1 dead cylinder

[posnick]

i tried that too. it backfired through the carb

 

[timbo]

sounds like rotary valve timing.no vacume to transfer fuel up the port.mabe gear stripped on rotary valve shaft.

 

[posnick]

how do i check that?

 

[timbo]

have to take off carbs and plate with carb boots on it.behind plate is rotary valve. top dead center on mag side rotary valve should line up with mark on block. i have a degree wheel for checkin this.
timbo

 

[posnick]

where do i get my hands on a degree wheel?

 

[99summitx]

There is only one pulse line from fuel pump to crankcase so your ok there. depending how bad the cylinders are I have a set of 1mm overbore Wiseco pistons, rings, wrist pins if you need them, my top end rebuild cost me $650.

 

[Summitric]

there is only one pulse line from fuel pump to crankcase so your ok there. Depending how bad the cylinders are i have a set of 1mm overbore wiseco pistons, rings, wrist pins if you need them, my top end rebuild cost me $650.

should doo the cranks seals and have the crankshaft trued at the same time.....

 

[posnick]

i didnt want to have to pump a bunch of $$$ into this winter. My plan was to make it a summer project

 

[posnick]

let me ask you this Summitric. Why would that cylinder have a loss of vacuum if the compression is still decent? does the compression not have to "suck" in order to loose vacuum?

 

[Summitric]

let me ask you this summitric. Why would that cylinder have a loss of vacuum if the compression is still decent? Does the compression not have to "suck" in order to loose vacuum?

"THEORETICALLY", vacuum is harder to produce than compression........ Eg, why does a car engine produce 135psi compression, but only have 18" vacuum when running......... See? .... so then score in cylinders may still have compression, but the little vacuum created by the engine will be lost through the gouges in the cylinderwalls.........

 

[posnick]

i understand now. it makes sense. I think im still gonna check the rotary valves. i really want to save the rebuild till after the season...but who knows!

 

[posnick]

what if i was to run some of that engine restore stuff...just a thought

 

[Summitric]

what if i was to run some of that engine restore stuff...just a thought

might be worth a shot.... Seen roundy-round cars run many laps with restore in them and a hole in the oil pan and no oil.... Supposed to work good on cylinders..... Just don't think i'd count on it, back 20 - 30kms in the mountains(know what i mean?). If the rave has touched the piston, then the damage is just starting..... Remember that, and it will get worse, afterall damage doesn't correct itself.

 

[posnick]

i spoke to Bill and i will likely bring thr cylinders to him next week. bore, rings and pistons. i will save the bottom end for summer. he seams like a good guy and knows his stuff

 

[Pappillion]

Just a dumb question. With my 670 i had a problem with one cylinder going bad. I found that one needle on the carb had broken off and was sitting in the carb. I didn't find it until i unscrewed the throttle cable part of the carb. the needle was still sitting inside. There is a small retainer washer that holds that pin up and it broke off. The machine still idled fine but once i pressed down on the trottle i had no go. when you look in the carb the needle is still there but it won't function.

 

[Scotty]

Reeds... noone has yet to mention reeds. I have seen broken reeds cause major headaches that are hard to diagnose.

Your compression is fine on both sides. it's a fuel issuse. not cylinder scoring or rings. If your cylinders were gouged you'd have low compression. If your rings were damaged... same result or they would have busted up a long time ago.

got a be reeds. You've swapped carbs from side to side so it can't be the carbs or plugged jets...

 

[posnick]

ski doo dosnt use reeds....i thought.....when i acquired the sled a couple weeks ago the bad cylinder only had a compression of 60 lbs. i had taken it apart with intentions of re-ringing it. there is score marks on the cylinder walls

 

[99summitx]

ski doo dosnt use reeds....i thought.....when i acquired the sled a couple weeks ago the bad cylinder only had a compression of 60 lbs. i had taken it apart with intentions of re-ringing it. there is score marks on the cylinder walls

Skidoo does use reeds but not on the 670, it's a rotary valve.

 

[Scotty]

Still having issues with this 98 summit 670. both cylinders is 135-140. cyclinder # 1 will not fire. I tried everything. i switched plugs and wires. i even thought it could be a carb issue so i switched the carbs around. still no luck. when the sled is running the temperature on #2 is 1100 to 1200 degrees, on cylinder #1 only 200 to 250 degrees. What could be causing it not to fire?

Sorry.. i thought you said compression was good on both sides. As far as the reeds go I may need to educate myself on the 670 rotax.

 

[posnick]

Scotty, compression is good since i put it back together. the sled sat for 2 yrs. it was 60 on one side. after running it a bit it must have re-seated the rings. it is now 135 ish