Check out this 4 corner seize...

[latheboy]

Here is what happened to my 350pv running on a big clay oval. 15/36 gearing running 4th and 5th gear. I am sure I needed more main jet. It was being ridden hard, always in the powerband. Lots of heat, temps at 200 coming off the track. 3 laps into it, it squeaked. I am running a 38 A/S with a 50 pilot and a 180 main. The plug color looked good. I should have ran a 195 main or a little less if it would have pulled it. What do you think the top of the piston looks like? lean?


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[DnB_racing]

im far from an expert but to me from the position of the scouring are you sure it wasn't an overheating issue instead of a jetting? are you getting good flow of coolant to all of the coolant ports?

[latheboy]

I guess it could be an overheat issue. I have a new waterpump that has good flow. I am also running a pro series oversize radiator. I have had overheat issues on previous builds of this cylinder, but that was a bad airleak at the base gasket. This build pressure tested good before I tore it down and saw this. But the day it seized, it probaly ran 200-220 on the ESR temp gage. It was also 85F and humid that day.

[DnB_racing]

I just think its more then your jetting .... your rings arnt even burnt. just looks like something either warped or worn, It just doesnt look like a jetting burn

I would look at everything real good before putting back together, all bearings and rod and make sure the cylinder isn't out of round,


but like I said im far from an expert, but something just doesn't look a lean issue to me

look at the top of the piston .. it looks like the heat was from the sides of the cylinder more then from the top of the piston, what were you running for a premix,

the reason I ask is it almost looks like a piston i have seen recently, a friend ran the wrong gas can with straight fuel no oil, and the piston looked real similar, almost like it swelled up in the cylinder, and that caused more then just top end damage

[wilkin250r]

I don't know, I AM kinda leaning towards a jetting issue. Look at the difference in color. Low combustion temps (caused by rich jetting) results in lots of carbon buildup, but that thing looks like all the carbon has been burned off at the edge near the exhaust port, like maybe the exhaust temps were a little hotter than normal...

[DnB_racing]

Originally posted by wilkin250r
I don't know, I AM kinda leaning towards a jetting issue. Look at the difference in color. Low combustion temps (caused by rich jetting) results in lots of carbon buildup, but that thing looks like all the carbon has been burned off at the edge near the exhaust port, like maybe the exhaust temps were a little hotter than normal... ya maybe,I see its definitely worse on the exhaust side

the thing that caught my attention was it was even starting to look like it burnt off even a little on the intake side,

I know if it was a no oil situation it would be much more on the intake, but I would still look at everything real good if it was me.

it looks like it came from definitely heat but I question if the heat wasn't actually from something besides jets..

I would just check everthing real good

[jcs003]

that is one BAD seizure. almost looks like it had a previous mild seizure that was just exacerbated with this most recent incident.

[latheboy]

I was running 110 race fuel and amsoil dominator at 40:1

[pinitatv]

Where were you racing?

What's the front of you quad look like? How much radiator is getting air around your bumper and number plate? If you don't have a good set of rad shrouds to scoop the air it may not be cooling as much as it should.

Just my 2 cents...

[rsss396]

The top of the piston with the bare spots is a perfect example of "piston wash"
Piston wash is from the fuel washing the piston as it comes out the transfer ports. The fuel will cool the piston crown and not allow carbon to be formed.
These washed areas will be inline with the transfer ports.

The wash on your piston looks very good, if you were lean either the whole piston crown would be brownn or everywhere except a few small bare spots would be brown colored.
Not many racers use the piston wash method but it is a very good way to determine jetting.

My guess is the motor got hot, you can try and increase the water to coolant ratio (80% water 20% coolant) increase oil ratio and run bean oil
I prefer klotz.

Even though the jetting looks good by the piston wash method it can be deceiving if it was colored with a different style of riding.
Long hard pulls or time wise long races do need a little more fuel to keep them cool.

[red88r]

I would also say it was getting hot and probably was not your jetting. Top of the piston looks like how I like to see them. I would also recomend running like 32:1 with a good oil. I run Klotz Benol oil and recomend it to everyone.

[latheboy]

It was definitly running a hotter coolant temp than I would prefer, but it didn't boil over or lose any coolant. This piston has several gallons of fuel thru it (prob 15 gallons) so some of the color was from ice riding this winter. I have a piston coming 4 it, and I will go a little richer on the jetting and try some things to keep the water temp down. It prob could have been richer for my application. It was held wide open in 4th and 5th gear on a big clay oval (15-36 gearing). No mercyon a big oval! Someday I will post the video of it in the lead, then seizing :{

[265 sleeper]

They usually run the best before they die

[C-LEIGH RACING]

That seize is kinda weard, cause you dont normally stick them on the right side that bad in a 4 corner.
250Rs because of the intake flow angle, will normally compact more fuel mix to the right side than to the left, so you'll normally if you seize, stick the left front side first because of being just a bit leaner on that side.

