1981 Suzuki GS650G powered by a 1999 Suzuki Bandit 1200

[tenderblender]

Howdy! So I bought the G when I was 17 (November 2014), just turned 23 last December. I’ve had quite a few piles you could loosely call motorcycles (15 other motorcycles, dirt bikes, scooters, and 1 bicycle with a motor contraption) since around age 14. My G is my favorite so far and one of two bikes I plan on keeping, the rest come and go. I bought the G with a bad connecting rod bearing in high school and threw a used crank with rods on it in after I cleaned all the bearing chips out and rebuilt it before I knew anything about motorcycle engine work and machining. It ran pretty well considering the carbs were dumping gas in at all parts throttle. (Didn’t know 10% of carburetor theory and practice that I do now.) I did the usual “tune up” stuff to it including a new ignition from crank to head by Dynatek which helped burn the copious amounts of extra gas haha. So fast forward to September 2017 where one of the transmission bearings (forward set of gears, outboard bearing) that was damaged by the original bad crank finally had enough and let go into the oil pan. Pulled that motor out of the frame (again) and put it aside in my garage and fixed and built a few of my other bikes and eventually sold. Out of all of these bikes I haven’t found one yet as comfortable, reliable (save the o.g. 673), sharp handling, and overall character of my G, so last April I did some reading and learned more about blandits and oil burners and really loved the idea of having a burner in my frame. I figure it’s about the same mass and cog as my air cooled (loosely) so my handing should stay where I like it, still be just as comfortable, and have a much needed kick in the pants. I read Wraith’s GSX1100F swapped GS550 so I figured to hell with it I’m going to try it. So Mid April 2019 I found a smashed B12 (decimated the front fork and wheel, everything else is somehow perfect) and brought it home. February 1st 2020 I got the B12 to run (somehow with only the lower halves of the carbs), tested the transmission (all five gears don’t pop out without a load so that’s something I guess? Hard to tell without it in the bike or splitting the cases so we will see once it gets going down the road.) February 3rd I pulled all the wiring off the B12 frame, pulled the oil cooler, oil filter, carbs, muffler, header, and frame member. February 4th I pulled the motor out, cleaned off most of the grease and oil off the outside, and placed it next to my g. February 5th I fixed my lathe and helped a buddy with his car, February 6th I checked the valve clearances and pulled as much stuff out of the way on the g (removed the air box, moved some wiring, and pulled the swing arm, rear brake system, and shocks out) and realized how wide the swing arm is. It’s about 12 inches! Most swing arms for other bikes aren’t even close at around 9 to 10 inch. Does anyone have any ideas for the swing arm? It has these threaded pivot plug things that thread into the frame and put preload on the tapered roller bearings in the swing arm. With my lathe I should be able to spin up some adapters but don’t like the idea of having super long adapters with all the forces a swing arm and frame put on each other so I’d like to get one that fits as close as possible. I really want to keep the twin shocks (no other reason than the aesthetics to me, and it worked well enough for me, plus I don’t know how I feel about adding mono linkage to this frame.) so my stock swing arm has a length of 18 11/16”, a pivot width of 12” and has twin shocks, is there any aluminum ones out there that are close? Will a 1981 Gs650e swing arm fit? Sorry about the naïve questions in advance, Thanks fellas.

[wraith]

Welcome to OSS  

If you're keeping the standard tank, you may need to move it up a bit so it clears the cam cover/carb tops.

@Nigkathas just done the same b12 motor in a gs650g frame may be worth a look 

I did a gs1000 using a G frame, made some top hats to weld into the frame where the swing arm threads are, then used a kwak zx9r swing arm (much wider at the pivot points than suzi) then made a one off spindle and some small spacers and weld shock mounts on the swing arm to keep it a twin shock. ( project is on the old site as project scrapheap.) Pic of the gs1000 chain drive in the G frame. 

