Those are not factory pistons as 850s are built with single ring .

 

Yes I know, they look to be wossner pistons, it’s defiantly not the first time that this machine blew up. What’s funny is the cross hatches on the cylinder look very fresh but the the date stamped on the cylinder is 2016, pretty sure the previous owner tried honing it, he even said, “I don’t think you can hone these” when I was asking him what parts he thought would need to be replaced. I don’t think that was the cause because one cylinder is perfectly fine while the other is not, anyone know what could’ve made it fail like that?

 

could possibly be a faulty fuel injector causing the one cylinder to overheat?

 

That piston failure is unusual. Seizing like that at the pin bores is not the usual thing to happen. The piston is typically a bit smaller diameter along the pin than it is perpendicular to the pin (at the thrust faces).

I see considerable assembly damage to the pin area on the close-up pix of the side of the damaged piston// those crescent shaped marks. Whoever did this did not have either the right tools or knowledge. It is possible that the pin bore was damaged so badly that the pin did not rotate freely, the pin bore area got hot and seized and that caused the damage.

Pin bore to pin clearance is VERY tight compared to other clearances, typically less than .001". Additionally, the pin bore and pin surfaces are suuuuper smooth.... far, far smoother than anything any of us could polish in a home or dealer shop. ANY distortion or damage to the pin bore is almost guaranteed to cause issues.

So I would start with the premise that the pin bore got damaged by the very bad work there, which caused the pin to seize and the piston to expand in that area.

But don't stop there. It is also possible that the cylinder got dropped and distorted across the same axis. Or the head bolts were overtorqued and distorted the cylinder. Or someone honed the crap out of them for oversized pistons, ignorantly thinking he could get round bores with just honing. What with the crap job on the piston pin, anything is possible, IMHO.

So one important thing to have done is to have the cylinders checked for diameter in all directions and make sure they are round and straight.. all the standard measurements of diameter, taper, and out-of-roundness. Even better, I would strongly consider just replacing the cylinders with new or remanufactured ones, with matching pistons, so you know you have good clearances, round cylinders etc.

In looking at the pix, there is no clear sign of detonation, which is good. But it would be good if you could take close up pix looking down on the tops if the pistons so we can confirm that none of the typical signs of detonation are present. Ditto for pix looking up into the inside of the heads... .i.e., the combustion chambers.

This is just from looking at your pix, and is not guaranteed to be the right thoughts or everything. But the assembly damage around the pins and the seizing at the pin bore area are so unusual that they make this a very likely problem area, IMHO.

 

I forgot to mention that the pin on the damaged piston was very hard to take out, it wasn’t stuck to the rod but the 2 sides where the piston touches it. I watched a couple YouTube videos on removing stuck pins and came up with that contraption (there’s an image of it) of an axle nut socket, a bolt and a nut and used an impact drill to force the pin out, that’s actually what those cressent shaped marks are from. Looking at the head and piston tops i just realized only the undamaged piston top had a film of oil or sludge on it the other piston was clean, the same is true for the head; one side has sludge, the other is dry. So maybe one side wasn’t getting gas or oil. I already have a new cylinder pistons and gaskets on the way, all genuine ski doo parts.


the scratches on the dome of one of the pistons was from the removal process that wasn’t there before I took it apart, actually most weirdly shaped or located scratches are from me taking the engine apart

 

Ah, thanks. I know what that big socket is for LOL. You work on a 4WD.... And now I get the marks... it was not important to keep the problem piston in pristene shape. I need to watch my 'crap job' comments!

Finding that sticky/stuck pin is the reason for the seizure, and the clean-ness of that cylinder is possibly a sign of lack of lubrication so you know to check the oiling carefully. When you assembly the pins into the rods/pistons, there ought to be no wiggle/wobble in the pin and bearing, and the piston ought to rotate smoothly, with no hint of binding, and maybe a tiny bit of drag from the oil film in there.

Detonation can have a scouring effect on the cylinder and piston crown, but there is none of the tell-tale pitting on the piston or combustion chamber from detonation, so that seems not to be the problem. Water in the cylinders can do the same thing: scour and clean the parts. Make sure the air box and all that is properly installed and connected

Good deal on the new pistons and cylinders. Make sure you check and set ring gap properly at a minimum. Also, check your head for warpage. I looked closely at the head pix and it looked pretty good, with no sign of gasket sealing problems, but you ought to take the time to check all that you can.

I am still trying to figure out if it is important, after the seizure, the engine did not seem to run on both cylinders. But that may add to your idea of inadequate gas/oil.

