FYI for those putting in Fix Kits

[geo]

It finally got cold enough to get some time off work (yeehaw) so I got to pull the cover of my sled and engine I took apart in the late summer and really put my nose in there.
I'm a pour-in-the-oil guy on two strokes because of what I have seen inside and trust that it will make my engine happy. I expect very little wear when I pull one of my engines apart.
Oil does that for me but will not compensate for a mechanical issue. Finding a mechanical issue usually takes some experience and a lot of careful looking through magnifying lenses for us old guys lol.

My '13 has been set from new (4.5 turns out from factory on my sled) to burn 25 to 1 (with the 100 to 1 tank mix factored in) on good days and 32 to 1 on hot chocolate-cheese puff days.

I put 1700 miles on this "time bomb" lol engine and tore it down for a freshen-it-up for the new season. It ran with a head and pipe for about 1000miles and had a fuel controller (set-up rich at first then conservative after dialing) on from 100 miles (another big help for power and longevity IMO). I also was aware of my coolant temps spiking and cured that with the "28 dollar" lol mod (thanx TRS) mid season.

I know most don't discuss this after a tear down so I thought I would post what I found in my engine and maybe it would help people decide if oil is a good thing or not and what I think is a very important tip so you don't have to do it next year.

My stock pistons measured 6ish thou on one cylinder and 6 and a bitish on the other (no collapse there). My Fix kit pistons measured 5 ish and 5 and a bitish. I expected more difference after what I've read.

Did I need to change pistons? Yes, but not because of collapse. My pistons were damaged (ring land seal) and rings scuffed (not pitted or broken down or anything mysterious)) from poor chamfer in the ports. Nothing that looked like carnage, just visible signs (through those granny glasses lol) of why the ring seal was disappearing. Had they gone another 1000 miles I could see a ring starting to catch every stroke putting huge strain on the skirts and cylinders.

The PTO side was terrible on the boost port and MAG (funny it always showed richer on the plug and wash) was terrible on the right transfers and boost port. I've seen worse from the factory but not often. So I don't know if this is the norm on the Poo cylinders.
I believe if I had not broken in the motor gently (helps with stuff like this) and ran high oil ratio from min. one. I would have started this process of destroying ring seal earlier. Once the combustion pressure starts to bypass the rings piston collapse is a common issue.
This would have further aggravated the situation to the point of possible piston failure (the blow up thing).

I'm pretty sure if I did not chamfer the ports correctly the Fix kit piston rings would not have lasted any longer.

So burn that oil and break it in easy until you do take it apart. Then give the cylinders to someone capable (because chamfer shape and thickness is critical) and have them chamfer your ports properly (instead of whoever on the assy line). The power will stay there for a lot longer this time. And ( a side benefit), port flow (power) is most critical in equal timing of opening and restrictions in the last .080".

This is my first time into this engine and not all will be the same but I'm surprised to not have read about this before. For my engine the fix kit would have been a book on how to chamfer different port shapes properly and a small rat tail diamond file and another set of stock pistons. Nickasil will never chamfer itself no matter how many rings you put through it. Feel them with your finger. If they feel at all sharp just think about what your ring feels everytime it passes.
If yours are bad you need to address it while apart. My block may be a good one! Chamfer of the ports is a critical part of two stroke ports for ring life, piston life, and power.
IMO if the ports were chamfered correctly from the factory I would have wasted my time taking it apart.

 

[4Z]

Great post! I am guilty of not paying close attention to OE chamfer when swapping pistons. Thanks for that!

George, in your opinion, do forged pistons suffer skirt collaps quicker than hyper/cast pistons do when excessive clearance is present (.06"-.09")?

 

[diamonddave]

0.006" with 1,700 miles....not to shabby. Don't believe I've ever heard of one that good.

It's funny when you think about it....ring wear in the CFI-4 was never an issue. In the CFI-2, it's very pronounced.

I keep waiting for that flatlander to come on here and argue with you guys about turning up oiler's. LOL

 

[rmscustom]

I was getting close to 8 thou and had flaked rings with 1300 miles running about 35:1 on the oiler and no mix in the gas. I wonder if the 100:1 premix and the fuel controller is a big help?