 

[Poldark]

Tenderblender,

First, welcome to OSS.  You say you really like the character of the GS650G.  Do you mainly want to get your bike running again or do you want to build a full custom.  By the time you do all the engineering and fabrication to fit the bandit 1200 engine along with a different swingarm and rear wheel, you are in full custom build territory.  There will be lots of other small fitting/mounting issues to work out.  You would be doing very well to have it riding this year.  Besides, the 1200 is a big power upgrade, it would benefit from also upgrading the suspension, wheels, and brakes.  Again, full-on, long term custom build.  If you want to just want to get your bike running again, just swap in another GS650G engine and get back on the road.  I have an extra engine.  Get your post count above 50 and we can discuss a transaction.  I have frames and swingarms from both E and G model GS650, along with GS550.  I can take measurements if you need it, but I am quite certain you won't find a simple swap swingarm for the shaft drive frame.

[clivegto]

Use the b12 backend as that's what you have. 

[tenderblender]

Thanks everyone for the quick responses so far!

(I’ll respond to everyone in order)

 

Wraith, excellent work on the swap, I’ll look into a zx9r swingarm as I have one on a friends bike I can use for measurements (he still wants to keep his bike haha) One of my goals is to keep it all Suzuki but that may change. Tank should be simple enough to figure out, either raise or modify I reckon. I’m going to try to find the thread of “project scrap heap” (parentheses because yours appears to be fully operational which is much farther than mine to say the least haha) 

 

Poldark, I’ve set a personal challenge with myself of riding it at least once to my girl’s school (2.5 hour one way) before she graduates In may, I love the character of the bike and it’s one of two I don’t plan on ever selling so I don’t mind fully custom. I’m going to be throwing all of my knowledge and skill I’ve collected so far at this one, and I’m going to continue to use it as a test bed for all of my ideas for the future as I come up with them, know what I mean? Full custom doesn’t scare me one bit (so far) and that’s something I’d like to do with it, I want to build on the soul it has to one day be a proper bike like the members of this site (all of y’all’s bikes are exquisitely done, the knowledge and creativity here is down right ludicrous, I love it.) If you could get a measurement of the Gs650e width at the pivot and the centre to centre of the pivot to axle that’d be wonderful, if it’s close (enough) to what I have I could use one as a roller and go nuts with the swing arm swap later and be closer to riding. Oh and I’ve thought about another G engine or rebuilding the numbers matching one but I would much rather have the oil burner and all the parts available for it.

 

clivegto, I would and that was the plan, but it’s much too thin at the pivot for my liking, I’d have to shave off the mono tabs and weld new tabs on the end, I feel as if it would be easier to mod an arm that’s closer to what I’d need and sell the stock bandit arm to someone that needs it yk? 
 

thanks again everyone, I appreciate all of your responses tremendously.

 

[wraith]

I used a slingshot rear wheel complete (sprocket carrier, brake etc) the main thing you need to do is make new swing arm chain adjusters to take the 20mm Suzuki spindle as the kwak one is bigger, so you could still use the b12 rear wheel 

[Poldark]

Swingarm specs:

The GS650E used the same swingarm as the gs550 of the same year.  The pivot to axle measurement is about the same as the 650G.  The pivot width is just under 9 inches.  Pivot bolt is 14mm, axle is 17mm.  A GS750 swingarm (I think GS1000 is the same) has the same pivot width, 16mm pivot bolt, 20mm axle, and the whole thing is about 2 inches longer.  You will need to either modify the frame or modify a swing arm.  You said you have a lathe; you could make your own bushings for the frame or you could make a new swingarm pivot tube that mounts in the frame the same as the shaft drive arm, weld to a chain drive swing arm.  You may have chain alignment issues; the B12 runs a much wider rear wheel than any older GS models, so the front sprocket will most likely be further off center.  

Having a full custom build ready by May is a really tall order.  I admire your determination, but want you to know what's ahead of you. 

Do you want to maintain the same look and feel of your GS650G, or do you want to go full custom?

