11'-12' Engine Issue

[yzviper366]

What are the other issues with the cylinder design?

 

[rydningen]

I have measured at least 100 cylinders of the Polaris 800 and have not seen 1 where the cylinder was out of spec in any way..
The problem is not the cylinder, however, there are "other" issues with this cylinder design..

The problem is the piston design and is easily fixed with a "correct" piston.

As for a long rod and choked off air flow in the transfer ducts... Please get back with us on that after you "compare".. I think you will be very surprised at the top end "performance".

Care to elaborate on the last part there, not sure what you mean? I have been thinking that the longer stroke could not hurt anything and decrease the side load on the piston/cylinder skirts. Chose the LR since alot of people have reported good results and I wanted a fresh good running engine for next season.


I am running components from alot of vendors, so I have no bias against any particular one....just want to build a good runner and maybe learn a thing or two in the process!

 

[RKT]

Care to elaborate on the last part there, not sure what you mean? I have been thinking that the longer stroke could not hurt anything and decrease the side load on the piston/cylinder skirts. Chose the LR since alot of people have reported good results and I wanted a fresh good running engine for next season.


I am running components from alot of vendors, so I have no bias against any particular one....just want to build a good runner and maybe learn a thing or two in the process!

I am always happy to address questions and will always get right to the point with hard facts and not conjecture or misleading information. To some this is offensive, but with my limited typing skills, it is the only method for me... sorry.

1st off Changing the rod to a longer rod does NOT change the stroke! You are still at the same stroke.. It changes many things but the stroke is not one of them..

2) With a longer rod, you change the "dwell" time that the piston incurs at TDC and BDC.. this greatly effects the combustion event, and its timing.. sometimes for the better and other time for worse.. It also effect air-flow and many other parameters (like is true with any 2 stroke engine). So, when this happens (for the worse), power is reduced.

3) The Long Rod can reduce side loading but to reduce side loading when not needed is like having a pot of boiling noodles that are submerged and getting cooked..then adding more boiling water.. The FACT is that the Polaris Rod ratio is better than Ski Doo or Arctic Cat. Again.. if the Polaris rod ratio was insuffient, then the DOO and CAT ratios would be even more insufficient... and they are not having issues related to side loads..

4) As for the air flow reduced comment.. This is true with a particular mod that is being done at one shop. ANYTIME, and I mean, ANYTIME you restrict air flow in a 2 stroke engine, you lessen/reduce that engine's ability to produce power. It effects how efficient the engine is over all, which limits the engine in many areas. So, reducing airflow is usually never a positive.

Hope this helps..

Note: There are bound to be some who read this to come on here and see all sorts of "hidden" meanings that are simply not present..
Like stated earlier, I prefer to present "facts" based on sound engineering and decades of experience..
I really have no intention of getting into any "personal" debates. So, as long as you guys want to keep it technical and factual, I will be more than happy to offer my experiences (right or wrong). But IF the responses become dorrogatory and attacking in nature.. You can count me out of the conversation..

 

[rydningen]

Thanks for the elaborate response Kelsey!

I am also VERY interested in keeping this thread clean and factual, people have different opinions and that is how things should be. I just want to learn and think out loud

I know that one of the mods available might affect the air flow, but this is related to a cylinder mod right? I can not se how changing to longer rods could alter air flow, the engine should "pump" the same amount of air at the same bore at the same RPM? more crankcase volume due to the shim...does that have an effect?

I was told by one offering a LR conversion that the altering of the angles due to the longer rods would lead to more efficient transfer of force to the crankshaft which in turn lead to better torque. Is there any truth here in your opinion?

Also, do you think adding a big bore top end to the LR bottom end would work? Or would mapping be an issue?

 

[tdbaugha]

Also, history has shown that not all mono blocks are not created equal. Expansion and contraction from heat is greater/less depending on the area and the amount of material in that area. Don't know this for sure, but I would be willing to bet there are some goofy expansion and contraction issues going on. Then couple that with inconsistent cooling system.

.02

Bingo Lynn,

Heat cycling is a killer. I believe that is why the mountain segment sees such a drastically different number of failures than those from the trail segment. Search on the flatland forums about the failures.... They paint a different picture.

Trail sleds start their motors and ride for hours on end all at the same coolant temperature. In the mountains, how many times per day does your sled get to operating temp (or above) and then shut off after only a few minutes? A LOT. Right after a shut down, the motor gets badly heat soaked - that's evident in the head temp reading when you start your motor back up... Goes from 170 down to 90 or less in a matter of seconds with a huge rush of cold coolant.

Microscopic cracks form during these heat cycles. It's a form of low cycle fatigue. Over time, the cracks propagate until complete failure. It doesn't help that the piston is rocking back and forth and slapping on the skirts either.

