Piston To Cylinder Wall Clearance [Archive] - Snowmobile World : Your #1 Snowmobile Forum

: Piston To Cylinder Wall Clearance

09-02-2003, 10:59 PM
What is the recommended clearance/tolerance between the piston and cylinder. Getting ready to do the top end, and debating whether or not to replace the pistons or just put new rings in. Thanks, Butch.

09-02-2003, 11:31 PM
what sled?


09-02-2003, 11:57 PM
it is usually based on that of bore size. The bigger the bore, the more clearance needed for expansion. About .009-.010 is about max on your sled (800 Twin Rotax) but most end up .012 or more.

09-03-2003, 08:38 AM
I have almost .009 on my 800 cylinders with Elko pistons. I have decided to go the wiseco route with coatings. I will now have .006. The high limit in the service book is .0057 for the Elko's.

09-03-2003, 09:23 AM
Originally posted by 377safari@Sep 2 2003, 09:31 PM
what sled?

MXZ 800

Has anyone had their pistons coated by any of the various high temp. coaters out there (swain tech., fireball, etc.)? Can they do used (but not abused) pistons or do they need to be new. Just wondering what options are out there and what those with experience would recommend. Thanks again, Butch.

Now off to measure I go.

09-03-2003, 09:23 AM
Wiseco recomends .0085 Pete. I would not run anything less. Mine is setup for .0092.

09-03-2003, 09:43 AM

The sticker on the piston kit I have from wiseco says clearance .0051. I am going to .0061.

Do you have a different kit than I do???

09-03-2003, 10:06 AM
Also how did obtain .0092 clearance?? The wisecos I have are bigger than the elko's. without coating there on the tight side. about .0045. Did you have the NIC honed???

My elko's were about 3.2202. The wisecos are 3.2231. is there that much difference from one wiseco kit to another???

09-03-2003, 11:18 AM
Dave, did you notice any problems with lean conditions, like those mentioned in the tech section. I believe it is talked about on the idooski project sled. The part about the sides of the pistons being cut out vs. the stock pistons having a solid area around wrist pin. Is this something to be concerned about?

09-03-2003, 02:35 PM
Butch... I believe you would be just fine with the Wiseco's. They don't have the recess around the pin. I believe that the recess is a real concern. I hear that a lot of people are having good luck with the ART pistons, but there are several that are having trouble. It has nothing to do with ART. It's just the recess in that particular piston.

09-03-2003, 06:58 PM
Thanks Kieth, I didn't remember which brand had it and which didn't.

Where's the best place to get Wiseco's, directly from them or a place like Shadetree or Dennis Kirk? Thanks.

speed is everything
09-03-2003, 07:30 PM
I had fireball coatings moly coat the skirts and ceramic coat the domes on my wisecos for my 01 mxz 800. Wiseco says to run .0051. I am running .0055 with the coating. The coating adds about .001

09-04-2003, 11:52 AM
Just measured my pistons and cylinders. The pistons seem to be tapered. They are 3.205/3.208 on top and 3.220 on the bottoms. Is this normal? Cylinders measure 3.229/3.230. I don't have a set of 3-4" mics so I have to use calipers. This may cause some of the variance but not .012 to .015 in the pistons. Also, my pistons say ELKO on the insides. Pardon my ignorance, but why is there a difference in these (stock) pistons and the ones that are giving people trouble (window cut in sides)?
Another thing, I did a stupid move, and pulled one of the pistons off the rod and OOPS! I forgot about the cageless bearings. Any tricks to making sure I don't any more dumb manuvers? Do the Wiseco's come with new bearings and are they caged? Thanks again.

09-04-2003, 12:02 PM
lol!! Ya you need to watch those needles!! There should be 28 of them.

All pistons are tapered. The biggest measurement is under the wrist pin 90 deg. to it and about 3/4" down. measure in several spots with a mic ( verniers ain't gonna cut it) until you find the highest reading.

The elkos are solid on the skirt where the wrist pin resides. The ART's have a cut out for weight savings in this area. Wisecos do not come with bearings, buy the doo setup.

How does your wrist pin look???

