GS400/500 Gr650 Hybrid engine

[60ratrod]

I wish i could have you bring some beer that i found while in Naples. I haven't gotten around to having it imported. Too bad you can't swing through nevada. I'm going to be at the topgun base there from the 9th-20th

[WolfTechnics]

Hi guys, I have studied the art of necromancy and bring this thread back from the dead!

I am just going to continue like nothing happened...well...life happened. And life has put this project up in the attic in boxes for a looooooong time.

Back in 2016, I had send out the crankshaft, custom CP Carillo rods and pistons out to a company that would balance the whole assembly. I have never seen my stuff after that, the company went bankrupt and I never got my money, or stuff. So I was left with a hollowed out crankcase and my wallet a couple thousandth of euros lighter. This was a massive blow to my morale and motivation. Other stuff happenend, life got busy and different projects came about, and so the bike was stored. Over time I have also sold some of the crazy titanium stuff, the C5 ignition, all the kipple valvetrain stuff, I needed the money back then.

Now I am planning on starting this project again...slowly. I plan to have it out and about on the street late 2025, let's see if I can make that.


Anyway, let's get to it then, here are my current plans:

• GS400 Crankcase with openings enlarged to accept bigger sleeves.
• GS500e barrels
• GR500/650 pistons (let's see what is possible)
• GR650 Cylinder head
• Oil cooler with thermostat
• External oil lines to the head
• Carbs with open, non-filtered VC's
• USD front fork
• Modern 17" wheels
• Strenghtened frame with custom rear swingarm

Any crazy ideas beyond this will only happen after the bike will be on the road as described above, some of those ideas I still plan to execute, like:

• Ducati dry clutch
• Cams
• High compression pistons
• etc.

Coming saturday I will be visiting a guy that sells GS400 parts, I first need to find a crankshaft and balancer to be able to build a complete engine, this will be the first step.
Updates will be slow, but I hope to tickle the interest of atleast some people still here!

Best,
Rens

[Chuck78]

AWESOME! I'm excited to hear that this project is back on the table again. My condolences to your loss with the custom rods and pistons and crankshaft / balancer shaft. With your drive and determination and skills, I'm sure you will build something else incredible out of this regardless.

I won't weld any of them, the outer stud holes don't have to be moved, it's only a 1mm difference so I can overcome that with offset studs.
The four inner stud holes will be moved by screwing down fine threaded aluminum plugs, then re-drill the new holes in their correct position.

I've been leaning towards the smaller lighter bikes in the past 8 years more and more. Now I may eventually sell my GS750 or my GS1000, one or the other, including all my spare engines for them. Although I'll be riding the 750 cross country here in 5 weeks! After the past 3 years of primarily riding my two-stroke dirt bikes, and having the obvious pointed out to me that I can't really go through corners any faster than I already do on my big GS bikes because I run out of cornering clearance due to the stator cover, and always liking the lightweight more nimble bikes, I plan to do more mods to my GS550/650 740cc build (these bikes are noticeably lighter and more nimble than the big 750/1000), as well as tinkering with my GS400 frame and pile of 400/425 engines and parts to build a custom track bike and twisty road canyon carver, and perhaps doing the same to my stock GS 425 eventually.

Could you tell me if the cylinder bore spacing was similar enough on the 400 versus the GR650? I recall the 400 stud spacing being different than the 450/500 to the point where going any bigger than GS 850 or 450/1000 sleeves would really be putting the sleeves close to some of the inner studs. I'd absolutely love to have a more advanced GR650 or GS650 head design than the hemi head 1970's GS engine designs. Perhaps this could be a long-term project goal to weld up the cases and relocate some of the studs, however I wasn't sure if the cylinder spacing could really be worked out for a larger bore or if the 450 & GR650 were the same with just different stud locations?

Is the GR650 head a closed chamber type combustion chamber design? If I recall correctly it may be but I could be mistaken. Being designed in the 1980s, I would assume that it is the same as the other two valve swirl chamber head on the GS 650 4 cylinder. Definitely a more advanced design.

