GS500 Engine.. or half a GSX-R750..?

[moto]

Hi Guys,

Some of you may know me from my (ongoing) GS500 Brat build, http://gstwins.com/gsboard/index.php?topic=71441.0

The time has come for me to build an engine for it. Ive come this far and want to build something special for it. I want to steer away from an engine conversion but i want to keep it air cooled and it needs to be based on a GS500.

I have read over alot of forum posts about tuning a GS500 Engine, and alot of it comes back to one engine build.


https://www.sportrider.com/oxymoron#page-7


Does anyone have any further information on this engine build? What the power output was? how reliable it was in the end?


Current Engine Spec

Current capacity 583cc @56.6mm stroke

Crank - Standard

Pistons -  Currently investigating 81mm standard Gen2 1300r Suzuki Hayabusa  18mm wrist pin - top of pin to deck height of 15mm - compression distance from center of pin to top of piston of 24mm

Con-Rods - Standard  Big end  33.976 – 34.000m Small end 18.006 – 18.014

Liners Sleeves - GR650 (Starting diameter 77mm can be bored to 82mm safely)

[moto]

Ive also just done another search  and come up with this thread.

http://gstwins.com/gsboard/index.php?topic=6843.0

Useful information!


"The head I have is an 89 gsxr 750. There was one on ebay last week, but I decided pass on it.
Here's the deal. The 4 inner stud holes lineup perfect. The outer 4 need to be relocated outward a bit. The GS head gasket works fine. The cam chain slot on the gsxr head is longer than the cylinders. So you need to fill it in at the rear. The GS cam sprockets will fit on the gsxr cams, so you can use the GS chain and sprockets. The bolt holes need be redrilled 1mm bigger (better yet slot them for degreeing).
The cam lobes need to be relocated for a 180 degree crank (Megacycle cams can do this). Might as well get higher lift at the same time. You'll need hardened rocker arms (Megacycle again) Valve spring set.
The inner cooling chambers normally drain down the stud into the lowerend on the gsxr. The GS studs are open in front (major oily mess  :lol: ).
Fill in the drain holes and drill other holes so oil drains into cam chain area.
Then you need to make end plates to seal the the sides of the head.
These need oil passages to oil the cams and rockers through the rocker shafts. And you need to make drain lines to drain the cooling oil.
I went the extra step of installing a second oil pump in the sump, driven off the transmission. The oil goes from the pump to the oil cooler (B&M Supercooler) then to the valve cover. It fills the cooling chambers in the head and then drains back down into the motor.
The original pump does the lubrication. I tapped into the plug just below the igniton cover. It goes into the side plates and into the rocker shafts.
I'm running Carrillo rods and JE pistons. I had the pistons designed for the gsxr head. The exhaust cutouts needed to be cut forward a bit more. That's why I broke the first head   
The weak link in the crank seems to be the right side rod journal where it connects to the outer weight. The drive gear is helical. This flexes the crank and snaps it eventually.
I've milled a slot for another thrust bearing into the cases in an effort to limit the movement in this area. The bearing shows definate contact, so it's doing something (time will tell  :mrgreen: )
I have pictures of all the mods. Was planning on putting them on my website www.gszilla.com but i've been too lazy to complete the site.
Email me for the pics and more details.
There's other things, like gsxr cylinder studs (APE). Stronger and equal length. GS studs are different lengths.
By the way how rich are you?   :lol:  :lol:  :lol:    "

[mr72]

The GS400 head looks more promising for hackers like me. But I'm still going to follow this thread with interest.

[moto]

I did take a brief look at the GS400 head but couldn't find an 8 valve.

Also heard that the exhaust ports hit the frame? which may be a show stopper sadly.

[moto]

Stage 1 of about 100 😂 where did I leave the big saw...

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[moto]

I'm also on the hunt for some uprated Conrods.



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[moto]

I havent split my project engine yet, and Im trying to calculate the length of Conrods that i need to connect the busa pistons to the GS crank, would anyone know the distance between the top of the wrist pin and the deck of the piston on the standard GS500?

[cbrfxr67]

Good luck!  sub'd

[The Buddha]

You could do what I did - but never finished - GR650 motor.
If you got a GS head on it - I think it will fit cos the GR is a 13mm longer stroke and 2 or 3 mm larger bore - you'd get more compression unless you get the head CC'ed up, or some other piston with larger reliefs or something and the exhaust will clear the frame - I didn't do that and I have to fab an exhaust for it ...

