Gs750 Motor / 850 Barrels Swap....

[mycb400f]

Hi all,

I 've read with interest the possibility of putting 850 barrels and pistons onto a 750 motor. This seems like a fairly simple swap, or is it??:?

The workshop manual states the 750 pumps out 68 HP...I haven't got an 850 manual, so can someone tell me what the 850 pumps out??

I've heard it pumps out the same HP figures, but that Suzuki tuned the 850 for a lot more torque, by changing the cams...is this true??

So, if I convert a 750 motor with the 850 barrels and pistons, what sort of HP figures should it pump out??

I know that HP figures shouldn't be the main reason for tinkering with a motor, but it sure makes it fun!!\\/

Obviously someone's done this, is there a link to the site??:razz:

Thanks
Nick

 

[BassCliff]

Hey howdy hey!

Hey howdy hey!

Mr. mycb400f,

Most of the documentation I've read says the GS850 is a punched-out GS750 with GS1000 cams and puts out about 77hp. I don't know if that's at the crank or the wheel. I'll let the more experienced folks here talk to you about your jugs swap. I'll just give you my totally outrageous, totally verbose mega-welcome! \\/

Let it be known that on this day you are cordially and formally welcomed to the GSR Forum as a Junior Member in good standing with all the rights and privileges thereof. Further let it be known that your good standing can be improved with pictures (not you, your bike)!

Perhaps you've already seen these, but I like to remind all the new members. In addition to the carb rebuild series, I recommend visiting the In The Garage section via the GSR Homepage and check out the Stator Papers. There's also a lot of great information in the Old Q&A section. I have some documentation on my little BikeCliff website to help get you familiar with doing routine maintenance tasks (note that it is 850G-specific but many tasks are common to all GS bikes). Other "user contributed" informational sites include those of Mr. bwringer, Mr. tfb and Mr. robertbarr.


And here are some edited quotes from one of our dear beloved gurus, Mr. bwringer, with ideas on basic needs (depending on initial condition), parts, and accessories.

***********Quoted from Mr. bwringer************
Carburetor maintenance:

Replace the intake boot o-rings, and possibly the intake boots. Here's the procedure:
http://bwringer.com/gs/intakeorings.html
Here's an overview of what happens with this particular problem:
http://cycleorings.com/intake.html
You'll also want to examine the boots between the carbs and the airbox. There's a good chance these are OK, but check them over.
And finally, if things still aren't exactly right, you'll want to order a set of o-rings for BS carbs from the GS owner's best friend, Robert Barr:
http://cycleorings.com
Once you receive these rare rings of delight, then you'll want to thoroughly clean and rebuild your carburetors. Here are step-by-step instructions that make this simple:
http://thegsresources.com/gs_carbrebuild.htm
***********************************
Every GS850 has (or had) a set of well-known issues that MUST be addressed before you have a solid baseline for further troubleshooting. It's a vintage bike, and it's quite common (as in, every single GS850 I have had contact with) that there are multiple problems that have crept up and slowly gotten worse over the years. It's not like a newer vehicle, where there's generally one problem at a time.

These common issues are:

1. Intake O-rings (install NEW OEM or Viton only - common nitrile O-rings will quickly deteriorate from heat)
2. Intake Boots (install NEW -- these cannot be repaired)
3. Valve clearances (more important than most people think)
4. Carb/airbox boots
5. Airbox sealing
6. Air filter sealing
7. Petcock (install a NEW one)
8. On '79 models, install new points or Dyna electronic ignition (or at least verify that the old points are working correctly)
9. On all models, it's fairly common to have problems with the spark plug caps. These are $3 or $4 each, and often worth replacing if you're keeping the stock coils/wires.
10. Stock exhaust with NO leaks or holes -- good seals at the head and at the junctions underneath.
***************************************
OEM Parts/Online Fiches:

I would definitely double and triple the recommendations to use Cycle Recycle II and Z1 Enterprises as much as possible. These guys are priceless resources. Z1 tends to have slightly better prices, CRC2 has a wider range of goodies available. If you're near Indy and can bring in an old part to match, CRC2 has a vast inventory of used parts.
http://denniskirk.com - Put in your bike model and see what they have.
http://oldbikebarn.com - seems to be slowly regaining a decent reputation, but it's still caveat emptor. They don't have anything you can't get elsewhere at a better price anyway.
http://www.babbittsonline.com/ - Decent parts prices. Spendy shipping. Don't give you part numbers at all. Useful cross-reference if you obtain a part number elsewhere. Efficient service.
http://bikebandit.com - Fastest. Middlin' prices. Uses their own parts numbering system to obfuscate price comparisons -- can be very confusing for large orders. Cheapest shipping, so total cost usually isn't too bad.
http://flatoutmotorcycles.com - Slow. Cheapest parts prices, crazy shipping costs. Don't expect progress updates or much communication. Real Suzuki part numbers.
http://alpha-sports.com - Exorbitant parts prices. Different type of fiche interface that's quite useful at times, especially with superceded part numbers. Real parts numbers. Shipping cost and speed unknown due to insane, unholy pricing.

