base gasket question

Well I took the carbs apart and they were spotless, I took the seats out to check the screens and they were spotless also. Carb boots look great, not sure what else to check, my plan is to raise the needles and how about adjusting the oil pump for alittle more oil?? Thats a good idea or no??
 

More oil will cause a leaner condition. Just setup oil pump to stock specs. Are the carbs stock jetting?
To me I have a hard time telling if there are signs of detonation on piston domes since some marks could be debris stuck to pistons. Almost looks like an outright parts failure.
 
Last edited:
srxguy said:
Thanks for the reads guys, I love reading and learning! I just don't understand how it ran for 10 yrs like a top and now she is melting pistons every other ride! I want to fix the issue and no have to do this again..lol
Click to expand...

In my opinion the quality of fuel degrading over the past years is leading to alot of problems. 3-4 years ago the fuel was actually still pretty decent. Hence the 10 years (6-7 with better fuel) and 2-3 as fuel was crapping out on us. X2 on might have ben part failure. entirely possible there was a chunk of crap floating around in the bottom for 198 miles....finally came up threw and took out the edge of the piston on its way out the exhaust port and the last 2 miles finished it up. Anotther thing to think about is the carb boot loose may not have ben the root cause of last burn down, could have ben poor fuel made worse by loose boot.
 
Devilin AblueDress! said:
In my opinion the quality of fuel degrading over the past years is leading to alot of problems. 3-4 years ago the fuel was actually still pretty decent. Hence the 10 years (6-7 with better fuel) and 2-3 as fuel was crapping out on us. X2 on might have ben part failure. entirely possible there was a chunk of crap floating around in the bottom for 198 miles....finally came up threw and took out the edge of the piston on its way out the exhaust port and the last 2 miles finished it up. Anotther thing to think about is the carb boot loose may not have ben the root cause of last burn down, could have ben poor fuel made worse by loose boot.
Click to expand...
I made sure to look down in the case before putting it back together but I know that does not mean much, The boot fell right off the carb and we were on a lake with a lot of snow blowing over the hood so thats why I thought it was sucking in snow dust, that was my theory anyways. I alwasy run premium in both my sleds all the time, but like u said todays gas sucks! So after not finding anything wrong with the carbs and boots should I just raise the needles up and cross my fingers?????? Not sure what else to do.
 
PTO piston is jetted good
MAG is a bit lean

Center piston looks like piston ring pin that keeps ring from turning come out and ring caught port and ended up pushing to top of piston breaking off a chunk of the dome.

When you put the new cylinder and piston on did you check the ring end gaps?
There is a reason why here do not guess and blow another hole in your wallet.
 
Have you decided whether or not your splitting the cases yet? Crank should be checked out. With sleds age prolly gonna be ready for crank case seals before to long anyways. If your pretty sure clutch alingment and center to center is good you can use a real small drill bit to mark location. Drill a holein the motor mounts and use same bit to line up when re-installing. Clutch tool is inexpensive and good to have anyways. For the time you will spend and some yamabond and crankcase seals you will have alot better luck with those crossed fingers.
 
Yeah, I can do all that and yes I do have clutch alignment tool but my question in the back of my mind is, what caused this to begin with?? If its lean why did it just do it after 4 thousand miles? Like I said, its stock, 91 premium fuel (alwasy) non enthanol, opticool headgasket and it has a rear heat exchanger, running in plenty of snow and running 30 to 40 mph all day on the trails and it happened at the very end of the day...
 
That is definately a lean burn down that occurs when the combustion chamber temp exceeds the melting point of the piston. Hottest part of piston is the exhaust side thats why its melted away down to the top ring.

Vipers have a lot of timing advance in the cruising RPM range at part throttle. The more timing advance a sled has the hotter the piston gets...reducing ignition timing transfers heat into the exhaust.

Low octane fuel increases combustion chamber temperatures and also has little resistance to detonation that can damage pistons and rod bearings.

Water in fuel can cause jets to ice up and lean out the fuel...ethonal fuel usually has fuel suspended in it as it is hygroscopic...really bad for our two strokes.

The exact cause of your centre piston damage is likely a combination of the above items and the perfect conditions for the damage to occur.

There has been a lot writen over the years about Vipers and avoiding piston and crank bearing issues, some you have already done.

Some items that can be done:
-check and elliminate any airleaks
-run oil pump setting on rich end of adjustment...you want to be using at least a quart or litre per tank of fuel
-keep carbs clean
-run premium fuel only
-add a SRX rear cooler for better cooling[helps keep heads cooler]
-add "opticool" head gasket for better cooling
-add SRX base gasket for better cooling
-head mod to even out compression...Vipers heads have varying volume between the cylinders...match all three to the LARGER volume one
-raise the carbs needles
-jet main jets to Yamaha's jetting charts on the conservative side
-run the stock pilots and fuel screw settings

JM.02c

Bob
 
sideshowBob said:
That is definately a lean burn down that occurs when the combustion chamber temp exceeds the melting point of the piston. Hottest part of piston is the exhaust side thats why its melted away down to the top ring.