[Poldark]

You say she goes to school 2.5 hours away, but you are in Rhode Island?  She must be going to an out of state school because you can drive across your entire state in a half hour 

In case you don't know; there are inexpensive big bore piston kits for the 650 which bring it up to 700cc or 740cc.

[tenderblender]

Wraith, The plan is full custom but not all at once, current goal by may isn’t to be completely done, just rideable you know? It’s just a personal goal, I won’t lose any sleep over it if not, just would be neat. 

My original thought and concern was if I had a thinner 9” swing arm that’s about 1.5” of a bushing or spacer on each side, I’m concerned with the force it would put on the arm, frame, and axle with that much spacer even if it was done up 100% correct. I could be very wrong but it’s a concern of mine at the moment at least. The info you gave is very helpful indeed. I suppose if I machined down some slugs on the lathe that screwed into the frame with a deep counter bore I could find an axle that’s an Allen and use a small nut on the other side. That or basically make little “inner bearing extenders” (like the swing arm extenders you see on eb@y, but just expanding the pivots) with a bolt and nut pulling them together into the races. I don’t mind making parts one bit, just want it to be safe when completed (Motorcycles don’t go hand in hand with safety compared to cagers but no need for the swing arm to suddenly not be attached after a big pot hole or something haha, maybe I’m just a worry wart) just rideable is all I’m looking for. I don’t mind buying a new arm, or modifying it, or making parts, ect, just want it to be solid and simple. I want to keep the same (ish) look and feel but am probably going to continue to mod until I feel happy (which sometimes never ends, who knows). I am not out to have the 180 tire, tire width doesn’t really matter to me (unless the blandit starts to break it free at speed.) currently has a 120/90-17 Michelin Anakee 3 on the stock 17x2.5 rim. I would have gotten thinner which is closer to stock because the rim does kind of wallow side to side in the tire just a hair, but that’s the smallest anakee 3 made at the time. For the new rim I’m likely going to pick the anakee 3 again because it’s an awesome tire so far, but just sized correctly to that new rim.

Does either frame (extending in off the frame flats to fit a stock swing arm off a different bike) or swing arm extenders (to fit the stock frame) sound like a good idea?

 

Poldark, ye she goes to school in New Hampshire. And I thought about it, but I did purchase the blandit for $500, going to sell the frame, tank, and other bits I don’t need, along with the stock 650 top end (I’ll make it a package for some one with a 550) the cases, ect, should keep the overall costs decently low.

 

I also made a couple adapters to fit the 650 lower rear bolt to the blandit and got some 1” 6061 Aluminum round bar for the spacers between the motor and frame.

[Poldark]

Do you have the entire B12 donor bike, including the wrecked front end?  If so what is the extent of the damage on the front end?  If just the fork tubes are bent, they may be easily repairable.  I assume they are 41mm Showa forks.  Lots of H-D models were made with 41mm Showa forks; so lots of inexpensive aftermarket forks in different lengths.  If you want to go full custom, you could keep the GS650G frame, tank, and seat, but mount everything else from the B12 on it.  That route would be no more effort than "just ridable" and " keep the same (ish) look and feel"  with the B12 engine.  

You say you really like your GS650G and you want to be riding it by May.   You seem to have goals that are working against each other.  Only the most experienced OSS members could comfortably pull it off by this May.  Most of us here would be more realistic to be looking at May of next year.  

If you can find another shaft drive 650 engine, you can be back up and riding in short time.  Meanwhile, you'll be under less pressure and you can plan things out better for you B12 powered project.  

[R1guy]

B12 motor fits in a 650g frame nicely

 

[wraith]

The swing arm, you can make spacers for the swing arm and it will safe, if you're worried about that make some sleeves out of steel to 1. Fit inside the standard swing arm points in the frame, make them to take up the extra room swing arm to frame 2. As they are make from steel you can then weld them to the frame and also brace them to the frame as well making them very safe 

You will find the standard gs650 tyres and size will not be able to cope with the extra power of the b12 motor, you will be adding about 50% power roughly. 

