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twin vs 4 cylinder rear wheel spacing/sprocket carrier?

Chuck78

Chuck78

Forum Sage
Past Site Supporter
If swapping a rear disc brake hub onto a GS twin, are the sprocket carriers on the 4 cyl bikes spaced out further offset from the center vs the wheels original to the twins? the twin engines are much narrower in front, but I wasn't sure about in the gearbox area.

Big Rich said his Avon 130/70-17 was quite close to his 520 chain. On my 750, my Shinko 140/70-18 is a fair enough distance from the chain. Also, the GS500 swapped into a gs450 frame requires some of setting of the rear sprocket outboard further I believe, as the gs500 came with a 130 or 140 stock.
 
Did some rough wheel/sprocket measurements today, the small GS twins have 8"+ hub/spacer/etc width between the swingarm axle dropouts. A '77 GS550 (narrower engine than the big fours) has about 9"+ rear hub/axle spacers width, & a GS1100E swingarm has about 10" width.

Roughly measured off center, running a GS1100E swingarm & rear disc brake wheel on a twin would require either 1/2" offset front sprocket, or milling down the cush drive sprocket mounting surface up to 1/2". The GS550 chainline was about ~1/4" more inboard than the big fours compared to the twins @~1/2" more than the big fours.
I am wondering if the smaller bikes just use a different rear hub sprocket carrier than the big bikes? Also wondering of the sprocket carriers/cush drive pieces from mag wheel bikes are the same as those from wire spoked wheels?

Running an offset front sprocket makes me worry more about the countershaft output side bearing wearing prematurely. In order to gain more tire clearance, I would potentially split the difference & try to get maybe 1/4" offset sprocket, & take up the rest of the difference in the rear hub with a narrower sprocket carrier or machining down the sprocket carrier slightly. 1/4" up front with a 520 chain should be enough of a total chain offset away from the tire to have adequate clearance on a 130/70 tire, & probably being able to squeeze a 140/70 or 150/70 in there.

The big research question/dilemma now is the potential differences in sprocket carriers. I will have to look into this some more. Anyone have any ideas???
 
The first generation GS400, GS550, and GS750 rear hub sprocket carriers all seem to interchange between the different hubs and cush drive assemblies, but they each have their own unique part number. Since the GS550B and GS400 share the exact same hub shell, and the GS550 takes a different sprocket carrier and has a wider engine and swingarm, it seems as if the sprocket carrier widths are the biggest differences.

I'm not sure about chain to frame clearance, but it seems as if running a rear disc wheel from a bigger GS on a GS twin will require something like running the GS400 sprocket carrier on the GS750/1000 rear hub, and using a custom mix and match of spacers and strings/straight edges/tape measures/laser alignment guides to get the rear wheel centered, get the chain line parallel to the bike's centerline, and get the rear disc caliper centered. Really, everything on the right side should remain stock if using a stock-ish Suzuki rear brake setup, but the left side spacer between the cush drive and the hub will have to change, as well as the outer spacer. May require a custom cut spacer to get it right, at least on the outer one. On the inner spacer between the sprocket carrier bearing and the hub bearing, maybe the spacer from the model of bike that the carrier came from would work, but that is assuming the disc and drum hubs have the left bearing located in the same exact position on the hub.
 
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