A coolant heat issue, you'll see more damage than that unless you catch it mighty early in the seize process, but the 200~220 didnt help any at all.

How tight was the bore ??.
What pipe you using ??.
Silencer core in place ??.
Compression amount ??.
Brand of race gas ??.
How much advance timing ??.

What type of vent you have on the gas tank cap ??, long hose stuck down into the steering stem or one of those little short hose machined pretty vent caps that has stopped up caused the gas to stop flowing out of the tank & leaning out the carb & sticking the piston.

Something ol folk know, those steering stems have a little small drain hole down at the bottom & real easy to stop up & then when you was the bike it fills up with water :eek: now what happens when the gas tank needs air from the fuel level going down & that vent tube stuck down into that steering stem :(

Piston seizure dont care whos engine its going to happen in, even mine, so best to be jetted big enough to keep it from happening even if you got to lose a hp or two.
All I know is what I've touched or been bit by over the years & rich 2 stroke engines dont normally seize unless theres another problem pop up.

180 main, 78mm piston, 200~220 temp & that ol R engine pulling hard from the center of the corner till it starts back revving up, is a gob of heat on top of that piston & probably lucky you got as many laps as you did.

When it spudders just a bit right as you pitch it going into the corner & the engine revs just a hair higher, you got it jetted right then.
Neil

[latheboy]

Thanks for your input C-Leigh!
Now to answer some of your questions....

The piston clearance was at .004. I know that is plenty. Too much by most standards. But that is what it was, strait from LED, for what its worth. I am a machinest by trade. I know my measurement was accurate, I used a dial bore gage and gage blocks. Also ESR told me last week to go ahead and run my new piston at .004-.0045 clearance.

I am running a hand coned pipe made by LED. Similar to other LRD big bore pipes, but larger in diameter. I am also running the ound silencer, sold by LED.

I was at 235lbs compression, before the seize. Actually, after the seize, I still had 220.

The race gas could be a problem, although I didnt hear it ping. I was running 110 race gas that I can get off the pump here in my hometown. It is fresh, because all the stock car racers in a 100 mile raduis use it. For what its worth, I am switching to VP. They have a new 113 octane that I can get for the same price.

I am running the 01 cr250 ignition with the esr adapter plate rotated the way you recomended in an old post I read at the time. That should put me at approx 7 deg advance, right?

I will be honest here, I do have one of those pretty machined gas cap vents. I will go back to a short hose down the steering stem... advise taken.

Thanks
LB

[RyanWsly]

he is correct about those little gas vents, I had a friend who had a CRF450 that started dying out after hard acceleration. pulled the cap loose after he rode it and it was doing it and you could feel and hear the vacuum as we removed the cap. stock cap on it ran fine, he drilled the other one or something so it would vent.

[C-LEIGH RACING]

Theres two thing you need to keep away from a 2 stroke.
#1, those pretty machined vent caps, cause they have a disk in them that will close & wont let the gas run out should the bike turn over & PRONE to stick closed.

#2, those small clear cone shaped brass looking inside inline gas filters, cause they will never flow enough to supply the engine. If your going to inline filter the gas, get the biggest you can mount in place.

Everything looks good in your answers, dont see any problems there, but I forgot one.
The pipe, you have it sealed up real good at all the joints, cause if not the returning wave can draw raw air back in & push it into the cylinder & cause a lean burn.
It can happen if your jetted on the edge for top power. Be ok while its cold & warming up but when up to operating tems it can happen.
Neil

[latheboy]

Well, I am back to rebuilding this motor. I got a new 78.5mm piston, and had my cylinder bored to match. I have it all together. It pressure test good, holds 10psi all day. It has 210lb compression. It had more on a prev build, but I went with a bigger dome this time around. Big problem tho... It has a coolant leak. Seems to burn coolant like the head gasket is out. I had the head back off once already to be sure the o rings are in place and they are.

How can I tell if the sleeve is leaking somewhere at the water jacket? I didnt notice the sleeve pushed up out of the casting, but I will take the head off and look tommorow. I read a few threads on herewhere people said the sleeve was leaking coolant above the exhaust port. How do I check for that?

[C-LEIGH RACING]

How you can test the cooling jacket.

I did it, by making up two pieces of heater hose to clamp on to the inlet nipple & outlet on the head & then a closed end clamped into the hose & a tire valve stem installed in it.
On the other hose, I clamped in a female garden hose end so I could fill the head & cylinder cooling jacket with water & then a closed end that could be screwed into that.

Once filled with water you can put air presure into the jacket through the valve stem & check for leaks.

Cylinder needs to be off the bottom end, o rings & head torqued in place just like it would be when the engine is together.

I have filled the jacket with water & then used a hot air gun to heat the cylinder real hot & the check for leaks.
You'll be surprized when your heating it up, at the places stuff will squirt out of between the casting & sleeve.
Neil