Advice for rebuilding blown 97 XLT engine - HCS Snowmobile Forums

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Old 02-05-2010, 09:25 PM   #1 (permalink)
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Hello guys, I am sorry to report that after 13 years and 7000 miles of trouble-free sledding, my 97 XLT burned a hole in the PTO side piston. I was driving along at about 70 mph with the temperature at about -20c. The sled died as if the kill switch was hit. Started up after a minute, but ran rough. Took plug wires off one at a time and the PTO cyl wasn't doing anything. Plug from the PTO cylinder had a nice aluminum paint job on the electrodes, but no large chunks of aluminum. Have a small 1/4 inch hole through the center/ top of the piston. I am hoping there was just a "dusting" of aluminum and no pieces to worry about in the bearings.

I haven't determined cause yet - I assume an air leak - the carb intake boots were changed last year, and I had sprayed carb cleaner on the PTO side crank seal with no change in RPMs, so assumed that seal was okay. I suspect that seal let go. Or possibly cylinder base gasket? Could be bad gas, but I always add isopropyl gas line antifreeze with each fill. What's your best guess?

Now, never having had to open the engine, do you have any words of advice? What is the easiest way to replace the seal(s)? Do I need to separate the crankcase to replace the seal? Should I replace both crank seals ( I assume yes, especially if I have to crack open the crankcase)? Is it necessary to replace the crank end bearings?

Can I replace the one piston only? How do I know if the cylinder needs honing/boring? (if there is no obvious gouging in the wall). Any special tools needed, or tricks to follow?

Thanks for any advice you have for me.
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Old 02-05-2010, 10:21 PM   #2 (permalink)
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QUOTE (GeeWiz @ Feb 5 2010, 09:25 PM)
Quote:
Hello guys, I am sorry to report that after 13 years and 7000 miles of trouble-free sledding, my 97 XLT burned a hole in the PTO side piston. I was driving along at about 70 mph with the temperature at about -20c. The sled died as if the kill switch was hit. Started up after a minute, but ran rough. Took plug wires off one at a time and the PTO cyl wasn't doing anything. Plug from the PTO cylinder had a nice aluminum paint job on the electrodes, but no large chunks of aluminum. Have a small 1/4 inch hole through the center/ top of the piston. I am hoping there was just a "dusting" of aluminum and no pieces to worry about in the bearings.

I haven't determined cause yet - I assume an air leak - the carb intake boots were changed last year, and I had sprayed carb cleaner on the PTO side crank seal with no change in RPMs, so assumed that seal was okay. I suspect that seal let go. Or possibly cylinder base gasket? Could be bad gas, but I always add isopropyl gas line antifreeze with each fill. What's your best guess?

Now, never having had to open the engine, do you have any words of advice? What is the easiest way to replace the seal(s)? Do I need to separate the crankcase to replace the seal? Should I replace both crank seals ( I assume yes, especially if I have to crack open the crankcase)? Is it necessary to replace the crank end bearings?

Can I replace the one piston only? How do I know if the cylinder needs honing/boring? (if there is no obvious gouging in the wall). Any special tools needed, or tricks to follow?

Thanks for any advice you have for me.[/b]
Sorry to hear about the burn down. Sounds like a textbook crank seal leak to me. You'll have to completely disassemble the engine including splitting the case in order to change the seals. The seals have a rib around them that locks into the case halves to prevent the seals from blowing out. While your in there you can check all your crank and rod bearing thoroughly to check and see if any piston debris got into them. There is no real tips or tricks to taking it apart. You'll need a good quality flywheel puller and I also recommend a wrist pin puller so you're not pounding on them with a hammer to remove the pins. You should have no issue with just replacing one piston as long as it's a match, if they're currently stock Polaris pistons then I'd buy another Polaris piston. Don't mix and match say..., Wiseco with Polaris, the weights will be different. I'd basically take a good look at the cylinder walls and look for scoring, also check that PTO cylinder and look for any aluminum that might be stuck to the cylinder walls. I personally use a dial bore gauge to check my cylinders and compare the size to my piston OD in order to get my piston to wall clearance. You could possibly find a machine shop locally to check that for you if you don't have the tools to do so. You can also use a 3 arm spring loaded type hone or you can get the proper size FlexiHone ball hone to hone the cylinders. Even if you reuse the stock rings on the other cylinders I'd still break the glaze with a hone. At 7000 miles I think I'd replace all the rings though.
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Old 02-05-2010, 11:34 PM   #3 (permalink)
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Thanks very much for the direction. Do you feel that any bearings should be changed, since I am splitting the case? I intend to flush all bearings out with solvent several times just to be sure all aluminum bits are washed out.
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Old 02-06-2010, 06:20 AM   #4 (permalink)
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dont use solvent, use transmition fluid atleast in a huge bucket. Moove it around and roll the bearing in it.

if your only replacing one pistons its very advised that you re-ring the other two just so you have constant PSI, and wont end up changing them again in a month anyway.

it cost me 35$ a hole to get my cylinders acid dipped, and diamond honed at polaris, It is a much MUCH better job than a 3 way hone ball can doo.

