1980 GS425, possible engine swap

[xlipower]

I am riding a GS425, and I am very pleased with it, being relatively unexperienced (1 year since I got my license) it is a great bike, with enough power to make it fun, and not enough to make it dangerous.

However, if I decide that I want more power, but doesn't want to change the bike, is it then possible to swap the engine to a 450, maby even a 500cc from the GS500E. The swap from 425 to 450 would probably hardly be worth the work, since it is only a little more power. More interesting would be the GS500E engine.

I have been searching for info on the web, and several places, it mentions that the GS500E engine, is an evolution of the GS400 engine... So will the mounting places fit? Cause as I understand it, the engine block i more or less the same as the original 400. Just with increased bore and stroke, and modified cylinder head.

 

[focus frenzy]

well I see cliff missed one!!

first, if it is a 425, it will be a 1979 model, the 425 is a odd one year only model. the 450 is a drop in swap, the only potential issue is with the ignition as Suzuki went electronic across the board for 1980.
you should be able to swap out the complete advance and points plate, or it is not to hard to upgrade to electronic.

the 500 engine will also bolt right up in the frame, but in my research I discovered one big potential problem.

exhaust clearance! the 500 has the exhaust ports rotated inward so they will clear the wide front down tubes. the 400, 425, and 450 have the exhaust ports spread out to clear the narrow front down tubes.

the problem is the 500 exhaust ports point straight at the down tubes of the 400,425,450 frame. you could have custom header pipes made but that gets real expensive real quick.

unfortunately you have the 425, the 425 was based on the first generation 400 and has a roller crank, the 450 and 500 use a plain bearing crank, and more importantly they use the exact same crank and rods!

a 450 can be converted to a 500 by just getting the 500 pistons and boring out the stock 450 cylinders.

 

[xlipower]

Thanks for the great info. So it sound like it is relatively easy to make some changes then...

But for now, I am happy with the power I have.

Sounds like this is a great forum. Can't find anything like it here in Denmark=D>

 

[SteveN]

Just found this old post. Focus, do you know if the cylinders from a 450 will bolt on a 400 case? I would like to keep the kick start, but want a little more ooomph. I'll also be putting the electronic ignition on if I can figure out how.

 

[Guest]

Don't think for a minute that you can place a 450cc engine in a gs425 frame without major frame modifications.

They look to be the same motor.

 

[Guest]

Trust me, I have had a GS425 looking at my other 2 GS450 engines and teasing them for over 20 years.

I even tried it once. You can't get it in the frame without cutting.

I put together an 86 GS450 for a friend. Good bikes. I looked like a fool on it.

 

[Nessism]

The 400/425 have a roller bearing crank but the 450 and 500 are plain bearing. I think it'd be pretty cool to have one of the originals.