 

[geo]

Both stock pistons were just over .006" but under 7 (go no go with long piston feeler gauges, bin doing quick checks like this for years, simple).

I'm pretty sure my Fix kit pistons will be .006" and a bit after 100 miles. So what did I gain? Ring seal (power) that will last because I fixed the chamfers as best I could after the factory botch.

On my cylinders the sides of the ports were chamfered way too much (making the port window wider than it needs to be so ring has lost support with no gain in flow), the corners were different radius's (starts the flow in a weird direction and the top and bottom edges end up being asymmetrical causing stress on the ring as it goes through the port window).
On the worst ports the one corner would be chamfered about 90 thou. the other about 50 thou and the top and bottom edges only 30 to 40 thou. Talk about ring snag potential! Especially after things are worn in.
Ideally (and this is the most important part of two stroke cylinder prep) the side chamfers should be minimal (020" to .030" max) to keep ring support and the corners symmetrical, increasing the radius to about 40 thou towards the top and bottom, then increasing chamfer towards the center of the port to about 60 to 80 thou depending on port width (sometimes exhaust ports that have been oversized need up to 100 thou to make rings live). Kinda like the top and bottom part of an elipse.
You have to picture the ring in you mind in slo mo lol slowly getting sucked into the window and you are trying to help it get out without catching an edge.
My ring lands at the back of the piston (where the pins are) have 6 thou clearance and the sides were out to 3 and 4 thou.
All the damage to my stock pistons was done because of poor chamfer on the transfer ports. Todays engines have lots of transfer ports with little ring support in this part of the cylinder so chamfer is critical in this unloaded, direction changing part of the stroke.
I see why MNTK (and others now) chose their method of approaching the fix. Different ring material will take longer to show up but the same end result will happen and will wear the bore quicker in the ring area especially at the directional change spots. Like I said before if I had a chance to chamfer my own ports I would be happy to stick with the stock pistons and expect 3000 mile change intervals.

Cast or forged? I prefer cast from past experience but I picked a forged piston kit because of the numbers out there lol (proof in numbers) I also wanted to add crankcase volume to hope to lower engine temps (weird eh lol). Piston metallurgy has moved on so we will see. I will take more time to heat cycle a break them in. Meaning the old forged "stick em" problem will be on my mind until I slowly work my max load into them over a couple three long rides.

Why do my pistons measure up good after 1700 miles? I believe it is everything I did to make it last lol. More oil, more fuel, easy break-in, and hand on the heat exchangers every day.

One thing I was very happy to see and may be the biggest factor is zero burn under the crown of the piston. It was clean like new so that meant to me the combustion temps never got so hot the crankcase air couldn't cool it. That's a healthy ratio and fuel numbers. To hot a crown means the heat migrates down the skirt further taking it beyond design.
The other thing I liked was the piston pin bore was clean and the pin slid out easy (meaning little or no ring blowby for any length of time to coke up the bore). That meant to me that I gave the rings a proper chance to seat even with poor chamfer. Had I "Moto Man'ed" it I probably would have ruined the rings immediately.
I was pleasantly surprised at the condition internally.
Oil is a no brainer in a two stroke for me. I slosh it in any way or port I can.

Break-in on a stock some-body-else-put-this-thing-together motor for me means 3 or 4 hours of taking it up and down the rpm with gradually increasing full load time because I have seen the insides of many a stock motor. The chamfer thing is not the first time nor will it be the last. It takes time to do it properly and that is something not usually taken on an assembly line.
In a perfect world (like if you assemble three identical motors and had your hands in all the way) break-in would be less than an hr. with full load after 5 or 6 laps but I still tore them apart to check if I screwed up lol.

2 stroke and four stroke are different animals.

Whew, that's all I have to say about that lol. Anyhow do your rings and pistons a favour if your putting on a new topend and don't put them through any poorly chamfered ports.

PS Maybe it was the Yamalube eh G-man lol.

 

[mountainhorse]

I can see your point on the chamfer.. wondering if the kind specs you are quoting are attainable in a production environment in the cylinders. I've seen the same thing in 2 strokes across the board (doo,poo,cat)... the best that I've seen are the KTM's in the small two stroke bikes (rotax I believe).