In the meantime I might just have some custom 73mm or 74mm Carrillo Pistons made and have a 425 cylinder sleeved with GS450 sleeves, and what I've been talking to Rapid Ray a couple years ago to have him install GS1000 valves and do some good Street porting work on a 425 head and run some GR650 cams or a custom Web Cams grind. My 489cc or 502cc GS400/425 with a ported head with oversized valves and Mikuni RS34 carbs most certainly would be an absolute screamer even with the antiquated hemi head chamber design. CBR600F4 forks and a braced GS400 frame would be the plan.
I do also have a Rickman CR 900/1000 frame that fits GS750/1000/1100E engines and needs professional repair. I thought about putting a GS550/650-740cc engine into it, but found the exhaust spacing on the cylinder heads would not work with that frame cradle downtube configuration. It never occurred to me that since I'm already going to have frame Crafters do some custom frame repairs, that I could have the tubes spaced differently as both down tubes were cracked when the bike saw hard racing use in the 1980s. They were repaired, but not to my liking, and the bike has never been back on the road since the repairs were started by the previous owners.

[WolfTechnics]

AWESOME! I'm excited to hear that this project is back on the table again. My condolences to your loss with the custom rods and pistons and crankshaft / balancer shaft. With your drive and determination and skills, I'm sure you will build something else incredible out of this regardless.

Could you tell me if the cylinder bore spacing was similar enough on the 400 versus the GR650? I recall the 400 stud spacing being different than the 450/500 to the point where going any bigger than GS 850 or 450/1000 sleeves would really be putting the sleeves close to some of the inner studs. I'd absolutely love to have a more advanced GR650 or GS650 head design than the hemi head 1970's GS engine designs. Perhaps this could be a long-term project goal to weld up the cases and relocate some of the studs, however I wasn't sure if the cylinder spacing could really be worked out for a larger bore or if the 450 & GR650 were the same with just different stud locations?

Is the GR650 head a closed chamber type combustion chamber design? If I recall correctly it may be but I could be mistaken. Being designed in the 1980s, I would assume that it is the same as the other two valve swirl chamber head on the GS 650 4 cylinder. Definitely a more advanced design.

Good to see you still active here Chuck, you enthousiasm is well appreciated!

as to your questions, A lot of the details have become blurry and I don't remember. I've been through some dark times in the last 4 years and a lot of this stuff has been pushed out of my mind. I don't remember if the barrel spacing on the GR650 is different, I believe not as the Cylinder head fits just fine on a GS500 cilinder. Give me some time, a couple weeks, I will bring all the stuff down from the attic and I can start tinkering around and answering questions. Very exited to start on this thing again!

[WolfTechnics]

In the meantime, I will post some photo's here of another project I am working on. It's a GS500e that I am completely rebuilding:
The idea is:

• Modified frame (mostly for looks)
• Shortened custom seat
• KAWA ZX-9R front fork
• Ducati monster front fender
• Stock engine but powdercoated and looking fresh
• All hardware yellow zinc-coated
• Black/Silver/Prismatic Universe color scheme
• Custom rear swingarm
• Powdercoated fuel tank (experiment)

I will split up the updates over multiple posts.

GS500 Update 1

I wanted to do something about the sidestand on the frame, simplify it's geometry so to say. I'm ditching the sensor switch and I want to create cleaner lines. The GS500e frame isn't that beautiful to begin with but that ain't no reason to improve it.


So I got some steel from a donor frame, and started playing with it.


And then I ended up with this, looks much better imho!


Then I added the side-stand bracket, and added some bracking in the corner. Also the center stand brackets got removed, but I have no photo of that.


Side-stand installed, it was pretty difficult to locate the spring retainer in the right position.


From another angle


Removed some more stuff, including the steering stem locking brackets



Sandblasted the frame


Et voila! High gloss black


Then I got a fuel tank, without any dents. I wanted to try and powdercoat it.


Stripped it of paint and sandblasted it.


