GSXR400/1135 hybrid race bike '80s

[sidecar bob]

The cams are a slight worry. This engine uses rocker arms and an assymetric cam to suit. Jags are symmetrical cams.
That's tight valve to piston too.
Worth asking if any mods were made to the lubrication system - uprated pump etc.

How long ago was it last run ?

I'd guess it hasn't been running for a minimum of ten years.
Yep, I agree with you about the piston to valve, might work a bit more of a margin in there.
As far as the rest of it goes, I'm going to put it back pretty much as it was & see how it goes.
I found these in a cupboard today, 29mm smoothbores, I thought I'd find a use for them some day.

[Grumph]

See what the pistons are like. OE GSX1000 are 69.4mm bore. Wiseco do a 70mm piston set for that motor which would solve any piston or ring availability problems.
Coincidentally, I'm respacing a cut set of 29mm smoothbores for a twin project. Bought a damaged set for peanuts years ago and made a pair out of them. This will be the third different spacing, LOL. Need to make bellmouths for them. I've got pressformers for this size - do you want a set for those ones ?
They'd be alloy and will take a polish.

[sidecar bob]

See what the pistons are like. OE GSX1000 are 69.4mm bore. Wiseco do a 70mm piston set for that motor which would solve any piston or ring availability problems.
Coincidentally, I'm respacing a cut set of 29mm smoothbores for a twin project. Bought a damaged set for peanuts years ago and made a pair out of them. This will be the third different spacing, LOL. Need to make bellmouths for them. I've got pressformers for this size - do you want a set for those ones ?
They'd be alloy and will take a polish.

Polished alloy bellmouths? Yes please, that's another problem solved!
Will strip it down & give it a clean up & measure, but by the sounds of it, storage aside, it's quite low mileage on a rebuild.
It's not going to get a hiding, so I might just safe it up & run it near enough as it is.
To be honest, I'm probably going to do a lot more looking at it than riding it.

[husaberg]

Polished alloy bellmouths? Yes please, that's another problem solved!
Will strip it down & give it a clean up & measure, but by the sounds of it, storage aside, it's quite low mileage on a rebuild.
It's not going to get a hiding, so I might just safe it up & run it near enough as it is.
To be honest, I'm probably going to do a lot more looking at it than riding it.

Judging by the comments the pistons should be 72MM?

-A replica frame built and welded by Chris Dowde in the same jig he built for the original
-Swingarm is an 1100 EFE item caged and moded to fit same as original
-I have the original front end including billet fork brace and EFE 1100 brake dive mods as per Chris Dowde
-Replica engine ESD 750 running the forged Katana Air Cooled 1000 pistons (the production racing special with wire wheels. actual capacity actually just under 860cc

72mmx53mm =863cc

[sidecar bob]

Judging by the comments the pistons should be 72MM?

That's what a standard 1075cc GSX1100 runs. I have a pile of them & 74mm 1135cc Suzuki and Wiseco branded ones.

[husaberg]

That's what a standard 1075cc GSX1100 runs. I have a pile of them & 74mm 1135cc Suzuki and Wiseco branded ones.

So are GN250's and they are more likely to have a similar valve angle.
Also the S3 GSX750se has closer ratios
plus very different primary ratios?
I know the Giles Katana runs GSX750 primaries.
https://bikereview.com.au/shawn-giles-19-tbr-katana/

[Grumph]

Slow down a bit there Husa. Builder said Air cooled gsx1000 katana pistons - 69.4 bore. std 750 is 67 so that's a 2.4mm overbore. Knowing suzuki barrels, I'd doubt if 72mm is practical - let alone 74mm - without resleeving.
It was built for the Aussie 1000cc limit of the time too.
Until Bob gets it apart, we're only guessing anyway. If it is 69.4 - and has sat for that long, rings could be a problem. Maybe the contacts made at team classic Suzuki UK might come in handy after all...

[husaberg]

Slow down a bit there Husa. Builder said Air cooled gsx1000 katana pistons - 69.4 bore. std 750 is 67 so that's a 2.4mm overbore. Knowing suzuki barrels, I'd doubt if 72mm is practical - let alone 74mm - without resleeving.
It was built for the Aussie 1000cc limit of the time too.
Until Bob gets it apart, we're only guessing anyway. If it is 69.4 - and has sat for that long, rings could be a problem. Maybe the contacts made at team classic Suzuki UK might come in handy after all...

I am only going from the builders claim of 860cc but yeah until it stripped who knows..........

Well this is grandfathers axe discussion. The original bike was destroyed in a fire at a workshop during extensive mods to go back on the track (so I have been told). The new owner who got it soon after the swan series wanted to invest heavily in a trick bike.
That means he did not use a lot of stuff from the bike as raced.
So what I have is:-
-A replica frame built and welded by Chris Dowde in the same jig he built for the original
-Swingarm is an 1100 EFE item caged and moded to fit same as original
-I have the original front end including billet fork brace and EFE 1100 brake dive mods as per Chris Dowde
-Replica engine ESD 750 running the forged Katana Air Cooled 1000 pistons (the production racing special with wire wheels. actual capacity actually just under 860cc
-I have the original Dymag front Wheels 16" and the hand widened (yes you are reading correctly) mag built by Chris when the racing wheel ordered from England did not arrive in time. The disks on the original are from the RG 500 Mk 5 and were floating disc. I used Brembo items.
-The crank is the original item with the alternator end lopped off. A secondary oil pump drive developed for the original but not used due to time pressure is fitted to this engine.
Sorry no carbs they were cannibalised. Grumph looks like santa.

