750 engine into 650 frame?

[Danie.e]

Have a 1981 650 with bad engine - can get a 1980 750 engine still in good shape - both shaft drive - can I do such a transplant? Are there issues, will frame hold up etc. Input will be much appreciated

[salty_monk]

You sure it's a 750 and not an 850? If it's a 750 maybe that's a SA special model we didn't get here......

The 650G & 850G engines are quite different I believe

[Admiral Beez]

Have a 1981 650 with bad engine - can get a 1980 750 engine still in good shape - both shaft drive - can I do such a transplant? Are there issues, will frame hold up etc. Input will be much appreciated

I don’t believe a GS750 was made with shaft drive for export markets. The progression on shafties from GS650G onwards is here

https://www.suzukicycles.org/GS-series/index.html

[Steve]

The 750G was for two years only, and only in Japan.

As Salty Monk mentioned, the 650 and 750 are considerably different. Until a few weeks ago, I had two 650 engines here, I could have measured the differences, but the 650 is somewhat based on the 550 and the 750 is the basis for the 850. I do not think the 750 will replace the 650 without major surgery on the frame.

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[Danie.e]

Here is a picture of the bike - owner assures me that it is a GS750 and that it is a shaft drive. - Thanks for the replies on my question. Guess I will not take the plunge for such a transplant as I do not wish to do major surgery.

[Steve]

Several things don't look quite "right" with that bike.

If you have the chance to examine it in person, look at the front of the engine to see what displacement is cast into the base of #1 cylinder. See if it says 673 or 748.

You can also look at the VIN plate or the stamping on the steering tube at the front of the frame, it will show the model. The engine itself also has a serial number. The first part will give a big hint to the displacement.

Not that it matters for the engine swap, but that bike is an L, and the seat is not securely attached. Not so sure about the tank, either.

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[Gorminrider]

From AdmiralBaez's link, it seems that the 750G's were 850G's with a smaller engine to suit japan's 750CC limit. So a transfer to the 650 frame is a nogo. Here's a 750GL from that site.

[allojohn]

650G with an L seat & tank?

[Steve]

650G with an L seat & tank?

Nope.

650GL.

Or, if you were in Japan in 1981, 750GL.

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[Danie.e]

Thanks for all the replies, I will continue to look for a 650 engine. The information that comes from one question is amazing. Just wish the 650 had a roller crank

[Steve]

Minor price to pay for such a pocket rocket.

The 650 (actually 673) is rated at 72hp. The 850 (843) is rated at 78hp. Not much of an increase, considering the bump in displacement, and certainly not enough to offset the additional 85 pounds (40kg). Yep, the 650 is a real hidden gem of a bike.

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[hank2]

I don't want to hijack the OP's thread, but as a new GS650g owner, I have been curious about the varying power ratings found for this bike. Also vs. the rarer GS650E. Although most sources list all the GS650's as 72 hp, I found a site with an old 1981 period review ( UK?) on the '81 models and spoke of the differences between GT and E models. That article claimed the GS650G had 65 hp @ 9000 rpm and 42 lb. ft. torque at 8000 ? The E model ( with roller bearing bottom end) supposedly had a different intake cam profile and bigger bore exhaust. The E was rated at 72 or 73 hp at 9500 rpm with 48.5 lb.ft. at 8000 ? I don't know if that's accurate, but it sounds believable. Still a gem.

https://www.motorcyclespecs.co.za/model/suzu/suzuki_gs650gt%2081.htm

[tom203]

Don't worry about the hp stuff..the shafties are a different animal. Get your bike running well and safely, and i think you'll find its performance interesting . I test rode one back in 1981 and was impressed: I got busy though ,and had to wait 27 years to get one.