1981 GSX1100 Katana Based Project

[Shin-Ken 1074]

The engine rebuild parts have arrived, the engineering shop that is doing the valve work has been booked for next week so its time to make a start. Removed the head this morning, soo much easier to work on the engine when there is no airbox to wrestle with, the carbs took about three minutes to remove, two bolts at the throttle switchblock and the four boot clamp screws and the carbs are off. I take the carbs off with the throttle cable still attached, just thread the cable through the frame and out she comes.

The carbon buildup on the head, valves and plugs is thick and nasty so there is way too much oil getting into the combustion chamber. The new pistons and valve work should fix that up.

1197 a by Max Mutarn, on Flickr


1197 b by Max Mutarn, on Flickr

[Shin-Ken 1074]

I Have to commend you for a fantastic build, Having owned an 1100 Katana and remembering how heavy they were,

I currently own two gs1150`s one standard engine and one rebored to 1230 cc,

1197cc will be a lot fun, however there are a couple of caveats, starter clutch is the main problem, as the increased 10.25:1 compression kicks the crap out of them (plenty of posts with workarounds on here )

you will have increased heat as the liners are thinner, but 1197cc shouldn't be to much of an issue, looking back at your build you have yoshimura cams in ?

Yes you will pick up some power with 5 angle cuts to the valves and seats,

But you would pick up more power with the head ported and flowed as it takes advantage of the increased lift and duration from the yoshi cams

Regards

Hi Katana 1074

Thank you for the kind words and positive waves regarding the Kat build, much appreciated. Thanks for the heads-up regarding the potential issue for the starter clutch. I have noticed it as an issue over the years however, it seems to be reported by owners in Europe and sometimes North America in many cases. Not so much here in Oz, I wonder if it could be fuel RON related rather than the 10.25:1 compression alone?

I still have the engine oil temp gauge fitted so monitoring temps will be critical for engine oil heat management during and after the run-in period. Yes, the GSX 1135 engine has Yoshi cams installed which no doubt contribute to the fun factor.

I have a spare 1135 head which has been ported / flowed, larger valves as well as the chambers being modified, way too much for a mild street bike. For now, I'll run with the stock head for reliability and street-ability. The Mikuni 38mm flatslides are still sitting in the cupboard so there is an option there for a few more ponies if needed. As it is the power to weight ratio is pretty good however, the new head should bring it closer to 1 BHP to 1.3kg which for a 44 year old scooter with a factory steel frame is reasonable I think.

Will let you know how it turns out when its all done.

Cheers.

[Katana1074]

O.K. there is now a Plan A for the engine re-fresh:

1) Have ordered a set of Wiseco 1197 cc pistons.

2) Barrels to be bored to suit new pots.

3) Valve seats to have a five-angle seat cut.

4) Valves to be machined to match the five-angle seat cut.

5) New OEM valve seals.

6) New valve stem guides to be installed.

7) Head inlet and exhaust ports to be cleaned, not polished or ported.

The shop that is going to do the work tells me they can have it done in 5 days or less after I bring them the head. It will be interesting to see the difference (hopefully increased) in power and torque with the improved air-flow and valve sealing after the five-angle seat work.

I have a few Club rides I would like to attend in the next month so the head work looks like being done in mid September, in time for Spring and Summer riding later this year.

I Have to commend you for a fantastic build, Having owned an 1100 Katana and remembering how heavy they were,

I currently own two gs1150`s one standard engine and one rebored to 1230 cc,

1197cc will be a lot fun, however there are a couple of caveats, starter clutch is the main problem, as the increased 10.25:1 compression kicks the crap out of them (plenty of posts with workarounds on here )

you will have increased heat as the liners are thinner, but 1197cc shouldn't be to much of an issue, looking back at your build you have yoshimura cams in ?

Yes you will pick up some power with 5 angle cuts to the valves and seats,

But you would pick up more power with the head ported and flowed as it takes advantage of the increased lift and duration from the yoshi cams

Regards

[Shin-Ken 1074]

O.K. there is now a Plan A for the engine re-fresh:

1) Have ordered a set of Wiseco 1197 cc pistons.

2) Barrels to be bored to suit new pots.

3) Valve seats to have a five-angle seat cut.

4) Valves to be machined to match the five-angle seat cut.

5) New OEM valve seals.

6) New valve stem guides to be installed.

7) Head inlet and exhaust ports to be cleaned, not polished or ported.

The shop that is going to do the work tells me they can have it done in 5 days or less after I bring them the head. It will be interesting to see the difference (hopefully increased) in power and torque with the improved air-flow and valve sealing after the five-angle seat work.

I have a few Club rides I would like to attend in the next month so the head work looks like being done in mid September, in time for Spring and Summer riding later this year.

[Shin-Ken 1074]

Hi Folks, its been awhile since an update on the Project Kat so here is where its at. All is going well and soo much fun to ride compared to the overweight stock Kat that now sits in the shed alone and looking pretty sad. Anyway its not about that Kat its about this Kat today. The engine was bought on its own so no clocks to show mileage, an unknown history and the engine was sitting on the floor of the sellers garage so it was the usual buyer beware when I handed over the folding stuff. Sometimes ya pays ya money and roll the dice however, it turned out O.K. and ran pretty well except for one issue, engine oil. She burns through oil like there is no tomorrow, one litre per 500km!At this rate it never needs an oil change, only the filter.

