It's bad....

[BeartoothBaron]

So, not the start to the season I wanted. I finally got out riding recently, and everything seemed normal. The first indication of trouble was after about five miles trail riding in and six to eight miles of playing around. It was a little hard to start, and didn't idle quite right, but didn't seem like anything major. A bit later, in a climb, it started cutting in and out if I went wide open - not like dying completely, more like I was dropping back to half throttle, and back in. I thought maybe it had something to do with the gas, so I switched to eth mode, but it only got worse, so we limped back in. Never a code or strange noise - about the only thing I noticed earlier on was it would hesitate just a half second from a dead stop, but it's done that occasionally as long as I've had it.

I got it home and took the plugs and exhaust valves out. The PTO side was sticky, and when I got a light in the port, I could see damage to the piston. So I continued far enough to get the head off, and sure enough, I've got a busted up piston, and worse yet, the bore has chunks broken out of it, I think all around the exhaust port. But the biggest chunk of broken piston is on the opposite side; I suppose one caused the other. It doesn't look like oil starvation or a lean condition - other than the obvious damage, the piston looks much the same as the other. I keep a pretty close eye on oil consumption, and it seems to have been feeding right. One other interesting thing is that there's not a mark on the head stuffer; I was expecting to see it all pock-marked from chunks of aluminum flying around.

Some history: it's got an Indy Specialties long block. 2012 Pro RMK, 163, all the upgrades you'd want for durability (like an extra cooler, Doo thermostat). I'm not sure how many miles, but I think around 1500 miles on the motor. It's always run well, other than being a little hard starting. I've never put anything but ethanol-free premium in it. For better or worse, what I've been doing in the off-season is storing it full with Sta-Bil, and started it up now and then over the summer. I won't call it ideal, but it didn't seem to be a problem in a couple years with this sled, or with the old 600.

So, what caused it, and what's the best solution? I want to fix it right, but at the same time I'm not in the best position to be dumping a couple thousand into it. I also wonder if there's something I need to be fixing beyond the mechanical damage, or if it looks like a locating pin failure or such. Of course, it has to happen at the absolute worst time to get anything fixed on a snowmobile. At least I can handle tearing it down and all. Just not where I wanted to start the season; I guess the old 600 is going to get some action again.

 

[xpturbo600]

Sounds like you detonated the motor. Either from a lean condition in that cylinder (bad injector) or you put bad or low quality gas in it. You assume you put good fuel in it, but an idiot may have put the wrong fuel in the wrong tank at the station. Detonation doesn't have to be catastrophic to destroy an engine. It just has to break a ringland on a piston.

I experienced a similar subtle hesitation on a turbo 4 stroke sled with forge pistons. I scoped the motor after the ride and found it seized the ring in the ringland and scarred the entire cylinder. I fixed the hard parts and never had another issue.

Regarding what to do...call the builder and send the motor back.

 

[dgiles]

Sounds like you detonated the motor. Either from a lean condition in that cylinder (bad injector) or you put bad or low quality gas in it. You assume you put good fuel in it, but an idiot may have put the wrong fuel in the wrong tank at the station. Detonation doesn't have to be catastrophic to destroy an engine. It just has to break a ringland on a piston.

I experienced a similar subtle hesitation on a turbo 4 stroke sled with forge pistons. I scoped the motor after the ride and found it seized the ring in the ringland and scarred the entire cylinder. I fixed the hard parts and never had another issue.

Regarding what to do...call the builder and send the motor back.

Send the motor back to the builder, why? I hope not for expected warranty.....

 

[BeartoothBaron]

Yeah, well outside any warranty. The motor is marked as having been built in Oct. of '15, although my understanding was that the sled wasn't rode a lot before I bought it in '20. I will definitely see about having Indy Specialties fix it. I hoped having a professionally built motor would mean less likelihood of a major failure (obviously I expected to be doing the top end at some point). I still can't complain though: I've got two seasons in it so far, and it was still a good deal even with this.

 

[volcano buster]

I'm no motor guru, but is the aluminum melted and forced out of its natural state?

 

[PSI 800]

Looks like it leaned out for sure, check injectors, change fuel filter, make sure fuel pump is providing proper preasure

 

[HECKS]

Sh!!!tie ! Not a lean condition, piston crown is covered in oil. What does the PTO exhaust valve look like ?

 

[spoon]

Looks like locating ring problem and gap caught the ports. Teardown will tell. Could have been a faulty piston. Seen this before and hard to tell root cause sometimes.

 

[Ultrasauras]

Pro crank seal/ bearing

 

[BeartoothBaron]

Well, I finished tearing it down, and I'm leaning towards a locating pin. I'm not positive, but I can't see anything to suggest a lean-out or oil starvation. The top ring on the PTO side wasn't just broken, there was only a third of it left. The locating pin on the bad cylinder looks beat down; might be hard to tell from the pictures, but take a look. Second picture is the good piston; third is the bad There's also an indentation in the PTO cylinder near the top, right in line with the locating pin.

