1981 GSX1100 Katana Based Project

[Suzukian]

Hey, you've got a plan. Sounds like even if you don't make your target weight, you're going to have one really nice bike. I knocked 45 lbs. off my Kawasaki ZZR1200 just by removing the catalytic converters and making my own mufflers with ceramic weave around the baffles, and "Radiant" exhaust tips on the stock pipes. That makes that bike only 30 lbs. heavier than my '83 GS750ES". You have a great sound plan, and I have seen you guys down under make some fantastic bikes and cars. Thumbs up!



zzr1200-exhaust mod.jpg

[Shin-Ken 1074]

Hey Glen,

I would say you would need really drastic measures to reach 50KG.
From your answer to Big Block i see you already started to compile a list, curious how far that will take you.
My guess is you need some very radical grinding and lots of use of light tubing, aluminium, etc.
Carbon wheels and other parts.
And very deep pockets ....

Like i said, really interesting.
Maybe complete the weight savings list before you start shaving off small parts ?
Would be a shame to discover during the project the goal is too hard/expensive to reach...

Hi Rijko, Yes, aluminium, carbon, titanium and chrome-moly is being used however, none of those sexy things will be replacing frame rails or tubes except for the aluminium sidestand and aluminium cowl sub-frame. The frame will stay almost stock with only lugs being trimmed nothing cut off so it could be returned to a stock Kat.

I looked into BST carbon wheels however, there were issues to consider and the numbers didn't add up, cost and weight.

Cost vs weight. A buddy has a set of BST carbon wheels on his Kat and they are lighter compared to cast ally wheels, but only when comparing the bare BST to the bare ally wheel.

The carbon wheels gain weight once the sprocket carrier, bearings and rotor plates are added and then the big one arrives, the tyres. Once the tyres are fitted to the carbon wheels they are heavier than the 18 x 110 and 18 x 140 radials fitted to the GSXR 750 wheels, it is the amount of rubber for the larger tyres fitted to the carbon wheels that bump the total weight up. The advantage of carbon wheels even when the total mass is the same as cast ally wheels is the mass of the carbon wheel is concentrated at the centre of the wheel and are lighter at the rim, the best place to reduce weight on a wheel.

For this project skinny tyres are the better option to reduce rotating mass and improve handling for a sport/touring Kat that would not see track use.

The cost of carbon wheels in Australia would have been around AUD $7,000 plus tyres.

Used GSXR 750 wheels were AUD $300 for the pair plus AUD $390 for both Bridgestone T32 tyres fitted, bike shop here does not charge to fit tyres if you buy the tyre from the bike shop.

The hard work is done, spending two years sourcing parts from around the planet during COVID was no fun at all. I didn't want to start the build until I had everything ready to roll and accounted for. Finding a GSX 1135 EF for the engine was the most difficult and time consuming thing to sort out. The EFFY engine is still a popular item around here and they don't turn up for sale to often so you have to be quick when an engine or a complete EFFY pops up, blink and you miss out!

Cheers,

Glen.

[Shin-Ken 1074]

Hi Suzukian, good job with the muffler it looks very tidy and sporty.

Cheers,
Glen.

[Rijko]

Hi Rijko, Yes, aluminium, carbon, titanium and chrome-moly is being used however, none of those sexy things will be replacing frame rails or tubes except for the aluminium sidestand and aluminium cowl sub-frame. The frame will stay almost stock with only lugs being trimmed nothing cut off so it could be returned to a stock Kat.

I looked into BST carbon wheels however, there were issues to consider and the numbers didn't add up, cost and weight.

Cost vs weight. A buddy has a set of BST carbon wheels on his Kat and they are lighter compared to cast ally wheels, but only when comparing the bare BST to the bare ally wheel.

