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78E to 81G 8 valve parts interchangability (top end)?

  • Thread starter Thread starter GS1000G Shopper
  • Start date Start date
G

GS1000G Shopper

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I have my '81 1000G motor's head off to be repaired, and am considering pulling the cylinder and replacing the rings. I found a deal for some Wiseco pistons and a matching cylinder and head from a 1978 1000 (probably an EC version, I'm not well-versed in these models). I know the output is different on them (shaft vs. chain), but will the pistons, cylinders, and head interchange onto my case? Bore & stroke are the same.

I looked up the part numbers on Basscliff's site for the crank, pistons, cylinder, and head. They are all different except for possibly the cylinder (1978 and 79 used different numbers, but the 79 one had a handwritten note with the same part # as the 81 G motor).

I found this on suzukicycles.org:
Except for cosmetic differences and the shaft drive, the GS1000G shared the mechanics with the rest of the GS1000 model family.

I found the below here:
Literally all the components from the crankcases up are shared by the 1980 GS1000E and G-models. The list includes the cylinders, carburetors, pistons, camshafts and the head. The two bikes' exhaust systems do differ: the G-model has an exhaust chamber which has relocated the torque curve in a lower rpm range and in the process bucked up the curve. According to Suzuki, the G has slightly less peak horsepower than the chain-drive 1000 (due, in part, to the G-shaft's use of a GS850 airbox and filter), but horsepower at redline is relatively unimportant in a motorcycle focused toward touring.

It seems like I could therefore use the parts from a 1978 GS1000 on my 81. Anyone ever done this or have anything to add to my conclusion?

Thanks.
 
The 78 head is designed for the VM carbs whereas the 81 suits the CV carbs. The 81 will also have the extra bolt in front of the cam tunnel on the head / cylinder; the 78 might have it or might not. Apart from that they're the same.
 
I'm confused as to why you are looking for new top end parts? Have you looked for a machine shop to fix your head yet (exhaust bolt holes)? As for the cylinder, all you should need is a good bottle brush hone job and new rings. Why start over with a bunch of unknown parts?
 
No machine shops in the area could do the job. The head is at the welding shop. He is gone for a week, so I will know next Tuesday if he can make the repair. His plan is to cut out the bad part and weld in a new piece of aluminum. I'll then have to drill & tap the hole.

I tend to overthink problems and plan multiple paths for repairs. I never count on anyone being able to do anything. The parts in question were apparently high end stuff that I may be able to get for a decent price. People spend big bucks for parts for projects and then can't or don't want to finish them and sell the parts for a fraction of the new cost.

I've used this strategy in putting cars together (I have a $400 30K mile 5.3L Chevy truck motor in an $800 Toyota Supra), so I was thinking it should be successful here as well. In this specific situation, I may be able to buy the head for less than the welding repair cost (and aggravation of me having to drill & tap the hole). I'll know if it is available within a few days.
 
GS1000G Shopper said:
I may be able to buy the head for less than the welding repair cost (and aggravation of me having to drill & tap the hole). I'll know if it is available within a few days.
Click to expand...
So, have you located a set of carbs to use with the '78 head also?
 
Along with the head you would need the carbs to fit it (vm type) and a new airbox. The cylinder and pistons might fit im not sure, check cylinder part #'s and wiseco part #'s . If you can get it for a song why not?
You dont need a machine shop to re-ring your old cylinder though, just a ball hone and a drill and some new rings:cool:
 
It looks like I need to educate myself on the differences between VM & CV carbs. I'm figuring there is a physical difference that prevents them from attaching to the boots?

Edit
Found the answer here courtesy of my friend tkent02. The VM carbs are 26mm, and CV ones 34mm.
You would have to make a little adapter plate, the screw spacing is different. It would be easy to make, no big deal.

Why do you want the the smaller carbs?
 
Last edited:
Thanks. No sense in trying to push a golf ball through a garden hose, so I'll stick with a G head.

If the head repair doesn't work out, I will either try to find another 1000G head, or a complete 1100G/GL bike and swap in the 1100 motor.

Looking at the ring issue, if I'm reading the prices correctly, a set of stock size rings @ Bike Bandit for the 1000G motor is $40, so it will be $160 for all 4. From what I've read here, it sounds like since I did my compresssion test cold, the numbers should have been low (90 PSI). Another member said his were in the 80's and after the motor warmed up he was within spec in the 130's.

If I pull that cylinder off, I know I'm going to want to put a set of big bore pistons in there, which means boring the cylinder, re-jetting the carbs, and many more $. I'll have to keep reminding myself that it ran/runs fine with the stock setup, although that air box is a major pain to remove & replace. :)
 
Find a D port 1100G head, they breathe a lot better. Might as well throw on the 1100 cylinders and pistons, too. It's an easy bolt on torque increase.
 
I order a lot of parts from Bike Bandit because they are fast, but if you want the best price partshark.com is much cheaper - rings are $25/set.
 
Ed,

Yesterday I checked 12140-49001, they were $32.24 a set @ partshark. if you check alpha sports P/N 12140-44110 (replaces 12140-49001-100) is for the 1.0mm O/S.

that is unless I'm reading things wrong.
 
Just looked at Partshark. Standard pistons are the same price, but oversize rings are less expensive.
Std:
Piston 12111-49001 $53.21 ea $212.84 for 4
Ring set 12140-49001 $32.24 ea $128.96 for 4 / total $341.80 for all

The 1mm oversize:
Piston 12111-49001-100 $53.21 ea $212.84 for 4
Ring set 12140-44110 (replaces 12140-49001-100) $25.35 ea $101.40 for 4 / $314.24 for all

I have an engine builder program (Dyno 2000) & I'm trying to find some specs for the stock motor so I can play around with a few things to see what type of benefit they may have.
 
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