To draw conclusions about the state of a stock engine with the fueling and oiling modifications that you have my not be a good comparison. I like the point you make about no burn marks under the piston. I've seem some with collapsed skirts that have had heavy burn marks lots of long duration mid-throttle running. I also like the point that you make about forged pistions not being what they have been...Heck, 10 years ago, an iPhone was a pipe-dream.... New technologies in design and metallurgy can make new forged pistons the correct choice (though some forged pistons out there still have the tech from 20 years ago)

"Throttle style", warm up, oil and many other variables are huge determining factors in longevity. I changed out a set of stock pistons with 2300 miles on them over the summer... they were in pretty good shape... 40:1 "ish" on the pump... with some in the tank for good measure and not much mid throttle use (brap brap). He is religious about warming up the sled and has an in-line coolant heater running the night before in the trailer (not sure on the effectiveness of a heater without a pump) .





.

 

[geo]

I agree with everything you said MTH, which is why I made the long posts to quantify and put it into the proper perspective.

Production worker properly trained could do a proper job in the same time but that doesn't seem to happen anywhere nowadays. The Poo cylinders I have are very bad IMO but like you said no worse than SOME others I have seen in the past.
The difference is this is my motor lol. So I get pretty excited when I see the good and how to make a drastic improvement in piston and ring life. AND, I was surprised that I had never read about this simple fix for an age old 2 stroke problem. Not a mystery to me anymore.

I've always had my doubts about piston design or metallurgy being the ONLY culprit during all the threads about my poo blew up. I mean Polaris is not stupid. They could change pistons if it was THE issue.
The only thing I believe ties their hands is EPA.

I'm a mid-range rider. I clutch for it. The ground I cover dictates it. So I focus on it. I've added over well over 20% fuel in that area on this package. I've made my ex valves open easier in that range. Everything I've done to make more power there also keeps combustion temps in a comfortable range because that's the way it should be. I will probably even add more this season until I am happy with the wash and plugs in this range.
I'm maybe using up all my carbon credits but my diesel is stock lol.

I hope the point of this thread gets across though. With what I did to be proactive with this engine platform and it's life, if my ports were chamfered properly I could have put it back together no probs (but I wouldn't have cause I had the kit on the bench anyway lol).

So again, if you have it apart, look at the chamfers close and if they're shiny, get them closer to ideal. Your kit will perform better for longer.

 

[08F6SP]

How were the ring grooves? I've seen a few posts about the ring grooves opening up. Seems to me that a substandard chamfer job might contribute to this. It would explain why some engines open up the grooves and others don't.

 

[gman086]

Interesting thread geo - would certainly explain why Curt at Fastrax is getting great results with their kits which use stock pistons (but they're meticulous with porting and proper chamfer). Things that make ya go HMMMMMM!

Have FUN!

G MAN

 

[kostly]

I agree with everything you said MTH, which is why I made the long posts to quantify and put it into the proper perspective.

Production worker properly trained could do a proper job in the same time but that doesn't seem to happen anywhere nowadays. The Poo cylinders I have are very bad IMO but like you said no worse than SOME others I have seen in the past.
The difference is this is my motor lol. So I get pretty excited when I see the good and how to make a drastic improvement in piston and ring life. AND, I was surprised that I had never read about this simple fix for an age old 2 stroke problem. Not a mystery to me anymore.

I've always had my doubts about piston design or metallurgy being the ONLY culprit during all the threads about my poo blew up. I mean Polaris is not stupid. They could change pistons if it was THE issue.
The only thing I believe ties their hands is EPA.

I'm a mid-range rider. I clutch for it. The ground I cover dictates it. So I focus on it. I've added over well over 20% fuel in that area on this package. I've made my ex valves open easier in that range. Everything I've done to make more power there also keeps combustion temps in a comfortable range because that's the way it should be. I will probably even add more this season until I am happy with the wash and plugs in this range.
I'm maybe using up all my carbon credits but my diesel is stock lol.

