My first trip of the year last weekend to the UP was pretty eventful. I put on 125 miles on my sled last Sunday. It ran good except I was having trouble with it running hot in 1 degree weather with marginal snow getting in and out of town. Monday with 6" of fresh powder everywhere was looking to be a good day. I let my sled warm up for a good 20 minutes. I had no temp issues with the new snow. At approx. 14 miles outside of Newberry I came to stop at a stop sign on the trail. I had just been running 60 - 90 MPH over a straight flat section of the trail with 3 - 6" of fresh powder. When I came to the stop the motor just died. You could not pull the starter cord. Seized motor.
My sled may have turned over 7,000 miles on this last trip. The motor has never been apart. It has always run really good except for the temp light coming on once in a while with marginal snow. When the temp light would come on I would park off the trail in some snow and let it cool down. I checked the compression this fall and had atleast 120 psi in each cyl. I finally pulled the motor apart today. It looks like I may have had a couple issues.
The center piston is pitted. Is this from being lean? The plug looks OK to me. There are some black streaks in it the cyl wall that you can kind of see near the top. The close up of the center cyl. is not real clear, but I think the cyl. is usable. Can the head be saved? It has a few pitts as well.
The bigger issue is that I think I lost a crank bearing. With the cylinders off you can barely turn the crank. It takes a lot of effort to turn it and it wil not rotate completly around.
Anybody have an idea what might have happened? I am trying to decide if I am going to rebuild the motor or scrap the sled out. I suppose I will not know what my total cost for rebulding the engine will be until I see how bad the crank shaft is. G.B.
My sled may have turned over 7,000 miles on this last trip. The motor has never been apart. It has always run really good except for the temp light coming on once in a while with marginal snow. When the temp light would come on I would park off the trail in some snow and let it cool down. I checked the compression this fall and had atleast 120 psi in each cyl. I finally pulled the motor apart today. It looks like I may have had a couple issues.
The center piston is pitted. Is this from being lean? The plug looks OK to me. There are some black streaks in it the cyl wall that you can kind of see near the top. The close up of the center cyl. is not real clear, but I think the cyl. is usable. Can the head be saved? It has a few pitts as well.
The bigger issue is that I think I lost a crank bearing. With the cylinders off you can barely turn the crank. It takes a lot of effort to turn it and it wil not rotate completly around.
Anybody have an idea what might have happened? I am trying to decide if I am going to rebuild the motor or scrap the sled out. I suppose I will not know what my total cost for rebulding the engine will be until I see how bad the crank shaft is. G.B.
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nightmanx1
New member
well if the crank is hard to turn, I would not put it back in till the bearings are changed and do ALL of them. The pitting is from running it on the lean side i would go up one jet size and be done with it.
skidooboy
New member
looks like detonation. don will come on and diagnose as best he can with the pics. i am guessing when you came off the throttle at 90 mph you just chopped it closed, and let her coast down with no more throttle. that is only giving the sled enough fuel to idle with a motor spinning at 8-9000 rpms. you can say it leaned out in those conditions. do you have any mods to the motor at all? tempaflow, jetted down ect...???? no sure about the crank not turning, needs to be looked at maybe split the cases for diagnosis and repairs.
bummer. ski
bummer. ski
chevy2
New member
No detonation there. The pitting is from the crank bearing cage that came apart and was bouncing around on top of the piston. 
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Thanks guys for your quick comments. The motor and clutch are bone stock. As far as I know, the carbs have never been apart or adjusted from new. It has always run great.
I did not close the throttle right after I touched 90 MPH. I think I drop down in the 60's for a period of time as I knew the stop was coming up and I was going to wait for my buddie to catch up. However, Ski you just reminded me that the motor did bog for a second before I backed off the throttle to come to a stop. I was riding on the right edge of the trail were no one had ridin yet and there was a good 4 - 6" of fresh powder. At the time I thought the bog was because I hit snow drift.
It may not be easy to see in the picture, but there is a sharp burr on the center piston on the bottom edge of the wrist pin. I did not see any deep scratches on the cyl wall from this burr. I think the rings are intact on the center piston, but I will look at them again today. Chevy2, I was kind of thinking the pitting could be from a crank bearing coming apart. Although, how would the parts get past the rings if they are intact?
My fear is that since the crank will not turn freely, it is either toast or will need machine work. Any idea on what machine work can cost for a crank?
Thanks, G.B.
I did not close the throttle right after I touched 90 MPH. I think I drop down in the 60's for a period of time as I knew the stop was coming up and I was going to wait for my buddie to catch up. However, Ski you just reminded me that the motor did bog for a second before I backed off the throttle to come to a stop. I was riding on the right edge of the trail were no one had ridin yet and there was a good 4 - 6" of fresh powder. At the time I thought the bog was because I hit snow drift.
It may not be easy to see in the picture, but there is a sharp burr on the center piston on the bottom edge of the wrist pin. I did not see any deep scratches on the cyl wall from this burr. I think the rings are intact on the center piston, but I will look at them again today. Chevy2, I was kind of thinking the pitting could be from a crank bearing coming apart. Although, how would the parts get past the rings if they are intact?
