GT750 6 speed

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madforitkev
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GT750 6 speed

Post by madforitkev »

Has anyone played with 6 speed conversions?

I am happy with the close ratio 5 speed GS conversion but would like to go one step farther on the special I am working on.

Has anyone ever tried grafting in a GSXR 6 speed box?
Honest baby....this is probably the cheapest bike I have ever bought!!
teazer
Posts: 1035
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: GT750 6 speed

Post by teazer »

I tired three different GSXR transmissions and none so far that came close to fitting. You could do it but it would be easier to cut off the transmission and weld on a whole new one....The ones I looked at are too wide. If you removed the side wall of the trans and replaced it with a new one it might be possible. I did have GSXR crankcase at one time to see if that was possible but I could not afford that much welding rod, let alone the cost of a welder to stick it in place.

Allan (waterbuffalo) was looking into a 6 speed at one time IIRC but I have no idea where he got to. Why not look at Ducati trans to go with a Duc dry clutch and see what's possible.

Suzuki and Barton had 6 speed transmissions for teh TR and it may be possible that there is a pre gsxr 6 speed that might work or perhaps a slabbie trans - I did not look at that possibility
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BATTS
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Location: Lancashire

Re: GT750 6 speed

Post by BATTS »

Nova Racing were working on a 6 speed GT750 gear set, if you've deep pockets might be worth dropping them a line.

http://www.novaracing.co.uk/index.html
Chris
76 GT750, 78 GT550, BMW K1600gtl
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Rijko

Re: GT750 6 speed

Post by Rijko »

a guy in Holland was working on adapting a 6 speed GS550 gearbox
for his GT750, no idea if he got it working though
madforitkev
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Location: Poole

Re: GT750 6 speed

Post by madforitkev »

Cheers guys

I did look at the NOVA one previously. Cash is king!!

I've got one or two other options I am playing with before I stick with the 750 close ration 5 speed.

Will keep you posted.
Honest baby....this is probably the cheapest bike I have ever bought!!
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PaulD738
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Re: GT750 6 speed

Post by PaulD738 »

Being honest apart from the "pose factor" the 750 doesn't need six gears even in tuned form. The motor has so much grunt it's more like a four stroke than a stinkwheel :lol:
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teazer
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Re: GT750 6 speed

Post by teazer »

Anything is possible, so thd question is always, how badly do you want it.

I have a GS550 bottom end and set of gears that must be from a different generation, but it's possible to deduce certain things. The cases claim to be 1983 but supposedly the same from 78-83 and teh gears are marked as 1980 but the end bearings are different.

GS550 transmission is wider than a GT570, GS750 or GS1100 and would need some machining just to get the shafts into the cases.

GS550 uses a single rail for the three selector forks and that rail is not in the same place as a GT750 and would require machining and welding to get it into place.

GS550 selector cam/drum is located in a very different location relative to the two shafts compared to a GT750 so more welding and machining.

Nothing beyond the realm of possibility though.

Shaft spacing appears to be the same as a GT or GS motor which is both interesting and useful.

GS550 has an oil feed to both gear shafts which is really nice. From the oil pump the feed goes to the main bearings which are plain shells and a cavity goes off to feed the ends of both gear shafts. The oil feed is into the end bearings and both have oil jets in there to regulate flow. A GT has a low pressure feed via splash and drip trays (those metal stampings in the cases) but fresh pumped oil sounds lie a much better idea. Late model TZ250s also used a similar pumped system compared to splash on earlier RD based racers.

So in answer to the question - What about a six speed from a GS550 the answer is that I'd like that in a race bike but for the street or drag strip I'll stick with GS750 (SOHC or DOHC) or GS1100 which fit with a lot less work. It is worth looking at for the challenge or if you are aiming from more that 120HP, but for the rest of us, not so much.
teazer
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Re: GT750 6 speed

Post by teazer »

Nope. Shaft spacing is 58mm on the GS550 compared to 55mm on a GT750, so that's more work to weld and machine the crankcases to move the shafts apart and wider too..

Nice idea but not happening here any time soon..
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Rijko

Re: GT750 6 speed

Post by Rijko »

EXCELLENT info !
madforitkev
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Re: GT750 6 speed

Post by madforitkev »

Thanks guys. All good info.

I've a couple of options under investigation right now and will keep you posted. Right now my project milestone is making the engine a structural element for the swinging arm and frame mounts. Then its back to the engine......

Cheers

Kev
Honest baby....this is probably the cheapest bike I have ever bought!!
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