09-04-2003, 12:15 PM
.....25.....26......27......??.....oh! there it is.....28. O.k. I have 'em all. I did loose one of the washer/spacers on the side. I'll have to keep looking though. Wrist pin seems fine a little discolored, but no grooves or burrs that I can see. haven't looked at it real close though. I was busy picking up needles.LOL.

09-05-2003, 12:23 AM
Butch, that is too much clearance IMO

The Wiseco spec is .009

Elko is the vendor that makes the Doo (and many Polaris) pistons. I know you had your recall done, and doo put in the same pistons. There is no "update" piston as of yet.

Many are having success with Wisecos that have been coated.

09-05-2003, 09:43 AM
Dave, did you have your Wiseco's coated? If so by whom? and can you buy them directly from the coating place? Is the coating really necessary and what is the ballpark price? Thanks, Butch

09-05-2003, 07:42 PM
Butch, I just wanted to point out the mistake I made in the earlier post. I was referriing to the ART's the whole time.

Okay...now another problem we need to address here. Who has the correct clearance for those Wiseco's? We can't be posting different clearances for the same product. .004" might as well be a mile (or two). I'm off to Wiseco land to see if I can find out anything.

09-05-2003, 07:54 PM
I sent off an e-mail. Hopefully, we'll have a definitive answer.

09-05-2003, 08:14 PM
The kit I have says .0051. I was told to go .001 bigger.

09-06-2003, 12:39 AM
Butch, fish all those needles out of the case with magnet put them in a ziplock and throw them in the junk box. Order a set of '99 670 formula Z bearings part#420832442 (no other 670 will work). For some reason that 670 had a bigger bearing. I also have been using circlips that have a little dogleg on them that make life much easier. They were a watercraft part but your sled dealer should have them, part # 420845106.

09-06-2003, 03:49 AM
Keith, I have seen two sets of clearance numbers from Wiseco. They used .0085 (overal) in 2002-2003, but last year they changed to .009. This number is what was put directly on the boxes. I bought a set early last year for myself and they were the .0085, but I ordered a set of Damon last year as he couldn't get any in NY, and they came marked .009. I rad my cylinders setup for .0093 clearance.

09-06-2003, 10:18 AM
Pounder, I got all the bearings out,. But, I'm still trying to find one of the washer/spacers that hold the bearings in place. I don't plan on using it , but I'd sure like to know where it went. The 670 bearing you mentioned, is that a caged bearing?The circlips I have now, have a dog leg on them. Maybe the dealer put them on when he did the piston update.

Doug, do you have any prices (just somewhere in the ballpark)

09-06-2003, 12:24 PM
Butch, yes they are caged. They don't use the part you lost (look in the gaps next to the crank?).

10-05-2003, 10:13 PM
:D I'll second that on using the caged bearing. List is like $18.75 and worth every penny. No more dropping and loosing parts. :doh:

10-05-2003, 10:39 PM
I checked the box for my Wiseco pistons on a 03 800 and it says .0051

Here is a pic of Fireball Coatings 800 Wiseco piston.

10-06-2003, 11:15 AM
Why do you guys insist on changing to caged pin bearings? The reason Rotax uses a cageless bearing is so that they can add additional rollers for more piston to pin support. If you take them apart carefully and install new bearings each time like you should, there would be know problems.

10-07-2003, 02:32 AM
rotaxlover has a good point, the caged use 15 needles compared to 28 cageless. I found out about the caged bearing cross reference from the raceshop guys a few years ago, they change a lot of pistons and the caged ease the procedure. I've been using them off and on in 700's and 800's since and haven't seen any problem. But logic (needle count) dictates that the cageless is probably better. Lots of caged bearings out there though in other makes and models and even 1000cc+ mod twins. So lets just say you have an option to consider.

10-07-2003, 08:19 AM
Ahhh good info. I have been wondering if I should go caged or cageless. Well you just answered my question... I will be ordering the cageless ones.

From what I understand installation is easier than in the past. Just push the pin through and your good to go.

I will be finding out soon.

10-07-2003, 10:13 AM
Hey 800REV,

Have you checked the clearance after the coating was applied?? I'm curious as to how tight it is now.