This engine appears to not have had many miles on it before this failure.

 

I am not sure what it is about 2017's, and two sleds with weird engine issues does not a problem make per se, but it does make one ponder.

This makes me stay nervous about my rebuild. Now I will pay very close attention to the piston pins, and make sure that when I have the shop put it back into break in mode they check/adjust the oiling pulses of the pump properly in BUDs.

I have taken the entire summer to do this project. A bit at a time. Focus, determination and patience. I just want to make sure that I give myself every opportunity to do it right. I chose to get cylinders that were properly prepared for my pistons. Their honing marks do not look like either cylinder shown on your (850 guy's) motor at all.

Even the original cylinders I sent in as core were nowhere near that bad. My compression was really low (like 95 both sides). Only solace I had is that at least the engine I am working on has no signs of being rebuilt before, just beaten up pretty good from the PO for the miles it had (~2200).

 

Groucho, are the cylinder wall pix that you show above the new/fresh cylinders going into your engine, or the odl ones coming out? Assuming they are Nikasil coated cylinders, some degree of 'splotchiness' is common. But there do not appear to be any hoing marks in your cylinder pix, or they are too fine to see. Who/what was the source of your new cylinders?

Nikasil cylinders can be honed with the right hones, but we do not know what was done to the OP's cylinders, or if it was done correctly. So using that as a reference may be problematic.

 

nm9stheham—The pics in my first post are of my original cylinders. I concur with you that I also didn’t see much honing on them at all and the Nikasil is splotchy which I agree is normal. To be honest I think they appear glazed over.

IMHO, the OP cylinder pics look like they were honed very aggressively, but like you said not knowing for sure what was done means it’s all speculation.

The new cylinders are currently holding 1/2 of the the bottom end as I am going to seal up the bottom end today, so good pics of their walls will have to wait. I looked at the walls briefly this morning and they show a light hone crosshatch and they’re evenly coated.

The new cylinders are from MCB Performance, same as the reseal kit and HD pistons. 98% of the rest of the new parts are Doo factory parts that I got through Partzilla.

New cylinders from when I received them.

 

Good quality pix, With it blown up, the honing marks are very clear to see. They look good to me for what that may be worth.

 

Yeah that engine looks to have been rebuilt fairly recently, I’ll try to contact the guy that I bought it from and ask him if he still has the old pistons or at least what they looked liked before he put the ones on that I took off. I took the power valves out and they look ok, doesn’t the oil go through them before reaching the cylinder and piston or does the top end get oiled from the bottom end kicking up oil. Another question, will I need to take it to the dealer to put it back in break in mode and to check if all the systems work ok. Lemme know what I need to tune or whatever else before riding it again, I really don’t know much about these so any suggestions would be apreciated

 

Those are your RAVE valve, which are variable exhaust valves. Nothing to do with the main engine oiling, but they look very clean, compared to other pix of RAVE valves posted in this forum. They do receive oil directly from the lubrication system.

This system has an electronically controlled oil pump and the ECM controls the oil flow to and through the crank, and the excess oil at the rod bearings is flung up and and round and oils the cylinders, pistons, and piston pins. So it is not the tradition 2S gas-oil mix type of lubrication.

Each cylinder has a line to the outer crank bearing. These lines are routed on the outside of the engine and have check valves. It is certainly possible that the line to the bad cylinder got pinched or has a leak, or a fitting is plugged, or something is wrong with the check valve, and that side got starved of oil. If that was the case, then the main and rod bearings at that end would be a suspect for damage too. (All of that would be coming apart for me anyway for inspection for issues like the crank, given the engine's recent serious failure.)

BTW, you can find your engine's manual here: Ski Doo Shop Manuals Bulletins Campaigns | Skidoo
Look for the "2019 600r-850 ETEC" manual. All of this lubrication system info came from there.

 

Those are your RAVE valve, which are variable exhaust valves. Nothing to do with the main engine oiling, but they look very clean, compared to other pix of RAVE valves posted in this forum. They do receive oil directly from the lubrication system.

This system has an electronically controlled oil pump and the ECM controls the oil flow to and through the crank, and the excess oil at the rod bearings is flung up and and round and oils the cylinders, pistons, and piston pins. So it is not the tradition 2S gas-oil mix type of lubrication.

Each cylinder has a line to the outer crank bearing. These lines are routed on the outside of the engine and have check valves. It is certainly possible that the line to the bad cylinder got pinched or has a leak, or a fitting is plugged, or something is wrong with the check valve, and that side got starved of oil. If that was the case, then the main and rod bearings at that end would be a suspect for damage too. (All of that would be coming apart for me anyway for inspection for issues like the crank, given the engine's recent serious failure.)

