PhatboyC
New member
As these stories usually goes, last ride of the season last winter and my lovely SRX 700 called it quits. I was racing my buddies Apex and a chipped Skidoo GSX 4-Tec. Long stretch on a lake and on the way back one of my piston melted.
Was referred to a farmer in town who loves Yamaha's and fixes them on his spare time. We took it apart and found a missing screw that hold the clamp between the carb and the cylinders. But when we pulled to remove it was still tight. Not sure extra air could get in there. That and he said the float in the carb didn't look adjusted properly but wasn't sure (he's in 4 strokes now and could remember exactly). He found a tiny tiny bit of water in the gas but not enough to cause my failure. Carb and jets where clean and the engines all stock.
I am putting all new pistons and my heads and cylinders has been sent to mrviper700 for inspection and trail port.
What you guys think?
Was referred to a farmer in town who loves Yamaha's and fixes them on his spare time. We took it apart and found a missing screw that hold the clamp between the carb and the cylinders. But when we pulled to remove it was still tight. Not sure extra air could get in there. That and he said the float in the carb didn't look adjusted properly but wasn't sure (he's in 4 strokes now and could remember exactly). He found a tiny tiny bit of water in the gas but not enough to cause my failure. Carb and jets where clean and the engines all stock.
I am putting all new pistons and my heads and cylinders has been sent to mrviper700 for inspection and trail port.
What you guys think?
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snoprokidf6
Member
that would make a great bong!!!
PhatboyC
New member
ha ha ha...I don't know what you mean? 
Couldn't remove the wrist pin so he left it there.
Couldn't remove the wrist pin so he left it there.
lol Don't pay any attention to the kid, it wont help you with the answer you need. I found this somewhere on TY(I think). Maybe it will help
http://www.smellofdeath.com/lloydy/piston_diag_guide.htm
http://www.smellofdeath.com/lloydy/piston_diag_guide.htm
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PhatboyC
New member
Thanks for the link. I believe the one that matches my picture is this explanation:
BURNT-OUT BLOW-HOLE This piston was overheated so badly that a hole melted through the crown and collapsed the ring grooves on the exhaust side. Normally the piston temperature is higher on the exhaust side so catastrophic problems will appear there first. There are several reasons for a failure like this, here are the most common; air-leak at the magneto side crankshaft seal, too lean carb jetting, too far advanced ignition timing or faulty igniter box, too hot of a spark plug range, too high of a compression ratio, too low octane fuel.
-air-leak at the magneto side crankshaft seal: I have no idea what this means. Crankshaft seal? Wouldn't my prestone leak?
-too lean carb jetting: I have stock jetting
-too far advanced ignition timing or faulty igniter box: never heard this happening on SRX. Beside my other piston are perfect, beside their age.
-too hot of a spark plug range: I am running NGK iridium BR9EIX. Pretty common here.
-too high of a compression ratio: stock engine
-too low octane fuel: Gas was from a local shell at 91 octane (presumably no ethanol). Love this gas, lots of detergents, my carbs are always where spotless. No name gas in the trail once last winter but it was long gone by this time.
BURNT-OUT BLOW-HOLE This piston was overheated so badly that a hole melted through the crown and collapsed the ring grooves on the exhaust side. Normally the piston temperature is higher on the exhaust side so catastrophic problems will appear there first. There are several reasons for a failure like this, here are the most common; air-leak at the magneto side crankshaft seal, too lean carb jetting, too far advanced ignition timing or faulty igniter box, too hot of a spark plug range, too high of a compression ratio, too low octane fuel.
-air-leak at the magneto side crankshaft seal: I have no idea what this means. Crankshaft seal? Wouldn't my prestone leak?
-too lean carb jetting: I have stock jetting
-too far advanced ignition timing or faulty igniter box: never heard this happening on SRX. Beside my other piston are perfect, beside their age.
-too hot of a spark plug range: I am running NGK iridium BR9EIX. Pretty common here.
-too high of a compression ratio: stock engine
-too low octane fuel: Gas was from a local shell at 91 octane (presumably no ethanol). Love this gas, lots of detergents, my carbs are always where spotless. No name gas in the trail once last winter but it was long gone by this time.
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tyler440
Member
yeah that means crank seal and no your antifreeze wouldnt leak out... which piston was it?
Those pesky 4 strokes! They have killed more then one 2 stroke trying to run wide open as long as them on long lakes!
Which cylinder was it?
IMO:
[Some of this has already been stated]
This is a melt down caused by a lean condition on that cylinder or something else that caused way to high of piston crown temperature.
Possible Causes:
-dirty carbs[even a little bit of a coating on jets can lean out the mixture to dangerous levels]
-low carb float level[lower is leaner]
-lean jetting[even stock can be lean under cold conditions]
-water in fuel[just a little can freeze and cause lean out]
-too low of octane fuel[lower octane burns at higher temperature]most fuel is crap today...its hit/miss at the pumps
-intake side air leak[causes lean mixture] could be from reed cages, carb boots ect
-high engine temp[back to back wide open runs can easily overwhelm stock cooling systems causing higher cylinder head/combustion chamber temps]
-low fuel in tank[when fuel is under approx 3 gallons, wide open runs can uncover the fuel pickup and basically run the engine out of fuel causing it to go extremely lean] I have witnessed this at Drag racing events many times
-crankcase seals leaking air[usually effects the cylinder closest to the seal] this is very common in older high mileage 2 strokes. These are the seals that seal the crankcase to the rotating crankshaft on the clutch side and the magneto side...they get hard with time and allow air to be sucked in causing lean fuel/air mixture to the cylinders.