Time for a refresh to give her a new lease on life. At this stage Iam thinking of going for a Wiseco 1197 cc kit, new bores to suit, new valve guides and seals along with re-cut seats and valves.


These mods should future proof the engine for many years as well as making the front wheel a bit lighter. Has anyone here installed an 1197 kit in their GS1150 and are you happy with the result?

And the bonus is the forged Wiseco pistons should be a few grams lighter than the current OEM cast pistons, if thats what is inside right now.

Cheers.

[Shin-Ken 1074]

The foam filters that were installed in the original build needed to be replaced however, I wanted to try stainless steel screens. The stainless screens last longer, easy to clean, don't breakdown with age and are less than half the weight! Fitted the screens last weekend and went for a test ride today, all went well, really well and I am very pleased with the result. Fuel / air ratio is good and the screens also have a cleaner look compared to the bulky foam filters.

Carbf1 by Max Mutarn, on Flickr


Carbf2 by Max Mutarn, on Flickr


Carbf3 by Max Mutarn, on Flickr


Carbf4 by Max Mutarn, on Flickr


Running tally: 199.557 kg.

[Shin-Ken 1074]

Will anyone venture a guesstimate as to the quarter mile times? With over a hundred pounds shed, she must be in the low 10's.

With a final drive ratio of 2.82 and one hundred and thirty two pounds lighter than Factory specified curb weight.

[Rob S.]

Will anyone venture a guesstimate as to the quarter mile times? With over a hundred pounds shed, she must be in the low 10's.

[Shin-Ken 1074]

Install Bandit 1200 cylinder liners on the original cylinder block and bore them for gen.2 Hayabusa pistons. You will save at least the weight difference of the RS Mikuni, the engine capacity will increase to 1360cc and the torque & power will increase nicely.

Yep, for converting an old Kat into a Hotrod that is one way to go for performance and perhaps shedding a few grams. Would be interesting to know how much lighter the Gen 2 Busa pistons are compared to aftermarket forged pistons?

[Shin-Ken 1074]

just go to the bathroom before you ride the kat with 38's that will get you back to base

Good thinkin' 99, there are no wrong ideas here.

[Blower]

Install Bandit 1200 cylinder liners on the original cylinder block and bore them for gen.2 Hayabusa pistons. You will save at least the weight difference of the RS Mikuni, the engine capacity will increase to 1360cc and the torque & power will increase nicely.

[first timer]

just go to the bathroom before you ride the kat with 38's that will get you back to base

[Shin-Ken 1074]

I would be surprised if the flatslides aren't heavier as I've always found them to be "weightier" in my hands than their CV counterparts. But the scale will tell.
Regardless of the weight I'd switch them over because I feel that your end result shouldn't be all about weight, but how you enjoy the motorcycle as a whole. I highly doubt in any case that the carbs will tip you back over the 200kg so the mental aspect of it should still be acceptable

The numbers are in and it isn't looking good for the flatslides.

The 38mm flatslides, two throttle cables and twin cable throttle = 4,140 g.

The 36 mm CV's, one cable and single cable throttle = 3,172 g.

So changing to the flatslides will add 968 g (and about 10 ponies going by dyno figures from previous 38 mm flatslides fitted to the 1135 engine) and take the weight up to 200.553 kg.

The raw numbers don't tell the full story, the elephant in the room is of course the extra performance of the 38 mm flatslides when compared to the 36 mm CV carbs. However, the Kat being 60 kg lighter than stock, the 36 mm carb jetting set up using an O2 sensor, the Yoshi cams and adjusted timing the Kat is plenty fast enough and has arm stretching acceleration in every gear. The balance and handling are excellent as is the comfort and seating position, for me this is everything I had hoped the project end result to be. So as it stands now, I am very happy with how the Kat rides and performs so I'll put the 38 mm flatslides away for now and keep on enjoying the Kat with the 36 mm CV's. Maybe oneday the 38's will get a run, but not today.

Running tally = 199.585 kg.

[Diirk]

I would be surprised if the flatslides aren't heavier as I've always found them to be "weightier" in my hands than their CV counterparts. But the scale will tell.
Regardless of the weight I'd switch them over because I feel that your end result shouldn't be all about weight, but how you enjoy the motorcycle as a whole. I highly doubt in any case that the carbs will tip you back over the 200kg so the mental aspect of it should still be acceptable

[Shin-Ken 1074]

Nice carbs, but maybe slightly too big for your engine. I had 38 Mikunis on my 1296 cc GSX and they worked quite well. Then I swap the engine to 1360 cc and now the carbs are working perfectly.
I think the 34`s would have been better for you if you are not going to racing.

Yes, maybe 34 mm flatslides would suit a stock 1135 and I know some who are running those carbs on their Kat. However, fitting 38 mm flatslides is not unusual with the 1135 and over engines in my part of the world. My engine will be running a set of 4-1 Yoshi 60 mm pipes with a 60 mm muffler, Yoshi cams, adjusted timing, velocity stacks and to get it sweet the carbs will be set up using an O2 sensor to sort out the jetting.

Right now the Kat is fitted with 36 mm CV carbs with 160 main jets and it is running strong and smooth in each gear all the way up to WOT.

The build focus is weight and not outright performance. If the flatslides are heavier than the 36 mm CV carbs that will pose a problem for me.