Potential Group Purchase - Wiseco GS650 741cc pistons

[Chuck78]

If shipping weren't so far, I'd be looking for a good spare 650 top end and carbs. But I'd urge you to stick with it & use the winter to get the bike freshened up & do the top end swap.

 

[Guest]

It's not about giving up easily....

I want to be on the road next spring. I'm also not looking for 550/650 conversion. I have a GS650G. Actually 2 engines. Both cylinders needs boring, because they were both sitting for ages and the previous owners didn't care.
In order to get the engine back to life, I need boring. With boring I need oversize pistons. Just boring and oversize pistons(if I even get oversize pistons) are CAD1000+. Plus gaskets, tires and a million other things. So I'm very quickly in a price range, where I get a decent Honda from the 90's or maybe early '00s that will last forever without a lot of maintenance.

Don't get me wrong. I would love to finish this project. But I want to ride and go on adventures. And because I don't have a lot of many to throw out of the window I need to prioritize. I hope that makes sense.

 

[Buffalo Bill]

It's not about giving up easily....

I want to be on the road next spring. I'm also not looking for 550/650 conversion. I have a GS650G. Actually 2 engines. Both cylinders needs boring, because they were both sitting for ages and the previous owners didn't care.
In order to get the engine back to life, I need boring. With boring I need oversize pistons. Just boring and oversize pistons(if I even get oversize pistons) are CAD1000+. Plus gaskets, tires and a million other things. So I'm very quickly in a price range, where I get a decent Honda from the 90's or maybe early '00s that will last forever without a lot of maintenance.

Don't get me wrong. I would love to finish this project. But I want to ride and go on adventures. And because I don't have a lot of many to throw out of the window I need to prioritize. I hope that makes sense.

It's ok Dude. I know I go through the economy of restoring any bike before purchase. Even have a GS650E under consideration, that might have to include engine boring and camshaft replacement. It does look kinda high priced to me right now.
Buying a vintage bike in very good running condition is just good sense.
Pistons and cams are available for select popular vintage bikes, I know these include the GS1000 and some Kawasaki GPz bikes including the 550cc. Some vintage GSXR years are supported some are not.

 

[Bikelife2]

If more get on board, I'm highly interested.
Also, has anyone considered instead of removing material from the 550 case to fit the 650 cylinders, to remove the individual cylinders and lathe the outer bottom of each cylinder to fit? Doing this route would eliminate potential case shavings from getting dropped into the bearings/bottom end. Just an idea I had.

 

[Chuck78]

EDIT - DO NOT BUY THESE! THEY DO NOT FIT A 650 HEAD!

So this big bore 550/650-740cc mod just got a lot cheaper... I had seen these last year on eBay, but being that the Wiseco are higher compression and able to run aftermarket camshafts (deeper valve pockets), I hadn't said much about the budget alternative, in hopes of others doing a second group purchase of these pistons.

But now it seems that getting another group buy together is a little lacking, I'll just offer up this option:

https://www.cruzinimage.net/2018/12/18/81-83-suzuki-gs650-740cc-bigbore-pistons-kit-65mm-piston/

81-83 SUZUKI GS650 740cc BIGBORE PISTONS KIT 65mm PISTON

-DESCRIPTION-◆10-GS650BB◆
*81-83 Suzuki GS650 Bigbore pistons kit with Head Gasket
Aftermarket
Piston size: 65mm( 3.00mm Oversize )
Head gasket: Bore size is 68mm
*Set includes: pistons, pins, clips,rings and head gasket
Note: Cylinder boring required
These pistons are aftermarket.different design from of the Suzuki genuine pistons





All that for $200 shipped to the USA! Japan seller, but made in Taiwan iirc. I have a set of 870cc 70mm pistons for GS750/850 applications, and they appear to be every bit as good of quality as the OEM Suzuki ART Pistons, and the first stuff this company was offering was old Honda CB big bore kits years ago, and those things have been proven to hold up as good as OEM and be of reputable quality... Highly advocated amongst the SOHC Honda Fours crowd. The rings I might suspect aren't as good as OEM, but maybe they will hold up as well as OEM anyways?