What you see here is one layer of Prismatic Universe powdercoat, and about 6 layers of wet clearcoat. I'm not happy with the results, the powdercoat is spotty and I have some drips. I will do it over but the idea is clear of what this is gonna be.

[WolfTechnics]

Update 2

I wanted to make the rear swingarm look a bit more aggressive, the GS500 rides amazing with an USD front fork and doesn't really need any bracing in the rear, so this is purely for looks.

I started out by drawing the brace on a piece of paper, cut it out and stick it to a rectangle shaped tube.


And here's the result, not much words needed here, pretty self-explanatory.


Then by using a ratchet strap I would bend the tubing into shape following the contours of the original swingarm, and tag-wel it in place as I go.


The brace


Weld everything, bout 2 minutes of work...lol.


Sand down all the welds, and make it look good.


Skipping a couple steps here, but this is what I have ended up with for now, the fender will need some more work, but it's close.

[WolfTechnics]

Small update regarding the hybrid engine, I went and picked up a bottom end for 25 euros, a steal! The seller had a lot of stuff so I got myself a whole bunch of seals, o-rings, and gaskets. Also I got a bin full of nuts, bolts, washers, 2 crankshafts including their balancer shafts and some other stuff. So now I own 3 GS400 crankshaft/balancer combo's of which 1 is ready to use as is.

IMG_20240412_185950_743.jpg

My initial idea was to modify the GS400 conrod small end to accept an 18mm wrist pin, but the GS400 conrod really lacks the material to do that safely. Now I'm thinking it might be possible to modify the GS500 conrod to accept the GS400 big-end bearing. GS500 big-end ID is 37mm, the GS400 bearing is 38 on the OD, you'd have to remove 0.5mm of material from the GS500 ID to make it fit. Side clearance can be resolved with washers (just like the OEM GS400 solution).

What I worry about is the split cap big-end of the GS500, you will have two "ridges" on either side of the big-end where the split-line is. The roller bearing might actually not like it, although the big-end is mostly loaded on top and bottom, not on the sides. Anybody got some thoughts on this?

[WolfTechnics]

Forget about everything I said below, I did some more thinking and although it would be possible to modify the GS500 crankshaft, the real issue is the big-end plain bearings. Mixing roller and plain bearings is not a great idea because of the needed oil pressure towards the plain bearings. I will leave the text in quotes just to keep clarity about my thinking process.

Currently looking into Yamaha XT250 pistons, They are 75mm bore size with 16mm gudgeon pin. This will give me 530cc at 75mm or 544cc at 76mm. Although I am not sure how far the GS500 barrels can be bored out. The XT250 pistons have roughly the same shape as GS500 pistons, it's a 2 valve motor as well. They are also cheap and readily available.
s-l1200.jpg

I just had another ophifany; It might be entirely possible to put GS400 crankshaft roller bearings on a GS500 crankshaft. The GS500 crankshaft journals are all 32mm, the GS400 main crankshaft bearings are also 32mm ID. The only issue is with the GS400 ball bearing on the LH side, it acts also as a thrust bearing and has a 30mm ID, the GS500 has 32mm OD in that location. Another issue is the balancer, the journals are 25mm OD compared to the GS500 32mm.

This might actually be the cheapest route to a working engine, as it will only require disassembly of the crankshaft en grinding down one journal on the crankshaft, and both journals on the balancer. If assembled correctly, no re balancing is required! This option leaves me with a GS500e crankshaft in the GS400e bottom end. I can use the stock GS500 pistons/barrels and use the GR650 head with big valves. Skim the head/cylinder to get the right C/R and off you go!

I have about 4 usable GS500 crankshafts laying around and 3 GS400 crankshafts, that will give me a lifetime supply of bearings and depending on costs, I can have a second GS500 roller bearing crankshaft on the shelf as a spare.

This is a SERIOUS option I am going to investigate.

Edit: Too bad with the option above you will lose the GS400 60mm stroke as opposed to the 56.6mm GS500 stroke.