The carbon wheels gain weight once the sprocket carrier, bearings and rotor plates are added and then the big one arrives, the tyres. Once the tyres are fitted to the carbon wheels they are heavier than the 18 x 110 and 18 x 140 radials fitted to the GSXR 750 wheels, it is the amount of rubber for the larger tyres fitted to the carbon wheels that bump the total weight up. The advantage of carbon wheels even when the total mass is the same as cast ally wheels is the mass of the carbon wheel is concentrated at the centre of the wheel and are lighter at the rim, the best place to reduce weight on a wheel.

For this project skinny tyres are the better option to reduce rotating mass and improve handling for a sport/touring Kat that would not see track use.

The cost of carbon wheels in Australia would have been around AUD $7,000 plus tyres.

Used GSXR 750 wheels were AUD $300 for the pair plus AUD $390 for both Bridgestone T32 tyres fitted, bike shop here does not charge to fit tyres if you buy the tyre from the bike shop.

The hard work is done, spending two years sourcing parts from around the planet during COVID was no fun at all. I didn't want to start the build until I had everything ready to roll and accounted for. Finding a GSX 1135 EF for the engine was the most difficult and time consuming thing to sort out. The EFFY engine is still a popular item around here and they don't turn up for sale to often so you have to be quick when an engine or a complete EFFY pops up, blink and you miss out!

Cheers,

Glen.

You put a LOT of thinking into this, and are up to 43 KG already .... geee .... respect Glen,
i look forward to the rest of your build.

Interested in the modifications needed and dimensions, i have a project coming for a GS1000 special, have a
Kat front fork for it and a GSX1100E swingarm for it already.

Do the 1985 GSXR-750 18' wheels fit in the original front fork / swingarm ?
Many modifications needed ?
Chain alignment ?

7KG weight off the rear wheel is a lot, what's the weight saving on the front ?

[Shin-Ken 1074]

You put a LOT of thinking into this, and are up to 43 KG already .... geee .... respect Glen,
i look forward to the rest of your build.

Interested in the modifications needed and dimensions, i have a project coming for a GS1000 special, have a
Kat front fork for it and a GSX1100E swingarm for it already.

Do the 1985 GSXR-750 18' wheels fit in the original front fork / swingarm ?
Many modifications needed ?
Chain alignment ?

7KG weight off the rear wheel is a lot, what's the weight saving on the front ?

Hi Rijko, thank you for your kind words, much appreciated.

A stock 1985 GSXR750 18" rear wheel will fit a GS1000E swingarm after swapping the 1985 GSXR 750 sprocket carrier for a GS500 sprocket carrier. You will need to make axle spacers to suit the GS500 sprocket carrier. You may need to run with an off-set front sprocket as well?

A stock 1985 GSXR750 18" front wheel does not fit in a Kat front end, the hub is much to wide. I took the Suzuki Kat cast front wheel and the Slabbie front wheel to an engineering outfit and they turned the Slabbie wheel hub down to match the Kat hub - problem solved almost. I want to use the original Kat speedo drive so I had to make the two speedo drive keyway in the newly machined Slabbie wheel. Aluminium is easy to work with if you use a very sharp Bahco wood chisel.

1985 Slabbie front and rear wheels use the same size axle as the 1981 Katana, using 1985 Slabbie hollow axles for the DW180. I had the Slabbie front wheel machined to accept standard Kat bearings.

I have not fitted the rear wheel to the frame yet so I can't tell you how much off-set is needed or rear axle spacer size. DW 180 rear wheel spacers may be different to your build as I am using an EFE engine compared to your GS1000 engine. Currently waiting for the engine paint to fully cure before installing it in the frame. Once the engine is in I'll be seeing the local engineering crew to make aluminium spacers to suit and then let you know what was done.

1985 GSXR 18" front wheel after lathe work to fit Kat forks and fitted with a Bridgestone Radial T32 18 x 110 tyre, hollow axle/Ti nut, aluminium wheels spacers, aluminium bearing spacer, both brake rotors with Ti bolts and the speedo drive, total weight is: 12,770 grams

Chain size can also influence off-set, I am going with 520 chain to reduce weight and rotating mass.

Cheers,

Glen.