You will still need to run a thicker custom base gasket with these unless the head gaskets are thicker than stock (compressed thickness) by at least .005" or more, but that's the easiest part. Cometic can custom make base gaskets for cheap if you tell them GS550 base gasket with GS650 sleeve sizes, and in custom thickness (refer back in this thread for actual thickness needed). Or if Cometic has a GS650E gasket on file, different than the 650G, it is exactly what is needed but in a slightly thicker gasket material. Perhaps the GS650G gasket method may be better though, as a thicker 550/650E style base gasket will leave the rear corner oil feed passage egg-shaped o-rings less compressed than with stock base gasket. Suzuki_Don and others who did the custom thicker base gasket I believe had the 650G style and let the egg shaped oil pressure o-ring seat against the bottom of the paper gasket, which would have it compressing .020" more than it was intended. So A LOT MORE compression vs slightly less compression of this oil pressure o-ring are the two options if you are going thicker base gasket. The verdict is up for debate.

With the cast piston option above, I'd be shaving the head slightly, and running just enough thickness of head and base gaskets to give the piston adequate clearance, in order to maximize the squish band and slightly bump up compression ratio...

EDIT - DO NOT BUY THESE! THEY DO NOT FIT A 650 HEAD!

 

[Chuck78]

One big argument I see here for the WIseco piston vs these, is that these state that they're a different design than the OEM pistons. I see waaaayyyy less quench area there, perhaps they are more like the 550 pistons in this regard? I'd really like to have a set of these in my hands to see what they are all about.

Perhaps that is a stock image and not actually the GS650 piston kit? Huge difference in dome/quench design, so I'm guessing yes. Comparison:

VS

 

[Guest]

Well, I bought these pistons and this is the result...

https://www.thegsresources.com/_for...ersize-pistons-hit-head&p=2651323#post2651323

 

[Chuck78]

Well, I bought these pistons and this is the result...

https://www.thegsresources.com/_for...ersize-pistons-hit-head&p=2651323#post2651323

Awww man that SUCKS! They basically sold you a hemi head domed piston nearly identical to the stock 77-79 GS750 piston...
I would DEFINITELY be contacting them to complain, at least so they pull them and don't screw over anyone else... Unless perhaps they actually did mix up and send you GS750 65mm stock hemi pistons vs big bore GS650 65mm closed chamber head pistons...
MAJOR BUMMER...
But... an 80+ 8v GS550 head may potentially work on that piston with minor dome machining around the perimeter. There's no way you could machine that big hemi dome down to the 650 dome shape/size, you'd cut through to the back side...

 

[Guest]

So this big bore 550/650-740cc mod just got a lot cheaper... I had seen these last year on eBay, but being that the Wiseco are higher compression and able to run aftermarket camshafts (deeper valve pockets), I hadn't said much about the budget alternative, in hopes of others doing a second group purchase of these pistons.

But now it seems that getting another group buy together is a little lacking, I'll just offer up this option:

https://www.cruzinimage.net/2018/12/18/81-83-suzuki-gs650-740cc-bigbore-pistons-kit-65mm-piston/

81-83 SUZUKI GS650 740cc BIGBORE PISTONS KIT 65mm PISTON

-DESCRIPTION-◆10-GS650BB◆
*81-83 Suzuki GS650 Bigbore pistons kit with Head Gasket
Aftermarket
Piston size: 65mm( 3.00mm Oversize )
Head gasket: Bore size is 68mm
*Set includes: pistons, pins, clips,rings and head gasket
Note: Cylinder boring required
These pistons are aftermarket.different design from of the Suzuki genuine pistons





All that for $200 shipped to the USA! Japan seller, but made in Taiwan iirc. I have a set of 870cc 70mm pistons for GS750/850 applications, and they appear to be every bit as good of quality as the OEM Suzuki ART Pistons, and the first stuff this company was offering was old Honda CB big bore kits years ago, and those things have been proven to hold up as good as OEM and be of reputable quality... Highly advocated amongst the SOHC Honda Fours crowd. The rings I might suspect aren't as good as OEM, but maybe they will hold up as well as OEM anyways?

You will still need to run a thicker custom base gasket with these unless the head gaskets are thicker than stock (compressed thickness) by at least .005" or more, but that's the easiest part. Cometic can custom make base gaskets for cheap if you tell them GS550 base gasket with GS650 sleeve sizes, and in custom thickness (refer back in this thread for actual thickness needed). Or if Cometic has a GS650E gasket on file, different than the 650G, it is exactly what is needed but in a slightly thicker gasket material. Perhaps the GS650G gasket method may be better though, as a thicker 550/650E style base gasket will leave the rear corner oil feed passage egg-shaped o-rings less compressed than with stock base gasket. Suzuki_Don and others who did the custom thicker base gasket I believe had the 650G style and let the egg shaped oil pressure o-ring seat against the bottom of the paper gasket, which would have it compressing .020" more than it was intended. So A LOT MORE compression vs slightly less compression of this oil pressure o-ring are the two options if you are going thicker base gasket. The verdict is up for debate.