[Poldark]

Fine example R1Guy.  How long did it take to build?  I doubt that was your first custom build.

Wraith: Thanks for being more concise and to the point than my long winded ramblings.  There are multiple ways the swingarm could be mounted, the method you describe should be the most simple and the way I plan to do it on an upcoming project (Gs650G frame with GSXF engine and suspension).  I think there was a false impression that the 650G and 650E were essentially the same machine simply offered in chain or shaft drive.  (different frame, different engine cases, different swingarm and rear wheel)  

[tenderblender]

Poldark, I have the bandit, but front wheel is bent beyond repair and the guy I bought it from didn’t have the forks. May would be neat, but I most definitely won’t lose sleep over it if not.

R1guy, perfect! Pretty darn close to what I want to do, inverted forks would be sick too but in due time haha. Is that a turbo I’m seeing? Do you have a build thread? Whatcha do for the swinger?

wraith, I imagine I’m going to need a wider rear wheel and tire, I’m thinking of a couple of slugs for the swinger that will thread together internally. 
 

Poldark 2, agreed and for sure. I knew the swinger, wheel, and cases were different, I should have interpreted that the frames were different because of how wide the pivot is because of the u joint.

[Poldark]

I hope I didn't come off too negative, but I was under the impression that you planned to slap stuff together and have it running in a few weeks.  You have a workable vision, pursue it, there is lots of help here on OSS.

Do you have the B12 rear wheel?  Using the complete rear wheel and swingarm from the B12 would be the surest way to achieve proper alignment; just get engine and swingarm centered in the frame.  If using mono shock, fabricate upper mounting point on frame.  If twin shocks, lower mounting points on swingarm.  

Front end:  Suzuki mostly used same size steering neck bearings between different models and years.  All-Balls Racing's website has a function that allows you to enter what frame you are using, it tells you what front ends you can use with what size bearings.  Just find something that mates well with the rear.

[R1guy]

7 hours ago, wraith said:

The swing arm, you can make spacers for the swing arm and it will safe, if you're worried about that make some sleeves out of steel to 1. Fit inside the standard swing arm points in the frame, make them to take up the extra room swing arm to frame 

This - although I didn’t weld them in. I made them oversize outer diameter so they couldn’t twist ( it made sense when I did it).

 

5 hours ago, Poldark said:

Fine example R1Guy.  How long did it take to build?  I doubt that was your first custom build.

18months ish.... it was my second build

 

3 hours ago, tenderblender said:

 

R1guy, perfect! Pretty darn close to what I want to do, inverted forks would be sick too but in due time haha. Is that a turbo I’m seeing? Do you have a build thread? Whatcha do for the swinger?

 

Swingarm used a Mille swinger and linkage with custom shock, spacers made of steel to centre the arm.

Build thread is in the old site- it may still be possible to find it but I’ve not looked 

[tenderblender]

Poldark, all good not too negative at all, just realistic, completely understood. I have the whole bandit minus the front forks and front wheels. I have the triples and brakes, but steering neck back I have just about everything. I pulled the stock bandit swinger off, cleaned it enough, and through it in the frame. Looks pretty decent, I may just use this and tig some twin shock mounts on it. (Still have to figure out the swinger spacers first though, that and get around to wiring my tig into my house wiring) Front end will stay stock for now, I figure my bike and the blandit are about the same weight and I don’t plan on going much more than legal speeds so I figure it’ll be fine for right now. I’d love to get an inverted front end but one step at a time haha.

 

R1guy, Mille swinger? I’m assuming off of an Aprilia Rsv1000 your talkin about?

