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Author Topic: Comstars + gsx-r front end  (Read 15891 times)

Offline rs_ss350

  • Posts: 88
Re: Comstars + gsx-r front end
« Reply #170 on: Dec 22, 2017, 20:35:31 »
Thanks! But I really couldn’t have done it without everybody’s help on this site!  Thanks everyone!
1979 CB750K - 10th Anniversary Limited Edition
1982 CB750K - Cafe/brat project under construction
1977 CB750K - another project!

Member of Moto Guild SF

Offline cxman

  • DTT SUPPORTER
  • *
  • Posts: 2548
Re: Comstars + gsx-r front end
« Reply #171 on: Jan 19, 2018, 13:15:03 »
i need another set of spacers
1978 CX650 Super Deluxe
1979 XS1100 Special
1974 xl350
1983 cx650 Custom
1973 cb750
1980 cb750
1981 cb650
1982 cb900 c
1974 kawasaki 350 bighorn
1983 GL1100 aspy full dress
1983 GL1100 Nekid
and a bunch of others

morgs88

  • Guest
Re: Comstars + gsx-r front end
« Reply #172 on: Jan 19, 2018, 19:22:08 »
Gsxr forks...
Cbr forks....

No matter what they are.
“Upside down” forks looks the dogs nuts on any older bike. Shame people want Ł300 quid plus for a old pair. Seen bent pairs go for Ł100


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Online crazypj

  • Posts: 13226
  • Split personality, I fake being smart
Re: Comstars + gsx-r front end
« Reply #173 on: Jan 20, 2018, 23:05:47 »
Realistically, there are only two Japanese manufacturers who supply the 'Big 4'.
Some of the manufacturer build requests are a bit weird though.
The picture of the Blue Kawasaki few years ago with fork leg snapping is only unusual because it was captured, the screwed on fork bottoms often came loose and leaked, I saw more than a few with cracks developing (and I 'don't do' Kawasaki's)
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline LeMarseillais

  • Posts: 3
Re: Comstars + gsx-r front end
« Reply #174 on: Sep 26, 2018, 12:36:42 »
Hi Everyone,

I'm working myself on a fork swap for my 1979 CB750 KZ, and found this topic to be a gold mine! Apologize in advance for my english, I'm french...

Bought the bike 10month ago and was so far focusing on having it running on it's four cylinders, which is now done! Carbs reassembly, change of gaskets, change of valves shims, and now pending a proper carb sync..
Attached a picture of the bike as it is now, not a fan of the look but still ok for the 2 000$ I had it.
Currently I'm trying to purchase the GSXR fork or R6 fork, so few questions here to anticipate and avoid potential mistakes...

I saw different way of doing the swap on the thread, and few questions below:
-  is the CB750 stem able to fit with the triple clamp of the USD fork without major adjustement? I saw it's feasible by machining & welding slighly the bottom clamp, but not really sure about it. Otherwise, conversion stem from Cognito seems to be THE best option to go for...
- in terms of geometry, does it change the behaviour of the bike significantly? Or is it just minor? considering I will be riding it as a pleasure bike (no track or agressive riding planned so far^^), if it's minor I can cope with it :) I will change the rear shocks as well, so it might be a way to adjust the stance / balance if needed
- is it best to keep the CB750 axle or to go for the USD one? Machining of the inner diameter of the wheel kinda affraid me a little bit...
- how is the steering radius after conversion? does it need special attention?

I also saw some of you having extra conversion hub / spacer available, so if it's possible to purchase for reasonnable price I would be more than happy to do the deal! ;D ;D I do not know machinist around there and the few I approached were giving crazy high prices...

Thank's for your help (especially @RS_SS350 & @focusinprogress who already gave me a lot of help!) and future feedbacks! I'll keep you posted about the evolution of the build

cheers

Online crazypj

  • Posts: 13226
  • Split personality, I fake being smart
Re: Comstars + gsx-r front end
« Reply #175 on: Sep 27, 2018, 04:00:17 »
- in terms of geometry, does it change the behaviour of the bike significantly? Or is it just minor? considering I will be riding it as a pleasure bike (no track or agressive riding planned so far^^),
Modern sportbikes have less offset (forks are more or less inline with steering stem) so you will end up with more trail making bike slower to turn. Forks are often shorter than old style as well which may compensate as you'll have  a steeper head angle- is it best to keep the CB750 axle or to go for the USD one?
Use largest diameter axle you can, original would be best as it's now possible to get odd size bearings for conversions
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline LeMarseillais

  • Posts: 3
Re: Comstars + gsx-r front end
« Reply #176 on: Sep 28, 2018, 05:55:30 »
thanks for the informations!

For the ability to turn, is it something that can be compensated with the rear shocks? And how sensitive will be this change in turn capacity? I'm not an experimented rider, so I might not even feel it if it is only "slight"...

Yep, understood for the wheel axle! Will try to figure it out.

Regarding the stem, any information about how to proceed?

Offline focusinprogress

  • Posts: 1007
  • City Limit Moto:Parts-Service-Apparel (716)8038606
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Re: Comstars + gsx-r front end
« Reply #177 on: Sep 28, 2018, 11:39:43 »
you may also lose steering radius due to forks contacting your fuel tank. geometry also heavily depends on front wheel/tire size as well. there are some good calculator sites available to help with the math for rake and trail where you can input stock numbers then play around with fork length, offset, and tire/wheel size to see how it gets impacted for riding.
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Offline LeMarseillais

  • Posts: 3
Re: Comstars + gsx-r front end
« Reply #178 on: Oct 03, 2018, 09:10:16 »
@focusinprogress
yep, I know that and will most likely need to work on the stopper of either the CB frame, or fork tee.
Do you mind sharing the link to those calculator?

Also, just bough a GSXR - 600 fork from 2005 for a good deal! 8) 8) GSXR 2005 rotors in 300mm are also coming soon, so I'm now starting the assembly sketch off all that!!

For the sake of precision, I'd like to make a small CAD of the assembly, but I can't find a 3D model of the Comstar wheel...
Does anyone here has that specific part? I found a GSXR fork, caliper & frame 3D model already on Grabcad

Offline focusinprogress

  • Posts: 1007
  • City Limit Moto:Parts-Service-Apparel (716)8038606
    • City Limit Moto
Re: Comstars + gsx-r front end
« Reply #179 on: Oct 17, 2018, 13:20:12 »
@focusinprogress
yep, I know that and will most likely need to work on the stopper of either the CB frame, or fork tee.
Do you mind sharing the link to those calculator?

Also, just bough a GSXR - 600 fork from 2005 for a good deal! 8) 8) GSXR 2005 rotors in 300mm are also coming soon, so I'm now starting the assembly sketch off all that!!

For the sake of precision, I'd like to make a small CAD of the assembly, but I can't find a 3D model of the Comstar wheel...
Does anyone here has that specific part? I found a GSXR fork, caliper & frame 3D model already on Grabcad

https://www.rbracing-rsr.com/rakeandtrail.html
For all your gear needs, check out CityLimitMoto.com
DTT10 code for 10% off at checkout