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Siezed motor

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:smirk: My 03 siezed racing last weekend. It seemed to be a light siezure since I could push start it and rode back to camp. I was on the gas hard, closed the throttle a bit for a turn and bwaaaah,stop. I thought maybe I locked up the rear brake too much but when I tried to restart it the compresion was low. I have always had a problem with detonation on this 03 RM 250 and race day was no different. As for jetting, the plug is coco brown and it still belches black mess all over the rear fender, so the assumption would be the jetting is correct. I think the head is too tight causing this. I have been told race gas is a must(mostly because of my size and the load I put on the bike when I race, 6'3 250lbs) but I cant afford buying race gas every time I am gonna race an enduro or desert race.

So the questions are:

Have you experienced with turning the bowl to reduce compression?

What effect did this have on the power?

Any recomendations for angle and squish band width?

I was running a forged Wiseco, could a stock cast piston dissapate the heat faster? never had an issue with Wiseco's in my KTM's.

Could a pipe switch lower my combustion temps? I run a Bill's now but have a PC works hangin in the garage. I have read FMF's SST's cause higher combustion temps so I wonder if this could be true of the Bill's too.

I have tried octane booster which doesnt seem to help. I have mixed race gas at 50% which helped a bit but didnt eliminate the problem.

The motor is stock porting, stock head,Boyesen Rad Valve, Bill's pipe,PC Nature friendly SA muffler, and my jetting is 40 pilot, 8.0 slide, N8RH in #3, 178 main, stock power jet.

My fuel is standard Unocal 76 91 octane(california fuel) using Motorex Crosspower 2T at 40:1

3000 -4000 ft elevation

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sounds like its super rich, im in phoenix at about 1800 feet and im running a 165 main, 40 pilot, stock slide and needle. check your squish measurement before doing anything else. if it is above0.8 MM then youre good to go. my cylinder is ported and my squish is set at exactly 0.8 mm (as tight as it should be on a 250) im running a modified boyesen RAD valve assembly and an FMF SST with the stock silencer.

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Update: got it all apart and inspected it really close. Looks like the top ring snagged on the power valve flap. My jetting appears to be perfect according to the dome of the piston, so I gonna say failure was caused by a ring snag. Marks on the power valve flap, cylinder port, and location of the ring stickage in the piston would make me believe this. Now, what causes this?

-Worn cylinder? what should the measurement be?last top end the piston clearance was .003 in 4 different spots on the bore, stock calls for .0025. What should the measurement be if I were to measure it with inside mic's?

-Not enough ring clearance in the grooves so when got hot from running it really hard the piston heated up and stuck the ring causing it to snag?

-Worn center flap for the power valve? it doesnt look worn or distorted where it seats(just a shiny spot on the coating on both sides but no missing material other than the goldish coating)and the steal seat is unmarked

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I think it stuck a ring from heat. Maybe your problem is not jetting at all, but your fighting heat. My first thought would be stator timing and plugged up radiator core. You know two stroke dirt bikes don't hold much coolant in the first place. Now add a plugged core or smashed fins. Also since your fighting heat, you may want to try Engine Ice coolant. Wouldn't hurt to try it.

The jetting on my 03 is #168 main, #48 pilot, #7 slide @ 32:1. If I go to a #165 main I get a little ping in the mid range. PC pipe and 304, light head mill just to clean up the gasket area. No more mods.

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Spoke with Bill and Jeff from Bill's pipes today. Showed Jeff my cylinder, which needs to be replated now. Talked to both Bill and Jeff about the signs on the piston. Black carbon burn on underside of piston says the crown was too hot and front center seizure says the exhaust gasses are too hot so the reflection wave overheats the skirt of the piston. These two combined caused my failure. Now, I couldnt run antifreeze the weekend I raced due to National Forest rules so I went with water wetter and distilled water. This also didnt help with heat dissapation according to them. So a few things caused my failure now. So the fix: Race gas, which I cant afford or reduce compresion. I chose to reduce the compresion so jeff is gonna modify the head. I should be good to run pump premium when all is done. Lets hope so. As for the timing, it hasnt moved and I will test for retarding at high rpm when the motor is running again.will keep you guys updated with performance when I get this thing back together, in a while since I am financially challenged right now. Guess I will have to ride and race my 01 for now.

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Have you thought about using an Avgas/ premium mix rather than the Race/ premium mix. Price is only a bit more than premium. I had detonation problems on my 03. I now run 2/3 91 no ethanol pump, to 1/3 Avgas. Eliminated detonation problems. Had to lean my jetting out a bit as well.

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Have you thought about using an Avgas/ premium mix rather than the Race/ premium mix. Price is only a bit more than premium. I had detonation problems on my 03. I now run 2/3 91 no ethanol pump, to 1/3 Avgas. Eliminated detonation problems. Had to lean my jetting out a bit as well.

Most AV gas is really high in lead, be careful with that. I have a local airport to me which used to sell Av gas to dirtbikers and such, but I have heard they stopped recently due to the emissions thing here in SoCal. I am still gonna try to run the lower compresion head and see where that gets me, from what I have been told it will add more mid to top performance too which is good for a desert sled.

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Most AV gas is really high in lead, be careful with that. I have a local airport to me which used to sell Av gas to dirtbikers and such, but I have heard they stopped recently due to the emissions thing here in SoCal.

Same as any high octane race gas, loaded with lead. It was used as the base for race gas for yrs. Here it is legal for offroad and highly available.

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Most AV gas is really high in lead, be careful with that. I have a local airport to me which used to sell Av gas to dirtbikers and such, but I have heard they stopped recently due to the emissions thing here in SoCal. I am still gonna try to run the lower compresion head and see where that gets me, from what I have been told it will add more mid to top performance too which is good for a desert sled.