 

[xpturbo600]

You shook the motor, breaking the ringland (detonation). The pin issue likely occurred after damage to the ringland was already done. There is no head damage, so the issue happened on the exhaust stroke. Repair the mechanical issues and check the injectors. A slight lean condition with low octane/bad gas will cause that problem.

The reason I said to call the builder is because you need to ask him why he thinks it came apart, giving him the opportunity to assess his work. Also, ask if the piston needs balanced to the rotating assembly. If so, what weight should you target for the new piston.

Like was said above, replace the PTO crank seal. That is someone who has dealt with that type of issue before.

 

[BeartoothBaron]

I'm not saying it can't be detonation, just that the sled's never thrown any code, let alone trip a det warning, or given any other indication. I do believe the ring moved first, snagged a port, and that's what broke a chunk of the crown. That could have been caused by it running just on the edge of detonation - too little to trip the sensor - resulting in the pin moving gradually until the ring could slip past and wreck havoc. I'm going to check everything over either way: fuel pressure, injector spray patterns, and replace the PTO seal. I'm not sure if you're referring to having seen this on a Polaris engine, but locator pin problems are endemic on Polaris engines that see long WOT runs, going all the way back to the Dragon, and continuing to the 850 (just saw a report of one taking down an 850 at 300 miles). I'm not one to hold the flipper to the bar for miles on end - I'm probably middle-of-the-road on throttle use. Of course, the pin could have moved enough to start the process before I even got it, and it just took hundreds of miles of the ring bouncing against it before it got loose.

I called Indy Specialties a couple times yesterday, but wasn't able to get through, so I left a message; will email them too. I'm pretty sure the cylinder is fixable, and that's going to be a lot cheaper than a new one. The trouble is, anyone who specializes in snowmobile work is swamped right now. I was able to check in with SLP: they don't do such repairs in-house, unfortunately, so they said probably four weeks. I'm not sure if Indy Specialties does repairs in-house. I've heard good things about Millennium Technologies, and I'll consider sending it there if they can turn it around reasonably soon. Otherwise, I'll be looking at an exchange, which probably means I get peanuts for my core, even if it's easy for them to fix. Finally, on the pistons, I'll probably use Polaris pistons again. They seem to give the best results, but there's the known issues with the locating pins. It's the kind of thing you'd expect from aftermarket stuff; unfortunately, what I've gathered about aftermarket pistons over the years is they tend to seal worse, need replacement sooner, and be more prone to catastrophic failure. Still, if anyone's used aftermarket pistons long term and had good results, I'm all ears.

 

[ditch1000]

Wossner Pistons..
Used them on my last 2 Polaris sleds and they have been awesome!! End gaps were perfect both times on the rings..

 

[BeartoothBaron]

Sh!!!tie ! Not a lean condition, piston crown is covered in oil. What does the PTO exhaust valve look like ?

The EV had a little damage to it too - just the part that faces the piston - but otherwise looked about the same. The pistons don't look exactly the same on top, but that could just be from the PTO piston not firing and getting washed down as a result. It had at least five miles of running after the piston blew.

 

[xpturbo600]

Also look very closely at the jugs, you may have a hairline fracture in the jug that opens up under high thermal load, leading to lean conditions at WOT. The fracture can be so slight that you won't see it just glancing at it under low light. Get a really bright light, and maybe a black light, and really inspect the entire cylinder and ports for each jug. I have seen fractures and leaky seals cause the stated issues on several Polaris engines.

It is interesting the ecu did not show a code, but that isn't surprising. There a several reasons why it wouldn't show up if you read the ecu at a later time. I will forgo that explanation. The trouble with 2 stroke motors is that they rattle quite a bit from the factory and a lot of clattering comes from the clutches. So, to actually run a det sensor requires one to isolate a specific sound frequency identified as knock or to raise the knock sensitivity threshold in the software before the ECU takes action to protect the motor. Most ECU strategies resort to the latter because the alternative doesn't work well in the lab. Thus, it usually takes a pretty strong detonation event/signal to trigger the factory knock sensor.

 

[HECKS]

^^ Makes a lot of sense. Wouldn't hurt to check crank runout, as it could be out of spec (0.0025") and vibrating PTO side

 

[BeartoothBaron]

I've got one last picture of the carnage. It's hard to tell what order things happened in, but a piece of the ring was definitely scrubbing against the exhaust port for a while. I think I finally have the parts here or moving my direction in time to get it together and take it to Island Park next week. Hopefully everything goes together right and it runs good off the bat. It's kind of crazy how long it takes to get anything done this time of year. The cylinder took a whole four weeks from the time I placed the order. I'd asked for them to exchange it if they couldn't turn it around in a week or so, and "no problem" as long as the core is good. I sent it to them the following week (I was out of town), and it's only when I call them to check on it that I find out they won't exchange it because it has Indy Specialties markings on it. And it doesn't seem they put it in the queue based on when I put in the order. I also dropped the clutch and shock off to be worked on in Cody, they said they were a couple weeks out, so I asked if they could work it in sooner, and they said they could probably get to it earlier since it was on hand. Only this week have they started working on it; they hadn't even taken a cursory look or ordered parts yet. Sorry for the griping; it's just a reminder of why I do as much as I can myself.