Edit 2: If using the stock GR650 pistons, capacity is bumbed up to 527cc

Edit 3: Found out the crankshaft and balancer on the GS400 use the same straight cut gears found on the GS450 and 500 with PN 1266644000. Later in the year 2000 a new version was made with PN 1266644001 but I would imagine they are interchangeable. This tells me the center distance between crank and balancer is exactly the same on all models from GS400 to 425, 450, and 500.

Edit 4: The shock when you realize the GS500 crank is one solid piece and cannot be pressed apart...now I have more thinking to do.

[Chuck78]

I was immediately thinking the GS500 plain bearing crank was a solid 1 piece crank, so yes, that's not going to work.

The easy route is to use a GS450 bottom end with GS500 cylinder barrel and a custom aluminum base gasket spacer and 2 base gaskets (1 on each side) from what I recall previously, + GR650 pistons + GR650 head. The head barely seals up at the cam chain tunnel area, but perhaps some of that DIY aluminum brazing rod alloy could help build up some material externally to file down to extend the gasket surface on one or the other. The Suzuki aluminum alloy may be a challenging one to TIG weld cleanly, so this is why I suggested that route.

I believe the GS500 crankcases are identical EXCEPT for different engine mount configuration for the later generation (500 vs 450) frames. And they have a reverse shift drum for the different orientation of shifter due to rearsets.

The YouTube video "GS527 Beast" was a build using a very similar formula I do believe, 450 bottom 500 cylinders GR650 pistons.

https://youtu.be/tQEVHd1cSyw?si=Ve5sWYdo2mGPT4Kv

The 650 pistons are a closed chamber design that really should be matched to GR650 closed chamber head's combustion chambers, and will be the most efficient out of any options. The head and piston need to be matching, including using a 75mm or 76mm XT250 piston to a GS450/GS500 head. There would be no squish area, and instead, piston to head interference. The other option would be to enlarge the combustion chambers. This may be a bit tougher to do. Perhaps a rotary table on a mill, or a face plate on a large capacity lathe with a very heavy mass.

The 1980-ish(?) XT250 pistons would need slight machining to give a 0.50mm squish area (flattened) at the edge of the piston as it's 1.0mm larger than the GS500 combustion chamber. The valve relief ls may also need their location adjusted due to the differences.

[Chuck78]

I'm still sitting on my stock GS425, but have since gotten a $300 GS400 frame, more engines, and crates full of parts. Although I'm likely to first build it as a 449cc with Wiseco K844 pistons and re-degreed GR650 cams or perhaps GS850 70mm +1.00mm oversized pistons for 462cc or 467cc if I recall, ultimately I'd like to get some custom JE Pistons 73mm pistons made for 502cc and higher compression, or potentially 74mm for 516cc. 502cc is a safer bet, as GS450 sleeves can be fit to the GS400/425 cylinder jugs and bored out 2mm oversized.
GS500 sleeves on a GS400 stud spacing is really pushing it around the inner 4 studs, and may not be feasible but could be potentially clearanced around.
Custom 73mm or 74mm pistons will work best.





If the inner cylinder studs could easily be relocated in the crankcase, a 450 or 500 cylinder with a GR650 head would ABSOLUTELY be the best way to go, with GR650 77mm type custom pistons. Closed chamber head, very superior...

The GR650 engine would be great to swap into the 400 frames but due to the longer stroke, I'd be it's taller and wouldn't be workable.

Back to the custom pistons and GS450 sleeves for a GS400/425 big bore. Oversized valves and mild porting for the cylinder head, Web or MegaCycle cams or re-degreed GR650 cams, and some dirtbike flatslide carbs or Lectron carbs, or some CR29's, and this would be a very potent little twin. This is my goal, although the 449cc Wiseco or 467cc GS750 +1.00mm pistons may go together first just to get the project moving, while I build another more performance oriented engine...

