[Daag44]

I'm thinking similar for my wife's. From what I've read, the fuel is the lube in these things.
Once they get hot, that is when they go past and detonate because the hot spots in the engine ignite the fuel before the spark plug fires - before the timing

Try to keep the temp down below whatever that magical number is. The extra fuel is also a coolant carrying heat out the exhaust. When it burns more clean / lean, and less heat is carried away creating even more heat in the combustion chamber.

The magical/maximum engine/coolant temperature that you referred to is somewhere around 170F - for a maximum. It will not self destruct above this temperature, but from there on the risk increases much like a parabolic curve. And each situation is different. Say it reaches 200F, what is the condition? Many E-TEC owners let their sleds warm up and count on the ECM to shut the engine which happens after idling for 5 seconds @ 204F. But when riding the same E-TEC and it reaches 185F, then it is considered an overheat and the engine is cut down on power to 5,500 rpm. In other words, there is a difference in overheat when riding under load compared to when it is idling.

When I see posts that a Ski-Doo was towing an Arctic Cat or Polaris or Yamaha, I get the humour, but it is so hard on the transmission and the engine that I find the humour at a loss.

On a side note, I think that you should continue to push the 500SS thread that you started. I am not worried about the OP (Original Poster) jon@nlxdirect.com because he brought an illuminating explanation to a common a SDI wiring problem. I am not worried about you either, mostly because you had the balls to post on a public forum. I am just saying to keep pushing, because these subjects do not often go far enough to reach maturity. The off-season provides more time to think things through. I think you started a real cool thread on the 500SS that begs to dig further.

2004 MXZ 500SS melted piston

 

[199Mods]

I did this after a preventative rebuild melted down before breaking in.

I had a friend pressure test my 500ss in chassis. No air coming or going from crankseal. Reeds y pipe rave sealed up good this left the carbs slides.
I put the thickest base gasket I could I.
Carbs up jetted 2 sizes. Piolts 1 size. Moved the needle clip down.
Switched to Br10ecs.
Premix 40:1 and oil injection.

The sled made more power with these settings (added pin weight) and I can confidently park the throttle on the bar what a feeling.

I know some won't agree with these and they are band aids but they rebuilt my trust in my sled.. that's worth something.

 

[Daag44]

The sled made more power with these settings (added pin weight) and I can confidently park the throttle on the bar what a feeling.

I know some won't agree with these and they are band aids but they rebuilt my trust in my sled.. that's worth something.

If you can make good power with those settings, seriously all the power to you! From your profile I suspect that you ride Iqaluit, NU, and the temperature is colder then where I ride. I imagine the jetting-up was appropriate. A little less compression with a thicker base gasket is not a big power loss. I am guessing that by now you have figured out the best engine mod for the buck is a running engine.

Good compression from the ring(s) with a thicker base gasket has more power than a thinner base gasket having poor compression from excess blowby. A thicker base gasket also holds the advantage of running 87 in remote regions where the gasoline tends to see longer storage which looses RVP and octane.

 

[199Mods]

I did it to help longevity but it made more hp.

The base gasket (thicker) also shifts port timing (up) and has a small effect on case (primary) volume.

Rotax Lake racer types did it but they recut the head.

My 500ss is in Muskoka Ontario. I left it at home it has 30 000km when the speedo last worked.

Bought a new 600efi 129 burnt a hole tank of gas today but no pistons.

 

[Dynachrome]

That all sounds right along the lines of what I'm looking for.

 

[Dynachrome]

...From your profile I suspect that you ride Iqaluit, NU, and the temperature is colder then where I ride.....

..I am guessing that by now you have figured out the best engine mod for the buck is a running engine....

-20F is a probable ride for us.

I'm getting that T-shirt made up.

 

[Dynachrome]

I did this after a preventative rebuild melted down before breaking in.

I had a friend pressure test my 500ss in chassis. No air coming or going from crankseal. Reeds y pipe rave sealed up good this left the carbs slides.
I put the thickest base gasket I could I.
Carbs up jetted 2 sizes. Piolts 1 size. Moved the needle clip down.
Switched to Br10ecs.
Premix 40:1 and oil injection.

The sled made more power with these settings (added pin weight) and I can confidently park the throttle on the bar what a feeling.

I know some won't agree with these and they are band aids but they rebuilt my trust in my sled.. that's worth something.

No chance you have either the base gasket Part Number or the thickness after 20 years?

 

[199Mods]

Honestly I bought the cheap spi top end kit 4 hole six and eight base gaskets were included. I used eight hole.

The # of holes has to do with thickness in mm.

 

[199Mods]

this is from a 2020 manual.

 

[Daag44]

-20F is a probable ride for us.

I'm getting that T-shirt made up.

That's cold enough to warrant higher jetting from the pilot to wot. If needed you can get shims for finer adjustment of the needle position. I don't normally ride under -4F (-20C), so it's not much of a concern for me. If I do then I am careful to avoid sustaining a throttle anywhere above 1/3 or 1/2.

Since I own a wideband, what I did on an 800R P-TEK is monitor the A/F with stock jetting at or under -20C. The DPM on the P-TEK compensates for air density, so it gives a good idea where what a/f to shoot for at different rpm and load (throttle position). I don't really want to worry about the load, so I pick a day when the trail is relatively well packed and take readings at different rpm, something like idle, 4,000 - 5,000 - 6,000 - 7,000 - and wot. It takes me no more than two minutes to take those readings. Then I repeat and spend ten minutes to take a rudimentary plug reading. I use BR9 type plug, so I am accustomed to reading that plug heat range. I haven't delved far enough to compare with the 8 and 10, but this is something to keep in mind when reading plugs. I also do not perform fancy plug chops. Instead I slow down safely, kill the engine and take a look. All the power to those who use kill the engine at speeds, use new plugs for each stage, and break them apart to read the deepest part of the porcelain. I never felt the need to go that length, especially that I am using a Wideband and EGTs for a total of three measurements. I am missing pipe pressure, but I find this to be plenty for a stock sled.

