Burnt piston

[bkconwayls1]

Hey all,

Burnt the piston today, with it pegged for about 1/8 mile. I noticed the spark plug was a good 3mm unscrewed when I tore it down. Will this cause this much damage?

[bkconwayls1]

The damage is at the exhaust ports

[Westro]

What plug where you running? She would be getting a little warm.

[bkconwayls1]

BR8ES

40:1

Not sure if the head was shaved...new to 250R

66.10mm bore.....stock I think??

FMF fatty pipe + Q muffler

[Westro]

Plug should be good.

Looks like she was too lean? But someone smarter than I should come along shortly.

Good luck with the rebuild

[atvmxr]

holy @#$@! I've never seen a piston melt all the way through like that in the middle. Mine usually just melt on the exhaust down to the point it bypasses the rings,

[bkconwayls1]

Thanks...plug used to look good!

[86 Quad R]

had ya ever run a compression check on that engine? what about a plug chop?

[GPracer2500]

Looks like pre-ignition or some combination of pre-ignition and detonation. Here's what could have happened:

Detonation (from being too lean and/or too hot and/or too much compression for the fuel used) caused all that errosion around the top ring land and top edge of the piston. This went on long enough that a hot spot was created. Now, not only are end gases detonating near the exhuast port but on some strokes before that can even happen the a/f mixture is pre-igniting from the hotspot. The pre-ignition probably began only a few seconds before the engine stopped.

Or

Spark plug came loose but not enough to loose much compression. The loose plug couldn't transfer it's heat into the head so it overheated, started glowing, and began to pre-ignite the a/f mixture. The excessive heat of pre-ign also cause deto of endgases which led to all the errosion around the edge of the piston.

The catostrophic results of pre-ignition are usually a hole burned right through the middle of the piston. Here's why: if the mixture ignites prematurely then the piston is forced into trying to compress an a/f mixture that is already expanding or perhaps nearly fully expanded. This action creates so much heat so quickly that the one place that's least able to shed excessive heat--the very center of the piston--will be the first point to completely fail. This can happen in only a second or two. At high RPM you can get a lot of strokes into 1 second and it doesn't take all that many strokes under a pre-ignition situation to melt almuinum.

[bkconwayls1]

[QUOTE]Originally posted by GPracer2500
[B]Looks like pre-ignition or some combination of pre-ignition and detonation. Here's what could have happened:

Or

Spark plug came loose but not enough to loose much compression. The loose plug couldn't transfer it's heat into the head so it overheated, started glowing, and began to pre-ignite the a/f mixture. The excessive heat of pre-ign also cause deto of endgases which led to all the errosion around the edge of the piston.

I think this is it..........GP. When I pulled the plug, it looked like it melted/dripped, then cooled fast enough that it was still some what attached to the plug.

I have no idea if this head has been shaved.....can you tell from the above picture?

No, I did not check compression or do any plug chops. This is what I get for trusting the morone that sold it to me.

[crazedape]

If your head gasket is leaking that can happen too. I had mine do the same thing. Tear her down and replace the bearings and try her again.

[C-LEIGH RACING]

When you ran it, did you mix up some fresh fuel or was there gas in the tank already from when you bought the bike.

That engine have an adjustable timming counter balancer bearing carrier & if so where was the pickup module set at timming wise.

When you were pulling the engine down, did you drain the cooling system first, & if so how much coolant did you get out.

Check your spark plug boot, if it dont fit tight on the plug it can come part the way off & then the spark will jump to the plug making the spark W A Y hotter than it should be.

We ran a 310 Pro-x cylinder out of coolant in about 10 laps racing TT, destoryed the top end but didnt burn a hole in the piston.

What ever it was caused it, with that much damage, your looking at a complete engine rebuild, even the crank.
Neil

[machwon]

Definitely a case of some serious detonation. Too much compresssion, too low of octane fuel, and/or too much timing advance. Almost as bad as when I used NOS on my R!

Detonation causes extreme cylinder pressures/heat and it is not uncommon to see a spark plug come loose or even pop out of the head under those circumstances.