I'm eager to get a lighter weight smaller vintage street bike and track day / twisty road machine like this. I may sell all my 750/1000 stuff and buikd a GS550/650-740CLcc as my primary long distance street bike as well for the same reason, lighter weight. Riding 2-stroke dirt bikes really has made me conscious of the hefty weight of full sized street bikes. And riding the twisty roads has made me very aware of the cornering clearance limitations of the veey wide GS750/850/1000/1100 engines. This almost makes me want to swap in an oil/air cooled Bandit 1200 engine into my 750 frame if I stuck with the big displacement sizes vs a big bore GS550... The GS550/650 engines as well as the Bandit 1200 engines are all significantly narrower in the stator area.

[WolfTechnics]

Small update, I have decided on the way forward and have ordered the parts.

I'll be using GS1000 con-rods on the GS400 crank, the challenge here is the difference in big-end size.

	GS400	GS1000
Stroke	60	64.8
Crank Pin	28	29
Big-End	38	39
Big-End Width	20	20
Small-End	16	18
Con-rod Center-to-Center	Unknown	Unknown

Using the GS1000 con-rods allows me to use the GS500 pistons with GR650 head on a GS500 cylinder. I plan to use 32x39x20 bearings on a 28x32x20 needle bearing inner race.
I see this as an intermediate solution to get this setup going for as little money as possible, later I'll have con-rods made with a 38mm big-end diameter so I can use the stock GS400 bearings.

One issue I don't have data on is the center-to-center length difference between the 400 and 1000 con-rods. Due to the longer stroke of the GS1000 I'm gonna guess they are slightly shorter. this can be solved by shortening the barrels and skimming the GS500 cylinder to get proper C/R ratio.

Things I should mention:

• It seems to be impossible to find a 28x32x20 needle bearing inner race with oil groove, a hole should be made in the hardened steel to allow for lubrication.
• Centering the needle bearing inner race on the crank pin, also aligning the oil feed holes. Depending on fitment I will use a interference fit or shims.
• A suitable 28x39x20 bearing does not seem to exist, I have looked extensively.
• A GS1000 crankshaft, needle bearings and inner races have already been ordered.

Expect an update soon.

[GregT]

Have you looked through the rod catalogues from ProX and others ? It's much cheaper to use an existing rod and big end bearing than to have specials made.

[WolfTechnics]

Have you looked through the rod catalogues from ProX and others ? It's much cheaper to use an existing rod and big end bearing than to have specials made.

I have looked through multiple catalogues to find fitting rods for the GS400 crank, no luck. I also have a preference to use OEM Suzuki parts, hence the GS1000 rods. I managed to find a GS1000 crank for about 110 euros, which will yield me 4 rods, 6 bearings, 8 rod washers. Figuring it's not gonna get any cheaper then that. Just regarding the crank, the only issue is the 1mm difference in diameter of the crank pins. I plan on enlarging the GS400 crank pins to 32mm using a needle bearing inner race with an interference fit. I'll modify this inner race with an internal oil groove and a lubrication hole so its rotation relative to the crank pin won't matter. This 32mm dimension is much better for bearing selection and allows me to fit 32x39x20 bearings.

I don't like "adding parts" to the crank hence why I said I will have rods made in the future. I'll do that when ready for a performance upgrade and after the bike is finished and fully road worthy, which might be another 2 years...

In the meantime, a small update:

Out of 3 GS400 crankshafts there is one that seems to have fully intact undamaged crank pins, so I have started measuring some parameters to get a feel for the condition of this crank. Also I need to measure up tools for pressing it apart.

Measuring the run out first



RH side measures in at 0.04mm
LH side measures in at 0.12mm
Side clearance is 0.30mm both sides

Weirdly enough, a bolt seems to be stuck inside the LH web crank, I don't know what the person doing this was planning. I'll get this out after pressing the crank apart.



Both rods had a sideplay of exactly 0.3mm

[WolfTechnics]

Progress!

During the last couple of days I took the time to create some tools to press both the GS400 crankshaft and the GS1000 crankshaft apart.
I made some exciting discoveries.

See the drawings below for what you need to make to press it apart.