A melt down usually is a combination of causes.
Some things I do to avoid this.
I use BR10ECS plugs as I do a lot of high speed running on lakes ect[this was the original plug for the 98 SRXs] this helps to keep piston crown temps a little lower
When snow/trail conditions are poor for exchanger cooling I don't run wide open much
But ultimately...
When riding with fuel injected 4 Strokes...
"DON'T TRY TO STAY WITH A FUEL INJECTED 4 STROKE ON A MULTI-MILE LAKE RUN!... THIS WILL END IN DISATER MORE TIMES THEN NOT ON A PERFORMANCE TUNED 2 STROKE!"
Just my .02c
Bob
Which cylinder was it?
IMO:
[Some of this has already been stated]
This is a melt down caused by a lean condition on that cylinder or something else that caused way to high of piston crown temperature.
Possible Causes:
-dirty carbs[even a little bit of a coating on jets can lean out the mixture to dangerous levels]
-low carb float level[lower is leaner]
-lean jetting[even stock can be lean under cold conditions]
-water in fuel[just a little can freeze and cause lean out]
-too low of octane fuel[lower octane burns at higher temperature]most fuel is crap today...its hit/miss at the pumps
-intake side air leak[causes lean mixture] could be from reed cages, carb boots ect
-high engine temp[back to back wide open runs can easily overwhelm stock cooling systems causing higher cylinder head/combustion chamber temps]
-low fuel in tank[when fuel is under approx 3 gallons, wide open runs can uncover the fuel pickup and basically run the engine out of fuel causing it to go extremely lean] I have witnessed this at Drag racing events many times
-crankcase seals leaking air[usually effects the cylinder closest to the seal] this is very common in older high mileage 2 strokes. These are the seals that seal the crankcase to the rotating crankshaft on the clutch side and the magneto side...they get hard with time and allow air to be sucked in causing lean fuel/air mixture to the cylinders.
A melt down usually is a combination of causes.
Some things I do to avoid this.
I use BR10ECS plugs as I do a lot of high speed running on lakes ect[this was the original plug for the 98 SRXs] this helps to keep piston crown temps a little lower
When snow/trail conditions are poor for exchanger cooling I don't run wide open much
But ultimately...
When riding with fuel injected 4 Strokes...
"DON'T TRY TO STAY WITH A FUEL INJECTED 4 STROKE ON A MULTI-MILE LAKE RUN!... THIS WILL END IN DISATER MORE TIMES THEN NOT ON A PERFORMANCE TUNED 2 STROKE!"
Just my .02c
Bob
PhatboyC
New member
Thanks for your input guys. Funny the 4 stroke comment. I will keep it under advisory but I have a hard time to say no at a once in a while friendly race. Which around here is all never ending river and lakes.
This piston was on the opposite of the clutch side, magneto side.
I find it strange that the other two piston are normal. Wouldn't this eliminate some of the possible causes listed?
When you guys say crankcase seal is it number 10 in this pic? If so I already planned on buying a new one. Same goes for head gaskets seals and reed valve gaskets.
This piston was on the opposite of the clutch side, magneto side.
I find it strange that the other two piston are normal. Wouldn't this eliminate some of the possible causes listed?
When you guys say crankcase seal is it number 10 in this pic? If so I already planned on buying a new one. Same goes for head gaskets seals and reed valve gaskets.
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staggs65
Moderator
no thats your base gasket.
staggs65
Moderator
numbers 25 and 26 here. (the ones on the crankshaft ends there is also a 25 in the middle of the crankshaft which appears to be mis-numbered)
when you look at your engine where the crankshaft sticks through where your primary clutch is on, you'll see the pto side crank seal around the crankshaft, the other one is behind your stator
when you look at your engine where the crankshaft sticks through where your primary clutch is on, you'll see the pto side crank seal around the crankshaft, the other one is behind your stator
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PhatboyC
New member
How hard is it to change? Do I have to take the crankcase apart? Do I have to then take the crankshaft apart?
If air is coming in from there wouldn't I see oil/gas mixture leaking out a bit?
If air is coming in from there wouldn't I see oil/gas mixture leaking out a bit?
staggs65
Moderator
yes you have to split cases. no you don't have to take apart crank. but a good time to check everything out. regardless of miles these sleds have been around a dozen years now and things start to dry out. my personal opinion is you've got this far apart. go through it right and get a dozen more good years
staggs65 said:
X2
Bob
PhatboyC
New member
Ok I will let my farmer/mechanic know of my new plans. Hopefully it won't cost me to much in labor.
I don't see any gasket in between the crankcase? Any other wear item I should replace down there beside two crankcase seals?
I don't see any gasket in between the crankcase? Any other wear item I should replace down there beside two crankcase seals?
i would say the water pump seals and check all the bearings before you yamabond (or its equivelent) the case back together.
PhatboyC
New member
There is no way to check if my crankcase seals are leaking before breaking the case open? Don't want my piston to melt again after all this work.
tyler440
Member
you can do a leak down test on the crank seals but that involves blocking the intake and the exhaust off, air tight. i have also heard of people filling the bottom end full of gas and checking the seals for leaks, not sure how well that works
What's the prefered Yamabond - #4 or #5 for the crank cases? The book on my viper says #5 but I've heard of people using #4. Does it even matter? Didn't mean to hyjack the thread but if PhatboyC splits the case it will be pertinent later.