[Eddiesanders250]

dont feel bad my piston kinda looked like yours causing me to recently do a whole engine rebuild... mine was caused from a leaking head gasket. while you tear into the btm end do everything right and youll do it once

[bkconwayls1]

Neil

I had been riding all day (50 degree weather), with fresh gas. There was a small amount of gas when I bought it, and then filled it up. Just came from an hour of woods riding, and was on the last leg before packing up and going home. I let it all all out going back to the truck. I put about 9 hours on the bike my self.

Is this bearing carrier what the coil pick up is screwed to? Just pulled the motor today, so I am not sure where it is set at

Cooling system was full...straight antifreeze though, so it may have been overheated somewhat from not having 50/50

Plug wire was very tight on plug...loose plug tip

It looks like a stock size PRO-X piston. Some of the piston is so small, it looks like someone dumped sand in the motor, ports, pipe...etc.

All the cylinder and head bolts were very tight.

Yea, I am not too bummed out, I will finally know what the motor is made of. I always thought you could here detonation, but I did not hear anything but the piston chewing itself up in my motor..

[bkconwayls1]

Eddie,

I've been snooping around your site...it is your site correct? I would like that 310 kit, but want to keep the pipe and carb I have now, you know.....$$$ So, do you build around what I have now?

FMF Gold Series Fatty pipe and "Q" muffler
Kehin carb, not sure what size just yet

It had vary little power if any, down low. Am I stuck with that type of power band with that pipe??

[C-LEIGH RACING]

Originally posted by bkconwayls1
Neil

I had been riding all day (50 degree weather), with fresh gas. There was a small amount of gas when I bought it, and then filled it up. Just came from an hour of woods riding, and was on the last leg before packing up and going home. I let it all all out going back to the truck. I put about 9 hours on the bike my self.

Is this bearing carrier what the coil pick up is screwed to? Just pulled the motor today, so I am not sure where it is set at

Cooling system was full...straight antifreeze though, so it may have been overheated somewhat from not having 50/50

Plug wire was very tight on plug...loose plug tip

It looks like a stock size PRO-X piston. Some of the piston is so small, it looks like someone dumped sand in the motor, ports, pipe...etc.

All the cylinder and head bolts were very tight.

Yea, I am not too bummed out, I will finally know what the motor is made of. I always thought you could here detonation, but I did not hear anything but the piston chewing itself up in my motor..

Yes, that carrier is what the pickup module is mounted to. A stock Honda carrier has no adjustment, just mounts the pickup in one place.
An adjustable one will have lines on it to set the timming by, just loosen the two screws & slide it where you want the timming to be.

You said fresh gas mix, was this pump gas or racing gas at least 110 octane.
Neil

[bkconwayls1]

I'll check that carrier tonight.

I was using cheap gas (9? octane) from Quick Trip, with 40:1. I do not see this ratio much....but some say 50:1 and some say 32:1....

[C-LEIGH RACING]

Ratios can vary, its the jet size that maters, got to keep everything cool, of course you can already see what can happen.

That pump gas could have done it depending on the compression though.

Heres the deal, pump gas, you sometimes dont know what your getting. Say like the tanker comes to the station to deliver & has 3000 gallons of reg no lead & 3000 of prem but hes in a hurry gets the drop hole mixed up & put the wrong gas in the wrong hole. It happens, I know cause I youst to drive a tanker.
Most times nobody ever knows like on cars, but a gas engined truck pulling a load & has to use prem to run right, about 2 miles down the road those piston will let them know.
God help if gas gets in the diesel hole, about 2 miles they will be sitting side the road with a big oil spot on the ground & piston pieces scattered up to the point.

With race gas, you dont have to worrie about that, not if you get it in a 5 gal bucket or drum for sure, most stations you dont either cause a small truck will deliver that.
Neil

[bkconwayls1]

So if we are using just using standard gas, is there really a need to use high grade? I am not going to rebuild this motor with intentions on using race gas, or premium for the matter...just too much to risk in my opinion. What kind of compression do I need to stick with for hard rec. riding?

By the way, Thanks for you help guys!

[garrettagr]

dude, from that picture it looks like the head was milled or re chambered and you had way too high of compression. But that is my two cents worth. Dont know if it is right though.