 

 

 

Edited February 9, 2020 by tenderblender

[tenderblender]

So some slight progress, got the new motor in with the rear mount after finalizing the spacer dimensions, and threw the bandit 180/55r17 wheel on the swing arm in the frame for reference. I’m going to figure out the other mounts likely next week. I’m wondering if I should look for a shorter swing arm to keep the same (ish) handling or keep the b12 swinger that’s about a 3” stretch because of the increased power, what’s the general consensus?

[Poldark]

I'd keep that rear wheel and swingarm combo.  The stance in the first two photos (seat raised high) will look better for the type of bike you are building.  Whatever front end you end up with will probably be shorter, stiffer, and designed for less rake than your GS frame.  Rear raised up and shorter front end will cause the frame to roll slightly forward and give the proper geometry for a "sport" feel and look.  In your last two photos, the rear wheel is tucked up into the frame; a good cruiser/chopper look.  Combine that with slightly longer front end, you would have good straight line cruising geometry. 

Scroll back up this page and notice the custom bikes by Wraith and R1 Guy, does it make sense now?

[tenderblender]

Poldark, makes sense, the seat raised high is probably going to be about how it will sit, the wheel in full compression is just to see how low it would go if it were to bottom out. I’d like an inverted front end some day but that will probably be next year, but I would like to keep as much ground clearance as I can get so nothing too short. I’m contemplating using the bandit shock/linkage because it seems to be a pain in the @śš to keep it twin shock but I’ll keep toying with the idea. Still have to sort out the swing arm pivot. I’m thinking of making inserts that go into where the bearings sit inside the swing arm that screw together and have the gs bearings on the outside if that makes sense (hastily drawn pic below.) So far I think the hardest part of getting it rideable will be the rear suspension. (The b12 already ran before plucked so just a matter of getting it running again in my frame I reckon)

[Poldark]

That could work, but a full length pivot shaft would be stronger than the dog-point set screws used on the shaft drive swingarm.  You will most likely have to make your own pivot shaft, if you want to go full length.  The 22mm threads in the frame can be drilled out.  You will need to make bushings.  Your swingarm looks like aluminum?  Welding on aluminum takes more skill and better equipment than welding on the mild steel frame; mono-shock may be the better option for you.   Look through the project builds to see examples of modifying GS frames for mono shock, or modifying swingarm for dual shocks.

[tenderblender]

Poldark, that’s kinda what I’m thinking, id like to keep the threads in the frame (gsx1100g cases and back to shaft drive someday? who knows haha, I do prefer shaft drive but anyways) if I keep the threads I’ll order a couple g slugs and drill them out to fit a full length pivot axle. The drawing I mentioned I would make those out of steel to fit the swing arm, it’d be like the stock bushing outer race that’s really wide. I just want to make it solid and safe, I want to do the easiest way I can do it correctly, no short cuts yk? I’ll do some more reading on the gs mono shock builds. I do like the idea of a solid pivot bolt, do you know any pivot bolts or even axles that are wide enough? (13”+)

*edit, I missed the part where you said I’d have to make my own axle, I’ll probably end up doing that*

Edited February 14, 2020 by tenderblender

[no class]

how wide is the frame at the pivot ?  looks fairly wide

[tenderblender]

no class, 12” inside of the pivots

Poldark, this is neat haha

Edited February 14, 2020 by tenderblender

[Poldark]

40 minutes ago, tenderblender said:

no class, 12” inside of the pivots

Poldark, this is neat haha

When I was signing up on OSS, I couldn't think of a user name.  "Poldark" was what my wife and I were watching on TV at that moment.  Does it make for a cool or lame user name?  The opening episode grabbed my interest when it opened on "the battlefields of Virginia".  So it starts in my back yard.  I have long been interested in the people and events surrounding the American Revolution, but there must have been stories about brave honorable men on the other side.  This story was fictional but fascinating, and became one of my favorite TV series.  If the character of Ross Poldark was with us today, he'd be riding an Old Skool Suzuki custom like the ones we see here. (Had to make the post OSS related)

The 850 and larger shaft drive engines may be swappable but the 650 is on a shorter frame.