Best Time to rebuild 900 motors?

[BIGTWIN900]

Sorry I'm taking over, my cousin just broke his crank and now i'm all sorts of paranoid about my motor. has about 2000 miles. all stock except a can and I just bought some vforce reeds to throw on but i'll probably wait now..
any help would be great

 

[RACINSTATION]

That motor is solid. What kills big blocks like that is snapping belts. If you have snapped a belt or a few of them, I would look and redoing the crank. If not, I would do a top end at 2000 to 2500 miles and a crank rebuild around 4000 miles.

 

[clutch]

So I should be nervous with 5500 miles on mine.Still runs like a champ. But it is a backup sled.

 

[BIGTWIN900]

Holy crap are you serious? well I'm hesitant to put my girl through the paces since we blew up 2 sleds last trip. first was the king cat about 2 miles from the truck. towed it back, jumped on the backup and then my dad blew up his m1000. both sleds had around 2000 miles..

 

[clutch]

Yep! Those are all mountain deep snow miles too, not running down the trail miles. It has had pistons a few times, but not because of failures, just maintenance. Heads are cut .010, and a D&D pipe, v force reeds.

 

[diggerdown]

I got a couple 900's pushing 6000 miles each. I did stick the carb top end, so that is new. The other is efi and has never been touched. I'm planning on doing the top end on that one next week, compression is down to 115 psi on it.

 

[BIGTWIN900]

we hardly ever ride the trail. I ride my sled pretty hard and it runs like a champ right now. anything I should be aware of to prevent any motor failure? I know its kind of a dumb question but This is only my second year riding sleds..I'm ADDICTED THOUGH!

 

[KMMAC]

If I may,,, after much thought I think some of the crank breakage can also come from too high of gearing and traction upgrade.. I can remember back to the triple mt, cats and knew of a few of them breaking cranks after going to a longer track.. I know,, they had a slightly smaller diameter crank but at the same time traction is traction and any time you make an upgrade like that and nothing else gets changed something has to give....................

 

[clutch]

If it is a King Cat with the A20 in the powder position, shouldn't be a traction problem. (They don't have any.)

 

[Extreme-One]

900 is a great engine if taken care of... owned 2, one carb and one efi at the same time. I trued the crank and did bearings and pistons and cut the head at 4000 miles on the carb sled. When we tore down the engine everything looked great. Ran the carb sled to 7000 miles. We decided to leave the efi sled alone and ran it to 6000 miles and sold it, never cracked the engine for any reason. One thing I did to both was balance the clutches, made the engine run super smooth.

 

[BIGTWIN900]

If it is a King Cat with the A20 in the powder position, shouldn't be a traction problem. (They don't have any.)

true that. I just went from the A20 to a 2.5 challenger extreme. holy crap what a difference.. and another 1M died today. I don't know what it is but this same spot has killed 3 sleds in two weeks. this one was an 03 mtn cat w/ 2600 miles. so I'm even more paranoid than before. my sled is clutched really well and pulls really hard but with the luck we've been having lately I might just try and baby it a bit more... if I can help myself

 

[BikerPepe`]

Best Time to rebuild 900 motors?

In the SUMMER, of course!



ok, ok... I know. But someone had to do it.

 

[fishtank]

we hardly ever ride the trail. I ride my sled pretty hard and it runs like a champ right now. anything I should be aware of to prevent any motor failure? I know its kind of a dumb question but This is only my second year riding sleds..I'm ADDICTED THOUGH!

Ive had an 03 900 for 4 years and never had engine issues. I was told to always warm the sled right up (5-10 mins at least!) before WOT time.

Also make sure you vary the throttle on the trails. If you sit at the same RPM for too long the engine will burn down (mid range lean). google it

 

[diggerdown]

The biggest issue with the 900 seems to be keeping the crank in phase. If you have a rather violent belt explosion, you can knock the crank out of sync. These things have unbelievable torque for a two stroke and if the belt blows just at the exact moment of a power stroke they will twist the crank out of phase a little.

 

[BIGTWIN900]

We always let our sleds warm up. We pull them out of the trailer and let them run while we get all our gear on. I waited a little longer than everyone else to take off but neither 1M was under huge throttle when they died. we were riding pretty high elevation (10,000). Should we all be running higher octane at this elevation? also the last 1M died after it was bogging down.. and I am aware of the lean spot with the King/mtn cat jets. I'm just supper confused as to why we lost 3 sleds at almost the exact same spot?

 

[BikerPepe`]

I honestly don't know enough to give any decent advice, but if you lost 3 similar sleds in the same spots, the same way... is there a jetting vs. altitude issue you're not properly addressing?

 

[wks]

It shouldn't be an elevation issue. The higher you go, the richer your sled runs. Too rich is much better than too lean.

 

[orange 1]

Maybe a silly question, is there a new fuel supplier in town?? !!

 

[BIGTWIN900]

I know that the sled will run more rich at a higher altitude.. less air etc. but would we need to run a higher octane? does altitude affect the compression?
i'm sorry if these seem like noob questions I just want to understand before I have to drop $ on a rebuild. The gas station is definitely not new, and we were all running gas from the same pump.

 

[diggerdown]

You need less octane as you go higher in elevation. You have less air so you have less compression. The earlier bogging down was a sign a piston was close to sticking. I've never heard of three of these going down like that, but running along easy with them is usually what does them in.