I hope the point of this thread gets across though. With what I did to be proactive with this engine platform and it's life, if my ports were chamfered properly I could have put it back together no probs (but I wouldn't have cause I had the kit on the bench anyway lol).

So again, if you have it apart, look at the chamfers close and if they're shiny, get them closer to ideal. Your kit will perform better for longer.

May I ask what pistons you went with weiscos or wossners, do you think the geomtry change ( ring location spaced further apart ) combined with the cylinder shim helps with ring support traveling threw the port area ? and are you reniking the cylinders after chamfer the ports

 

[rocket]

0.006" with 1,700 miles....not to shabby. Don't believe I've ever heard of one that good.

It's funny when you think about it....ring wear in the CFI-4 was never an issue. In the CFI-2, it's very pronounced.

I keep waiting for that flatlander to come on here and argue with you guys about turning up oiler's. LOL

Interesting someone should mention this. I tore my CFI-2 down this past week for fresh pistons - found flaking rings as many have. Pulled out the old used pistons from my CFI-4 and found similar flaking, though much less severe and and about twice the hours on them to get there.


On a side note, someone commented about Polaris not being "stupid" and willing to change parts (pistons in this case) if that was really the problem. I'd agree that they aren't "stupid", but rather "cheap". Somewhere in an office sits a group of accountants and actuaries, who analyze the cost of warranty claims vs. numbers of unit solds, costs of the components used to build them and makes a determination that if component A costs $X and component B costs $Y, but component A is a certain percentage more likely to fail and average warranty cost of the failure is $Z, a choice is made based on maximizing profit margin, not building the best snowmobile they can. If they can boost the bottom line, I don't think they care if the failure rate is 35%, especially if they can deny warranty in 50% of those cases because the owner didn't do everything just right...

 

[geo]

I don't agree with you rocket. Bean counters have a big say in things but they have to balance the whole picture. Labour on a topend warranty job is more than the parts. If pistons that cost 8 dollars more was the answer then it would be a no-brainer to get that changed.
Poo is probably big enough to dictate to their supplier what they want or else lol. Long term contracts are something you want to hold on to.

I believe that Poo is really trying to make us the best most reliable sled they can within the budget. My Poo has Japanese bearings (my last brand had Chinese). It has a belt holder, rubber strap, and moldings in the hood (my last brand didn't). The bars could be thin wall mild steel instead of aluminum. It doesn't have a bunch of self tapping screws that only last so long but is cheap to use. The plastic is unique to the industry (thin, light, yet rigid and strong) to save weight. Why waste the money putting on extruded running boards when stamping out the tunnel is cheaper? Why not make one chassis fit both ends of the country? Nuts and bolts are a washer head type. Why introduce carbon fiber instead of a wrap? Why change the wiring harness every year? I could go on with observations from a mechanics point of view but right there is at least couple of hundred bucks they could save at least.

I believe the engineers at Poo have a lot of say at the big round table meetings (unlike my last brand). Compromises are always made. How you do it is sure sign of your intent.

Kostly, I went with the MNTK kit because I got answers from owners and dealers that installed them in the past. Things like " Never see them back." and "So far so good for the last couple of years." made me feel more comfortable.

More on the chamfer thing to make you think. If your ring catches a bit from new, how many times does the piston skirt get a small hammer blow as it tries to stop every stroke, every ride? How many times does that happen in a season? What does that do to the ring land (to answer the above question, yes mine were worn and the rings were tired from the abuse lol)

I have a question to those that have pistons on the bench. This may show the importance of chamfer that may be unique to the casting. There is a tiny hole close to the exhaust port for the ex. valves. It's in a thin aluminum location (compared to the one dead center above it). It receives very little attention during the chamfering at the factory.
How many people have a score or shiny wear streak on the ex.side of their pistons at that point. If you look at your top ring there (use a light and magnifying glass) do you see the scraping from the thrust on the up stroke?

Mine show those obvious signs that will make me pay extra attention to the chamfer of that tiny hole. I thought it might need to have the cylinder wall relieved in that distance but my 500 stones in the Sunnen hone showed me it was simply chamfer.
Another port that will take special attention on my cylinders is the back boost port. It leaves the ring exposed and unsupported at BDC.