Vipers have a lot of timing advance in the cruising RPM range at part throttle. The more timing advance a sled has the hotter the piston gets...reducing ignition timing transfers heat into the exhaust.

Low octane fuel increases combustion chamber temperatures and also has little resistance to detonation that can damage pistons and rod bearings.

Water in fuel can cause jets to ice up and lean out the fuel...ethonal fuel usually has fuel suspended in it as it is hygroscopic...really bad for our two strokes.

The exact cause of your centre piston damage is likely a combination of the above items and the perfect conditions for the damage to occur.

There has been a lot writen over the years about Vipers and avoiding piston and crank bearing issues, some you have already done.

Some items that can be done:
-check and elliminate any airleaks
-run oil pump setting on rich end of adjustment...you want to be using at least a quart or litre per tank of fuel
-keep carbs clean
-run premium fuel only
-add a SRX rear cooler for better cooling[helps keep heads cooler]
-add "opticool" head gasket for better cooling
-add SRX base gasket for better cooling
-head mod to even out compression...Vipers heads have varying volume between the cylinders...match all three to the LARGER volume one
-raise the carbs needles
-jet main jets to Yamaha's jetting charts on the conservative side
-run the stock pilots and fuel screw settings

JM.02c

Bob
Click to expand...
Thanks bob, the sled has only ever run premium fuel with no ethanol, carbs are alwasys cleaned, It has the opticool headgasket and a rear cooler on it. I was told adding more oil would lean it out more, this true? When I put it back together I will use the srx base gasket, its a direct fit?
 
Last edited:
srxguy said:
Thanks bob, the sled has only ever run premium fuel with no ethanol, carbs are alwasys cleaned, It has the opticool headgasket and a read cooler on it. I was told adding more oil would lean it out more, this true?
Click to expand...
only if you go way overboard. running 50-40:1 shouldnt hurt anything
 
staggs65 said:
only if you go way overboard. running 50-40:1 shouldnt hurt anything
Click to expand...
Can someone tell me how to richen up the oil pump alittle, I see what looks like an adjustment screw next the the center carb,,,ty
 
srxguy said:
Can someone tell me how to richen up the oil pump alittle, I see what looks like an adjustment screw next the the center carb,,,ty
Click to expand...

That screw you see is the bleeder screw. There should be and adjustment barrel so to speak in the cable. Will have a rubber boot that needs pulled off. Pull the cable (on the pump side) out of socket and measure it. To give more oil make that gap smaller by threading adjuster out.

http://www.totallyamaha.net/forums/showthread.php?t=89312&highlight=gap
 
Richening up the oil pump a little would not have avoided the melt down you had as that would not have been an oiling issue. A litre or quart useage per tank of fuel would help with crankshaft longevity...not your current issue.

To richen up the oil pump you reduce the gap in the oil pump cable when adjusting it per Yamahas adjustment speps in the manual.

The SRX base gasket will just slide right on with no mods...the 2000+ SRXs and the Vipers use the same cases.

If everything checks out mechanically on your sled, no air leaks ect I think your issue was probably fuel and or needle setting related.
 
Another thought...
Check the thermostat...if in doubt buy a new one as they sometimes stick or quit working and your middle cylinder would probably suffer the highest temps if it was acting up. The overheat lights don't come on until the coolant is already very hot.

Also ensure the coolant is circulating through the exchangers...a good time to check your water pump impellar has not come loose and that the shaft is turning when rotating engine.
 
Just want to add to bobs post. Even if you buy a new one check it. Put a pot of water on the stove. Once its boiling use a pair of tongs and stick thermostat in water and make sure it opens. I had a faulty brand new one that had me pulling my hair out. Hadnt ever checked one before that. Now I check every one before it goes in. Havent found a second faluty one yet but only takes a few minutes.
 
sideshowBob said:
Another thought...
Check the thermostat...if in doubt buy a new one as they sometimes stick or quit working and your middle cylinder would probably suffer the highest temps if it was acting up. The overheat lights don't come on until the coolant is already very hot.

Also ensure the coolant is circulating through the exchangers...a good time to check your water pump impellar has not come loose and that the shaft is turning when rotating engine.
Click to expand...
Def going to change the t stat anyways while I have things apart...ty
 
Devilin AblueDress! said:
Just want to add to bobs post. Even if you buy a new one check it. Put a pot of water on the stove. Once its boiling use a pair of tongs and stick thermostat in water and make sure it opens. I had a faulty brand new one that had me pulling my hair out. Hadnt ever checked one before that. Now I check every one before it goes in. Havent found a second faluty one yet but only takes a few minutes.
Click to expand...
Ya thats a good idea!!
 
So I am friends with the guys at a local artic cat dealer and I was there lastnight and I showed them my piston and they told me I better check my oil pump...What do u guys think?
 
You must log in or register to reply here.


Back
Top