BTW, you can find your engine's manual here: Ski Doo Shop Manuals Bulletins Campaigns | Skidoo
Look for the "2019 600r-850 ETEC" manual. All of this lubrication system info came from there.

@850 guy -- The website @nm9stheham shared is INVALUABLE to get the shop manual. (-I highly suggest to at least send the folks enough for a beer or six pack). My recommendation is to get both the MY 2019 850 ETEC and the 2017 850 ETEC. While the differences between 2017 and 2019 are almost negligible, the 2017 has graphics in color and they are very clear. The exact same pages dealing with the exact same areas of the sled in the 2019 are b/w and a little fuzzy. The text is the same for both. Like I said, the differences are almost negligible, however, depending on how you go forward rebuilding the engine, there are a couple very important details. I am describing a little bit of that in the other thread 2017 Rotax Rebuild Questions, where there is an update to the "engine support plate" that eliminates all but two of the lowest oil tubes to this part on the engine. As I assume there are others who may look to this thread for similar reasons to yours and mine, I wanted to offer the following as encouragement for the process--

If someone has any engine rebuilding experience, the shop manual helps quite a bit in this process for the 850 ETEC. While everything isn't as straightforward as a rebuild manual like the iconic "How to keep your VW alive--A manual of step by step procedures for the complete idiot" book, it does have 98% of what you need in pretty clear language. Basic rebuilding skills and tools should make the process something most can accomplish successfully. However, if someone knows only enough to put fuel in the tank and maybe change spark plugs, I wouldn't say rebuilding an 850 is in their wheelhouse without considerable guidance and maybe even someone else who does have those skills lending a hand. Take that for what it is--the last thing anyone needs to do is cause themselves to be stranded (or worse yet hurt) due to not doing a complete rebuild job. There are quite a few reputable places to have it done, and the cost is definitely worth it for the reasons I mentioned. I have quite a bit of experience from being a mechanic in the military all the way to rebuilding my own engines and I still worry. However, I enjoy taking things apart and putting them back together, so taking this slow and methodical has been my focus. Plus, if something doesn't go quite right all I have to blame is myself.

With all that said, yes, you will have to have the machine put back into break in mode, as well as have the oil pump calibrated by a reputable shop with BUDS software. You will have to decide how far you tear into the engine and as @nm9stheham mentioned, based on what you found so far, the prudent mechanic will most likely want to inspect the crank bearings and runout to ensure those crucial items were not impacted by whatever led to the visible damage to the pistons.

If you take a look at the other thread I mentioned, I show the lubrication "flow chart" from both the 2017 and the 2019 service manuals. It shows how all things get lubrication, and from my VERY basic sleuthing on the 2019 part change of the "engine support plate", Doo simply changed that part for MY 2019 without making any changes to the flow in the case itself. Now, for MY 2020 and after, I do see that the case (block, whatever) part number changed in the fische, whereas 2017-2019 it was the same PN.

Lastly, as I knew I would be sooooo far into the sled by doing all of this, I budgeted to replace LOTS of things. Magneto, starter bendix (mine has electric start that was intermittent), all the cooling hoses and clamps, thermostat, some busted up plastic items on the airbox (damage from one or all of the PO's) and even got a brand new factory 165"/3" track. When I bought my sled it had Silber Turbo on it, so my choice of pistons with new cylinders was based on my riding elevation (9,000'-12,000' ASL) as well as potentially putting the turbo back on. My sled ran when I purchased it, but it had an annoying check engine beeping when I tried to go WOT, and even with Dynamo Joe's iBackshift clutching on it wouldn't hold above 7,000 RPM for more than a few seconds. Did a compression check and found both pistons were at or below 95psi. So I decided to do this over the summer/fall, before the snow flew again this winter.


Just a couple screenshots showing the easy to read 2017 color graphics vs 2019. Both are great, but if you need visual clarification for taking apart or assembly, 2017 is much clearer.

 

Very good info and explanation, Groucho. I never compared the 2 different year's manuals.

Now I gotta ask, where you ride (pure curiousity). And at what elevation is your home/shop, and if you compensate for elevation when you take compression readings..... compression readings are gonna drop somewhere between 20 and 30 psi at 6,000' for example. (It is not that wide of a range of pressure drop, but I am too lazy to figure up the exact drop right now LOL.)

Oh and as you know, at some point, you just have to hit the starter and see what you built ! Once you get enough builds under your belt and your track record is good, then the worries go away. Doing things well and thoroughly is part of building that 'good track record', even if it is only you that knows it. Well, enough engine building philosophy....

