How much can you bore an 850?

[Spiff]

I'm having a hard time getting a hold of a 1000 engine so I'm starting to wonder if I should just keep my 850 and spruce it up instead.
Cam/headwork and some higher compression pistons, and overboring? But how much and where do you get piston kits for these?

 

[Dogma]

IIRC, there isn't a big bore kit or performance parts in general for the 850, just oversize rings for worn bores.

What about skipping over the 1000G and looking for an 1100G? I think there were more of them.

 

[Spiff]

Yeah but I need a chain driven engine, not shaft.
Haven't been able to find an overbore kit for the 850 either, that's why I'm asking here if anyone knows anything.

 

[Guest]

You're putting a chain drive into a shaft drive frame?

 

[Spiff]

You're putting a chain drive into a shaft drive frame?

No my bike has always been chaindrive. It's originally a 750 but with 850 cylinder block and head

 

[Guest]

Ohhhh...too bad you're not closer, I'd have a 1000 engine for you.

 

[Spiff]

Well, there where sold some gsx1100 bikes here though, so that's one option.

 

[GregT]

In theory most air cooled Suzukis will take a 3mm overbore safely which would put you at 72mm which is quite a common bore size.
Your problem is I think the gudgeon pins are 1mm smaller than the 1000 if I remember right.

If someone can quote pin size and height from pin bore to top edge of the piston, I'll compare that to some Z1 pistons I have here.

Just out of curiosity you understand....

 

[uk gs nut]

GS850 +GS750 pin size is 16mm GS1000 is 18mm. Kwaks I believe are 17mm. You could possibly get custom made pistons but not cheap !. I have heard of the con rod little end being bored 17mm to take Kwak pistons, split cases and remove crank to machine the rods.

 

[Spiff]

I don't think something like Wiseco pistons f.ex would cost that much extra if you wanted 16mm wrist pins instead of 18 as I believe most their stuff is machined and made to order anyways. At least when I bought forged ones for my Datsun truck they where made to order and not that much more expensive than ordinary oem pistons...

 

[Chuck78]

Wiseco these days generally wants to make a minimum batch of 12 pistons if you talk to the right person there. Call them up and speak to Al. He hooked us up via Andy Ace07 on here to get a custom run of 40 or so 740cc GS550/650 pistons made a while back. Others have contacted them since asking for the same pistons and they say "we haven't made those for 30 years." Just have to telephone and talk to the right person.

I am running a New Old Stock set of MTC 72m 920cc pistons in a 750/850 chain drive engine with the stock cams advanced quite a bit to boost mid range torque. It is a terror in the city and on the streets. Lots more torque. I did lose a bit of that insane high rpm pull that it had with stock cam timing after re-timing the cams more advanced, but it made it just insane in the midrange (i.e. can't get enough traction from any tire combo now on the rear wheel, and when it heats up, the front end gets lofted toward the sky when I finally do get enough heat in the rear tire to get traction...)

I'm surprised you can't find a 1000 engine. I've seen some on ebay for $400 recently. Or find a 78-79 1000 L model on craigslist to part out...
The 1000 makes so much power that sending your crank out to Pearson, Stan Gardner, or that other place in Florida, to get welded...is a must with any hard riding or modifications.

Get a 79 GS750/850 head, call up Rapid Ray in Calli and tell him you want a full on head job done to it. Have him do a street/road race porting job, +1mm oversized valves possibly, and a serdi radiused transition valve job. Get the proper springs installed for MegaCycle .380" lift camshafts, or Web .365" or .395" lift camshafts.
Then call up Wiseco and talk to Al, tell him you want to get a limited run of their K844 pistons, but you want them to be 72mm 920cc. Even asking for 10.5:1 wouldn't be too bad, but you'd be required to run nothing less than 93 octane on hot summer days though. I'd be interested in a second set or 3rd set even of the 72mm 920cc pistons if you and anyone else went in on it. If we got enough people together, it may not cost any more than a standard set of K844 pistons.
This combination would yield a very impressive amount of power.

