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.