[Rijko]

Thank you Glen, that info saves me a lot of time

[Shin-Ken 1074]

Thank you Glen, that info saves me a lot of time

No worries Rijko, glad to have been of help.

Cheers.

[Suzukian]

The 17" Katana wheels on the older bikes seem to fit a lot of bikes. Usually bearings have to be changed, and dis rotors to match whatever calipers you are doing know. I am switching my '83 GS750ES to an GS1150 front end, using 3 spoke Katana 17" rims front and rear, as 16" tires aren't getting easier to find, and the 1150 front end will be better for my '83 GS750ES. I just have to change some bearings, I have the calipers, and make some bushings to make sure the wheels align. I also needed to get different discs for the front, but I was lucky, as this had been done before, I just had to read up on the modifications. A little harder when you're doing the exploration, but totally doable. You have a plan which is a lot of theprocess.

[Shin-Ken 1074]

Hi Rijko, here are the weights for OEM v DW180 front wheel:

1985 GSXR 18" front wheel after lathe work to fit Kat forks and fitted with a Bridgestone Radial T32 18 x 110 tyre, hollow axle/Ti nut, aluminium wheels spacers, aluminium bearing spacer, both brake rotors with Ti bolts and the speedo drive, total weight is:

12,770 grams

1981 GSX 1100S 19" front wheel fitted with 100/90/19 Pirelli Sport Demon tyre and inner tube, stock axle, wheel spacers, bearing spacer, stock rotors with bolts and lock tabs, speedo drive, total weight is:

15,055 grams

Shaving 2,285 grams from a front wheel helps to improve handling as well as contributing to the goal of shaving 50kg off the Kat project, every gram helps.

Cheers.

[Rijko]

Thank you Ken, that is indeed a good weight save and handling improvement ... didn't think it would add up so quickly.
TBH i thought 50KG would be much harder to achieve without drastic surgery, but you are at 45KG already ...
Learning something new here every time, thanks !

[Suzukian]

That's what great about this forum, the right people read your thread and you save a lot of time, and also get some really good deals on used parts.

[Shin-Ken 1074]

Thank you Ken, that is indeed a good weight save and handling improvement ... didn't think it would add up so quickly.
TBH i thought 50KG would be much harder to achieve without drastic surgery, but you are at 45KG already ...
Learning something new here every time, thanks !

Hi Rijko, the frame was spared drastic surgery however, some parts have been tampered with and in a way that some may find perhaps unappealing both from a visual and functional perspective.
The sump as an example now weighs 574 grams, much lighter than OEM. There may be an oil temp issue without fins on the sump but I will monitor engine oil temp under riding conditions and see how it goes. Can always install an OEM sump if needed. There are other parts that have been altered to reduce weight:

rear brake lever, electrics panel, rear brake res, sprocket case, oil filter cover, seat mounting bracket, front foot pegs, swingarm, fuel tank.

Some parts that will be deleted completely:

centrestand, helmet lock, lift handle, front wheeel dust cover, anti dive units, anti dive hoses and hose brackets, front brake line manifold, rubber speedo cable guide, seat strap, tool roll holder, number plate bracket, airbox and filter, rear foot pegs, rear guard sub-frame, front guard inner brace - (replacing it with an aluminium fork brace).

Cheers.

[Rob S.]

...rear guard sub-frame, front guard inner brace...

Please remind me what those parts are. I know what the rear sub frame is, but you seem to be talking about something else.

[Shin-Ken 1074]

Please remind me what those parts are. I know what the rear sub frame is, but you seem to be talking about something else.

Hi Rob,

the Kat front guard has a U shaped pressed steel brace that sits inside the front guard and bolted to each fork leg. Without the four bolts/washers it weighs 800 grams. The rear sub-frame I have removed is the steel frame that secures the inner rear guard to the main frame, without bolts/washers = 260 grams.

Cheers.

[Rob S.]

What is a "rear guard"?

What is a "front guard"?

Are you talking about fenders, or mud guards?