I had a fantastic welder friend who made the mounts, and it is easier to take it out of the frame than the GS motor, and make that top T brace unboltable. so you can do a valve adjustment without having to take it out of the frame.


Cool.
Buddha.

[crackin]

Your ambition is admirable moto.
Have you considered going with oversize valves, porting and double valve springs on the standard head? I'm sure you could gain some good horsepower with that set up.

Just had a look in my gs manual and it seems that it has double valve springs already. I wonder why they bounce valves all the time. Maybe they need to be upgraded?

[moto]

The GR650 sounds like an interested idea! i had a look and the parts are extremely hard to get hold of in the uk, not sure it was every sold over here?

Has anyone ever tried to put a XS650 engine into a gs frame? looks like it might fit... could rephrase and bore to 750 with not much effort!

Update * Just checked.. an xs650 lump is 530mm tall, almost exactly the same as a GS500. Just need to check the exhaust outlet positions

[crackin]

I thought you wanted to base it on a GS engine.
If your going to do an engine swap, why not put an IT 465 engine in it?

[moto]

I'm sticking with the GS lump, more intrigued than anything. Suprised an xs650 hasn't found it's way into a GS frame!

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[moto]

So I've made a start on splitting one of my parts engines, it's a shame as it's in really good condition except for the engine mounts exhaust studs that have sheered. My other good engine had a sprocket welded on by the previous owner.. thanks. So I'm pulling the output shaft from this one for the full build. We'll see what conditon the crank and rods are in too.


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[moto]

So an hour ago I was asking myself whether you could get to the bottom end without disrupting the head. Turns out you can!


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[J_Walker]

suzuki shares parts across many bikes... most people don't know this until they try to "build a bike" and realize that suzuki bikes are like lego. i suspect its from re-using casting dies probably.. and I have no idea if this stands true for post 2010 bikes.

[crackin]

So an hour ago I was asking myself whether you could get to the bottom end without disrupting the head. Turns out you can!

Thats really good information thanks for sharing. Have you considered pulling out the crankshaft balancer?
I'm really intrigued with what Cedric Smith has done with the left hand side cover on his engine. Its obvious he has removed the starter motor and related junk. it seems he has used a donor rotor and stator and made a custom side cover. It looks as though there is no oil in that side of the engine anymore.
It looks cool as hell, even though you would have to push start the bike all the time. Any one know what rotor and stator he used? Im keen to run a total lose electrical system on my bike, just for the sake of weight reduction as it would make it possible to lose the starter motor and associated parts. Is it possible to make the standard GS electrical system a total lose system?

[moto]

Im assuming you want to run total loss on a race bike?

I think you would need to rewire the bike. To get it to work you would need to strip all lights, and anything with a current draw anyway otherwise you would have a huge battery instead of a small battery and alternator.

If your considering bump starting you would probably be better switching the battery out for a capacitor and keeping the electrical system standard.  I had that on my CB200, but that had a kicker.

I love my starter motor too much 😂

[crackin]

I'm sorry moto if i'm derailing your thread because i'm really interested in what you are up to, but i'm going to go total loss on my street bike.
I don;t use it to commute ,only for street racing so i think it will be ok. I'll use two batteries, one for ignition and one for lights.
Back to what Mr smith has on his bike, if he is running total loss then there is no stator behind that rotor. I guess its only there to give the engine some run on, and being smaller than the original GS rotor the engine will spin a bit up quicker.
I'm going to strip my rotor on the week end just a an experiment, and see how the engine behaves and what battery life i can expect. If all goes well i will strip the rest of the crap.
I'm chasing max horsepower and performance from this engine, not fuel economy. Im' going to do a port job soon too. I'm not sure that the head has room for oversize valves but if it does, i'm going to do that too, we'll see.
I'll probably remove the crankshaft balancer as well.
I will start a new thread on my experiences.
Regards Johno
P.S Excuse my lack of grammar and punctuation LOL

[crackin]

So I pulled my rotoe and noticed that you have to have oil in the left crank cover. There is no seal on the end of the crank. I can't figure out how Mr smith has done what he's done. He's a pretty clever fella.