Honestly if the money wasnt in the budget for all that head work and custom order pistons, just installing Wiseco K844 10.25:1 pistons into good freshly honed and mic'd 850 bores, or +4mm overbored fresh GS750 cylinders, and adding a fresh valve job with Megacycle .380" lift camshafts and valve springs will make a huge boost in power for you. Good carburation, k&N pods, and a good exhaust like a Vance and Hines at least, or a Delkevic stainless system would make for a screamer of a 750/850.

The same displacement you have, but added fresh valve job and big lift cams with added compression ratio will make a big difference. Go 1 up on your rear sprocket size to further enhance the street performance...

you can squeeze a 1000 engine into a 750 frame but it is TIGHT! I think you have to have the top cover off, and it's still a struggle to wrestle it into there.
A 1000 engine can fit GS1100G cylinders and pistons if you run the 1000 base gasket and deck the head around .020" and deck the block around .020-.035" as well (to make up for differences in the 1000 vs 1100 deck height due to the 1100 having a longer stroke. You can also do the easier budget route and bore used GS1100G pistons with some fresh rings into a 1000 block, but if paying the machine shop for work, may as well drop the money on new Wiseco 1085 pistons....
Running an 1100 block and pistons on a 1000 without any milling will give you tons or extra torque, but your power will still not reach it;s potential because the whole thing will be down on compression ratio due to the 1.2mm shorter stroke of the 1000 vs the 1100's.


You could also do it in stages... Wiseco custom small batch order of 920 pistons now bored into 850 cylinders, add stiffer valve springs while the head is off, then you can drop in cams later. If you are still wanting more power, you can send a second head to rapid ray for porting and oversized valves. Then swap them out in your down time sometime. pull the cylinder again if pulling the head, always a good idea to have a fresh base gasket if you remove the torque from it.

Email me anytime about 750/850 or 1000/1100/1085 advice.


-Chuck in Ohio

 

[Steve]

Chuck, did you notice that he is in Norway? :-k

Might be a bit easier and cheaper to find someone on that side of "the pond" to do the machine work. :-\\\

.

 

[Chuck78]

Ahhhh.... Did not look at his location, Steve! If he could not find someone semi-local wth air cooled motorcycle head porting experience, I'm sure Ray would be happy to have him buy a head on eBay US and have it sent to Ray, then pay international shipping only once... the added cost increases the chances of him not considering it necessary, but head porting is just as crucial in making massive power improvements as big bore, high compression pistons, and bigger camshafts are....

 

[Spiff]

Chuck that is an insane amount of info :-D appreciate it.

I found a gs1000 engine last year, but had a couple of other things going on so couldn't afford it, found a bike braking for parts a month ago but it was gone before I even got home from work to call the guy. :O it's a small community and just a few bikes being broken so the competition is hard when parts are for sale.

I could probably get a gsx engine fairly easily but I wanna try and keep it authentic so that's why I'm searching for an 8 valve engine.

I have actually thought about sourcing an engine from the US if I can't find anything here. I have an account with a shipping company that works out of new jersey so they could ship it via sea and it wouldn't be that expensive.

 

[Chuck78]

844cc Wiseco pistons & Web .395" lift camshafts and a performance valve job in a GS750 8v engine will yield impressive performance if you don't source a GS1000.
If we contacted Al at Wiseco, we may be able to get them to make a limited run of 920cc 72mm pistons based on the Wiseco K844 design.

Professional head porting is the key to really unlocking the performance potential of an engine, if you could find any experienced porters in your region.

There is a GS1000 engine for sale here in the classifieds in Florida, USA

 

[850 Combat]

I beleive that Suzuki was racing a 920cc 750 in Superbike prior to racing the 1000 based bike. Possible that was in the class preceding Superbike.

 

[Chuck78]

The first Yoshimura GS race bike was a 944cc '77 GS750. Pops Yoshimura hand modified 73mm Honda pistons to fit the GS head. I believe they must have re-sleeved the block, as 72mm 920cc is the limit of what I'd feel comfortable with running reliably based on the thickness of the 850 sleeves after I bored them to 920cc.

Of course the Wiseco 844 69mm kit is approved to bore straight into the 65mm bore stock gs750 sleeves for +4mm overbore.