here's a question.  APE came out with a 75mm and 76mm piston for the GS1000 two valve.  They're a 18mm wristpin.  Isn't that what we have.  Are the heads similar and would this be a better solution than what has been available with kawasaki pistons?  Is this a new possible piston swap?  Any input?

Here's a link.   

http://gszone.biz/

The chances of them dropping straight in without issue are slim, piston diameter and the wrist-pin hole diameter are only part of the big picture. Other factors to consider are.....

The distance between the centerline of the wrist-pin hole to the top of the piston side.
The crown profile and its clearance against open valves.
The skirt depth and its clearance against the crank webs.

Idealy you need the two pistons in front of you to compare.

I have the Wiseco 78mm piston (for Kawasaki) on my bench at home. If you want pics / measurements let me know. I won't have my engine open for the piston swap for another week yet, so I can still measure it.  Once I put it in the engine, though, I ain't takin' it back out! Hopefully within a couple weeks I'll be able to do the swap.

p.s. I can't say enough good stuff about the service I've had from Wiseco -- including a prompt response to a nooB question I sent them via email. There's a company that supports what they sell even after they get your $$.  I wish more people and places were like them!

im watching this thread this is something i would love to do if things work out.  keep us posted with details.  ill be goin to naps house next winter for a bit of motor building.....lol  like how i just invited myself over for some motor building.

Quote from: sledge on March 25, 2009, 01:43:14 AM

The distance between the centerline of the wrist-pin hole to the top of the piston side.
The crown profile and its clearance against open valves.
The skirt depth and its clearance against the crank webs.

this is what made me curious.  My GS still runs fine but the motor is getting a little tired.  When I swap it out I would like to go with high compression pistons in a +1 or +2 mm.  Do we already have a piston that will do this?  I was hoping this would be good way to make that happin.


I don't know if we run the wiseco because it happins to work, or if we run them because the measurements are ideal.  I've never done that swap.  I would think with a little luck the APE gs1000 pistons might be a good candidate.  I guess I'll have to try and figure this out.  Anybody have a good stock piston they want to sell?  How about a cylinder and head too?  Let me know how much you want and how much for shipping to michigan. 

GS1000 was too close to the GS500 to need to even bother worrying I heard ... dunno if true or not.
Cool.
Buddha.

now when you say close enough you dont have to worry do you mean that the specs on theres are almost the same as the gs500 and to go with a oversized gs1000 piston you would be fine or its so close that it wont make a difference?  knowing that you havnt tested this.

side note i just emailed ape from there gs page and i will update as soon as i find anything out.

Stock GS1000 piston is almost the same as stock GS500 piston. I heard.
Oversized is always going to be well ... over sized ... so it should fit and give you more displacement I would think.
I thought GS used a 17mm pin though, dont remember now, it was 2+ years ago.
A GR stock piston is actually 3mm larger and almost straight swapper for the GS one.
Its will make a 555 or 562 or something displacement in a GS motor.
That extra 100 CC comes from a monstrous 13 mm extra stroke length. Booya ... cruiser motor.
Cool.
Buddha.

I've never measured a gs wrist pin.  According to the part numbers for the dgyver kawasaki piston swap that everyone does the wrist pin is an s555 which is an 18mm pin.  Since that piston fits the connecting rod, I guess we have an 18mm pin. 

so what would someone be looking at cost wise for a swap like this?  and im guessing some carb work would be needed as well?

You wanna swap GR pistons into the GS cylinders, that is nearly the same as a 3mm overbore ...
Heck over bore can get you better pistons.
Cool.
Buddha.

is that a gr650 buddha?

Quote from: The Buddha on March 25, 2009, 08:49:01 AM
Stock GS1000 piston is almost the same as stock GS500 piston. I heard.
Oversized is always going to be well ... over sized ... so it should fit and give you more displacement I would think.
I thought GS used a 17mm pin though, dont remember now, it was 2+ years ago.
A GR stock piston is actually 3mm larger and almost straight swapper for the GS one.
Its will make a 555 or 562 or something displacement in a GS motor.
That extra 100 CC comes from a monstrous 13 mm extra stroke length. Booya ... cruiser motor.
Cool.
Buddha.

Definitely 18mm wrist pin.

GR piston (77mm) would change the displacement only by virtue of bigger bore size.

@ 74mm (stock)  with stock 56.6mm stroke = 487cc displacement  < bone stock
@ 75mm ( +1) with stock stroke = 500cc   < from APE?
@ 76mm ( +2) with stock stroke = 514cc   < from APE?
@ 77mm ( +3) with stock stroke = 527cc   < from Suzuki GR, on GS crank and conrod, assuming the wrist pin matches at 18mm size
@ 77mm ( +3) with 70mm stroke = 652cc  < using Suzuki GR650 Crank, rods, pistons. Why not just put in the whole engine? It's going to be easier.
@ 78mm ( +4) with stock stroke = 541cc   < available from Wiseco
@ 79mm ( +5) with stock stroke = 555cc   < no longer available from Wiseco


Stroke remains the same UNLESS YOU ALSO SWAP IN A GR CRANKSHAFT.  That needs some mods to the bottom end, I think, can anyone verify? Does it need a taller cylinder, too? Yikes. Better just to put in a whole GR engine.

no idea what it costs.  My goal is to increase compression without decking the head and keep the overbore under 2mm.  I figure if I can pull that off there shouldn't be any reliability issues.  I don't like the idea of removing too much material from an air cooled cylinder.  Also then I won't have to deal with the crazy cam timing change from a radically decked head either.  That's why the idea of getting more compression from just a piston swap intrigues me.  

The way I look at it I'll have to freshen up the head and bore the cylinder no matter what I do, so I can't count that as money spent.  I'll also have to buy $200 worth of pistons whether they be wiseco kawasaki or suzuki .5 overbore so I can't count that either.  So if it costs me a few hundred more to get what I want than so be it.  

I figure I'll box all of this up and send it to APE to have the machine work done since I need it anyway.  If we think the GS1000 pistons might work they can take a look at it since it's there already.  If that doesn't work out there's always JE.  If it doesn't pan out all I'll have to do is bore the cylinder out another 2mm for kawasaki pistons.  

That's the theory anyway unless we come up with a better one. Any input would be much appreciated.  

Quote from: 5thAve on March 25, 2009, 09:57:19 AM
Yikes. Better just to put in a whole GR engine.

Yes, done.
Cool.
Buddha.

horay.  Found a good solution.  I just talked to one of the guys at JE piston.  They need measurements and a mold of the combustion chamber and they can build me +1mm and +2mm pistons with any compression ratio I want.   Awesome.  They guestimated less than $200 a piston with a minimum of 4 pistons.  Now I just have to find an extra head...and someone who needs 2 pistons...and some bondo...and a deck height for stock pistons...and head gasket thickness...

i could be in on this.  what compression are you looking at raising it too.  pm me  bud

Stock is 9 to 1.  I was thinking 10 to 1.  Should still be low enough to run premium pump gas on a stock motor.  It should be high enough to allow for the increased compression requirement of a more aggressive megacycle cam if I decide to swap one in.  I tried to call megacycle to see what they recommend for compression on their middle sized camshaft  ( 384-70 the one recommended for best street performance) but the line was busy. 

Any suggestions?

so we are looking at 400 for pistons and how much we looking at cams?

$0 for stock cams

$288 for their smallest performance camshaft. 

same plus $35 for a set of valve springs for the 384-70 camshaft

No idea what it would end up costing for the full on race shim under bucket cams some of the racers run...but at least the pistons could handle it.