Now why would you have to be careful of leaded fuel??????????????????????????????????????????????????????????????????????????????????????????????????? That, I am not understanding. It burns cleaner and your engine runs cooler.:smirk::thumbsup: Double thumbs up if you ask me. The only reason we can't run leaded gas in our cars anymore is because of all the electronics and the O2 sensors...................Well atleast i can run leaded race fuel or AvGas in my bike and my Camaro. Gotta love carbs and no O2 sensors

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Bambam.

There are a few things here that will cause your overheating.

there's a good chance you are running lean on the jetting, especially since you do have the pinging so start richening that up. Sounds like you hammer this bike to begin with so a little more oil is gonna help keep that cylinderwall and skirt lubed and cool... Zerex or someone else makes an Ecoantifreeze... all organic and designed for extreme temps.

Good luck

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Thanks. My choice yesterday as I ordered my parts was to go with all OEM and return to stock reed cage. Also to try my jetting stock at 32-1 using race gas. Completely start over. That is the problem with running someone elses mods to a bike. I am gonna start as it came from the showroom minus a stock pipe and reeds. I will switch to a PC works with my PC spark arrestor muffler and Boyesen pro series reeds and stock jetting. Break the motor in and then jetting tests. I am personally tired of running uphill here and need a good starting point, STOCK as possible. Thanks for your help and ideas though. I am capable, but sometimes it takes that off the wall experience from someone else to help. The problem with asking on here, as you notice, is that too many people offer their opinions on the products rather than experience and knowledge. Wiseco thread come to mind.LOL

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The problem with asking on here, as you notice, is that too many people offer their opinions on the products rather than experience and knowledge. Wiseco thread come to mind.LOL

So true, even though we all mean our best. I dig the "start from scratch" idea. Wanna sell your Reed cage? hahahaha-

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:ride: My 03 siezed racing last weekend. It seemed to be a light siezure since I could push start it and rode back to camp. I was on the gas hard, closed the throttle a bit for a turn and bwaaaah,stop. I thought maybe I locked up the rear brake too much but when I tried to restart it the compresion was low. I have always had a problem with detonation on this 03 RM 250 and race day was no different. As for jetting, the plug is coco brown and it still belches black mess all over the rear fender, so the assumption would be the jetting is correct. I think the head is too tight causing this. I have been told race gas is a must(mostly because of my size and the load I put on the bike when I race, 6'3 250lbs) but I cant afford buying race gas every time I am gonna race an enduro or desert race.

So the questions are:

Have you experienced with turning the bowl to reduce compression?

What effect did this have on the power?

Any recomendations for angle and squish band width?

I was running a forged Wiseco, could a stock cast piston dissapate the heat faster? never had an issue with Wiseco's in my KTM's.

Could a pipe switch lower my combustion temps? I run a Bill's now but have a PC works hangin in the garage. I have read FMF's SST's cause higher combustion temps so I wonder if this could be true of the Bill's too.

I have tried octane booster which doesnt seem to help. I have mixed race gas at 50% which helped a bit but didnt eliminate the problem.

The motor is stock porting, stock head,Boyesen Rad Valve, Bill's pipe,PC Nature friendly SA muffler, and my jetting is 40 pilot, 8.0 slide, N8RH in #3, 178 main, stock power jet.

My fuel is standard Unocal 76 91 octane(california fuel) using Motorex Crosspower 2T at 40:1

3000 -4000 ft elevation

I know I sound like a broken record but no one answered this. The grain structure of the forged piston allows heat to be transfered much more efficiently than a cast which has more space in the grain structure. If you understand anything about insulation you know its that the heat needs somewhere to go so if there is more space between atoms the heat transfers slower. This is why a forged piston will handle heat better than a cast piston. This is the reason cast also expands less (not significantly).

Most AV gas is really high in lead, be careful with that. I have a local airport to me which used to sell Av gas to dirtbikers and such, but I have heard they stopped recently due to the emissions thing here in SoCal. I am still gonna try to run the lower compresion head and see where that gets me, from what I have been told it will add more mid to top performance too which is good for a desert sled.

AVgas is the same throughout the country as it is closely governed by the FAA. Its around 2 grams of lead per gallon and race fuel is usually 4 grams.

Thanks. My choice yesterday as I ordered my parts was to go with all OEM and return to stock reed cage. Also to try my jetting stock at 32-1 using race gas. Completely start over. That is the problem with running someone elses mods to a bike. I am gonna start as it came from the showroom minus a stock pipe and reeds. I will switch to a PC works with my PC spark arrestor muffler and Boyesen pro series reeds and stock jetting. Break the motor in and then jetting tests. I am personally tired of running uphill here and need a good starting point, STOCK as possible. Thanks for your help and ideas though. I am capable, but sometimes it takes that off the wall experience from someone else to help. The problem with asking on here, as you notice, is that too many people offer their opinions on the products rather than experience and knowledge. Wiseco thread come to mind.LOL

I don't know if your referring to me but there is plenty of experience and knowledge in this area that says to go Wiseco or forged by those much smarter than me or you in many forums, you just have to look.

I hate this topic because there is so much emotion put into it and not much fact.

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I have the answer for you my friend. After trying lots of things to fight detonation, the best two mods are first find gasket material that is .75 mm thick. The stock base gasket is .5 thick and using 2 stock gaskets is just too much. Use the .75 material to build a base gasket and you will erase detonation without changing the powerband. Also, the timing is adjustable on this bike. You may want to retard it a bit as this will also help with detonation.

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