 

[RKT]

Thanks for the elaborate response Kelsey!

I am also VERY interested in keeping this thread clean and factual, people have different opinions and that is how things should be. I just want to learn and think out loud

I know that one of the mods available might affect the air flow, but this is related to a cylinder mod right? I can not se how changing to longer rods could alter air flow, the engine should "pump" the same amount of air at the same bore at the same RPM? more crankcase volume due to the shim...does that have an effect?

I was told by one offering a LR conversion that the altering of the angles due to the longer rods would lead to more efficient transfer of force to the crankshaft which in turn lead to better torque. Is there any truth here in your opinion?

Also, do you think adding a big bore top end to the LR bottom end would work? Or would mapping be an issue?

Everything effects everything in a 2 stroke engine!!! This is why they are so sensitive to "changes/mods" because everything is directly related...

This also why you can do the same "TYPE" of mod on the same engine but do it in a different way or using different components and acheive completely different results.. some favorable, some not with the SAME mod type..

Again.. this is what the makes the 2 stroke so challenging and fun to develop..

As for more efficient transfer of force (as you call it) with a longer rod... That can be the case or, it may be the opposite.. You could have more efficient transfer of force but if that force we are transfering is LESS due to LESS power being produced during combustion... .well.. what have you gained?

Again, you never know until you do the mod and do an actual comparison to see if you gained or loss.. The dyno test is good for this as well, but you would have to do the test with the same engine in the same time frame..Most will not do it this way..

As for a long rod on the RK Tek Big Bore.. I will not even offer it as an option since EVERYTHING we produce is backed by rigorous testing BEFORE released to the public.. and the scenario of the long rod on the big bore will have no testing behind it.. So, while it may be an awesome combination, it will never be offered or recommended.

 

[dttrusko]

2) With a longer rod, you change the "dwell" time that the piston incurs at TDC and BDC.. this greatly effects the combustion event, and its timing.. sometimes for the better and other time for worse.. It also effect air-flow and many other parameters (like is true with any 2 stroke engine). So, when this happens (for the worse), power is reduced.

Just curious on how a longer rod changes the dwell time since your piston speed is based off crank radius (stroke) and engine speed? Is it longer or shorter? You're still at TDC and BDC for one CAD with the same stroke, so how does a longer rod effect anything other than balance and side loading? I have always heard that dwell time (combustion characteristics) is changed with stroke. I agree that poos rod ratio is normal.

I agree that in a 2-stroke the air flow would be effected since there is likely a larger crank case volume and the transfer port will be longer, but IMO that is effected by the 'spacer' required and not the longer rod.. just my .02

 

[RKT]

Just curious on how a longer rod changes the dwell time since your piston speed is based off crank radius (stroke) and engine speed? Is it longer or shorter? You're still at TDC and BDC for one CAD with the same stroke, so how does a longer rod effect anything other than balance and side loading? I have always heard that dwell time (combustion characteristics) is changed with stroke. I agree that poos rod ratio is normal.

I agree that in a 2-stroke the air flow would be effected since there is likely a larger crank case volume and the transfer port will be longer, but IMO that is effected by the 'spacer' required and not the longer rod.. just my .02

Please remember it is not about velocity but about acceleration.

Also remember, that the piston will come to a complete stop at TDC and BDC (ZERO velocity).. So, from this "STOP" it must accelerate in order to "move".

With a longer rod, the piston acceleration is slower, the stroke remains the same, yet the piston is accelerating slower.

So, the transfer of rod angle with respect to the crank rotation changes more slowly when rod length is increased. you can simplify it thinking of the D=RT formula.... distance = rate * time.... so time = distance/ rate.... Distance is constant(or the same), rate of acceleration is slower.. so time is longer..

You can plot this out and see the dwell times around TDC and BDC will always be longer... there is also software that can demonstrate this as well

Having a piston dwell longer around TDC will also increase the chance for detonation to occur.. that is another negative with the longer rod.
Also, with this longer dwell around TDC, all the other "processes" that must occur (intake filling, exhaust outlet etc) get "shifted".. Again, sometimes this shift can aid in performance, othertimes it can hinder..

 

[m1kflyingtiger]

So in the context of the disadvantages of a longer rod; is there any differance in the slowing of dwell between a long rod kit and a "fix kit" with taller pistons and a spacer, or is it one in the same because the distance from the crank to the combustion chamber are the same?

Also how does it change it if the rods or new fix kit pistons are lighter than the stock parts that are being replaced?

 

[RKT]

So in the context of the disadvantages of a longer rod; is there any differance in the slowing of dwell between a long rod kit and a "fix kit" with taller pistons and a spacer, or is it one in the same because the distance from the crank to the combustion chamber are the same?