Like I said in the beginning, my pistons in my CFI did not just "collapse" from poor quality and my rings did not just "pit" for no reason or being from the lowest bidder. Anytime a poorly chamfered cylinder gets another set of piston and rings in it the second set will have a easier times from the shining the first set did and the re-hone.
But, if you do a good job on the ports the second set will be very happy for much longer.

 

[rmscustom]

I don't agree with you rocket. Bean counters have a big say in things but they have to balance the whole picture. Labour on a topend warranty job is more than the parts. If pistons that cost 8 dollars more was the answer then it would be a no-brainer to get that changed.
Poo is probably big enough to dictate to their supplier what they want or else lol. Long term contracts are something you want to hold on to.

I believe that Poo is really trying to make us the best most reliable sled they can within the budget. My Poo has Japanese bearings (my last brand had Chinese). It has a belt holder, rubber strap, and moldings in the hood (my last brand didn't). The bars could be thin wall mild steel instead of aluminum. It doesn't have a bunch of self tapping screws that only last so long but is cheap to use. The plastic is unique to the industry (thin, light, yet rigid and strong) to save weight. Why waste the money putting on extruded running boards when stamping out the tunnel is cheaper? Why not make one chassis fit both ends of the country? Nuts and bolts are a washer head type. Why introduce carbon fiber instead of a wrap? Why change the wiring harness every year? I could go on with observations from a mechanics point of view but right there is at least couple of hundred bucks they could save at least.

I believe the engineers at Poo have a lot of say at the big round table meetings (unlike my last brand). Compromises are always made. How you do it is sure sign of your intent.

Kostly, I went with the MNTK kit because I got answers from owners and dealers that installed them in the past. Things like " Never see them back." and "So far so good for the last couple of years." made me feel more comfortable.

More on the chamfer thing to make you think. If your ring catches a bit from new, how many times does the piston skirt get a small hammer blow as it tries to stop every stroke, every ride? How many times does that happen in a season? What does that do to the ring land (to answer the above question, yes mine were worn and the rings were tired from the abuse lol)

I have a question to those that have pistons on the bench. This may show the importance of chamfer that may be unique to the casting. There is a tiny hole close to the exhaust port for the ex. valves. It's in a thin aluminum location (compared to the one dead center above it). It receives very little attention during the chamfering at the factory.
How many people have a score or shiny wear streak on the ex.side of their pistons at that point. If you look at your top ring there (use a light and magnifying glass) do you see the scraping from the thrust on the up stroke?

Mine show those obvious signs that will make me pay extra attention to the chamfer of that tiny hole. I thought it might need to have the cylinder wall relieved in that distance but my 500 stones in the Sunnen hone showed me it was simply chamfer.
Another port that will take special attention on my cylinders is the back boost port. It leaves the ring exposed and unsupported at BDC.

Like I said in the beginning, my pistons in my CFI did not just "collapse" from poor quality and my rings did not just "pit" for no reason or being from the lowest bidder. Anytime a poorly chamfered cylinder gets another set of piston and rings in it the second set will have a easier times from the shining the first set did and the re-hone.
But, if you do a good job on the ports the second set will be very happy for much longer.

I do on both the piston and top ring....... Dammit Geo why couldn't you have posted this 2 months ago? lol. Work is overrated

 

[Trenchmaster]

Thanks Geo I haven't started mine yet (on holidays, waiting for a fuel filter) but after reading this I'm going to tear mine apart again and check the chamfers on my ports. Rather do it right once!!

 

[geo]

I do on both the piston and top ring....... Dammit Geo why couldn't you have posted this 2 months ago? lol. Work is overrated

Freaking right work is over rated. Today I'll finish my Allison and put it back in the truck.

THEN I CAN FINISH MY SLED LOL.

 

[Reese]

Always like your posts geo. Thanks for sharing your insights.

 

[damx]

You're Allison, did you have some km on it or did you're ripe it out of the truck with under 3000km to beef it up, for a 80mm over the stocker lol, not that I know anyone who would do that.

 

[Jaynelson]

Excellent synopsis....thanks for the read. Way over my head to complete the work, mechanically speaking, but interesting nonetheless