Pro RMK Piston rock (a video-if I can get this to work)

[Murph]

http://www.youtube.com/watch?v=4496rTnKZMg&feature=youtu.be

For those of you that have not seen the inside of your cylinder first hand.

Always heard about the rocking of the piston in a Polaris Pro motor-- never realized it was so extreme. Never seen a piston that loose in the bore before. Both pistons rock at ALL locations in the stroke BDC, TDC, and everywhere in between.

 

[EASY]

just tried it. doesnt work yet

 

[Murph]

Think the link is good to go now.

 

[EASY]

Thanks worked. Great vid

 

[Vfrtrader]

what are the normal clearances of a liquid cooled 2-stroke? Normal cfi-2 is 4 to 5 thousands? Which slops around and becomes 10? Then ka-boom.

 

[AKSNOWRIDER]

murph..all motors do that to some degree..the issue with the poo is the bores are normally tapered and bigger at the base..the reason for so much clearence is due to how fast(or slow) the piston can transfer heat from the piston dome to the cylinder wall, cast pistons are weaker..but can run a tighter clearence(normally.002-.004 )where a forged piston normally needs more(.005-.006) to not scuff..the polaris, when you add on the thinner casting of the cylinder, large exhaust port, large powervalve and limited cooling around the exhaust, all combine to make a cylinder bore that moves far more then a normal cylinder(hence you need more clearence on the piston)..the fix..thats easy...better after market cylinders with more coolant around the exhaust, better flow, and thicker heaveir casting..then you can tighten those clearences up to normal ranges....nice vid though.....

 

[snowmobiler]

never seen a sled do that.must not have any rings.

 

[AKSNOWRIDER]

never seen a sled do that.must not have any rings.

biler..have you ever even seen the inside of a motor in person before?..and I am not talking about the one in your doo that has the hampsters running around in the little wheels..................

 

[flying frenchman]

Is this your 2011 and how many miles.

 

[Murph]

never seen a sled do that.must not have any rings.

Rings are in. That is exactly how it was when the head was removed. The cylinder has not been removed yet.

 

[Murph]

Is this your 2011 and how many miles.

Yes. My 2011. 2500 miles. Will check the cylinder skirts next.

All stock. Still under original 4 year warranty.

 

[flying frenchman]

Did you do a comp test before taking it apart. Thanks for the info.

 

[sketch96]

Yes. My 2011. 2500 miles. Will check the cylinder skirts next.

All stock. Still under original 4 year warranty.

so you got 2500 miles with no troubles?

 

[black swan]

nice vid

EXACTLY!!!!


mine seemed worse 1700 miles, when the piston was top-dead in stroke the gap felt 1/16th on each side.

Or press the piston up against 1 wall and if felt like 1/8-1/4" of gap on the backside....


thanx Murph!

 

[Pro Wrench]

Thanks

I got to say Murph I appreciate the video but am a little disappointed. I was expecting a video showing the piston rock while engine was running.lol

 

[Murph]

Did you do a comp test before taking it apart. Thanks for the info.

Took sled down to my other place at sea level. 110 psi and 105 psi @ sea level.

 

[Murph]

so you got 2500 miles with no troubles?

Yes. Three Pro RMKs.
This 2011 2500 miles no engine troubles.

GF 2011 2000 miles no engine troubles.

My 2012 1500 miles no engine troubles.

6000 miles total. 6-9000 feet, rarely on trails, deep heavy Tahoe pow.

 

[Murph]

I got to say Murph I appreciate the video but am a little disappointed. I was expecting a video showing the piston rock while engine was running.lol

Yeah my see through cylinder is at the lab!!

 

[Jmgsnowman]

Heat expansion

I would be interested to know how much the diameter of the piston expands when up to operating temperature.
Any thoughts?

 

[poorider]

EXACTLY!!!!


mine seemed worse 1700 miles, when the piston was top-dead in stroke the gap felt 1/16th on each side.

Or press the piston up against 1 wall and if felt like 1/8-1/4" of gap on the backside....


thanx Murph!

You have to be exaggerating. We're talking about 10 thou being a lot. You're saying you have somewhere between 125 and 250 thou clearance between your piston and cylinder?