New to the forum and having Polaris Problems

[Tryingtobeyoung]

High All,

I'm new to the forum (in terms of registering and posting anyway, I've been reading the forum on and off for a little while). I grew up snowmobilling, with my family having machines when I was a kid. Life and career came up, though, and took me around the world. I quit riding right after high school. Back in 2018 I retired and moved back to Northern Utah. I always enjoyed snowmobilling and eventually I bought a couple of older machines and started riding again. It didn't take long for me to realize that things had changed quite a bit in the snowmobile world, and although the machines and style of riding was different, I still enjoyed it. I started to try to become better at it. I eventually decided that the (real) old machines weren't going to cut it for me so I upgraded a little and bought a 2016 Polaris Pro RMK 800. In many ways I was still pretty ignorant of newer snowmobilling information and technology and I hadn't progressed in my skills enough to understand where I wanted to go with this hobby (If I had been more informed, I'd probably have bought a newer machine). At any rate, I've ridden the RMK for about 2 years and it's performed pretty good. This year I decided to go up to Island Park and take a couple of days of instruction at Brett Rasmussen's school. It was awsome, but after the first day, on the trail ride back to the hotel, my machine started acting up. It started to cut out at high RPM, and by the time I got back to the trailer, it started backfiring through the exhaust and idled at 3500 rpm (which wouldn't allow it to go into reverse). I ended up riding one of the school's machines for the second day. Now the RMK starts fine, and runs normal until the throttle is triggered the first time, afterwhich it stays at the 3500 rpm and backfires occasionally. I'm a cetified aircraft mechanic, and I've even spent some time as a mechanic at a powersports dealership (although I did it to learn and I'm still pretty inexperienced with snowmobiles). I thought about trying to tear into the machine an try to fix it myself but I knew it would take me awhile to figure things out and I didn't want to miss the riding this season. I decided to take the machine to the local Polaris dealership near my home. They had a little trouble figuring it out but they're now telling me that the problem is a leaking crank seal which will require them to split the case of the motor to replace (they did give me a pretty reasonable estimate to do the work though).

The machine is coming up on 2000 miles, and I have read that these Polaris 800s often have problems at about this time (needing a top end rebuild and such). I checked the compression on the machine and it's lower than I'd like (about 105 on one cylinder and 110 on the other) but I did cylinder leak tests on both sides and the tests turned out good. My question to the forum is (all of you who are much more knowledgable than I), since the engine will need to be removed to fix the crank seal, would I be smart to go ahead and just do a complete overhaul to the engine, check the reeds, the power valves, replace motor mounts and such? If it were smarter to do the bigger job, I'd probably go ahead and do the work myself but if I was just going to have crank seal repaired, I'd probably have the dealer do the work. Also, I'd be interested in recommendation on where to get a good overhaul kit and such. Any wisdom you all could provide me, would be greatly appreciated. Thank you

 

[PSI 800]

Yes 2000 miles is an issue for most but not all. If your going in there you might as well rebuild the whole motor while it is out of the machine. Way easier to rebuild on a bench than later in the chassis. Use the stock Poo stuff for your rebuild especially the pistons. Indy Dan at Indy speciallies has a good write up on why to use stock Poo pistons.

 

[BeartoothBaron]

If the diagnosis is accurate, I'd agree with @PSI 800: have the top end done while you're in there. The crankshaft is probably ok, but you'll want to check crank runout and look over the bearings. I think it's less of a problem on the 800 HO than it's predecessor, but if it's seen some abuse, been run a long time with a poorly set up clutch, that kind of thing, it's definitely possible that needs attention. It's very simple to check if the engine is out and you have a dial indicator. Other things you'd do while it's apart would be to check the reeds (I wouldn't replace just because), clean and check the exhaust valves, replace engine mounts (they're a wear item, so unless they were just replaced...), clean the injectors, and do a thorough check of the wiring. I'd also agree on using OE pistons. Some of the aftermarket pistons are ok, but I can't say any of them are better than OE.

Going back to the diagnosis, it makes sense, but if it were me, I'd dig a little bit and make sure they did their diligence. I've never done it, but the best way to check for failed crank seals is a pressure test. If that's what they did, then I don't doubt it. On the other hand, I wouldn't put it past some dealers to get stumped, but throw something out there anyway. Hopefully not, but I haven't had a dealer do work on anything of mine in around eight years, and there are reasons... One of the other common trouble spots with these is electrical gremlins. Given your background as an aircraft mechanic, I'd say you have more than enough skill to tackle it yourself (if you want to). One of the best reasons to stick with Polaris is that they are the simplest to work on, and there isn't much you need for special tools for. That said, you know the dealer you took it to better than me.

 

[PSI 800]

I always found to spray some Either/quickstart at the crank seal while running, if rpm picks up you have a faulty seal.

 

[retiredpop]

It seems strange that a crank seal would go out so quickly but maybe due to the backfiring it blew out a seal.
I would check the throttle body adapter boots for cracks. Start the sled and with it idling spray some Quick start fluid at them while wiggling the throttle bodies. If the adapter rubbers are cracked the rpm changes. I had that happen to one of our sleds.