94 XLT... ran the best ever just before it died! - Snowmobile Forum: Your #1 Snowmobile Forum

Skid · 01-10-2012, 04:48 PM

Racing around the field the XLT was running great...best it ever had and then lost power and I barely made it home. Cylinder #3 plug was wet and had an aluminum BB wedged between the insulator and plug body. Compression was 95, 95, <50.
Took the head off of it today and couldn't help but notice the two chunks out of the top of #3 piston in line with the intake ports. All 3 pistons have what seems like a lot of slop in the cylinders but the cylinder walls all look clean with no gouges or scratches.
With 5500 miles what are the chances I can get away with just honing and replacing pistons and rings....or, should I just buy oversize pistons and bore it out?
Either way I will tear the whole engine down to replace the outer crank seals and check everything out.

ppolaris1010 · 01-10-2012, 05:04 PM

always the first sign there leaning out and starting to melt pistons when there running the best ever.that sucks with 5500 miles the pistons will be pretty worn and sloppy i would check and make sure the cylinders are not out of round and hone it.new pistons and rings will tighten it back up.you can also get the specs and measure the cylinder to make sure your with in spec my guess is it has nikisil cyliders so boring it is expensive as it will have to be replated.nikisil is pretty tough and doesn't wear out to often.

Skid · 01-10-2012, 06:48 PM

I don't think it was running lean. The plugs are a dirty brown after 40 miles this season and the wet pattern covers most of the top of each piston. I think it's just worn.
If the cylinders are plated then they should be Ok but I'll measure them anyway just to be sure.

aduck · 01-10-2012, 09:21 PM

bummer for sure they always seem to run the best before they die tho

98yota · 01-10-2012, 09:38 PM

I'd be happy with 5500 miles! You'll know more of what you need when you pull the jugs. You might get away with new pistons, pins, bearings and rings. You won't know until you take a peek.

XCRacer440 · 01-11-2012, 01:19 AM

Those 94 Cyls are not nikasil. If the cyls are out of spec or round, bore it and put some new pistons and rings in. Iron cyls are cheap and can be bored multiple times which is nice.
And 5500 miles is nothing for these motors. My parents had 2 sets of XLT's. 2 brand new ones, sold still running good with 10,000 on all original motors, and the next set they sold at 9000 all original.

**RJ Gleason** · 01-11-2012, 04:05 AM

I would also replace the crank outer seals to prevent this from happening again.

jrscars · 01-11-2012, 07:15 AM

Personal observation, "running the best it ever ran" just before it quit tells me you were running lean, Stock jetting on a sled is always a little fat so you dont melt pistons, and its right on that fine line of perfect to slightly lean that a sled will run like a spotted dog, giving you that sensation of, "damn this thing is running good today"

so I second all thats been said about the cylinders and especially the crank seals.

Skid · 01-11-2012, 09:01 AM

Was not running lean...plugs are a dark tan with a little carbon and the wet pattern covers almost the entire top of the pistons. #3 is just plain worn out. The piston isn't burned, chunks were mechanically removed by the edge of the intake ports.

Good thing these are not nikasil since #3 cylinder is oversize .007 and egg shaped about .011. Considering piston wear it has about .022 clearance in line with the intake ports which exceeds the .008 service limit enough to allow the piston top to catch the edge of the port. The other 2 are worn too but not as bad. Looks like I'll be adding some displacement!

The plan is to tear it all down and replace all the seals that I can get to while inspecting everything. Just got to figure out what pistons to buy .... not Weisco

Was probably running the best it ever ran because I built a manometer and took the time to balance the carbs properly after rebuilding them and replacing worn parts but I kept all stock jetting....and....usually things work best just before they break. Isn't that one of Murphy's laws?

**RJ Gleason** · 01-11-2012, 10:20 AM

It was running lean.
You told us that by saying that the plug had melted aluminum in the gap and the piston had eroded by the exhaust port.

Even any water/moisture/coolant that might have gotten in there will cause that to happen.

snoguy · 01-11-2012, 03:42 PM

94's are not nikasil,is that right? Good to know.

Skid · 01-11-2012, 04:48 PM

Quote:

Originally Posted by RJ Gleason

It was running lean.
You told us that by saying that the plug had melted aluminum in the gap and the piston had eroded by the exhaust port.

Even any water/moisture/coolant that might have gotten in there will cause that to happen.

I removed the cylinders today and discovered the #3 piston is missing the skirt on the intake side. The damage to the top of the piston was on the intake side and likely caused by the skirt passing through the combustion chamber as was the chunk of aluminum wedged between the insulator and plug body. There is no sign of heat erosion...just mechanical damage.

I will still replace the crank seals while I have it apart....an ounce of prevention if you will.

Just hoping I don't find any damage to the crank!

jrscars · 01-12-2012, 07:31 AM

Ha Ha, good ole Murphy and his Da** laws !

snoguy · 01-12-2012, 07:06 PM

Well SKiD, at least you'll have her all fixed up an new before the snow flies

jones1995650 · 01-12-2012, 08:22 PM

5500 miles is damn good better then what i got havnt even had 5cm of snow land here ffs

magislander · 01-12-2012, 10:29 PM

Make sure you put the new piston ring pins towards carbs, if not they'll end up f ing up your exhaust ports..happened to me. guy who rebuilt didnt have a f ing clue i guess

Skid · 01-13-2012, 12:49 AM

Quote:

Originally Posted by snoguy

Well SKiD, at least you'll have her all fixed up an new before the snow flies

Yep, before the snow flies NEXT SEASON!

I have another sled to ride so no big deal. Just like this one better.

Debating weather to have the jugs professionally matched to the new pistons ($180) or buy a rigid hone and do it myself ($145 + my time). Never bored cylinders before so I'm sure I would learn something and save $35. On the other hand there's some merit in having someone who's done it hundreds of times fix your hosed up stuff.

Will be ordering .040 over pistons and the gasket kit in a few days....after payday. Also need to come up with a clutch puller so I can get the bottom end out of the sled and torn apart. May as well add some displacement while the work's being done anyway.

Skid · 01-24-2012, 01:29 AM

Got SPI t-moly pistons @.040 over stock and took the jugs and pistons to Advanced Sleeve to have them match bored. Should have it all back and put together by the end of this week.
Now all I need is some snow before the end of the season!!

Should I worry about changing the jets and needle positions since I'm adding about 20cc displacement?

Also need to know if over revving could have caused this engine to eat the piston skirt? Seems my clutch was sticking a bit and would reach 9000rpm momentarily before settling in at 8100 every time you pin the throttle.

**RJ Gleason** · 01-24-2012, 06:32 AM

You may need to go up one jet size, but piston wash and plug color will tell you if it is needed.
Servicing the clutches, particularly the secondary should solve that problem.

Skid · 01-24-2012, 01:00 PM

Quote:

Originally Posted by RJ Gleason

You may need to go up one jet size, but piston wash and plug color will tell you if it is needed.
Servicing the clutches, particularly the secondary should solve that problem.

Plugs were pretty dark with the stock jets. I may just run it for a while and check the plugs and pistons before making that decision.
I agree about the clutches but one problem with servicing the secondary is that I couldn't get it off of the shaft. Seems to be rusted on so I took things apart from the gear case end when I changed the track.