Anyway, I'm prepping things to go back in, and took the opportunity to clean out the engine bay. I mostly used engine de-greaser and hot water, with some scrubbing with a brush. It definitely looks better; I'm sure it'll be back they way it was this time next year though... I also checked the crank runout at the PTO side: it showed .001, maybe a hair more, if I'm measuring the right spot. The FSM says "first taper after bearing flat," so I assume that means right up against the radius where it transitions to a taper. Going out closer to the middle of the taper shows around .0025, maybe a little over. So it's not perfect, but is well in spec if I'm doing it right, so not worth messing with. Side note: last time I checked my old 600, it'd barely move the needle... why can't they all be like that? Anyway, the cylinder comes Tuesday (apparently Millennium just threw it in the mail, after they said they'd contact me about shipping options), so it's going to be a full day to get it together.

I've got the Wossner piston set on hand along with a bag of other new parts to throw at it. I'll definitely verify the piston-to-cylinder clearance, and the ring gap. On the ring gap, the Wossner instructions are a little uncertain. They have three specifications for ring gap per inch of bore (NA - .004; NA racing - .0045; turbo - .0055, and add .001 for the second ring). That would mean a .014 end gap; the FSM gives a range of .017-.025 and no difference for top or bottom ring. It really doesn't make sense to me that the top ring would have a smaller end gap than the second. The top ring will be hotter, and if anything, should have a bigger end gap - to my mind. Unless I hear or find something different, I'll probably shoot for just under .020 for both...

 

[BeartoothBaron]

One other quick thing on this: I've only found two things off in tearing things down. First is that the alignment marks were off on the clutch. The cover and spider were aligned, but a turn off from the outer sheave. The next is that the spring on the oil pump itself wasn't engaged. It looked like that might have been causing the arm to hang up and not go back to the stop, but if so, I would have been getting too much oil, not too little. The oil pump has been turned up since before I got it, and the arm wasn't over center or anything.

 

[BeartoothBaron]

So, it was a rush job getting everything back together, but I did, and she seems to be running well. I had to burn the midnight oil, and ended up missing most of a day of riding at Island Park, but at least I seem to have done a sufficient job. Time will tell... Anyway, I was expecting it to be a little finicky for the first few runs, but once it fired off, it was like nothing ever happened. I did three warm-up runs, with about two hours of cool-down in between. It would probably have been better to allow more time, but it was cold and super windy, so it was pretty well cooled off between runs. Then I did a quick run around to get another heat cycle and a little more pressure on the rings before I rode it.

Incidentally, I couldn't find a firm spec on the rings. They checked out at around .015 out of the box. I found a couple posts indicating that was too tight, plus Polaris's spec is larger. I also don't know what's up with Wossner's bigger spec for the second ring, but I figured better safe than sorry on that. What I ended up doing was taking the recommendations for forced induction, which came out to .018 for the top ring and .022 for the bottom, so I set them at that. There's probably a magic number that gives you the best sealing without being too small and causing the ring to bind, but I'm not interested in digging for that. Piston wall clearance also seems to be nearly perfect: .0055 is the spec on the box; my .005 feeler gauge felt snug, but .006 would bind (obviously, I didn't push hard on that).

So far, it runs great. The clutching is off for sure. Thank God I picked up another clutch, because some clowns did nothing with the one I left to be worked on, then told me it'd be >$600 in parts alone to rebuild it... And a new core is $700... Anyway, I had to throw it together, and switched belts because the Gates 47C4572 that I like to run on both my sleds is wider; thankfully, I had a 45C4553 that had the right side clearance. It feels strong, and even though I put more weight in (63g currently; I switched to SLP Mangnum Force that I'd been running in my old sled), it seems to overrev if you go wide open but don't do it gradually. I think it's hitting the rev limiter, because I can get to WOT if I ease into it (and it's overrevving), but it'll give you a split second of go then cut back otherwise. Maybe that "new" clutch is sticky, although it looks good; secondary seems good too. No codes or anything on that; also, I've been running it in eth mode with 50:1 premix.

One last concern is that the PTO rod bearing side clearance is too wide. The FSM gives up to .0295, and mine measures at .034. That makes me think it might be worth sending it back to Indy Specialties; hopefully they could true it without having to spend a ton of money. It might not be that big of a deal, and I'm going to chance it the rest of the season, but it doesn't seem worth taking any more chance than that. I just hope it's possible to pull the engine apart from the bottom: it'd be nice not to disturb all those new top end seals I just put in.

 

[Sheetmetalfab]

If you send it to indydan he can freshen up the bottom end. (Likely the top end will get checked over regardless)

Pro ride chassis 800 rmk’s are prone to low level detonation which WILL make the locator pins fall out.

That’s what ate your motor.

The detonation can come from many causes.

Failing injectors are suspect.
Poor fuel quality can also happen to anyone.

After rebuilding or being involved in around 9 800cfi engines.

The oem 2015 pro pistons keep the locator pins and tolerate poor fuel the best. (They are really hard to find these days)