So I dropped off my cylinders and one of the Wiseco 78mm pistons with a respected machine shop in town and a couple hours later fella calls me and says I'm crazy to try to run this piston in the stock sleeve. He says by his measurements if bored to 78mm (with .002 clearance, of course) it'll leave only one millimeter of sleeve, and that's too thin where the sleeve projects below the block into the crankcase, says fella. Says I'm nuts to try it. (Yeah, OK, fella is used to building car engines, but he's machined on his share of bikes, too, over the years).

Now, I know of at least three or four members here that are running the Wiseco 78's and I am under the impression this is with the stock block and sleeve. Is fella's measurement off? Cylinder walls 1mm thin does seem kind of fragile in my mind's eye.

I'm looking for confirmation of what I think I already know -- that this combo has been done successfully before. How much of a bomb am I building here? I was planning on riding this on the street, not track.  I accept that I'm ultimately reducing reliability by doing this, but I assumed that it would have reasonable life expectancy!

Comments, anyone? (prefer voices of EXPERIENCE) here. 

Thanks.

Resleeve ...
Give me the 78's and I'll bore my GR 1mm and run em ...
I know of people who bored a GR to 84mm. 77 to 84 ... he also stroked it 5mm and has a 851 up from the 651 stock, and he's got a aluminum sleeve with nikasil in it. Basically remove the steeve, punch the block to fit a new larger sleeve, and fit the piston of your dreams in that.
Cool.
Buddha.

You can do a search but I am pretty sure 78mm requires a you to put in larger sleeves. I would actually recommend you search because I am almost positive I read a few posts discussing this exact issue.

Pm dgyver or werase643 

Yeah, well, I re-searched the forum and confirmed I read everything right the first time:  people here have run the 78mm in the stock sleeve.  I'm going to try it. What the hell? LIVE ON THE EDGE!

More than likely it will break in the boring machine when you remove the pressure plate.
Then obviously you keep boring it till you get to the aluminum, then continue boring it till it has become large enough to take the right sleeve.
Obviously you ahve to releif cut your cases for it. But well, that's what over boreing is all about.
Conversely, you could just give it to me, on my GR, its only 1mm over bore for the 78 ...
Cool.
Buddha.

think....GR....1mm overbore.....

might want to look into a set of GR sleeves...
or some other similar

you might get it to work
but a pitty to risk good pistons on a bad build

the machinist might know a thing or two about metal

I see your strategy, Buddha. Obviously I don't need the pistons when I have no exhaust pipe, shock, or drive sprocket.   

Werase, you're running / have run a set of these pistons. Did you resleeve?

I'd almost think the over bore phenomenon is over rated.
You will get much better performance gain by putting in a better head, 4 valve if you can ... else larger and lighter valves, necked stems, trimmed guides, stiffer springs, decked or milled, ported and flowed and taller and more duration cams as well as larer carbs and better exhaust.
After getting the head to where it needs to be, think about larger bores etc.
A 4 stroke is all head really.
Cool.
Buddha.

I collected all the gud parts over the years
cams
77mm pistons
i had 8 valve head
I had GR 651 engine parts

and then sold them to get them out of the way


the GS will do a Ton on the street
what more do you need
when i wanted to go faster....I bought a GP race bike       same $ much more gudder

45 HP
165#!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
135 MPH
FOOKIN SCHWEEEEET

also....cheaper to buy RG's bike just for the engine
and the kewl suspension parts will convert right onto your bike

win win situation

Thanks Werase.  All very true.  But I'm in it for the challenge and the learning even more than the 'performance' boost. I don't kid myself about hot rodding a GS into a speed machine.

lee adams put 10-15 k in engine development

as long as you know you are polishing a turd.......go for it
i install really kewl($$) suspension parts for my turd polishing exercise

I install titanium parts ... basically aluminum, titanium and carbon fiber parts ... and have a dozen double cheese burgers and a 40 oz beer for lunch ...

My bike isn't lowered ... just that with me sitting on it it just works like that.

Cool.
Buddha.

the above is all true

Hey I resemble that remark.
Cool.
Buddha.