Two smoke boring

[halmc]

I have a Yamaha IT 175 that needs an oversized piston fitted. Everyone in my neck o' the woods wants to hone the cylinder, but I want it bored.

My question: any folks out there in ADV land have a machine shop that they use to bore small (~67mm) jugs? Although I'm in N. Fla, I don't mind shipping via ups, etc to a machine shop in a distant place.

PS: I've looked for a two stroke section of ADV, but never found one. If this note belongs somewhere else, please PM me and let me put it there.

Thanks!

[SpeedFourJoe]

I'd check with Enduronut on http://yamahaenduro.com/. He really knows the old Yamahas. I think he charges $40 for bore, hone, and chamfer.

[mykill]

Try Gary at http://www.spec2.com/

He has been doing 2 strokes forever and knows Yamahas intimately. He also did all the boring for Moto Carrera as well as numerous other shops around So. Cal.

[MSrider]

Send me a PM. We can do it here.
http://www.titanracinginc.com/

[concours]

Originally Posted by halmc

I have a Yamaha IT 175 that needs an oversized piston fitted. Everyone in my neck o' the woods wants to hone the cylinder, but I want it bored.

My question: any folks out there in ADV land have a machine shop that they use to bore small (~67mm) jugs? Although I'm in N. Fla, I don't mind shipping via ups, etc to a machine shop in a distant place.

PS: I've looked for a two stroke section of ADV, but never found one. If this note belongs somewhere else, please PM me and let me put it there.

Thanks!

The oversize piston fitment process involves both, first we bore, then we hone to final size and cross hatch pattern.

[Strong Bad]

Originally Posted by concours

The oversize piston fitment process involves both, first we bore, then we hone to final size and cross hatch pattern.

This normally is the correct procedure. However, it does depend upon how much material needs to be removed.

[concours]

Originally Posted by Strong Bad

This normally is the correct procedure. However, it does depend upon how much material needs to be removed.

All japanese motorcycle pistons are offered in .5mm, 1.0mm, 1.5mm O.S., and so, the minimum bore is .5mm, (he didn't specify the amount needed to clean) way more than is practical to hone out.

[stainlesscycle]

Originally Posted by halmc

I have a Yamaha IT 175 that needs an oversized piston fitted. Everyone in my neck o' the woods wants to hone the cylinder, but I want it bored.

surely there's a shop in your area that could bore it. the real question is why does everyone want to hone it? is it not bad, and you just wanna bore it for peace of mind? i know on my it200 that is now on last bore, i wish a hone was all it needed - it200 cylinders do not grow on trees... make sure the ports are chamfered too.... have had a few cylinders come in that were not chamfered, don't know why....

[Duck_Pilot]

Originally Posted by concours

All japanese motorcycle pistons are offered in .5mm, 1.0mm, 1.5mm O.S., and so, the minimum bore is .5mm, (he didn't specify the amount needed to clean) way more than is practical to hone out.

You are incorrect here, Sir. Some OEM & aftermarket suppliers offer in increments of 0.25mm....especially in racing-specific engines. I know this to be true of the Suzi PE-175 - the Yamaha IT-175's ISDE arch-rival. It's worth a look-see in Yamaha's FREE online lookup to be sure.

*EDIT* I took a quick look on "Yamaha-Motor.com" and saw that the 1982 model had 4 oversize piston kits available, in +0.25, +0.50, +0.75 & 1.0mm. I had not noticed the OP's model year, but I suspect that the same pattern follows for most years, based on my past professional experience with Yamaha.

[anotherguy]

Two stroke cylinders are hard on boring tools. The interrupted cut beats the hell outta carbide. That's why I prefer to hone .010"/.025MM. If it needs more than that boring is OK but I'd rather not. Modern stones can take a lot of material out fast. Sometimes with cast in liners boring is needed to square the bore up. Yamaha is particularly bad with that.

[baloneyskin daddy]

If the cyl .isn't worn and clearances are fine don't waste the money on a bore job. Theres very little hp.to be gained by simply boring it out, however it will run hotter with each increase in size causing more rapid wear.

[concours]

Originally Posted by Duck_Pilot

You are incorrect here, Sir. Some OEM & aftermarket suppliers offer in increments of 0.25mm....especially in racing-specific engines. I know this to be true of the Suzi PE-175 - the Yamaha IT-175's ISDE arch-rival. It's worth a look-see in Yamaha's FREE online lookup to be sure.

*EDIT* I took a quick look on "Yamaha-Motor.com" and saw that the 1982 model had 4 oversize piston kits available, in +0.25, +0.50, +0.75 & 1.0mm. I had not noticed the OP's model year, but I suspect that the same pattern follows for most years, based on my past professional experience with Yamaha.

LOL, I knew it. I thought of writing "most" but got lazy. Carry on. Hone away.

[halmc]

Thanks for all comments. I was interested in boring as opposed to honing as the conventional wisdom holds that honing alone (not the finish honing to which one inmate refers) replicates out-of-round condition, whereas boring ensures a constant radius and squares the bore with the base. No?

[anotherguy]

No. A properly honed bore is as round and true and they get. The guide shoes keep the stones from removing in the low spots. It goes-drill-ream-bore-hone-lap in order of precision. I use a hone/stone set similar to this for big bore two strokes or smaller bore with large ports. The guide shoes follow the high spots and make the stones do the same until they're gone. It does take an experienced touch to get a two stroke right.

Does that explain it well enough?

[showkey]

One thing no matter how the cylinder is resized:

If it is not done correctly and the shirt clearance is not exact to the new spec (about .0009 to .0012") check the book) and have near zero taper and zero out of round the OP will continue this thread with:

NOW the engine has ring rattle or piston slap noise

Bore ( to get a perfect hole) and hone to the perfect size and cross hatch is the best way to insure success

There are dozens of other threads stating 2 stroke bored or honed by a guy use to chevy block clearances and now the new piston has .003 or .004" skirt clearance with piston rattle after rebuild.