1983 XC250 piston clearance

I picked up an 83 Husky xc250 a while back. The current piston to cylinder wall clearance is .007". The cylinder is on its first over bore I believe as it has a Wiseco .020 piston. The cylinder walls are decent and not out of round. My question is, hone and new rings or rebore and install larger piston? What is the max clearance before a rebore is necessary? Thanks in advance.

Todd R.

Forgot to add bore is 70.04 mm

check out the HVA fctory website as there is a section on manuals etc that should provide you the info

wait- ive got a spec sheet here for 81 - 84 and the rebore spec is 0.088mm

ring end gap max is 0.8mm

your good to go

Checked out the site, thanks. As per the owners manual the max clearance is .3mm or .011 inches. Sounds like a lot. My piston to cylinder clearance is .007 inches. The number you reference, .088mm translates to .00346 inches. Could this be the clearance required on a new bore and piston?

O,007 inch equals 0,18mm tolerance.
Factory replacement spec was 0,15mm.

Thanks for all the comments. Ordered a second oversize 70.5 Wiseco piston kit. Clearance specs on the box states .002 in. From some of the comments I see on this site regarding Wiseco forged Pistons, I am concerned .002 inches may be a little tight. What is the collective opinion on the clearance for Wiseco pistons?

I run a Wiseco piston 3 thou clearance..

On the air cooled 250 I prefer to start at .003" and replace at .006". Run .012" ring gap.

You also need to check the bore for out off roundness and to make sure the next size will clean up when bored. I have had to go up to 2nd oversize from an egged std bore on my 84 250WR cylinder and also on the 86 400WR cylinder. All those wonderful ports remove surface bearing structure from the piston. This results in the condition I just described.

much like the above posts state. you must bore first..until the cylinder is round. then you will know which piston to order. once the piston is in the machinists hands he can finish hone it.

I rough bore it till the bore is clean of all scoring to get the next piston size, then when the new piston comes I measure it then finish bore it.

250 bores

Piston size wossner
69.45 mm is 69.50mm bore
69.94 mm is 70 mm bore
70.44 mm is 70.5 mm bore
70.94 mm is 71 mm bore
71.44mm is 71.5 mm bore

Just to give you a rough idea what the next over size is.

Check the bore size twice on top making a X and do the bottom too. This will let you know if it's round top to bottom and check for taper top to bottom.

You guys sure make a simple thing complicated!

It's not complicated we just want the bore correct. It's in our control. When using the gear driven adjustable hone to finish the size or before you need to make even slow strokes with the hone. If you move it too fast the bore will be tapered or out of round. I accept nothing but zeros. On the bore it's .0000" on the taper it's .0000" perfect. If it's off and still under the bore size it can be rehoned by spending more time with the hone on the end with the error. I put more honing oil on the end I don't want to change.

I've done so much boring you learn.

You should not even be removing stock when honing. An excellent machinist can quite often finish bore down at a fine rate, reverse bore back up and completely eliminate the requirement for a finish hone as that technique will yield a very shallow crosshatch that will break in in a fraction of the time.

its like oil mixes, everyone has a plan

No way you need a 500 grit stone for the finish. Can't do it with out honing. I can use the gear driven adjustable hone and make the bore any size. I have 80 grit, 180 grit, 280 grit, 400grit and 500 grit stones for the larger hone. The smaller gear driven hone I even have nikasil stones I just purchased. I'm new to this too. I also have a scotchbrite ball use use to clean up a bore. It's new to me.

My older sunnen gear driven hone was worn out where the gear racks were. It's like a $800 hone. These gear driven homes aren't your spring loaded hone or ball hone.

https://goodson.com/collections/cyl...MI7KDw_4S_1gIVw7fACh0wVw8cEAAYASACEgKgafD_BwE

http://www.enginehones.com/?gclid=EAIaIQobChMI4KSs7YW_1gIVx7bACh164g-0EAAYASAAEgLbW_D_BwE

For going up one over size these are perfect. To go larger better to save time and bore with a cutter close the finish hone.


Go on you tube see Ken O Connor his videos explain boring and honing.

I only do the way I was taught. I had a chance to learn from one of the best. I listened and did it his way.

The people who knew the most likely died before youtube or were retired and very old.My father had shown me his Puch cylinder after he got it done by a very talented jig mill machinist. I asked about the honing as it was very fine and very clearly defined.I was told to look at the pattern under a loupe. I was a 14 year old freshman and about 2 weeks into high school metal shop when I learned about this. Under the loupe and a directed light source I could easily see the definition of the pattern as having been cut with about a .002 corner radius boring bit and certainly not torn by honing media.

So Bill, just because you have never done it, it does not mean that no one can. I did it myself as a test when I was training on a jig bore. The machine needs to be rigid and well lubricated

Thanks for the replies folks. I couldn't respond sooner because the site would no longer allow me to navigate from the logon page. I had to register for a new account in order to use the site again. Is there no way to ask an administrator?