 

To keep on the original post first, I forgot to mention that a leak down test is also mandatory on a rebuild like this. The service manual lines that all out too. There are also several decent ways to get it done successfully without the exact shop tools.


Now for the chit-chat.
@nm9stheham thanks. I ride in Colorado. Rabbit Ears, Church Park, St Elmo (Hancock Pass) and possibly Cumbres Pass (just on the north side of the CO/NM border) if I can do 3-4 days. I’m no spring chicken, so I love blz deep or chest deep pow days just as long as I spend more time riding than digging out 😂. No stunts or big jumps. I’ll leave that to my college/teenage kids.

Home/ garage shop is on the front range, just a little north and slightly east of Denver at just over 5,100 feet ASL.

I am still in my infancy/toddler stage for knowing all that makes a 2S tick, much less the electronically controlled 850 ETEC. I did this rebuild to really familiarize myself with as much as possible on this machine.
Initially ran into my issues with WOT being at 7,000-7,200 RPM and decided to dive head first instead of just continuing to R&R parts. Compression was low. Had done stuff with RAVE valves, had TPS set again, had an injector wire fixed, new fuel pump & filter, etc. Nothing changed the fact that no matter what elevation and clicker/weight combo I had on the clutch, the sled would beep at me and flash “CHECK ENGINE” when I hit the throttle with no stored codes. It would go up to 8,000 and then immediately go back down, sometimes as low as 6,500-6,600. I’m sure there are 100 more different things that I could’ve checked, but it felt like chasing my tail every time and frustrated at the beep to boot. So here I am.

 

To keep on the original post first, I forgot to mention that a leak down test is also mandatory on a rebuild like this. The service manual lines that all out too. There are also several decent ways to get it done successfully without the exact shop tools.


Now for the chit-chat.
@nm9stheham thanks. I ride in Colorado. Rabbit Ears, Church Park, St Elmo (Hancock Pass) and possibly Cumbres Pass (just on the north side of the CO/NM border) if I can do 3-4 days. I’m no spring chicken, so I love blz deep or chest deep pow days just as long as I spend more time riding than digging out 😂. No stunts or big jumps. I’ll leave that to my college/teenage kids.

Home/ garage shop is on the front range, just a little north and slightly east of Denver at just over 5,100 feet ASL.

I am still in my infancy/toddler stage for knowing all that makes a 2S tick, much less the electronically controlled 850 ETEC. I did this rebuild to really familiarize myself with as much as possible on this machine.
Initially ran into my issues with WOT being at 7,000-7,200 RPM and decided to dive head first instead of just continuing to R&R parts. Compression was low. Had done stuff with RAVE valves, had TPS set again, had an injector wire fixed, new fuel pump & filter, etc. Nothing changed the fact that no matter what elevation and clicker/weight combo I had on the clutch, the sled would beep at me and flash “CHECK ENGINE” when I hit the throttle with no stored codes. It would go up to 8,000 and then immediately go back down, sometimes as low as 6,500-6,600. I’m sure there are 100 more different things that I could’ve checked, but it felt like chasing my tail every time and frustrated at the beep to boot. So here I am.

The 850 seems to read low for some people. I would try again with the exhaust valves closed. Best of luck.

 

I would strongly suggest that you also change all new fuel filters, inside the tank too. Also the main injectors are crucial for the engine, if not 100% sure that they are good replace them. We have found that some injectors have been blocked by micro plastic for some reason. Plastic has been found inside the injector blocking the fuel flow.

 

I would strongly suggest that you also change all new fuel filters, inside the tank too. Also the main injectors are crucial for the engine, if not 100% sure that they are good replace them. We have found that some injectors have been blocked by micro plastic for some reason. Plastic has been found inside the injector blocking the fuel flow.

Prior to tearing down and doing this rebuild (Just to clarify, I am not the OP, that is @850 guy):
--Both fuel filters have been replaced. One on the pump inside the tank as well as the one between the tank and the fuel rail.
--RAVE Valves were swapped with a known working unit. They were also checked on BUDS and verified.
--Brand new and properly indexed plugs were installed.
--TPS was set at the same time as the RAVE valves being verified.

During the rebuild, the main MAG and PTO injectors (ones on top of the cylinder head) were taken apart to be cleaned, screen filter was cleaned (they weren't dirty), new o-rings (blue and orange) installed as well as new crush rings. Neither one had any foreign objects on the inside, none near the tips either open or closed and as that circular filter inside the main injectors has lots of filter area so it would be very interesting to have it be blocked enough by items small enough to make it through both filters first.