I am not suggested that you need to do all this. However, those are affordable tools that are available to become self sufficient with the jetting. I have not taken a measurement on the 500SS, but let's assume the measurements are taken with stock jetting @ -15C which gives a 5C allowance since the stock jetting is outlines by BRP to be good down to -20C. Whatever A/F shown @ -15C is the A/F that I shoot for at -30C. Too little gets the pistons hot. Too much fuel cause rich misfire which is seen as poor response and bogging. Too much fuel also lowers the Fuel/Oil ratio unless the oil pump cable is adjusted accordingly.

The way you guys are doing it is similar and it does work. That is why I mentioned the A/F reading, to show that you are doing much the same by using stock jetting as a baseline for air density, and the stock base gasket as a baseline for the available fuel octane.

There are a number of others things to look into which requires to make a list and do your best to understand the most important aspects for each. For example I use a Mytivac to test the oil check valves, but a simple oil line has proven to show one type of problem with the check valve stuck in the open position, and a high spinning drill to confirm the oil pump output through both check valves.

An engine leak-down test is another example for needing non specialty tools other than a low cost vacuum/pressure gauge, and all other things provided at the local hardware and auto parts store. Once you the common leaks, then all you need to learn is first how to best prevent them, and second how to diagnose them early. They are not all easy to diagnose early, but it shortens the list by learning those that are easy like coolant ingestion from the head.

There are other things to consider, but those many of the ones lead to come up with the simplest idiom for two strokes, that the best mod for the buck is a running engine. I imagine that you have hear your share of idiom for two stroke failure like the luck of draw, and there are countless more. I have yet to find a two stroke that failed because it was running right.

 

[Daag44]

Honestly I bought the cheap spi top end kit 4 hole six and eight base gaskets were included. I used eight hole.

The # of holes has to do with thickness in mm.

Whatever you use as pistons, it is good as long as it works. I don't particularly enjoy working with certain aftermarket pistons/rings for a number of reasons, but I still use them. I have seen an aftermarket ring having ok ring clearance to far too little clearance that needed filing which I loathe doing. I have also seen aftermarket pistons having a little more piston clearance which I did like to see, and some with too little clearance. Another thing that I saw with aftermarket rings is not being trued and leaving symmetrical scuff marks all along the cylinder wall. This last one has been far too common for my liking.

The cylinder plating presents a several other issue such as the quality of plating, truing, sizing and honing. Usually the plating holds and doesn't flake, but the odd time it may not. The truing and sizing should be ok, but this is not always the case. I use a dial bore gauge to check. The honing can be a real problem for not having deep enough grooves to hold enough oil. This is one thing that is not easily measured by us week-end warriors, so the only way to ensure a proper hone is to sources a replated cylinder from a reseller that is equipped to take the measurements and ensure the quality, like MCB.

BRP understands all of this, and work to offer a certain standard much like MCB does for the aftermarket. If I ask BRP for the ring clearance, they will tell me what is in the shop manual, which I can read for myself and see there is a wide range. If I ask MCB, then I am given a suggestion and I am told it depends on the engine output such as racing versus stock. I actually get the same answer when I ask BRP Racing.

For a 500SS that has less power per cc, I may not give as much attention as a 600HO or 800R P-TEK, but I will run along the same lines. For example, I am not allowing a ring to have under 0.016" gap, and I will choose to go higher such as 0.018" or more. My own measurement is so many thousandths of an inch per cm of bore, and I rather have a little too much gap than not enough.

With the honing, I do not own a profilometer to ensure it was done correctly to hold enough oil, so I error on the safe side when it comes to fuel/oil ratio. In my own opinion, too much oil causing a lean seize is BS, so this is something that I do not worry about. I can site a really good article that says the amount of oil does impact the fuel/oil ratio and support it, but it is a non issue for what we are doing on our sleds. And even if too much oil is used, it will still not cause a lean failure, and that article never said it would either. A word of caution, if you do attempt to compensate an already lean fuel burn with excess oil, then that will lead to an engine failure. In other words, the attempt to compensate for a lack of fuel by using more oil is a problem, but too much oil for a proper jetting engine is not an issue. So if you have your jetting right for ambient temperature, and you want to go from a 50:1 to a 40:1 premix ratio, or 40:1 to 30:1 or even down a 20:1 ratio, this is not a problem. But first it needs to be jetted right for the engine power and air temperature (or air density). My own preference is to use a combination of the oil injection and premix to achieve the best of both worlds.

Hopefully this provides an idea on how to go beyond the anecdotal experience that such a fuel/oil ratio has worked for one person, yet not the other. Without knowing the particulars of each engine, I don't see how can we draw from them. I am good with whatever fuel/oil ratio you choose as long as you think it through and make your decision though experience as opposed to from fear. I personally want to use the least amount of oil, while erroring on the safe side.

I think what you have been doing is really good, which is what is leading me with concepts that will hopefully allow to push yourselves further. Of note, if I am pushing, it means that I picked-up one or more things of value from your experience. Make no mistake, this has been an exchange for me which I thank you for sharing.