Converting GS750 front end to GS850 setup,need advice please-

[Tola]

Well that sucks. I've come across numerous posts stating its a simple bolt on upgrade?? Must be for newer 750's and not the 77 but 77-79 appear to be the same and I've seem those with 850 forks?

[hampshirehog]

Well that sucks. I've come across numerous posts stating its a simple bolt on upgrade?? Must be for newer 750's and not the 77 but 77-79 appear to be the same and I've seem those with 850 forks?

It is simple. Just look up what bearings you need - try the SKF site for example - order them and fit. Dreef showed you how to do the sum and I gave you the numbers.

1980 onwards 750s had the same bearings as the 850s.

[Manzarr]

So would the equation that dreef used for the top also work for the bottom of the tree? I'm doing the same in swapping out my front end. using 80 850 tt/forks.

[Dreef1999]

Well that sucks. I've come across numerous posts stating its a simple bolt on upgrade?? Must be for newer 750's and not the 77 but 77-79 appear to be the same and I've seem those with 850 forks?

I think just a bearing change qualifies as bolt on

[Dreef1999]

So would the equation that dreef used for the top also work for the bottom of the tree? I'm doing the same in swapping out my front end. using 80 850 tt/forks.

Exact same principle for top as for bottom. Height and OD are based on the bike frame. ID is based on the triple tree.

As long as you stick within the GS family the only issues you can have are steering stop differences, fork spacing differences, and possible rake(?) difference.

If you get the axle & spacers then all GS front wheels should drop right in. The steering stop difference will require either grinding a stop on the tree off or installing a stop onto the tree. Personally I would never modify the frame and I would probably install a stop by drilling and tapping a hole so I could screw a bolt in as my stop.

The rake difference I think is only between those with leading axle forks like the L model forks... but that might be wrong?

[Manzarr]

I figured it would be the same. Thanks guys, had been quit awhile since I've done anything like this, relearning it as i go, remembering what everything is exactly.

[Tola]

So allballs has a fork conversion chart so one can figure out what fitshttp://www.allballsracing.com/index.php/forkconvertion . It looks to me that if you buy the bearings listed for the shock you are upgrading to based on the info you put in for the original bike then it should work out but it still list three different heights for bearing upper/lower.

These are ALLBALL's dimensons:
Stock '77 GS750 bearings upper and lower are as follows;

Top 25 48 15 or 16, Bottom 27 48 14 numbers refer to ID OD and Width in order.

1982 GS850 dimensions are:

TOP 25 48 13,15 OR 16 BOTTOM: 30 48 12,14,15,16

So it looks like the top shouldn't be a problem, bottom OD is larger, has 4 height choices and the difficulty I'm having is trying to measure what I have (ball bearing race) and order the right ones the first time.

These come as kits from what I understand to take the place of the ball bearings. I assume you have to remove the chrome inner bearing races??

[Tola]

the race height from the steering stem determines the bearing height.
The bearing ID is determined by the triple tree diameter.
The Bearing OD is determined by the stem diameter.

I'm basing my terminology from my years of bike building (pedal) So ID to me would mean equal to the OD of the steerer tube which goes through head tube of frame. The OD I would think would match the ID of headset cups?

[Dreef1999]

So allballs has a fork conversion chart so one can figure out what fitshttp://www.allballsracing.com/index.php/forkconvertion . It looks to me that if you buy the bearings listed for the shock you are upgrading to based on the info you put in for the original bike then it should work out but it still list three different heights for bearing upper/lower.

These are ALLBALL's dimensons:
Stock '77 GS750 bearings upper and lower are as follows;

Top 25 48 15 or 16, Bottom 27 48 14 numbers refer to ID OD and Width in order.

1982 GS850 dimensions are:

TOP 25 48 13,15 OR 16 BOTTOM: 30 48 12,14,15,16

So it looks like the top shouldn't be a problem, bottom OD is larger, has 4 height choices and the difficulty I'm having is trying to measure what I have (ball bearing race) and order the right ones the first time.

These come as kits from what I understand to take the place of the ball bearings. I assume you have to remove the chrome inner bearing races??

I'm basing my terminology from my years of bike building (pedal) So ID to me would mean equal to the OD of the steerer tube which goes through head tube of frame. The OD I would think would match the ID of headset cups?

I think you and I are saying the same thing.
an 82 gs850g kit has
47x25x15 top
55x30x18 lower

77 750
48x25x16 upper& lower

if it were my bike I would order a 48x25x16 upper and 48x30x16 lower.

you will have to remove the existing stainless race from the head tube. A dremel cutting through it in a very shallow V I read works well to cut the race without nicking the frame too much.

[Tola]

Here's a tip on a tool that may work to get the races out easier. http://www.cambriabike.com/shopexd.asp?id=32142 I'm going to make a similar one out of some proper sized steel tubing, just hacksaw 4 vertical grooves in it, spread the four pedals out, put the uncut end up through the race you want to remove until it catches behind it then bang out the race. This always work on the most frozen cups when I was working in bike shops. Another tip for frozen/rusted races is to let them soak in anti-freeze. When we had a set post stuck in a frame we'd plug the post, tip the frame over and fill the seat tube with antifreeze. After a day or two of soaking it would come right out. If tool works I'll post it in the tips section w/ pics.

[Tola]

- at least not here. .

Where's here?

[hampshirehog]

Where's here?

England. The old version.