Stainless Bolts, Viton o-rings, metric taps, dies, assorted hard-to-find supplies and materials, etc:

http://mcmaster.com - Fast, cheap shipping, good prices. No order minimum, but many items like bolts come in packs of 25 or 50. Excellent resource.
http://motorcycleseatcovers.com - Great quality, perfect fit (on original seat foam), and available for pretty much every bike ever made. Avoid the textured vinyl -- it's perforated.
http://newenough.com - You DO have riding gear, don't you? Great clearances, always outstanding prices and impeccable service.
***************End Quote**********************
Here are some extra links:
GSR Forum member Mr. duaneage has great used upgraded Honda regulator/rectifiers for our bikes. Send him a PM.
New electrical parts:
http://stores.ebay.com/RMSTATOR or http://www.rmstator.com/
http://www.ricksmotorsportelectrics.com/index.php
http://www.electrosport.com/
The Rice Paddy (salvage/used)
http://www.ricepaddymotorcycles.com
Ron Ayers Motorsports
http://www.ronayers.com
MR Cycles
http://www.mrcycles.com
If all else fails, try this:
http://www.used-motorcycle-parts.org/
Lots of good info/pictures here:
http://www.suzukicycles.org


Thanks for joining us. Keep us informed of your progress. There's lots of good folk with good experience here.

Thank you for your indulgence,

BassCliff
(The unofficial GSR greeter)

 

[tkent02]

I am doing this now to my 1978 750, working on getting the head ready now. Planning on using stock 850 cylinders and pistons. Staying with the 750 cams, to keep the higher powerband. The two heads are identical unless you go with the later style 850 head with CV carbs. We were trying to do a group buy for JE pistons to give 10.5-1 compression but it fell through due to no interest. Wiseco has a set for around $500, think I will try the stock pistons first to save money, may go with Wiseco later depending on performance. I haven't opened up the 750 engine yet, I think the early 850 cylinders fit into the 750 cases with no grinding, the later 850 cylinder sleeves are a little too big to fit without grinding. Will let you know when I get into it, maybe later this week.

 

[mycb400f]

Thanks guys,

tkent02, if you can post some pics of the dissasembly, tinkering and reassembly procedures, that would be great. I would be interested to know what sort of performance boost this would give....given it's an extra 100cc's, I think it will be quite reasonable.....kinda like a big bore kit!!!

By the way, I would assume the 850's intake valves are a little bigger?? I haven't checked the microfiches yet, but if they are, and someone can rework the head to accept the bigger valves, would that be another 'simple' way to go for a little more power??

Just wondering.......

Thanks
Nick

 

[mycb400f]

I've just checked the microfiches and the intake and exhaust valves are the same on both the 750 and 850....so just ignore my last comment...feeble excuse to play with the heads!!

The cylinder base gasket is the same on both models..

The cylinder head cover gaskets are the same..

But the cylinder head gaskets are different...(obviously to allow for the larger bores...)...so far so good....

So...I reckon it should be a fairly straightforward swap....


Now....I wonder if the gs1000 intake valves will fit???......

Nick

 

[tkent02]

GS1000 valves, I like the way you think. There are more knowlegable folks than me here, a little research is in order. Will certainly take pics of the process as I go.

 

[mycb400f]

Just checked the microfiche...GS1000 intake and exhaust valves have different part #'s than 750/850.....so I assume they are a little bigger??

It will be a good little project if someone tries to fit the 1000 intake valves, yes?? Assuming the stems are the same thickness and length...it should be just a 'simple' job of changing the valve seats and installing the valves....(maybe not worth the expense....but certainly an interesting option if you have access to that sort of equipment.....)

Looking forward to seeing the 'project' photos....

Nick

 

[mycb400f]

By the way kent,

I've posted a couple of threads about 750 engine dimensions and no one has answered....

Since you have a motor pulled out, can you measure the motor for me?? I need width across the frame, length from front to rear and most importantly, height.

I am planning a frame swap, but I am kinda doubting it will fit, but just want to make sure...

Nick