Also how does it change it if the rods or new fix kit pistons are lighter than the stock parts that are being replaced?

Sorry, I do not understand how any "Fix Kit" changes dwell time??

 

[m1kflyingtiger]

I guess that's more or less what I'm asking.

Forgive the rough measurements as they are made up for the explination as I don't know the true ones;

But let's say you put rod in that is 1/4" longer than stock rod + piston length (X) and a spacer to match it. so now your distance from the crank to the top of your piston is X+.25".

If you put a fix kit in with pistons that are 1/4" taller than stock rod + piston length (X) and a spacer to match. Your distance from crank to the top of your piston is still X+.25"

In either situation you have added the same distance, does the piston still accelerate slower than stock with the fix kit as with the long rod?

 

[RKT]

I guess that's more or less what I'm asking.

Forgive the rough measurements as they are made up for the explination as I don't know the true ones;

But let's say you put rod in that is 1/4" longer than stock rod + piston length (X) and a spacer to match it. so now your distance from the crank to the top of your piston is X+.25".

If you put a fix kit in with pistons that are 1/4" taller than stock rod + piston length (X) and a spacer to match. Your distance from crank to the top of your piston is still X+.25"

In either situation you have added the same distance, does the piston still accelerate slower than stock with the fix kit as with the long rod?

OK, I understand what you are asking.. good question

The acceleration is not related to the piston it is related to the the stroke, rpm, and rod length.. so, you can change the piston but it will not change the acceleration.

Remember we are referencing the rod angl with respect to the crank rotation.. So, the piston is not a player in this..

On second thought... It stands to reason that a lighter piston would accelerate faster than a heavier piston... so, I suspect the lighter the piston, the faster the acceleration and vice-versa...
So, I would think that the piston would effect dwell time, but not because of its LENGTH, but because of it weight/mass... Nice thinking there.. I never really thought about that aspect.

 

[Hairy Mark]

kelsey do the drop in pistons that you sell change the compression of the motor any? and are you running a different dome shape to counteract some of the affects of detonation? these are questions from a turbo application in a pro.

 

[likkerpig]

Excellent discussion! Thanks for the knowledge and insight from everyone! Please keep it going, I'm learning quite a bit here!

 

[m1kflyingtiger]

So could we counter act the negative effects of a longer rod with a lighter rod or lighter piston?

And has anyone heard of experimenting with combining a long rod with a fix kit or your drop in kit?

 

[LoudHandle]

I have heard of one guy getting a long rod engine and getting the cylinders fit by Indy Dan to run Kelsey's pistons. So maybe he will chime in if he reads this thread.

 

[BILTIT]

I had asked indy dan about fitting kelseys pistons with his long rod setup, he did not reply to that email so i assume it was a no.

 

[rmscustom]

I had asked indy dan about fitting kelseys pistons with his long rod setup, he did not reply to that email so i assume it was a no.

Dont feel bad he wont answer my emails that weren't about fitting Kelseys pistons...

And before anyone says just call him. Why do some of these guys list an email address if their not going to answer? It just seems it would be so much easier to answer emails at their convinence rather than being bothered by having to pick up the phone all day long. At least thats what I prefer my customers to do...

Oh well, now the question is drop in or 858.

 

[RKT]

So could we counter act the negative effects of a longer rod with a lighter rod or lighter piston?

And has anyone heard of experimenting with combining a long rod with a fix kit or your drop in kit?

The lighter or heavier piston is not going to counter act any ill effects of a long rod.. the acceleration difference (if any) will be very minimal it at all and not able to calculate very easy (if at all)... but the dwell of the longer rod is 100% calculatable(word?) and easy to see, touch , and feel...

The longer dwell times are a reality and offsetting them will be difficult to prove..

As for piston and "fixing" piston related issues..

The problem with the piston is NOT at the ring area but at the skirt area. So, doing a compression or leak down test will show you nothing about the condition of the lower piston.. The piston MUST be removed and measure in order to measure it.

Adding a Wiseco piston of any sort, will suffer the same fate UNLESS you make the piston so thick atthe skirts that the piston weight will be gretaly increased..

So, point being.. they will run with ANY piston right up until they fail. But just because your engine will pass a leak down or compression test tells you nothing about the wall clearances. I would suggest anybody with ANY piston (including mine) to tear down and measure the skirt area.. THIS will tell you what is working and what is not..

I can guarantee you will be VERY surprised at the results of these tear down measurements once you do them.. Guaranteed!

 

[wfieldin]

My experience with Dan is he answers his phone and emails promptly, perhaps he is out of the office on vacation or something like that.

As far as responding to Snowest, I believe he stated awhile ago that he was going to take a break from this forum, not sure if he intends to come back on or not.