With the cast piston option above, I'd be shaving the head slightly, and running just enough thickness of head and base gaskets to give the piston adequate clearance, in order to maximize the squish band and slightly bump up compression ratio...

wow that is cheap! I am considering buying a spare engine for my 1979 gs500e. And cylinder and head from a 650. Now to get this to fit what is needed to be done? This thread is so long it would take ages to read thru but if i recall correct after reading this a year ago I need to bore the 650 cylinders. And some grinding/machining on the bottom end to make the cylinders slip in?? And was there something needed to be done to the camchain tensioner? Thanx for any answers and advice in advance! Highly appreciated.

 

[Chuck78]

I hope I caught you in time, do not buy that Cruizin Image kit. Although they make some great pistons for other applications, this was a huge blunder on their part. These are basically just GS750 stock bore pistons and have only the correct pin size and compression height to fit a 650 or 550. That's where it ends. The dome and valve reliefs are completely completely wrong, and are not compatible with the 650 head.
The 650 combustion chamber shape and intake runner shape is why the 650 is such a superior engine, it is the best two valve for cylinder design Suzuki had back then. It's possible that someone could machine out the 650 head to go back in time to an inferior hemi dome chamber to fit these, but you would lose about the same amount of power that you would have gained just by running stock 650 pistons and stock 650 head...
They make a note saying that these are not the same design as the factory 650 pistons. That basically means they just saw that they were the correct height and wrist fin size to make a 3 mm overbore 650... So the manufacturer made the same assumption / mistake that a lot of amateurs do, and thinking that they can stuff listons from a different application into their engine and everything will work perfectly...

Cruizin Image made a huge mistake by just assuming that all two valve per cylinder GS models would be similar, they probably never even looked at a 650 combustion chamber. Very surprising because all of their hemi pistons are same quality as OEM, impressing a lot of people for their price especially.

 

[Guest]

I hope I caught you in time, do not buy that Cruizin Image kit. Although they make some great pistons for other applications, this was a huge blunder on their part. These are basically just GS750 stock bore pistons and have only the correct pin size and compression height to fit a 650 or 550. That's where it ends. The dome and valve reliefs are completely completely wrong, and are not compatible with the 650 head.
The 650 combustion chamber shape and intake runner shape is why the 650 is such a superior engine, it is the best two valve for cylinder design Suzuki had back then. It's possible that someone could machine out the 650 head to go back in time to an inferior hemi dome chamber to fit these, but you would lose about the same amount of power that you would have gained just by running stock 650 pistons and stock 650 head...
They make a note saying that these are not the same design as the factory 650 pistons. That basically means they just saw that they were the correct height and wrist fin size to make a 3 mm overbore 650... So the manufacturer made the same assumption / mistake that a lot of amateurs do, and thinking that they can stuff listons from a different application into their engine and everything will work perfectly...

Cruizin Image made a huge mistake by just assuming that all two valve per cylinder GS models would be similar, they probably never even looked at a 650 combustion chamber. Very surprising because all of their hemi pistons are same quality as OEM, impressing a lot of people for their price especially.

Yeah i noticed this error. So no 740 conversion for me. But i saw they had 650 +1mm overbore and that will be almost 700cc if i am correct. I can get 650 head and cylinder. So if i am correct i need to grind out a bit on the bottom end to make cylinders fit, and something about timingchain tensioner? Or was it to use the 550 camsprockets on 650 camshafts? And 650 exhaust and carbs? and need a thicker lower headgasket too? Please advice if i missed something or got it wrong.

 

[Chuck78]

Yes, cam sprockets from 550 or GS650E cams, NOT GS650G cams.
thicker custom head gasket ot base gasket.
I may have a big bore gasket to spare that didn't meet my specs, I cant remember if I sent them all back or not.
Cometic can make a custom thicker base gasket,but the oil pressure o-rings would then need to be thicker, & they are a proprietary shape, egg-shaped. I shoopose one vould possibly manipulate a specially selected thickness and diameter round viton o-ring through clamping and heat gun to take that shape if one got ambitious, then all that'd be needed would be a custom thickness Cometic GS550 base gasket to fit 650 sleeves, or a GS650 custom thickness base gasket to fit 550 oil/stud outer rear passage o-rings.