Piston to Cylinder Clearance....Save my Motor

theshadowrider · Apr 13, 2011

After reading numerous threads my theory is that two many reasons the dragon motors are going down is lean midrange, I have a fuel controller and egts now, and pistons slap causing piston scuff/failure. I want to put a new topend this summer as preventive maintenance, but want to make sure things are up to spec. My understanding is that some oem pistons are out of spec causing slap and either scuffing them or breaking off piston/cylinder skirts. Also wondering if maybe the cylinders are out of spec also.

Wondering what the piston to cylinder clearance should be on a 2008 dragon 800, and more importantly how to check it? Some have told me to use a feeler gauge but that seems not that accurate. I am thinking of using a micrometer to measure the pistons and then this dial bore gauge http://www.eastwood.com/dial-type-cylinder-bore-gauge-kit-2-6in-range.html?srccode=ga150120
to measure the cylinder. I am putting a new topend and I am going to put the wiescos in it. On the pistons they say to run the clearance to oem specs. The manual that I have says .0037" to .0053". Any tips, or is this correct? Thanks

milehighassassin · Apr 13, 2011

I talked to a machine shop about having them measure my cylinders for me, they said using a bore gauge on a 2-stroke is pretty hard. He said you can get just as good of a reading with a good set of calipers.

augerin · Apr 13, 2011

There's lots of great information in some of the threads on here. Look at "get your fix for your dragon" and "another fix for the 800". I might not have the exact titles but you should be able to find them easy. Good luck.

2XM3 · Apr 14, 2011

on2 strokes I use a inside (tube) mic, as there are 2 many ports to get good reading with dial bore guage. Caliper actually can work pretty good,but can't tell you about the middle and other areas of the bore or taper,hourglass shape ect.
IMHO i'd set the weiscos at .006 and no tighter.

theshadowrider · Apr 14, 2011

2XM3 said:
on2 strokes I use a inside (tube) mic, as there are 2 many ports to get good reading with dial bore guage. Caliper actually can work pretty good,but can't tell you about the middle and other areas of the bore or taper,hourglass shape ect.
IMHO i'd set the weiscos at .006 and no tighter.

Cool thanks. Basically if they are to tight or loose then the only way to adjust things is have my cylinders re-coated to the spec needed, correct?

augerin · Apr 14, 2011

If they are to tight you can have them honed a little more. Too loose, renic.

milehighassassin · Apr 14, 2011

augerin said:
If they are to tight you can have them honed a little more. Too loose, renic.

Honing nickasol really doesn't work in my experience. It is too hard.

I think my wisecoes said no less than 0.0049

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slash · Apr 14, 2011

get the kit from PMS polaris in IDAHO it works and you get about 5 extra hp
two pistons shim and gaskets

theshadowrider · Apr 14, 2011

slash925 said:
get the kit from PMS polaris in IDAHO it works and you get about 5 extra hp
two pistons shim and gaskets

Already have the pistons. I was thinking of that kit but was worried about my intercooler not fitting correctly with my cylinders shimmed up a 1/4 inch.

slash · Apr 14, 2011

not sure there, you dont think you have 1/4 inch above the head . sounds way tight

theshadowrider · Apr 14, 2011

slash925 said:
not sure there, you dont think you have 1/4 inch above the head . sounds way tight

no, its not the head clearance, its the aft portion of the intercooler is hooked to the tunnel and with the cylinders higher I don't want to have to change the location of the mount for the intercooler. May not have to change anything, I just didn't want to get into it and realize things needed to be changed so I just went with the wisceos.

milehighassassin · Apr 14, 2011

theshadowrider said:
no, its not the head clearance, its the aft portion of the intercooler is hooked to the tunnel and with the cylinders higher I don't want to have to change the location of the mount for the intercooler. May not have to change anything, I just didn't want to get into it and realize things needed to be changed so I just went with the wisceos.

I have the wisecoes as well.
How many miles do you have? I assume you have a turbo. What was your wall clearance? Did you have to file the rings at all?

Are you running the thermostat?

I have not had the thermo in prior to this but am thinking about it because I am worried the cylinders won't heat up as fast as the pistons.

I would think your turbo setup would be a good test for avoiding cold seizure.

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theshadowrider · Apr 14, 2011

milehighassassin said:
I have the wisecoes as well.
How many miles do you have? I have 1600 total miles and 600 miles boosted. Sled was updated to 09 spec at 800 miles. I assume you have a turbo. Yes, a BD. What was your wall clearance? ? Thats what I am trying to figure out. I have not pulled the motor apart yet. I am just getting all the parts for it. I really want to measure my clearance before the weisecos and then once I install them. Did you have to file the rings at all? I have not installed the pistons yet.

