last year one of the times my engine was running extremely hot, and I never knew about it. This is an example of poor planning on my part.
Thanks to everyone for posting your thoughts. I will decide something by the time I get off of work.

[udontknowme]

if you have the money fix it but i woulndnt let that scare me too much. if i wanted to ride.

maybe amsoil will pay for the repair ?

[KASEY]

jerry and neil,,, is it possible to put web cooling holes in the piston for the bridge  between exhaust ports on these cylinders? or would it do any good?  I have never had this issue but I am not real hard on stuff... just a thought,,,,,

[rablack21]

maybe amsoil will pay for the repair ?

This is not a lubricant quality related issue. Don't confuse that with a lack of lubrication issue. Almost all seizures are due to 1 of 3 causes, rapid expansion of the piston in a cold cylinder, the cylinder bore being too small for the size of the piston, and lack of lubrication. But there are many causes of lack of lubrication including overheating the engine, the engine running too lean causing too much heat, and an air leak which causes the engine to run lean leading to heat buildup, and lack of enough oil in the gas. There was no indication from my parts that there was a lack of proper lubrication due to lack of oil in the gas or that the film strength of the oil was not adequate under normal riding conditions. If there is a lean condition or an air leak or if the engine is overheating greatly for any reason, the piston and/or rings can expand or bulge to the point that it scrapes the oil right off of the cylinder wall creating metal to metal contact , and it doesn't matter at that point what oil or oil ratio you are running it will wipe it off as well. If this was an oil ratio related issue, then this would have continued to happen and should have completely seized by now. I have run the same ratio with the same engine for several years now, and ran the engine the same way. I find it hard to believe that it all of a sudden became a problem. There is just not enough evidence to support that. Plus, all the internal parts were coated with a film of oil when I tore the engine down, the crank rod showed zero discoloration, there was no discoloration in the wrist pin or on the underside of the piston, all indicating that oil migration was taking place in sufficient quantities.


There was, however, several indications that my engine had run lean, had an air leak, and exhaust leak, and overheated several times in the period of last year's racing season. All of the issues are associated with creating seizures. I cannot pinpoint which one was the cause or when it actually occurred. All I can do moving forward is to make sure I don't have any of these issues from this point forward.

[mx250r91]

is it possible to put web cooling holes in the piston for the bridge  between exhaust ports on these cylinders?

That's what I was just thinking, drilling a few little holes in the piston on each side of the main exhaust port to help lubricate the area between the main and sub exhaust ports. Like how pistons for a stock cylinder are drilled down the center front of the piston to help lubricate the bridge.

Like this one:

[F-Red]

At one time, Eddie had Wiseco put those lubricating holes in his pistons. They can't hurt, but if all parts are working correctly, not necessary.

[jcs003]

i feel a better way to lubricate a specific area is with a angled/chamfered "hole" of sorts  for example; using a spot drill instead of the small oiler holes as on the pic above and what is common by piston manufactures.





john

[rablack21]

That's what I was just thinking, drilling a few little holes in the piston on each side of the main exhaust port to help lubricate the area between the main and sub exhaust ports. Like how pistons for a stock cylinder are drilled down the center front of the piston to help lubricate the bridge.

Like this one:

i feel a better way to lubricate a specific area is with a angled/chamfered "hole" of sorts  for example; using a spot drill instead of the small oiler holes as on the pic above and what is common by piston manufactures.





john

I like this idea ^^^.

[mx250r91]

i feel a better way to lubricate a specific area is with a angled/chamfered "hole" of sorts  for example; using a spot drill instead of the small oiler holes as on the pic above and what is common by piston manufactures.





john

This sounds like a good idea, chamfer the side of the hole that is against the cylinder so as to slow and diffuse the fresh oil mix as it passes through the piston from the crankcase and distribute it over a larger surface area than just a plain thru hole.

[rsss396]

Its hard to gauge if a motor is getting enough oil by looking at the amount of oil on a piston when dissembling a motor.

The way to know if it has enough oil is to put in its worst case scenario which is a long wide open run of say 500 feet

A two stroke will normally have a excess of oil in the crank case under normal driving conditions with allot of on and off throttle positions but the longer you hold it the more of this excess that gets cleaned out of the lower cases.

Woods bikes and MX bikes can probably get away with less oil but long runs and high heat do require more oil

Now I am not saying this was the cause but it may have helped, loose pistons do run hotter and high coolant temps only compound the problem.

[mx250r91]

Has anyone tried the "Wet Oil Line Method" for jetting? The theory seems sound but it is more tedious and time consuming than the traditional plug chop.

http://www.702sportbikes.com/showthread.php?14147-Two-Stroke-Jetting-The-Wet-Oil-Line-Method