Sled died but not sure why

[Newfee]

so first off I have a 96 summit 670 and im going across alberta beach today (saturday jan 17) and the sled is pulling good going steady at 120 km/h at 8000- 8500 rpm and I slowed down to 80 and after about a few seconds at 80km/h the sled just died the tack droped to 0 and everything was quiet under the hood(didnt sound like just hittin the kill switch or anything rattling around in the motor) just rolled to a stop. I pulled out the plugs and they look fine(cardboard brown), checked for spark and there was lots, checked fuel seemed fine, held my finger over the sparkplug hole and lots of compression on the exaust side but not much at all on the clutch side. tried many pulls of the cord and no fire or sputter so i gave up and I got a buddy to tow me back and now im going to pull it apart to see what the pistons have to say. anything anyone can help me look for to help solve my issue please let me know. also I jetted it from 330/320 to 280/270 to compensate for the warm temp

 

[powder junkie]

at first guess i would say u blew a piston. pull the head off and c. or look thro the hole wit a flashlight. did that plug have ne metal on it or was it melted? i had a 700 polaris that once it got good and hot it would stall and wouldnt start till it cooled off. the prob was that the stator was gone. just a thought.

 

[rsaint]

Does your sled have the HAC on it and if it does you dont have to dick with the jetting because it is temp sensitive also so by jetting down most likely will be replacing a piston. Just wonddering the stock jetting was 370 mag 380 pto with aa2 tubes jetting seem low to me with the HAC without HAC 290 mag 300 pto.

 

[Newfee]

the sled dont have the HAC on it anymore the 2 tubes on each carb are just wrapped around the carb and left unpluged should they be pluged? or connected together? per carb? I pulled the motor apart and the clutch side pistion was scored on each side bad enough to flaten out the rings and leave slight scraches on the sleeve the exaust side lookes fine. so im going to hone it out a bit and find some wiseco pistions and hopefully be ready to go this weekend. Im still lost on why it wouldent even try to start. there was still lots of compression on one side with still 35 psi on the bad side im thinking the sled should have still fired and got me home. any more info on this issue would be great let me know what you think

 

[Pappillion]

Pending the temp, you probably had some water in the lines going to your carbs and then it froze. What temp was it outside. Older fuel or a dirty carb could be the culperate. I had the same sled and had the same problem. Also, check your carb. Unscrew the top and make sure the needle is still connected to the spring. I lost the c-clip that holds the needle in place and it got lodged in the carb. Took two weeks before i found the problem. You got spark, you got fuel, but it won't run.

 

[Newfee]

it was +5 outside and it happen just after filling up with gas. I checked the carbs and everything sems ok. got lots of spark and fuel going to the carb. I am now on the look out for a wiseco pistion kit part number sk1238 if anyone know where I can get one Or who I can talk to to get a good deal on some parts im also looking for a 25 top gear and 43 bottom gear also

 

[SLEDBUNNYRACING]

My 670x had the same happen. Motor ran fine and then it didn't. Compression on one side was good and on other was off slightly but didn't feel like a piston. Tore is down and yep...slight chip off the piston...Rebuild time...lol...

 

[Newfee]

yea but I still dont see why the sled wouldent start and run poorley rather than not start at all any info on this

 

[SLEDBUNNYRACING]

I can't answer that either, mine was the same, had to be towed back. Thought it was fuel but after exasperating all other avenues and pulling it over what felt like a million times we pulled the heads...piston

yea but I still dont see why the sled wouldent start and run poorley rather than not start at all any info on this

 

[Dano670]

before yu rebuild,check pto side crank brgs,buddy of mine had same outcome and found 4 or 5 balls missing from outer bearing and found there way into that cyl. I`d hate to see you do this twice.Would also recommend balancing clutch if in fact the bearings are gone.