Are you running the thermostat? Yes. Mine is a 155 2008 dragon 800 so it had the front cooler. I had to remove the front cooler in order for the charge tube to fit. When I did that I switched the thermostat to the 163 thermostat which is intended to run without the cooler. It has a bigger cooling hole in it I guess. But I have always run the thermostat in it and intend to after the wiesco top end.
I have not had the thermo in prior to this but am thinking about it because I am worried the cylinders won't heat up as fast as the pistons.

I would think your turbo setup would be a good test for avoiding cold seizure. I am kind of new to snowmobiles so I am not really familiar with "cold seize" I have ran dirt bikes and 4 wheelers for years and have always ran wiesco in everything I run. I have ran the trinity racing pro-lights that they machine out the understand to make them lighter with noticable improvement over stock. Never had one problem with "cold seizes." I know the theory of a "cold seize" and have ran my bikes and 4 wheelers in temperatures comparable to snowmobiling temps. I have always thought the only way to seize a motor is to much heat; keep enough fuel/lube going through it and it won't seize. Of course I have always let things warm up before getting on them. I have always liked Wiesco and thought they were considered one of the best pistons, but coming to snowmobiles there seems to be this feeling that they are the "huffy" of pistons. Seems like they have gotten a bad rap for some reason but I am much more willing to run them the the "quality" stock pistons that seem to be out there. Just looking at the quality of the wiesco's to the stock ones seems night and day better quality. In my dirtbike/4 wheelers and drag bike I have never checked the piston clearance or ring gap. I have always just put them in and gone for it. I am learning that I was a little ignorant though. Of course snowmobiles engine are a little more pricey so I am wanting to check my setup! When I tear things down I will take some photos and post some pictures along with specs of what I find of the stock compared to wiescos.

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Anyone know where you measure the piston for the wall clearance at? My wisecos measures 3.314 at the top and 3.340 at the bottom.

milehighassassin · Apr 14, 2011

I was going to start a Wisecoe piston thread, I think I will now. The intention was to take some measurements as well as weights.

Does the 163 thermostat open up sooner? Just have a larger hole?

Wisecoe does seem to have a bad rep in the snowmobile world. I think it is because of cold seize issues. I am thinking of putting the thermo back in to make sure the block gets up to temp and expands as fast as the pistons which get hot because of the combustion. There is significant evidence that shows timing gets pulled at some point (130 degrees?) and the lower you can get your coolant temps the more power is being made. Is the HP gain worth reliability? I'm not sure it is.

I plan on playing with various thermostats, drilling extra holes etc. The problem is they are not very large so drilling is going to be hard. Does anyone know if you can buy generic thermostats that will fit this motor or maybe ones that open sooner from a 600, 700, or maybe an older sled?

Polarisrocks · Apr 21, 2011

Milehigh, I used a little tapered carbide with a point for a die grinder and made some small holes in the last one we did. Since the part of the water stop is smaller that the spring top and is rounded a bit and in further than the spring top, drilling is almost impossible. Have you put yours in a pan suspended above the burner in the middle of the water and tested to see what temp it opens? How did you hear about some timing being pulled above 130? The old 800's had a idiot light that came on at 160 and the cdi would retard the timing till 220 I believe. wonder why the dragon is soo much less?

milehighassassin · Apr 21, 2011

There is a thread in here with dynos that talk about the timing and power.

I also spoke with a guy that had the 800iq on the dyno, several times. He made the comment that the lower they could get the coolant, the more power it made.

I have not put it in water, I do plan on it.

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Super Dave3 · Apr 21, 2011

theshadowrider said:
no, its not the head clearance, its the aft portion of the intercooler is hooked to the tunnel and with the cylinders higher I don't want to have to change the location of the mount for the intercooler. May not have to change anything, I just didn't want to get into it and realize things needed to be changed so I just went with the wisceos.

You should have no issues with regard to the innercooler. It fastens to the throttle body and tunnel. Being that the engine is a case reed your PMS kit will raise only the cyl and not the throttle body. It will slightly raise the exhaust but should not cause any fit issues.

theshadowrider · Apr 21, 2011

Super Dave3 said:
You should have no issues with regard to the innercooler. It fastens to the throttle body and tunnel. Being that the engine is a case reed your PMS kit will raise only the cyl and not the throttle body. It will slightly raise the exhaust but should not cause any fit issues.

Duh, I always forget that these engines are a case reed engine. Thanks

hymarkin754 · Apr 21, 2011

I just finished installing the stock wiseco replacements and I had to trim the piston rings a fair amount to get to specs. Just heads up. Don't just slap 'em in. Like I've done on past sleds.

Arctic Thunder · Apr 21, 2011

How to measure clearance

Here is some information in the Arctic cat service manual.

It works the same no matter the sled type.

I would also bet the clearances for the 800cc cat motor are pretty darn close to the 800 pol motor.

Maybe it will help out.

Thunder