It is my very loose belief that the PO (or multiple PO's) ran it hard and put it away wet. A turbo was thrown on it and was expected to run like it was new. Again, I am no expert. The machine as designed is an awesome machine. I am just trying to get it closer to its designed build parameters.

 

Very good info and explanation, Groucho. I never compared the 2 different year's manuals.

 

I never compared the 2 different year's manuals.

I missed that part, but for what it's worth I build myself of document of the various errors. It's an ongoing process that has helped me to verify my information and think things through.

 

So I actually got most of the parts in, aside for a couple gaskets that the guy at the dealer didn’t order. The new jugs look pretty good, no damage or cracks. I did notice it’s missing threads for the intake boots and wiring harness holder blots, the holes are there but no threads. Anyone know why ski doo did that or is that a defect during the manufacturing process, aside from that everything else looks good. I’m still contemplating tearing the bottom end down, both rod bearing don’t have up and down play and it all spins around smooth, I also see pools of oil at the bottom so I’m I’m not too worried about bottom end issues, this sled has around 1700 miles (or so the guy that sold it to me said, there was no way of checking without the sled running) so it shouldn’t of had enough time to wear the bottom end out with proper luberication of course. Anyway I examined the top end some more and it’s all pointing to insufficient oil or coolant somehow getting inside, I’ll check for clogged oil lines tommorow as well as call the dealer and see what’s up with those threads. I’ll put some pics of the new cylinder.


you can see first pick has no threads for the intake boots,the second pick( old jugs) has threads, I’m thinking it’s a defect but I could be wrong, maybe they’ll charge me extra to tap those holes🤷‍♂️

 

Mine are tapped but my “new” cylinders are from MCB performance and I’m not sure if they’re new or reman.
Here is a pic of the ID of the cylinder with coating and hone. Also, the bottom side of the casting as well as the reed valve threaded parts.

 

I did notice it’s missing threads for the intake boots and wiring harness holder blots, the holes are there but no threads. Anyone know why ski doo did that or is that a defect during the manufacturing process, aside from that everything else looks good.

Normal as they are self threading holes. It may not seem normal, but once the bolts are in they hold in place very well from having near perfect thread engagement.

 

I examined the top end some more and it’s all pointing to insufficient oil or coolant somehow getting inside

It could be coolant ingestion, but I don't know. For this kind of failure I pay close attention to the carbon deposits and compare both cylinders and note if one side is abnormally clean of carbons than the other. I just looked at the heads and realized that yours fits the bill to at least suspect question coolant ingestion.

 

I’m not too worried about bottom end issues, this sled has around 1700 miles (or so the guy that sold it to me said, there was no way of checking without the sled running) so it shouldn’t of had enough time to wear the bottom end out with proper lubrication of course.

I worry about the lower end when a piston shows to have melted from too high combustion temps. There are other situations to consider, but I am keeping this short.

 

I’ll check for clogged oil lines tomorrow

Ideally we would have an apparatus to manually trigger/pulse the pump to verify oil flow.

 

I did notice the crankcase had some coolant mixed in with the oil, but it could’ve been from the disassembly process. I also found that out of the 3 longer cylinder blots (ones closer to the exhaust side) one had the little seal torn, it was the one that’s in the center, if that was an issue I would think both pistons would’ve been junk. I also looked into the holes of those blots and they don’t seem to be connected to any coolant ports so I’m not sure if that would be of any concern. I could be wrong so lemme know what you guys think.


Pic of the block is just to show where that bolt with the torn seal would go

 

The seal along the bolt is an important one to keep the coolant in those passage ways to reach the head.

The further I go, the more I think we need BRP to weight into these things. So take anything I write for what it's worth.

In your case it appears straightforward and a no brainer. Note these seals are only on the 4 bolts on the exhaust/coolant side of the cylinder. I always assemble these four bolts with a light coating of Dow 111 (Molykote). I don't really play with 850 rebuilds, so again take it for what it's worth. I mostly work on the engines that preceeded the 850 that led way to the 800s and 850s.

My best advice is to focus on engine rebuild and coolant pressure.

 

Ok, I’ll get some replacement bolts for that. Other than that are there anymore tips that anyone has for me, like things to check over before I fully assemble it or things that I might need to know about the assembly process. I’ll be taking it to the dealer and they’ll put into break in mode and All that other stuff so that’ll be taken care of. Basically any other stuff I need to know before I button this thing up. Thanks

 

I would think of a number of things like tacking the base gasket.