XR11/73

[garry55]

Garry, Garry, Garry,

That's so old school thinking. Think modern engineering solutions such as stacked gearbox shafts. Check out a GSXR and maybe you could cut the back end off the GT and stick on the box from a GSXR. That will save you 4-6 inches for only a small amount of machining and welding and machining etc.

I have a GSXR trans chopped off its crankcases here that I keep threatening to weld on the back of a GT but my head hurts each time I look at it.......

If you have access to CNC machining, it might be feasible and as an added bonus if you order right now, you will get one extra gear for the price of 5. That's right. 6 gears for teh price of 5. We have operators standing by for your call.

Ah - the stacked gearbox - that is on my "to do" list after the cross-plane crank mod.

[garry55]

some pictures - saves a thousand words.............

first trial fit of GT750 motor in GSXR400 frame - the front mounts



and the upper rear mounts



my solution - make new mounts and attach in-line with existing mounts, but spaced much wider





the front mounts had to go..............





that allows the motor to sit a lot higher in the frame



I was about to take the frame for welding of the new rear upper brackets when I realised I could move the motor further back to give more clearance for the headers, so......................

[Suzukidave]

You sure you dont want to switch frames as the GT750 engine doesnt even look to be a fit ??

[garry55]

You sure you dont want to switch frames as the GT750 engine doesnt even look to be a fit ??

No Dave - that would be too easy !
plus I have a garage full of GSXR400 parts ready to bolt-on - thats what defined the choice of frame.

[Suzukidave]

Ok Garry ..i always say if there's a will there's a way

[garry55]

Agree there Dave - its the way I will that bothers me...........

[tz375]

I tried to stuff a GT750 into an FZR1000 frame because that bike has a long laid forward motor, and it's still a tight fit in places. Then I tried a 94 RF600R steel perimeter frame which is a much better fit but looks pretty naff and is not easy to make it look better. Dave chose what is probably the most suitable chassis and it's still a tight fit.

Maybe a "K" motor would work better in that it is much shorter.

Or should I be packing that stacked gearbox to send you?

All jesting aside, the issues with a GT750 are excessive length, excessive weight, and the fact that the barrels are not on the centerline and in a GT the right barrel hangs out more than the left side. If the motor is centralized it may complicate wheel and chain alignment.

With that cute but diminutive chassis, the motor may be too large for the available space. How about a small compact two stroke twin say 180HP, 700cc, DFI coupled to a 6 speed trans with a belt drive. That could be made a lot more compact and might be more compatible with that frame. A bit like a Tularis design of powerplant.

[garry55]

yes - ship the stacked gearbox ASAP!

I take on board your comments gleaned from your experience in test-fitting the GT motor into other "donor" frames, but I will persevere with the 400 frame for now.
Not that I have anything to prove - I would like custard served when eating my humble pie - but I have so many GSXR400 parts littering my garage that I feel obliged to use them on something.
The "alternative" engine is plan B.........

[Suzukidave]

It would be interesting to try a test fit in a Busa frame but Richards right .. i did some measurements at the bike junk yard and the 99 i tested had the best fit side to side but as i posted the length of the GT engine is a problem

[garry55]

............so, time to fire up the grinder again and remove some more metal - this time, all the rear motor mounts



the frame, de-mounted



fitting the swingarm allowed me to shift the motor as far back in the frame as the swingarm pivot would allow - I shimmed it at 2mm from the pivot and 2mm below the cross-piece and it starts to look promising...........









next step is to fabricate some new rear upper motor mounts and clean the frame where the original mounts once were

[Suzukidave]

Oh yes .. that helped and the different angle picture does make the fit look more do able can you raise the rear of the engine a bit as that will tilt the exhaust ports down some and will help line up the front sprocket with the swingarm pivot .

[garry55]

It would be interesting to try a test fit in a Busa frame but Richards right .. i did some measurements at the bike junk yard and the 99 i tested had the best fit side to side but as i posted the length of the GT engine is a problem

is that your SRAD / Kettle Dave ?

Busa's handle OK for what they are, but nowhere near as agile as the lithe GK73A chassis. Its compactness may be my undoing though...........

[garry55]

Oh yes .. that helped and the different angle picture does make the fit look more do able can you raise the rear of the engine a bit as that will tilt the exhaust ports down some and will help line up the front sprocket with the swingarm pivot .

No Dave - I can't raise the rear of the motor any more as the upper cross rail limits it. Encouragingly, the cylinder head now sits well back from the radiator mount, so I may have liberated enough space to clear the headers.
Fingers crossed !

[Suzukidave]

is that your SRAD / Kettle Dave ?

Yes

[garry55]

when space is at a premium, every little helps. This casting on the back of the Kettle gearbox is what I used to shim the motor away from the swingarm pivot - it's approx 3mm wide -



but not anymore.............