SnoWest Snowmobile Forum - View Single Post - 850 gone down already??
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Old 12-16-2018, 10:50 PM
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Originally Posted by ANTHONY11 View Post
3rd ride on my Assauly 850. Not sure wtf happened. Started from garage (not heated) and put it into my truck. Started right up as usual.

Drove 20 min to location and sled would not start. Plugs dripping wet. Pulled plugs and pulled over engine multiple times to clear fuel out of engine. Dried plugs off and finally got it going. It ran like a bag for a few minutes until i cleared it up.

After about 15 minutes, I took off from a stop about 1/4 throttle and sled shut right off and died. I almost flew over handle bars. Engine feels tight when trying to turn over and started it but shut it right off. Sounds like something bad in the bottom end (crank bearings?)

Has anyone ever seen this or heard of this? Sled has 80 miles on it 91 octane only VES Extreme and has not been beat on and following proper break in procedure.

Pulled plugs after I got towed back to the truck and they look slightly tan.

Thoughts?
We unloaded our our new 174" - 850 and pulled the head to check the bench volume..... Found the cylinder finish to be as bad as the 2008 Dragon motor.

Also looked like the early 800 Ski Doo's that were eating ring faces.

We built a cylinder base torque plate, & Head torque plate and measured it up and put it in the power stroke for about 20 minutes with our finest super abrasive shoes.... And then plateau polished it with 2 finishing shoes.

Total time in the hone 40 plus minutes plus set-up. ( took out between .0003 to .0004 tenths )

Whatever 850's have the finish this one had won't make it thru the first season.

It's funny the cut away motor at the Polaris show had a cylinder finish like a mirror just the way Silcon Carbide cylinder have to be for long piston & ring life.

I'll try and post the before and after pics of the difference.

On our stock cylinder you can feel the cross hatch deep grooves with your thumb nail. ( this is a death sentence to a ring and piston )


After enough miles the Pistons will look like the oil pump stopped. ( the intake skirt will look like it was dragged down a gravel road. )

Silicon carbide should not have deep cross hatch like a cast iron bore. ( even cast iron should be plateau honed )

The silicon carbide process is so porous you have to plateau polish off the sharp peaks as much as possible .

Honing is a process required ( on a cast iron bore to remove threading from the boring process..... ( and to create an ( X ) cross pattern to #1 cut in the rings #2 hold oil. ( cast iron bores are very soft )

In a silicon carbide ( there is no threading ) from plating...... The silicon carbide
Is electronically applied..... ( very thin to under size it )

And it's harder then a honeymoon hard-on..... The hone is needed to then cut ( with ( DIAMOND ) impregnated super abrasive stones.

I said ( only needed to cut to size ) not to created cross hatch.... Cross hatch is a by product of sizing...... ( it's actually a bad thing ) on plated cylinders.

On silicon plated cylinders the cross hatch needs to be polish away as much as possible. ( from what I have found ) it's almost impossible to over polish and it is next to impossible to remove all the cross hatch.

Once you get that fine of polishing shoe the plateau gets long and smooth and it will no long remove anything it just creates heat.

You seem to hit a wall at about .0005 tenths.

Dan
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Last edited by indydan; 12-16-2018 at 10:54 PM.
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