And here is the final product with the GS400 crank inside, ready to be taken apart.


I started with disassembling the GS1000 crankshaft halfway. I didn't take it apart any further because I am waiting on tools to remove the bearing on the other side.
The bearings costs about 165 euros each so I am trying to remove them in such a way that I can re-use the bearings.
I had to elevate the tube with two metal blocks because I made it ever so slightly too short, should have cut it at 400mm, not 350mm.


This is how far I got with disassembly:


Like I said, I'm waiting on tools to remove the bearings, but getting this far atleast allowed me to take some critical measurements.
One mystery has, up to this point, always been if the center-to-center length of the GS400/1000 rods are the same, now I know they are.
Both rods measure in at 114.9mm.


The rods are 100% identical except the GS1000 rods are a bit beefier around the wrist pin area, and of-course the big-end is 1mm bigger


This is very exciting news, as it means when these GS1000 rods are put onto the GS400 crank you basically have a normal "stock" gs400 crank with 18mm wrist pins.

Now for the pistons, I believe it is best to use GR650 pistons and increase the C/R somehow.
A GR650 head with GS500 pistons is not optimal as the compression chamber is shaped differently.
GS500 pistons with a GS450 head is possible due to the exhaust angle, but it just doesn't seem ambitious enough, only 516CC
GR650 pistons with a GR650 head and the GS400 60mm stroke will give me 558.8CC or 573.4 if I go oversize +1.

From my initial measurements today it seems as you go up in capacity with the GS motors, the distance between crank center-line and piston crown at TDC increases slightly.

Engine Type	Piston Pin Height (mm)
400	24.2
500	26.1
650	27

.

Engine Type	Crank center-line to piston crown (mm)
400 (60mm crank)	30+114.9+24.2=169.1
500 (56.6mm crank)	28.3+114.9+26.1=169.3
400 with 650 pistons	30+114.9+27=171.9

.
From the information above it seems that the 400/500 motors are very identical, but this is deceiving as apparently the cylinders are of different heights.
It would be interesting to test if both engine types have their pistons flush with the cylinder deck, as that would mean the crankcases have different dimensions.
I am taking about the distance between the cylinder bottom gasket mounting surface and the crank center-line.
.

Engine Type	Cylinder Height (mm)	Barrel Length (mm)
400	81.6	102.6
500	83.1	83.1

.
The information above is not enough to make any good conclusions, but making some assumptions, at-least a plan is visible here, namely this:
If I use a GS400 crank, with GR650 pistons, the piston crown will be at +2.8mm over the stock GS400 piston.
If we then mount a GS500 cylinder, which is taller, we reduce crank center-line to piston crown by 1.5mm, taking us to +1.3mm crown height (you still follow?)
This +1.3mm might, or might not be, too much to increase compression ratio properly and not hit the valves, time will tell once I mock-up this combination of parts.
However, it's all terribly close to where it needs to be, and none of this can't be fixed with thicker gaskets and or milling the cylinders/heads.

Also, I will put some GR650 barrels into a GS500 cylinder just to make sure I have enough wall thickness, Then modify the barrel length as needed, to make them fit.
If I go with oversize GR650 pistons or even big-bore custom pistons, I will just have a lot more barrel wall thickness to play around with.

Next update will be about pressing the GS400 crank apart further and how I plan on solving the big-end bearing issue.

[Chuck78]

Wow, very interesting and awesome news for those wanting to build a maxed out big bore 400/425! This also could mean the potential of running GS1000/1100G pistons in a big bore GS400...

I'd be very interested in the GR650 pistons and head, but am concerned about the modifications needed to the crankcase to move the inner cylinder studs to match the GS450/500/GR650 stud pattern...
The GS650 4-cylinder and the GR650 2-cylinderby far are the best head and piston design on any 2-valve per cylinder GS ever built... As they use the bathtub/kidney bean shaped combustion chamber to induce the modern swirl concept into the air/fuel mixture that the TSCC 4-valve per cylinder 16v GS big fours really pioneered - a drastically better combustion design.