I have 97 Indy trail touring with 7000km (5000miles).
Last week, it blew a piston

http://www.stewartchurchill.com/piston1.jpg
http://www.stewartchurchill.com/piston2.jpg


I am not sure why it happened, or what to do. A friend was using the machine, and I understand he was trying to pull a heavy load at he time. I had replaced the piston two years ago when it broke its skirt. That makes me think there is some piston slop, but I don't know if that caused this.

As you can see, there is some plating on the cylinder, and that makes me wonder if I need to replace the cylinder.
I can get a replacement cylinder (1) with about 2700KM on it for around $100.

As well, I am wondering if I should rebore the cylinders and go with oversized pistons.

I'm not an expert on this but from what it looks like the intake side melted down (I can't quite tell from the pics but it looks like the intake side) from a lean running condition somewhere in the intake. If the exhaust side were melted it would more likely be a massive exhaust hole/leak very near the engine. In any case, way too much air got in there and it's like blowing on coals. The scoring is from where the piston crown and ring expanded beyond tolerance right in that spot while it was overheated. So between the burning/melting from the lean running and the extra friction at the port and sleeve from being overheated, that's what you are left with when it quits running. That's what it looks like to me.

So you might want to check for the cause before you run it again, or it might happen again. If it melted on the exhaust side it would pretty much have to be either a loose header or a big hole or crack in the header. My Indy 500 LC had a cracked header, they are hard to see with the naked eye so inspect carefully at the seams. Intake side could be a lot more things, off the top of my head: Lean jetting on any of the circuits, or a clogged or partially clogged jet, airbox modifications or leaks, "boot" or "Flange" leaks and cracks (the rubber things that connect the aribox, carbs, and engine), loss of primary compression from either a seal or base gasket problem, or even loose base bolts as I unfortunately experienced this year. There are others. Anyway, you may be aware of these possibilities but I'm just throwing it out there.

My first thought was, it's spring and you're running a fanner in warm weather. This doesn't really look like a simple case of cooling failure but I've never worked on the fanners, and I haven't seen enough cases to be the last word on this. But maybe that will help. The cylinder could be resleeved, I believe. There are a lot of options on how to fix it, I have no idea which would be best for you, hopefully someone else can opine.

hi,

thanks. The blown piston is on the left side of the engine, and it was on the mufller (outtake) side, not the intake.

there is some more damage just below the top of the piston, but I couldn't get a pic of it.

That appears to be a general overheat, meaning that the cylinder was running hot - too hot- for a period of time causing the edge to wash off. That looks like a rather unusual, or less common, failure for that engine. Typically, more of them will stick a ring as they get hot and then failure as the ring scores and then piston melts and scuffs.

In your case I don't think you have a slop problem there. 5000 miles is not a lot unless that engine has been *abused* and yours looks like it still shows original hone lines so cylinder wear is not likely a big problem yet. There are other things like whether the cylinder, rings, and piston are actually working (sealing) in like new condition. Since that piston was replaced, it is possible that the cylinder was not returned to pristine condition. I know many folks simply drop new pistons (and rings) into and engine and go with very little thought to the cylinder. The factory manuals clearly state that new rings need to seat properly. (Not saying this to scold as it may have been done anyway.) My point is that if the cylinder was not perfectly clean and smooth again - and new rings not allowed to seat properly, the engine may have had an ever so slight leakage problem which wouldn't normally matter until it got under load, and perhaps a continuous, steady condition, for a period of time. (That was certainly more than a 10-15 second crown melting type lean condition IMO.) So, this side may not have been "pulling and purging" quite enough - lean, but not the usual air leak/inadequate fuel leanness; more a slight starvation of both.

The other thing is that it is on the PTO side of the engine which also runs just a bit warmer since its cooling comes off the fan after being pre-heated by the mag cylinder.

IN this part of the world, most of those older fans are used up/worn out. However, when they were still around, they were used as work machines a lot and pulled sleds and loads of considerable weight. IOW the engine is capable. Judging from your screen name you may have the sam edeal where you are. In any case, pulling loads does require a different sort of driving technique which perhaps the driver wasn't aware of - or didn't have the engine savvy to realize that the engine was being loaded too much.

I suspect you can repair that cylinder without too much trouble. It may clean right up with a rigid hone if you can access one. OTOH, being able to get a little used one so cheap may be another good solution. In either case, make sure you get the cylinder and rings back to like-new in their mating. Also, since this is a second time failure, you might consider going through the whole engine and changing crank seals and and all gaskets. It hurts to spend money when it doesn't seem necessary. Then again, it can be cheaper in the long run. And those old motors were very good, reliable motors so the service it can still give you will probably be worth it. 5000 miles is very low mileage, especially for a 10 year-old engine. (And if you do use it for a lot of pulling, you may want to gear it down just a bit more - one or two more teeth. I know the touring already has been down-geared just a bit compared to its shorter tracked version.)

Thanks,

that is useful advice.

the cylinder is " from a 1993/94 500 Indy Deluxe, will fit many other sleds, Model EC50pm-03 488cc ".

The owner claims this will fit my 97 indy trail touring, but the part numbers don't seem to be exactly the same.

can anyone tell me if this will work? or am I better avoiding it?


P.S. I live above the arctic circle on Baffin Island.

I know the part numbers are different on the two machines: the 93 Indy [Trail] Deluxe and the 97 Trail Touring. (The 500 is a liquid.) If your pics show the worst that you have in your cylinder, I think I'd stick with it since you know it is the right one. (Though I suspect any other EC50PM-03 would work as well - I'm not sure though.) If you have the means locally, have it honed (and get that aluminum out of there.) If not, send it out and have it done, even if it means going .010" oversize. You can run standard and over in different holes on the same engine without any trouble whatsoever. (I'm not advocating it, but I have oversized my own cylinders on occasion with the Amocco hone Polaris sells. You do need to keep everything true but it has worked for me.)

Looks like your crankseal(s) is bad, is a possible source why you blown a piston. From the looks of it. I had that similiar thing to happened to me with my old '89 Indy 500 caused by a bad crankseal. WL

http://www.polariswatercraft.com.au/pistondiagnosticguide.htm