[C-LEIGH RACING]

If you were to just use reg no lead gas, I say somewhere around 165/170 psi compression to be safe, but, what kind of engine will that be.
You could take that low compression engine & port the cylinder for top end, you could do that with it. That means though the power output would be high in the rpms & that can get out of hand on a tight trail ride.
Compression is the key on a 250R engine producing power, hard pulling power a rider can control.
Neil

[86 Quad R]

neil is correct. from personal experience, if ya wanting to stay with pump gas then i'd atleast run the compression @ 180psi (91-93 octane range). with the fmf pipe and a few other add ons, you'll have great all around power that you can manage and enjoy.

[C-LEIGH RACING]

One thing I would like any & everybody reading thing to take note on this pump gas deal.

This could apply over the entire United States, but on the east coast I know for sure this is how it is.

Exxon is the only true gas you can buy, meaning only Exxon tankers & drivers will be hauling it to Exxon stations & it will only come from a Exxon depot. Less chance of error by doing it this way.
Only time any other driver or tanker line will haul Exxon products is if all the Exxon drivers are out of driving hours & cant operate the rigs, & that very seldom happens if dispatch is on their toes.

90% of other brands of gas can be loaded from any other depot, meaning, a driver can load Texxaco gas at a BP or Citgo depot.
So if you want to take some of the chance of getting the wrong gas out of the pic, use Exxon.

I dont work for Exxon, never have, just to clear that up if anyone is thinking that.
Neil

[wilkin250r]

Originally posted by bkconwayls1
Cooling system was full...straight antifreeze though, so it may have been overheated somewhat from not having 50/50

Bad bad news. Glycol (antifreeze) has very poor thermal conductivity, it doesn't cool very well.

Neil has some very good theories, let me throw another one into the mix. I think the engine was overheating due to the running straight antifreeze. It's also very likely the engine was near detonation, for many of the same reasons that other people have posted, and the overheating pushed it over the edge into detonation and eventual failure.

You have to run water mix, you can't run 100% antifreeze (you also can't run 100% water, it will corrode). If I were to put a number on it, I'd say running pure antifreeze added at least 30 degrees to your engine temp.

[C-LEIGH RACING]

I dont know about the glycol deal ??, he said it was about 50* but he rode all day. Could have been him not knowing the compression was high, cause he hadnt checked & that pump gas. After reading more, if it was spark knocking from that gas & riding all day, its a wonder it lasted long as it did. That highway run was the last straw & did it in.

Some time back I rebuilt a LT500 for a guy that had a Terry Varner engine build & after everything was back together, compression was around 180 cold, which was close for that big engine.
Guy picked it up & in about three weeks he called & said it had blown up again & had no compression.
When I got a chance to pull it down & check things out, the piston edge on the exhaust side was melted off completely, even to behind the ring grooves. When I finely talked to the guy again I found out he was useing pump gas & couldnt remember if it was prem or reg no lead.
I did remember when he picked it up the first time telling him to use race gas & where to get it from & why he needed to use that type of gas.
Anyways, I built it again & hes been useing the race gas & no problem sence then.
Neil

[bkconwayls1]

Looks like 88 cases, long rod (HA2), and 86 piston....since it has the spacer. Am I correct? On these motors, you adjust the compression with the spacer or shaved head or both..??? Here is the pick up, looks stock to me. At this point, I guess I need to know what specs to stay within when ordering a head, cyl and piston. Is it possible that the crank is stroked?

[wilkin250r]

Originally posted by C-LEIGH RACING
I dont know about the glycol deal ??,

I worked for a company that helped design a water-cooling system for computer microprocessors, we did a bit of research on cooling capabilities.

I do know that glycol will reduce the efficiency of your radiator. By running 100% pure water, you'll reduce your coolant (and overall engine) tempurature by 7 degrees at least. The problem is, you CAN'T run pure water because it will corrode. Antifreeze has corrosion inhibitors.

This is half the efficiency of products like Water Wetter. Getting rid of the glycol will reduce temps by 7 degrees, and decreasing the surface tension of the water will drop another 7 degrees, and Water Wetter also has corrosion inhibitors. It doesn't provide protection from freezing, though.

