Kickstarter GS1000 in a GS750 crankcase???

[Chuck78]

I have read of this being discussed before with serious intent to attempt it, putting a GS1000 crank into a GS750 crankcase, but wondered if anyone could elaborate here on the details of the transmission and clutch basket swapping in order to get a GS750 kickstarter assembly and crankcase merged with a GS1000 top end (longer stroke taller cylinders and head), GS1000 crank and rods, GS1000 transmission with helical cut gears to match the teeth on the crank (750's are straight cut), GS1000 clutch basket to match the helical cut gears, etc... Is swapping the transmission necessary?

I know the GS1000 introduction was a revision of the very stout GS750 crank, and the GS1000 crank was lightned up something like 7lbs over the very massive 750 crank. I wonder if they use the same size main bearings? If the clutch basket would swap without a transmission swap, and the main bearings fit, it seems as if the 70mm GS1000 sleeves shoudln't be much more of a chore to fit into the GS750 crankcase than the clearancing needed to fit the 69mm GS850 sleeves into the 750 crankcase.

Details, please...

 

[Chuck78]

If you don't understand, I am just completely hung up on the weight savings, simplicity, and admiration of kickstarter engines, as well as giving it a more vintage feel and appearance. On the other end, I am very driven to mod out vintage bikes to the most extreme level of reliable performance and handling as I possibly can with modern brakes and upgraded suspension, big bore engines, cams, head work, etc...

I wonder how the base gaskets on the GS1000 would compare to the GS850 base gaskets? I suppose holding the two of them up against each other would be a quick comparison of how it might work out. I know that swapping a 1000 head on a 750 may present cam chain tunnel or tension/tensioner issues from a post I recall from ages ago, but the details are very fuzzy years later.




People swap the straight cut gears from 750's into GS1000's for racing use, don't they? Seems the crank bearings may be the biggest determining factor.

 

[Chuck78]

Well it looks as if the GS1000 shares the same 5 crank bearings as the GS400, GS550, GS850, etc, but the only one any of these share with the GS750 crank is the right hand crank bearing! The 750 appears to have I assume a much larger bearing i.d. on the rest. Bad thing is, this bearing is obsolete, so partzilla tells me!!!! So if we ever need a 1st gen GS750 crank bearing, we might be forced to get creative with the crank or bearings!

Darnit...

The right hand bearing Suzuki part # tag shows the bearing dimensions, but the other 5 bearings in both the GS1000/400/550/850 bearings and the obsolete GS750 bearings show no dimensions. If the o.d. was the same, that would be awesome. If smaller on the 1000 bearings, then perhaps some adapters with locating pins could be made to fit those bearings and a GS1000 crank into the 750 case?

I'm pretty bummin' here after discovering those 750 crank bearings are obsolete now. I love the first gen 750's with a serious passion.

 

[Z32650S]

Hey Chuck, I'm also a fan of a powerful kickstarter GS engine. I've been looking around for the best option for my upcoming build, which would seek to have a large displacement kicker engine in a 1976 GS750 frame using a 750cc engine of the same year. The closest my plan came to 1000cc was to overbore the 850 jugs, use 850 pistons and wrist pins, then use the oversize 850 piston rings (a.k.a. the STD size rings for the GS1000).

I haven`t done this yet but it seems very likely that it could be done. And it looks to be pretty much the same work as dropping an 850 top end in. Not sure if any head work would be needed to accomodate the overbored 850 jugs if using the OEM 750 head/cams, etc.

Not sure if I'm missing your point, but would this scenario not save you from fiddleing around with the crank, etc? Or are the oversize 850 jugs not a viable option?

 

[Chuck78]

Yes, but are you saying get +1mm oversized OEM Suzuki pistons? I am skeptical on whether or not they are still available even. standard gs1000 rings would likely be the same as the second oversize in the 850 pistons.

for a high performance build, you are much better off with the 69mm Wiseco forged high compression pistons and a good condition set of 850 cylinders that have low miles, no rusting/scoring in the bores, and check out with a dual bore gauge to be perfectly round still and not worn much at all.

I'm running some custom 72mm pistons in GS850 cylinders bored +3mm o.s., but that is pushing it for the the 1mm (or is it 17mm?) wrist pin size so I have heard from custom high performance piston manufacturers 2nd hand.

JE, Wiseco, or Carillo Rods (CP Pistons) will be able to make 71mm custom 894cc pistons at around $600-800, but this requires A LOT of custom precision measuring, plaster/clay mold of stock piston/head squish, a stock sample piston shipped to them for reference, etc. Rapid Ray can do all of this for you, as well as high performance head work in-house.

The 894cc 71mm is the biggest I would say is a reasonable amount to go for cylinder cooling, wall thickness, reliability, etc, although my 72's are doing just fine so far. My sleeve thickness at +3mm o.s. is a bit thin.

I was really looking at options for the ultimate kicker engine, as I may be able to get a hold of the ULTIMATE vintage Japanese bike vintage aftermarket frame, a Rickman CR that was originally built for a CB750 (Z1 & GS1000 etc models later as well) but has been modified to use a GS1100E engine. Hung up on the kicker engines, I looked for a custom route to build the baddest big bore kicker bottom end.

Looks like the 1000 crank with some adapters machined to fit the 750 bearings (speculating there, have not compared o.d. on bearings) and 1000 clutch basket with 1000 top end is the only way this could happen unless resleeving the 850 cylinders to run 73mm 944cc 74mm or 75mm 1023cc pistons (2 members have done the custom 75mm piston route so far, TeamDar & Ian from NZ. Ian hasnt put the engine into a bike yet, but is happily running an 894cc 11:1 JE piston set in his GS850.