2 cycle engine diagnostic..

[bmwscoot]

OK all you mechanical geniuses, got one for you.

 

This is not an April Fools joke, btw.

 

A guy I work with was up North on a snowmobile trip. His older Polaris sled has a 3 cylinder, 2-stroke, water cooled engine. It has oil injection.

 

He was out running fine when the sled bogged down, and then just quit as if you hit the kill switch.

He tried to start it, but it wouldn't turn over...that is it seemed "tight". The recoil wouldn't budge the thing. So he towed the sled out, and brought it home.

The engine had been using the oil out of the injection tank, and it had not run dry.

So last night he pulled the belt off the centrifugal clutch so the engine was not connected to anything in the driveline. He pulled off the recoil start. He then pulled the head.

The pistons, cylinders and head look fine. When he turns the crank in one direction it still is "tight". When he turns the crank in the other direction, it turns freely.

There are no "bits" laying around. There are no unusual noises when turning the thing over.

If it were a bottom end bearing, why does it turn in one direction, and not the other?

Before splitting the case...any ideas?

[Calvin (no socks)]

I just put a new crank in a 500cc honda dirt bike. It had a siezure. A fellow changed oil brands and asked the sales-fellow how much to put in. The salesman said it can be mixed down to 70/1....He mixed it at a higher ratio than recommended for the bike. Piston ok, rod toast, side to side clearance gone, rollers climing over rollers. It acts like a roller clutch in one direction, and rolls more freely in another...DAMHIK

[big-t]

When he turns the crank in one direction it still is "tight". When he turns the crank in the other direction, it turns freely.

 

 

The only thing I can think of at the moment would be a crank bearing thats coming apart.I have seen them do just that,turn one way, but when its turned the other the loose parts in the bearing jam up.

 

One thing he might want to check is the water pump seal and drive..I had a similar polaris a few years back and it sucked water into the crankcase,dealer rebuilt the engine under warranty and took it for a test ride,only to blow the engine again,before they found the seal problem.

 

Never did tell him I was in excess of 100 when it sucked the seal the first time.

 

Good luck

[BCRider]

I had 2 Polaris triples, a 91 650cc and a 96 600cc, The 91 was known for crank problems. I had a rod bearing and crank bearing go at seperate times. The triple crank just doesn't hold together over time. The 96 was a little better but still did not last for very long. Triple sled motors have gone the way of the Dodo bird now as most are twins.

You could pull the carbs or exhaust manifold and take a look, there are also crankcase drain plugs on the exhaust side of the block that can be removed. Usually unused 2 stroke oil will drain out but you may notice some metal filings in the oil.

Good luck.

[bmwscoot]

One thing he might want to check is the water pump seal and drive..I had a similar polaris a few years back and it sucked water into the crankcase,dealer rebuilt the engine under warranty and took it for a test ride,only to blow the engine again,before they found the seal problem.

 

Hey guys thanks for the input.

I'm liking the water pump seal theory. I'm at work now, and the guy states the head and pistons were almost like new. VERY CLEAN!!

I told him, yeah like they were steam-cleaned, huh?

He's pretty much resigned to splitting the cases now, and having a nice summer project.