I never did any research on pure antifreeze, but I DO know that it has very poor cooling capabilities compared to water. It just doesn't transfer heat well.

[regg187]

Lots of good advice here. I'm going to say I don't think it was mainly an overheat , there are no signs of the 4 corner seize on the cyl wall. most damage seems near the exhaust port. could be lean with Det. He rode woods first-- mainly low and mid riding- which could be jetted fine. Then at the end of the day He let it rip W.F.O which is prob jetted lean . Hot spots near exhaust port beacuse of poor heat tranfer, lean jetting= major Det just before it all melted. slightly pluged Rad from riding woods earlier also adding to poor cooling along with 100% A F.

It's hard to say for sure but that head does look shaved , I'm sure it should have had race fuel in it, which was contributing to the Det , and the Melt down.

Don't feel bad about not knowing much from the Previous owner, When I first bought my 250R I took It straight to glamis. Stock filter, had a tear in it, where it couldn't be seen. Ran like crap after 30 min. started fouling plugs, losing power on the way back from the hill. I ran it till it scattered piston all through the engine. It took the crank bearings and the rod bearings with it, scored the cyl through the first O.B. and into the last O.B.. I found a piece of skirt in the exhaust pipe. So just like you. new quad to me, and I had to replace the crank and the top end ,which is a fair some of money after just paying for the quad. I was young and didn't make much money then, so It hurt--ALOT.

Good luck with yours, just re-do it right !

[bkconwayls1]

Thanks, Regg. It's a good thing for this site, I will know what not to do with the "R", when I get it back together.

[bkconwayls1]

Been awhile, but finally put this thing back together...$$$ issues ya know. For those interested, I realized today, that it had to have had, higher than stock compression. The head gasket that was on it is about 1/4 the thickness of the stocker I just installed. Still trying to track down the right reeds too, and then start her up. Thanks C-LEIGH, and everyone for the help!
Brian

[C-LEIGH RACING]

Sounds good, now spend some more money & buy a compression gauge so you can be sure what the compression is & know what gas to use.
If you use pump gas, look at the pumps good because lots of stations are selling ethanol mixxed gas now. It should have a label on the pump giving you notice if the gas is mixxed.

For god sake dont use the new E85 fuel for sale these days.


OH!!!! clean off that rust off the flywheel.
Neil

[atvmxr]

but doesnt E85 have a higher octane rating? so you can run higher compression = more power across rpm range? or is there an issue with the corrision of the fuel versus gasoline? and in Houston all the gas is 10% diluted

[bkconwayls1]

Originally posted by C-LEIGH RACING
Sounds good, now spend some more money & buy a compression gauge so you can be sure what the compression is & know what gas to use.
If you use pump gas, look at the pumps good because lots of stations are selling ethanol mixxed gas now. It should have a label on the pump giving you notice if the gas is mixxed.

For god sake dont use the new E85 fuel for sale these days.


OH!!!! clean off that rust off the flywheel.
Neil

Both are checked off on my list, thanks Neil!

So no ethanol at all???

[bkconwayls1]

Fired right up yesturday, needed the air screw all the way out to idle, so I assume this is due to the 55 jet.

I found a small crack in the external fuel filter. Would this cause a lean condition....or at least contribute to the burnt piston?

[Aceman]

Originally posted by bkconwayls1
Fired right up yesturday, needed the air screw all the way out to idle, so I assume this is due to the 55 jet.

I found a small crack in the external fuel filter. Would this cause a lean condition....or at least contribute to the burnt piston?

If it was just a really small crack that didn't leak much, I highly doubt it.

[wilkin250r]

No, the crack isn't going to affect anything.

To have any effect on your mixture, the crack would have to be SO big that it was literally pouring fuel. Large enough to empty your fuel tank within minutes. But if it was leaking that badly, you would have most certainly noticed it.

[speedfreek]

Originally posted by garrettagr
dude, from that picture it looks like the head was milled or re chambered and you had way too high of compression. But that is my two cents worth. Dont know if it is right though. Yes, the head does look shaved.

[bkconwayls1]

Originally posted by speedfreek
Yes, the head does look shaved.

That's what I was thinking....

Has about 175psi right now with a thick oem gasket.