Axys Piston In Pro?

I just want to offer my experience as an engineer and an enthusiast who has broken parts. Pistons that are not direct replacements, meaning they weigh the same, are not drop in. Rotating assemblies must be balanced. Dropping in a lighter piston or rod throws the assembly out of balance. Balance is often determined to be within one gram of perfect balance by a seasoned machinist. That being said, you have some wiggle room you can live with in a short lived two stroke motor. The impact will be increased vibration and a shorter rev range...in short, your rev limit will decrease mechanically. The more out of balance you get, the more premature wear will take a toll on your motor and shorten its life. At the extreme, you will break the crank.

So, if you want a lighter assembly, put the axys crank, rods, and pistons in. That way you know the factory has balanced it. Otherwise, throw a good similar weight piston in with a fix it kit to reduce rod angle which will reduce stress on the rotating assembly. As a turbo sled, you should put a fix it kit in and run it. The change over to an axys setup is expensive for small gains in rev. Just my thoughts. But, how you ride will determine if that rev is important to you.

xpturbo600 said:

I just want to offer my experience as an engineer and an enthusiast who has broken parts. Pistons that are not direct replacements, meaning they weigh the same, are not drop in. Rotating assemblies must be balanced. Dropping in a lighter piston or rod throws the assembly out of balance. Balance is often determined to be within one gram of perfect balance by a seasoned machinist. That being said, you have some wiggle room you can live with in a short lived two stroke motor. The impact will be increased vibration and a shorter rev range...in short, your rev limit will decrease mechanically. The more out of balance you get, the more premature wear will take a toll on your motor and shorten its life. At the extreme, you will break the crank.

So, if you want a lighter assembly, put the axys crank, rods, and pistons in. That way you know the factory has balanced it. Otherwise, throw a good similar weight piston in with a fix it kit to reduce rod angle which will reduce stress on the rotating assembly. As a turbo sled, you should put a fix it kit in and run it. The change over to an axys setup is expensive for small gains in rev. Just my thoughts. But, how you ride will determine if that rev is important to you.

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From an amateur that have also broken things..

I am NOT an engineer, but I have followed the two stroke world of snowmobiling for a couple of decades now and I have to disagree with you. The piston is a weight going up-down and cannot be balanced fully by a rotating weight.

The snowmobile world messes around with motors so much, I'll just point straight to some pretty credible (in my book) examples:

Polaris made a 600 and 700 engine in 1998 where the difference was cylinder bore, heads and pistons. Aftermarket bored them to 85mm and used 800 pistons to get a 770 (less stroke) and these engines lived long happy lives.

Jason Houle of Straightline Performance used to dragrace Arctic Cats, also the T-Cat and he stated that they messed with different pistons (weight) a lot and what mattered was equal weight in each cylinder.

My own dinosaur engine, a Price Performance 1029cc is built on a 680cc Ultra (66,6mm) and spins those 82mm big-bore pistons at 9800rpm!! No problems.

As for this specific engine, MtnTek came out with the first "Fix-kit" piston set many years ago and have sold literally thousands of them. These are facts.

MY advice to OP: watch compression as the rings seem to go bad first. Remember, the piston relies on good contact with the cylinder through rings to bleed of heat. And if you do change pistons, whatever brand, please check piston to cylinder clearance and ring-end gap!

Cheers,

I believe that Indy Dan does not recommend this piston swap...

The AXYS piston is not worth the extra money, buy a set of '14 on up PRO pistons.

I'm one of those Engineer fellas too with lots of experience on this subject. Get yourself a Wiseco piston kit. Comes with 2 Forged pistons and all the seals for like $200. You will see reduced vibration and slightly better response. Fix kits with the shim are a gimmick and Polaris pistons are overpriced.

LOL...

Many have ran the axys pistons in the pro's.

I personally chose the RK teks over the axys pistons because of price point and over stock pro pistons for the different dimensions.

The Pro piston has been upgraded over the years since it was initially introduced. I would personally stick with that piston as it was designed for that engine. They may have tweaked different aspects of the Axys piston for that engine. Just my $.02.

RKTek direct replacement pistons in my Boosted 13 pro. Ran it last year with no problems at all. If you get RK Tek pistons take a look at the piston skirt and compare it with your stock pistons. You can easily see why they are a stronger piston.

Skip the fix kit and just but some good quality wossner pistons, 3k turbo miles and no problems with several in our group.