I have a few sets of barrels and a couple of heads etc that go with it.
If you are still interested I will photograph the bike and send them.
Happy to sell to a good home.
No bodywork , I changed all that to get rid of the sitting on a fence seating position.
Regards Leon

Here is the stuff you wanted anyway

There's more than one way to do it...
Pressed these out today. 3mm wall 6061 alloy tube in a size where the ID doesn't need to be touched to match the carb.
40mm long, recess machined at the carb end to suit the body OD. The main portion of the length is then machined to approx 1.8mm wall thickness - taking it off the OD. Lightly polished on the lathe to assist pressing.
Pressed onto a male form made up in mild steel and highly finished. Well lubed when pressing.
I've done bigger ones before and it's possible to get an impressive flare on the end before it splits...

Press forms for 2 sizes of bellmouth and a couple of samples. Forms are just turned up from scrap mild steel. The shape and form of the taper can be whatever you prefer.
It would in theory be possible to actually do a roll on the outer edge of the bell, I've made a form for that on steel silencer ends way back. As what i'm using is 6061 in T6 condition, I'd doubt if it would form that much without annealing - which i've not found necessary yet.
The disadvantage of using tube for the raw material is of course finding the correct size...The last lot was particularly hard as i could have bought a 5m stick but not the small quantity I wanted. Solution - ask the wholesalers who they last supplied and go beg an offcut.

[Grumph]

Thanks Husa. The 29's take the larger ones in the 2nd pic. The set of four in the first pic use the smaller size. They're actually Kawasaki Z650 carbs narrowed and remounted to suit the big CB350/4 I built. 26mm bore vs the OE Honda 20mm odd.
I have enough tube left in stock to do a batch for myself and Bob's set - if I don't split too many.

[Drew]

Still got my hand up to ride for ya.

[sidecar bob]

Still got my hand up to ride for ya.

What age are you considering riding to?

[husaberg]

the GS1000s was 69.4mm std bore. they have 1.5mm higher domes.
The biggest listed piston on the std sleeve for a 750 is 70mm or 3mm over.
My thoughts are if you are going against 1000cc bikes in the swan series and you go to all the trouble of adapting a outboard mag and other mods a new set of sleeve isnt an issue
On the other hand its a lot of trouble to go to on a replica.
Warwick likely has access to a Gn250 piston to measure. Which have likel had a fair few designs over the years along with the DR and sp versions.
Diameter(mm): 72
Pin(mm):18
Total Height(mm):53
Compress Height(mm):27
Doom Height(mm):0


The 18mmx63 pin was std on Suzuki GS750 80-81 4-valve- GS1000 78-81 2-valve- GS1100 4-valve


Pretty sure the older roller bearing GS's had the same rods and the Gn's with odball bearing sizes. the Kawasaki from what i found ran Kl250 Kz200 rods

[Grumph]

Forget GN250 pistons. The exhaust valves are wide apart compared to any of the fours. The cutaways would have to be reworked severely.

The GS/GSX confusion is coming back too. The 16V750 GSX uses the same pin size as the GSX400 twin - but not the same as the GSX1100 - and the 1135 is bigger again. If you were serious about a big GSX750, you'd have to use aftermarket rods in order to use pistons made for the bigger 16V engines.
Then you run into the well known lubrication and bottom end issues of those motors.
Simpler to bolt in an 1100 - which uses pretty well the same mounts anyway.

[husaberg]

Forget GN250 pistons. The exhaust valves are wide apart compared to any of the fours. The cutaways would have to be reworked severely.

The GS/GSX confusion is coming back too. The 16V750 GSX uses the same pin size as the GSX400 twin - but not the same as the GSX1100 - and the 1135 is bigger again. If you were serious about a big GSX750, you'd have to use aftermarket rods in order to use pistons made for the bigger 16V engines.
Then you run into the well known lubrication and bottom end issues of those motors.
Simpler to bolt in an 1100 - which uses pretty well the same mounts anyway.

Pretty sure the 1100 is lighter even but that raises a point why did they use the os 750 engine?
the pins stuff was from here the yanks often call the first 4v GS
https://www.z1enterprises.com/piston...hromed-gs.html
https://books.google.co.nz/books?id=...eworld&f=false
https://www.yeoldecycleshoppe.com/?offset=1481127704944
from memory the gs400 was eventually half a gs750
i had all the dimensions on the early gs and GSX internals on my old laptop but that was lost in a crash i think.
you have seen the insides of far more than i have but there is a fair bit of changes in them even in the GSX series model to model.

[Grumph]

I've just pointed out the same confusion on a GS forum. Idiot yank said that an 8 valve GS400 twin - a GSX - took 14mm plugs cos the NGK catalogue said so.
The early 4 valve GS400 twin does - the GSX uses 12mm. Bloody silly marketing decision to keep calling the family GS in the US. Confusing.

Why use the 750 engine as a base ? well early on in the thread I posted pics of the Moriwaki Honda 750 that Phyllis had ridden in Japan. Very similar to what they built. Yosh was working on the 750 at the time cos TTF1 - and the AMA superbikes - were going 750. I sent Bob a copy of a Revs with an article - and pics - of what Yosh were racing in japan. From 400/4 through 750 to 1000, all were using a frame which is a dead ringer for the GSXR400.
The Honda VF750 was just coming in - and was very fast when it held together. Phyllis had been racing the 1000 Katana and was struggling to match the VF750's. Less power, yes, but lighter and more nimble. There was also a move at the time to make the top class in OZ 750's. Happened of course when WSB arrived.
The 750 was seen as the future. Better head than the equivalent Honda. More revs than the old roller engines could sustain safely. But then we found the weakness. Yosh got around it by making their own cranks...