This is the email I got from wiseco today:

Hello Pete,

Yes you do have an M series piston. Your top end kit is the correct
one for your snowmobile. Your piston measurements are correct, as well as
the piston to wall clearance of 0.0051" as a recommended minimum. Your
engine originally came with a Nikasil cylinder, which is not machine able by
standard means. If someone is installing a sleeve in your motor, than the
sleeve will need to be bored and honed to fit the piston. In a stock
machine under standard uses, these pistons will work great for you. If
modifications are being done, then your piston to wall clearance may need to
be adjusted, and you should consult your engine builder. If you have any
more questions regarding this situation, please contact me at 1-800-321-1364
x3109. Thanks, Tom Davis.


800MXZ is running .0092 clearance?? Are you using a cast iron bore instead of the nicasil??

PETE: I got your e-mail. It sounds like you got your answer straight from wiseco. Myself I am running .0055 and that includes the moly coating. So far so good but time will tell. This clerance should be enough as long as you give the machine time to warm up. Good luck and let me know how it turns out. P.S. dont forget to run
premix after you put it back together being that these animals dont inject oil at idle.
:D

Now, it depends on how they measure. If they are talking "per-side" I am right in the ballpark. That means they recomend .0051 per side, so you double it as I measure it. I set it up to the clearances that came with the piston, plus about .0005 for safe measure. I had the engine apart after about 500 miles to re-shim the cylindres and it looked perfect, so Im not worried.

I have always understood clearances to be based on diameter not radius. Doubling .0051 would yeild .0102.

I understand the bigger the bore the more clearance you need.... but .010??? Am I not thinking right here??? Just doesn't sound right.

Not trying to argue, just want to get to the bottom of this as there has been alot of different answers.


My elkos had .008 total clearance and I thought this was big.

To compare, a car engine of a similar bore will have more clearance.

Make sure to measure at the bottom of the cylinder .008 overall is fairly tight IMO, but I like them a little looser than most. Mine was .015 after 1200 miles with the Elkos

Now i'm intrested. My question for wiseco would be why the 2 different measurements. I talked to a machinist tonight for a different point of view and he told me that the clearance on the box is the total clearance, meaning that if the box says .0051 that means the cylinder should be .0051 bigger than the piston, not .0051 for the right side plus .0051 for the left side. My guess is that they changed the amount of silicone in the pistons creating less expansion. I ordered my pistons about 6 months ago and it said .0051 on the box. Has anyone ordered any lately or maybe a year or two ago, i am going to call wiseco tommorrow and get to the bottom of the different measurements required. DAVE how did you get that much clearance, i think the thickness of the nikasil is about .004 to .006 that would mean you would have to go through most of the nikasil to achieve this clearance. P.S. hows the 800 project coming along haven't talked to ya for a while.

Speed is everything,


I have to agree with your machinist friend. I myself have been machining for over 20 years and have always understood piston to wall clearance to be a diameteral dimension not radial. All engines I have ever assembled were set up this way.

Some automotive engines I have put together with cast pistons were set as tight as .0015. That's .00075 per side. But that's a 4 stroke turning way less RPM.

I'm sure Wisecos recommended .0051 (which my box reads, purchased 2 weeks ago), means total clearance. About .0025 per side.

I also feel you are right there with the clearance you have, even though I have been told by others to go a full thou. bigger than recommended. I am going to set up mine just a tic bigger like you have.

Alot of this descrepency could be coming from the way the bore and piston are being measured. Hell I have heard of some guys using feeler gages?? WHAT!!! The only time I have seen this method done is in the service books I have for FORD 8N tractors from 1930.

IMO, at least a good telescoping gage and mic are needed. I use a bore gage and gage blocks with 3-4" mic. This setup will measure to the nearest 1/10 of a thou. The other way you can get close but need to take the measurement several times, looking for repeatability.

Let us know what wiseco says..

Dropping the Wiseco into my cylinders gave a clearance of .009, and the pistons I had (bought 1 year ago) asked for .0085 or .0083. Then i bought a set for Damon McCarther aftert he couldnt get any out in NY, and they were .009 recomended clearance. Around here at the marina, when using Wiseco, if a clearance is not available, we try to use stock +.001, and stock spec is .006 i believe.

Also, I called Wiseco 1 year ago when I had the discrepinancy of the two sizes, and they gave me the .0085 spec over the phone. They might have made a change in the piston not requiring so much clearance.

I agree on the different piston. This set I have is what they call an "M" series piston. The instruction say to try and maintain the recommened clearance. My guess is that they have the expansion rate under control vs. earlier pistons. More silicon content. I heard they use so much that they are almost hyperutectic.

Well i called wiseco. I asked them if there were different clearances required than in the past for these pistons on the 800 twin. He told me no! The problem is that i know that DAVE knows how to read so i tend to believe DAVE, these companies change things all the time then deny it. As far as the clearance required they told me that the specified number on the box is total diameter, meaning that the piston should be .0051 smaller in diameter than the bore size, + .0005 to .001 for moded motors.

I talked to the local doo dealer yesterday about the Wiseco pistons. He order 4 pistons for a Funkhouser Racing, The build racing karts. Anyway, all 4 pistons were the same part number and all 4 measered different. Different diameters and deck. He said it was just a thou or two but, when you build high hp engines, everything has to be right.

I would send them back. My pistons both measured exactly the same. Sounds like a quality control dept. issue to me and i sure would be #####in!! that could cause some serious problems for an unsuspecting engine builder. :cussing: :cussing:

The correct clearances should be manufactured into the piston (at least they try, + - what ever). If you look at the wiseco ring Part # (3228KD for the 800 twin) it is the needed bore size for the correct clearance in inches 3.228” Also that will be the OEM bore spec. 82mm (800 bore) = 3.2283”. They manufacture the pistons undersize of that spec for their needed clearances (OEM and Wiseco). There are + - tolerances in everything, if the cylinder is smaller than 82mm it will be tight, larger, loose. If you measure exactly 82mm and still too loose I would think you’d have an issue with Wiseco.