And take your time, and remember no matter what it is its only as good as the prepwork you did.
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Old 02-06-2010, 08:45 AM   #5 (permalink)
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QUOTE (RatRod @ Feb 6 2010, 06:20 AM)
Quote:
dont use solvent, use transmition fluid atleast in a huge bucket. Moove it around and roll the bearing in it.

if your only replacing one pistons its very advised that you re-ring the other two just so you have constant PSI, and wont end up changing them again in a month anyway.

it cost me 35$ a hole to get my cylinders acid dipped, and diamond honed at polaris, It is a much MUCH better job than a 3 way hone ball can doo.

And take your time, and remember no matter what it is its only as good as the prepwork you did.[/b]
I've never had an issue with a 3 arm spring hone or a ball hone. This is a trail ridden XLT not a high HP drag sled. All you're looking to do is break the glaze not hone to size or try and remove any pockets or low spots. If that were the case I'd recommend a Sunnen Rigid hone. If you find aluminum stuck to the cylinder you can get some Muriatic acid and apply it with an acid brush and it will eat the aluminum off the bore and not harm the cast iron sleeve.

And like RatRod said, just clean out the bearings and give them a spin to see if they're binding or making excessive noise. Most likely you'll be fine.
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Old 02-06-2010, 10:01 AM   #6 (permalink)
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As with any burn down or squeaker especially these 600 monoblock motors....you need to check the crank very closely for being out of phase.
Check your carbs also for any icing or water in them.....whether a seal or not you need to know the exact cause of the burn down so it doesn't do a repeat.
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Old 02-08-2010, 05:46 AM   #7 (permalink)
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I've been thru this scenario countless times with customers when I was still doing sleds.At 7000 miles your cylinders are worn.They will be out of round.I WILL NOT rebuild a top end with that many miles unless the customer/buddy will spend the extra $35 per hole to bore it out and fit 3 NEW pistons.Then the crank must be checked for phase and most likely I would change PTO and mag end bearings.Solvent is fine to use to clean out the bearings just oil up well after your done and NO spinning bearings with and air hose.If you walked in my shop with that engine and said just change 1 piston and ring the other 2 and put it back together I would point you to the door.If the sled has treated you well this far doesn't she deserve something back???
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Old 02-08-2010, 08:23 AM   #8 (permalink)
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QUOTE (HSR @ Feb 8 2010, 05:46 AM)
Quote:
I've been thru this scenario countless times with customers when I was still doing sleds.At 7000 miles your cylinders are worn.They will be out of round.I WILL NOT rebuild a top end with that many miles unless the customer/buddy will spend the extra $35 per hole to bore it out and fit 3 NEW pistons.Then the crank must be checked for phase and most likely I would change PTO and mag end bearings.Solvent is fine to use to clean out the bearings just oil up well after your done and NO spinning bearings with and air hose.If you walked in my shop with that engine and said just change 1 piston and ring the other 2 and put it back together I would point you to the door.If the sled has treated you well this far doesn't she deserve something back???
Steve[/b]
You were also at a shop. Shops need to cover there rearend so they don't have a returning upset customer. I worked at a shop also and we'd check everything before we just started boring and replacing unneeded parts. When you're doing the work for yourself you can use your best judgment. Dial bore gauges work wonders, you can check for out of round cylinders. Micrometers also work wonders, you can check your piston to wall clearance to factory service limits. If you're still within the service limit, why start replacing stuff? That seems like a waste of money to me. But when it's customers money, hey who cares right?
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Old 02-08-2010, 10:07 AM   #9 (permalink)
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It was and still is my shop I just turn away more work than I take because I have a full time job and it started small and just grew too big for me.I'm just speaking from my own experience and with that many miles on cast iron bore,,,,there is usually significant wear.Just last week a good friend had another fella throw 3 new pistons in 5000 mile cylinders without measuring the bottom of the jugs.Made it 10 miles.Sent cylinders out,,centre cylinder needed to be bored to .060" just to straight/round it out.For the extra few bucks if you can go .010" your buying pistons anyway with that many miles on it or be prepared for a broken skirt,,,again just my experience.
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Old 02-08-2010, 12:10 PM   #10 (permalink)
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Well that failure was due to not measuring things, that's just silly. Now a broken skirt comes from excessive piston to wall clearance, piston slap will destroy a skirt in no time. Again, measuring everything will verify what needs to be done. Just my experience. Maybe my being a machinist by trade makes measuring things just second nature. If you just walk off the street into a Polaris dealer it's about $90 each for a piston, then you've got to buy rings, wrist pin, circlips, and wrist pin bearings add on top of that $35 for a bore. Now you're looking at $180 +/- PER CYLINDER. That is if you go all Polaris parts. You can get a Wiseco kit for around $400 +/- depending on where you get it from then you need to add $105 to that to bore all 3 cylinders. To each his own I suppose.
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