 

[powderpusher]

Piston will cause the problem as when hot your compression would have been lower,you can also check with randy at RPM POWERSPORTS in whitecourt for the parts you are looking for as he is pretty decent on his prices and he may even have a good set of used gears kicking around

 

[Zar]

My 670x had the same happen. Motor ran fine and then it didn't. Compression on one side was good and on other was off slightly but didn't feel like a piston. Tore is down and yep...slight chip off the piston...Rebuild time...lol...

Sledbunny

My friends 900 Cat did the identical thing in Millage on the week end. We were able to get it started and it would idle but no power . It would burn real rich . The thing that baffles me is that it ran crisp and then instantaniously very poorly. We checked the compression and the compression is 120 on Mag and 105 on PTO. My friend did say that the EGT said he was at 1350 F on one of his pulls up a hill earlier in the day but no pop or anything obvious to indicate a pistion failure. We checked for spark and there is plenty of spark I was just curious on your comments on how subtle a piston failure can be. I am more familiar with piston failure that it is no doubt that piston blew up. We looked thru the spark plug hole and we can't see anything wrong. I can't help but start looking at fuel problems ( like a stuck needle ). Would a broken reed make the enigne run rich ?

 

[Summitric]

sledbunny

would a broken reed make the enigne run rich ?

670x doesn't have reeds, it has rotary valve.....

 

[Culvert]

Ric.. I think Zar was refering to his friends 900 cat. I cant remeber all the sysmtoms of broken reeds. But I would think it would be rich as it wouldnt be closing, thus sucking fuel in through all the piston strokes.

 

[Modman]

Sledbunny

My friends 900 Cat did the identical thing in Millage on the week end. We were able to get it started and it would idle but no power . It would burn real rich . The thing that baffles me is that it ran crisp and then instantaniously very poorly. We checked the compression and the compression is 120 on Mag and 105 on PTO. My friend did say that the EGT said he was at 1350 F on one of his pulls up a hill earlier in the day but no pop or anything obvious to indicate a pistion failure. We checked for spark and there is plenty of spark I was just curious on your comments on how subtle a piston failure can be. I am more familiar with piston failure that it is no doubt that piston blew up. We looked thru the spark plug hole and we can't see anything wrong. I can't help but start looking at fuel problems ( like a stuck needle ). Would a broken reed make the enigne run rich ?

Yes a broken reed will make things run rich but doesn't account for the low compression. Sounds like a broken ring maybe. Compression is low and running rich. High EGT reading could have been a symptom of it running rich and burning fuel in the pipe. Yank pipe and Y-pipe and look at pistons to see if you can see anything.

 

[powderpusher]

it is quite possible that a read could cause that problem as i do beleive that a broken reed will acually cause you to lose some compression on the cylinder that the reed is broken on as it no longer has a proper seal on that head and could cause compression loss and that would be the first thing i would check is the reed on the side that has low compression as the reeds are the cheapest fix before you have to start doing internal repairs if that is not the problem then id suspect a ring is starting to heat seize on that hole

 

[Zar]

it is quite possible that a read could cause that problem as i do beleive that a broken reed will acually cause you to lose some compression on the cylinder that the reed is broken on as it no longer has a proper seal on that head and could cause compression loss and that would be the first thing i would check is the reed on the side that has low compression as the reeds are the cheapest fix before you have to start doing internal repairs if that is not the problem then id suspect a ring is starting to heat seize on that hole

I am curious about the broken leaf on a reed valve - does it get blown out of the exhaust or does it sucked in to the crank case and beat the beat the crap out of the bearings , crank etc. ?

 

[powderpusher]

in most cases it goes out the exhaust havent found any in the crank cases of any of the sleds that ive done the reeds on yet to date

 

[rmk mod]

i have just reacently pulled apart a sled engine for a guy and he broke off a reed last year, and thean replaced the read valve thinking the old one would have gone out the exhaust. Not so, when i pulled down the engine i found the missing read valve and it took out the bottom end. now its a complete overhaul.