piston problems

chris189 said:
Hey if you can't find anything wrong on the intake side then make SURE you have NO EXHAUST leaks.

Exhaust system is just as important as proper carburetion on a two stroke, if there are leaks it will run lean for sure.

Also, it was not you thermostat as a bad thermostat would cause the engine to run cold and probably the scoring would be on the intake side in the case.

Hope this helps.
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thermostats can fail closed too, causing the engine to run hot and overheat and even sieze pistons then too. not all thermostats fail in open position.
 
ok your right mopar, my bad.

However, I have fixed two different srx's with failed open thermostats.

ALso, if it failed open that would cause a more gradual warm up which SHOULD trigger the light to come on.

Just my opinion.
 
there u are u find your problem if the jetting still stock with your cold air kit
 
staggs65 said:
i'm taking my cold air kit off this season,very inconsistent jetting, i've read here that venting in the airbox helps with this, but i don't feel like messing with it any more
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my '99 700 srx that had a bender cold air kit, seemed to be a little picky w/jetting.
 
So what gets blamed?

I burned my 500 down just like it. WFO at night on the way home with brisk temps and a gutted air box. Poored some oil down the hole and got it home. Had to stop once in about 8 miles to add more oil and blipping the choke helped to get it all the way back.

The good news is that there PROBABLY isn't anything in the crankcase. I didn't slit the case on my 500 and all was fine until the next time I burned it down for another reason/time, LOL. Any longer on the bar and I bet a hole would've shown up somewhere and/or cracked skirt. Then splitting the case isn't an option anymore.

Your call to make and not an easy one if you're on a budget like most of us.


So, what was the cause?

Too lean?

Detonation?

Combination of the two?

Something else?

I'm guessing the main cause was lean a/f due to ragged edge jetting. I don't see any sign of detonation, but it may have melted away so I wouldn't rule it out as a contributor. I'd dump the fuel that's in it just the same.

What does the cylinder head look like?
 
The cylinder head looks fine there was a heavey layer of carbon on all three.The cold air kit was on the sled from at least 12000kms.He did go on a trip to the u p it must have been -25f or colder.
 
from what i see, the top of the piston has a sand blasted look from the exhaust edge to center that is a sure sign of detination, now the skirt doesnt have any scoring, so i would say lube was ok, so fuel delivery was ok, now on a single pipe triple, all the heat goes two the center, so if center is hotter and fuel is marginal there is a good chance of detination, even worse if exhaust is blocked momentarly in the deep stuff, or power valves malfunction on triple pipe or single. octain/heat=detination i would guess its detination caught before preignion failure
 
vintage srx said:
The cylinder head looks fine there was a heavey layer of carbon on all three.The cold air kit was on the sled from at least 12000kms.He did go on a trip to the u p it must have been -25f or colder.
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-25deg ferenheit, w/stock jetting and cold air kit, would be too lean and cause a meltdown. the exhaust side of your piston is starting to melt away, from the extremely hot exhaust gases, caused from a lean air/fuel ratio. also, when you say that there was a large layer of carbon on the heads, leads me to believe that the jetting was too lean. if you have safe jetting, the extra fuel will help keep the piston crown and head cool and wash some of the oil off, so w/the head and piston crown being cooler and the extra fuel washing off the oil, there is more areas of clean piston crown and the head will be cleaner. i would like to see some pics of the mag and pto piston crowns. we can tell imediately, if the jetting is way lean or not.
 
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He just told me today that while they were in the u p that he got gas in the middle of nowhere .He thinks all they had was 87 it cost him $5.00 a gallon which is crazy.The jetting is per bender speck.
 
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lol

I had my srx apart last night checking her over...same thing middle cylinder started going like that...And power valve cable broke...
so assuming all this I would think that the power valve stuck open and exhaust flow was burning the top of the piston...but I'm going to check the jetting again, carb boots, reads and exhaust leaks to be sure...great post by the way..
 
007redline said:
I had my srx apart last night checking her over...same thing middle cylinder started going like that...And power valve cable broke...
so assuming all this I would think that the power valve stuck open and exhaust flow was burning the top of the piston...but I'm going to check the jetting again, carb boots, reads and exhaust leaks to be sure...great post by the way..
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better check the things you have listed because power valves don't burn pistons, no matter if they are working ,stuck open or stuck closed.
 
a stuck closed power valve is a exhaust restriction, that will make that cylinder run hotter on exhaust side, when its supposed to be open, and will restriced fuel flow to that cylinder, by not allowing all exhaust to escape. stuck open would do nothing but effect low rpm running, making it richer just my two cents
 
no1chevyboy said:
a stuck closed power valve is a exhaust restriction, that will make that cylinder run hotter on exhaust side, when its supposed to be open, and will restriced fuel flow to that cylinder, by not allowing all exhaust to escape. stuck open would do nothing but effect low rpm running, making it richer just my two cents
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maybe it was stuck close...who knows it broke...lol
 
vintage srx said:
I was cleaning power valves in my brothers 01 srx and i was looking threw the power valve port with a flashlight. This is what i found in the center cylinder.What do you think caused this .
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let see the gas wash on other piston it will give u a good idea
 
process of elimination,jetting plugs... many good posts here all possibilities, except the reeds, i think that usually will run rich instead of lean cause usually when the engine is cold you will not notice worn reeds as much cause at that point a little more fuel isnt much of a problem but as it warms up will show itself more. good luck with it.
 
Well i found a bad mag crank seal in my brothers sled cot it just in time.Replaced both seals i wonder if that caused the middle cyl to go the first time.
 
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