Wiseco Pistons - Secret Mens Business?

[Lozza]

Our own JimG had his early YZ 125 nip up several times at last years DT titles in Griffith, every time was at the end of the main straight while he had backed off.

That will be to lean in general usualy the pilot and the main.

Just bake at 200c for an hour and then take it to have it rebored.

[john d]

dale,
 We had a small Penton , Hodaka , Cam Am shop back in the early 70's and did our own boring.
We found that Wiseco pistons made at that time were prone to sticking if set up to Wiseco's specs.  End result , we would only fit one to a cylinder on the customers request.
10 years ago we started restoring and riding vintage dirt bikes in the woods and at the yearly ISDTRR we have on this side of the pond. Pistons ( NOS ) were in short supply for one engine we were using so we called Wiseco to see if they could come up with a cross for another brand they made that would work.
 Wiseco had a Tec line back then and we brought up the sticking problem we had experienced. The Tec  went into why the old pistons would do this and what they had changed over the years to correct the problem.
 Wiseco in 2001 was using the same alloy they used in their pistons in the 70's. The difference in a new Wiseco was in the way the piston was machined.
  Pistons are egg shaped front to back and tapered from top to bottom. This is ( we are told ) done to allow for the different rates of expansion caused by the differences in the amount of material present at any one spot in a given pistons design.
The pistons are " Cam " Ground to a shape that approximates round when they are at temp and under load.
 New Wiseco's have worked well for the Penton , and Hodaka guys here in the US in competition .
If all you can find are the old run pistons then fitting them looser is an option but still may give you trouble in the end.
  Best thing we have found ,  you can do in a home shop , is run the engine in with a good high output fan blowing over it for 10 or so minutes . Pull the top end down and hit the high spots on the pistons with 400 grit wet dry. Reassemble and do it again until you no longer find signs of high spots.
 Its something the Road Race folks had to do years ago. Its a pain in the lower extremity's but is is do-able with limited resources and if no other pistons are available.
hope this is some help,
john d.

[dalesween]

Great input Jonn D, i have grown to trust my mechanic(and that does'nt come lightly)being Shane Ireland who owns Slipstream Motorcycles here in Melbourne,he is slightly older than me and is a Yamaha trained mechanic but also is not afraid to mix it with a few Victorian road race titles under his belt plus being a sponsered KTM enduro rider a few years ago now,was sponsered by JD motorcycles and yes Jeff cofirms this, but anyway he says he has worked on alot of bikes over the years(race teams etc) and says the piston failures from wiseco you could count on one hand,thats a shitload of bike racing in 25 odd years ,plus he uses wiseco in his current KTM 450 taken to a bigger size, and he said "i would not sell you a piston i would'nt use myself, your bike is ready to thrash with a few simple breakin proceedures" but that was only the heat cycle for a start and just use up to 80% throttle for the first tankfull and i could honestly not be happier with the way my IT has run in the past year and a half.

cheers Dale.

[Woody]

I've gathered from this thread that 'pistons aint pistons' to coin the ole Castrol phrase.

I have picked up two Wiseco piston kits of the same bore size for my YZ125G. The first kit is an old version and even has 'spiral' clips. The other has a newer logo and it is bevelled (?) between the ring and crown, but still carries the older model numbering of 435P2 (now 435M05650). 

Based on what's been said in this thread I gather it would be unwise to replace a worn piston with another from a different era? Should I toss the older one?

The other issue is clearance. The sheet with the old piston says .038mm for 52 -60mm bores and newer one says .051mm.

I guess it would be best to stick with the latest #435M0XXXX versions from now on
cheers

[Freakshow]

JUst GIve it clearance. 
and dont use those Loop clips, use the later circle clips, there is a large chance the wire that goes back into the centre will vibrate -break off and go into the motor.
 if the piston doesnt thave the tear drops in the gudgeon area like the one on the right, just grind a little spot there so you can fish out the normal circle clips out easier.

[Mike52]

.038 is .0014 thou and .051 is 2 thou.
Yep that might just nip up real easy.
Those are watercooled clearances.
Did my trade as a engine reconditioner , started at Bryant Engineering in fortitude valley.
Have kept my hand in ever since.
My favourite is the boring bar.
Have bored thousands of engines.

[Woody]

thanks guys,
so Mike52 what clearance do you recommend for an aircooled 1980 YZ125G 56.50mm bore. the later Wiseco pistons suggest to go for .051mm.

also when did drilling the three lube holes in the piston become common practice?
cheers

[Mike52]

thanks guys,
so Mike52 what clearance do you recommend for an aircooled 1980 YZ125G 56.50mm bore. the later Wiseco pistons suggest to go for .051mm.
also when did drilling the three lube holes in the piston become common practice?
cheers

Cast or forged?
.051 [ .002 thou] across the bottom at right angles to the gudgeon on a cast piston would be fine.
Give the forged one an extra .001 to .00125 thou at the same place.
Have never understood the metric system.
Really prefer imperial stuff because I can picture it in my mind.

[Freakshow]

= a poofteenth or beesdick, banana hair all very close in size

[Curly3]

A mickey whisker.

[Mike52]

= a poofteenth or beesdick, banana hair all very close in size

A mickey whisker.

Which are all the same as a cigarette paper of course. 

[LWC82PE]

I think its just the Wisecos on the blue boxes that need to be pre heated. Im sure i read that somewhere on here. Never had problems with Wisecos. before.