My fear is that since the crank will not turn freely, it is either toast or will need machine work. Any idea on what machine work can cost for a crank?
Thanks, G.B.
Sorry hear about your sled. If the crank will not turn, then it sounds like that is the problem or combination of two.
daman
New member
That sucks...looks like alot of blow by wow...
I also see what looks like foreign matter causing the engine failure, the pieces of the rod bearing cages become hot and molten from added friction caused by rusty crank bearings and the little pieces get up on top of the piston thru the transfer ports, everything thats brought into the engine goes thru the cranckcase then up thru the transfer ports to the top of the piston. The motor was plenty tired, if you look at the pistons the black thats all over then is blow by and what I can see in the PTO side is that little silver spot on the backside near the bottom, thats from the piston rocking back and forth in the bore, because the rings are worn out and the piston loses its stability in the cylinder, they will all be out of spec if you check them. This is a case of proof as to why a compression guage doesnt tell you the correct information as to how good your engine is wear wise. If this motor would have been checked with a leak down tester it would have failed.
I would also be willing to bet that if you didnt fog the engine when you stored it, or keep it in a heated or climate controlled garage that the bearings had small amounts of surface rust on them. The rust comes from the rise and fall of the outside temps, and then condensation sets in and you get water droplets that form inside the engine. The water droplets quickly go to the crank bearings, pitting them. When you fire up the sled the pits and rust scales act as sandpaper if want to call it that and just eat away the races and bearings, and lead to failure. Its best to either fog the engine if left in a trailer or shed, or dirt floor garage/sheds, or even just in the corner of a non heated storage building. If you dont want to fog it, its best to simply pull the oilpump cable apart and run the engine as long as it will run with the oilpump wide open and the sled at a lower rpm like 2000-3000rpm, this floods the cranckcase with oil and it will settle at the crank bearings(where you need it).
I dont think the sled is hardly worth junking or parting it out, with the amount of viper parts out there it could be repaired fairly easy. At worst you need a replacement crankshaft or possibly just some bearings replaced. The engine will need 3 new pistons, rings,circlips, wrist pins, wrist pin bearings, a hone on the cylinders, some new gaskets/seals and a waterpump rebuild kit, all in all not worth junking the sled over.
I would also be willing to bet that if you didnt fog the engine when you stored it, or keep it in a heated or climate controlled garage that the bearings had small amounts of surface rust on them. The rust comes from the rise and fall of the outside temps, and then condensation sets in and you get water droplets that form inside the engine. The water droplets quickly go to the crank bearings, pitting them. When you fire up the sled the pits and rust scales act as sandpaper if want to call it that and just eat away the races and bearings, and lead to failure. Its best to either fog the engine if left in a trailer or shed, or dirt floor garage/sheds, or even just in the corner of a non heated storage building. If you dont want to fog it, its best to simply pull the oilpump cable apart and run the engine as long as it will run with the oilpump wide open and the sled at a lower rpm like 2000-3000rpm, this floods the cranckcase with oil and it will settle at the crank bearings(where you need it).
I dont think the sled is hardly worth junking or parting it out, with the amount of viper parts out there it could be repaired fairly easy. At worst you need a replacement crankshaft or possibly just some bearings replaced. The engine will need 3 new pistons, rings,circlips, wrist pins, wrist pin bearings, a hone on the cylinders, some new gaskets/seals and a waterpump rebuild kit, all in all not worth junking the sled over.
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Thanks Mr Viper for your analysis. It all makes sense. I bought the sled with 4,400 miles on it. I do not think the previous owner fogged the motor for storage. I had planned on doing the top end before this winter as a PM, but I obviously did not get around to do it.
I also did not fog the motor. For summer storage I would clean, grease the sled, and run gas stabilizer through the motor. I stored it in my fully insulated attached garage. I did notice the rust on the conrods when I took the motor appart. I guess I may have to change my ways.
I have a couple more questions:
1)Can I polish some of the pits out of the head?
2) As long as the center cyl. does not have deep scratches and it measures with in specs, it should be OK, right?
3) How do you check to see if the oil pump is operating correctly? Other than a cable check, I did not see anything in the Yamaha shop manual to tell me how to check it?
I realize that i need to tear the rest of the engine down to see what the damage is. Anything else I should look for?
Thanks very much, Brett
I also did not fog the motor. For summer storage I would clean, grease the sled, and run gas stabilizer through the motor. I stored it in my fully insulated attached garage. I did notice the rust on the conrods when I took the motor appart. I guess I may have to change my ways.
I have a couple more questions:
1)Can I polish some of the pits out of the head?
2) As long as the center cyl. does not have deep scratches and it measures with in specs, it should be OK, right?
3) How do you check to see if the oil pump is operating correctly? Other than a cable check, I did not see anything in the Yamaha shop manual to tell me how to check it?
I realize that i need to tear the rest of the engine down to see what the damage is. Anything else I should look for?
Thanks very much, Brett