Gs550 or 650 swap into gs400 frame...

[Ziggy400gs]

Hello all. I'm thinking about future projects as I have fallen in love with my first bike (gs400). But I already want something with more power. Maybe next year... But with that being said. Has anyone pulled off swapping a 550 or 650 engine into a two cylinder frame? I'd be more than willing to but the complete engine and trans from a bike and swap it over if it can fit with minimal fabrication. I love the bike and don't see a point in spending another couple grand on a faster bike if I can just tinker with something over the winter and build something badass myself. I'm just day dreaming at work here so hopefully you guys can help me make more of a clear picture. 650 engine in gs400 frame. GO!!

 

[Grimly]

This question was asked a couple of months ago.
It's indeterminate until you do it.
https://www.thegsresources.com/_forum/showthread.php?254896-GS400-to-GS550-Engine-Swap

 

[Steve]

What is it about your 400 that you "love" so much? If it's the low weight, the change might not be worth the effort. The dry weight on the 400 is 407 pounds. The dry weight on the 550 is 431 pounds. Power does increase, from 36 to 47, but all that work to save 24 pounds?

Also consider that the frames of the day were somewhat marginal. They were built with the smallest/thinnest tubes that were easy to work with, and tended to do strange things when the bike was pushed to its limits on winding roads. Put a more-powerful engine in that marginal frame and things could get interesting even more quickly.

Except for the obvious difference of two exhaust pipes vs. four, the two bikes look remarkably similar. Considering the amount of work that will likely be involved, I would just put up with the 24 extra pounds and get a 550.

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[Ziggy400gs]

What is it about your 400 that you "love" so much? If it's the low weight, the change might not be worth the effort. The dry weight on the 400 is 407 pounds. The dry weight on the 550 is 431 pounds. Power does increase, from 36 to 47, but all that work to save 24 pounds?

Also consider that the frames of the day were somewhat marginal. They were built with the smallest/thinnest tubes that were easy to work with, and tended to do strange things when the bike was pushed to its limits on winding roads. Put a more-powerful engine in that marginal frame and things could get interesting even more quickly.

Except for the obvious difference of two exhaust pipes vs. four, the two bikes look remarkably similar. Considering the amount of work that will likely be involved, I would just put up with the 24 extra pounds and get a 550.

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It's not the low weight. I guess that's a perk. It's more or less having to start over. Bike is already pretty bare. It's a cafe style bike. I bought someone else's project and I don't feel bad hacking it up cuz it's already been done. And I don't race the thing so I'm not too concerned about weird things on twisty roads. I'm looking to practice welding and when I'm good enough apply it to a project. I can make some reinforcements in weak spots on the frame. But it all just comes down to sentimental value, keeping my first bike doing *@%^$*@%^$*@%^$*@%^$ my own way maybe saving some money not buying another bike. Also highway cruising I could be wrong but 550s come with 5 speeds? It's more of a commuter and weekend warrior than anything I doubt I have the balls to push the thing to the point weird the frame flexes hardcore. I guess I'll have to just find a 550 or 650 or something compare the differences and get creative. I don't like to just buy something I just did that. Now it's time to make it into what I want. There's always other upgrades to improve handling as well. Be a good winter project.

 

[Steve]

Now you are throwing in a bunch of curves. :-k

- The 400 is already stripped down and cut up.
- You are not worried about how it handles.
- You are going to practice your welding on something that you will be trusting your life to.

Sounds like you have the big stuff figured out, let us know how the project goes. Do us a favor and add some thoughts to the thread linked in post #2, in case anyone is still fofllowing that one.

By the way, 550s came with a six-speed transmission. :encouragement:

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[Ziggy400gs]

It looks like the only thing cut is the rear tubes to be flush with the shorter seat. And the airbox has been taken out replaced with pods and custom battery box moved to that spot.
I am concerned about handling but know that there are creative ways to improve this area.
Lastly I am not going to jump in and start welding scrap to my bike. There's lots of scrap here at the shop to screw around with well before I'm confident welding something I trust my life with. If I do this over winter I'll document it. I more or less wanted dimensions of the 550 or 650. And I was told that the engine is smaller just wider being a 4 cylinder. Basically just shooting *@%^$*@%^$*@%^$*@%^$ daydreaming at work haha. I'll just do it and then talk about it next time. Thank you though

 

[Grimly]

If you're seriously considering it, just measure it up before you part with any money.
As I mentioned in the other thread, if the twin frame is the same in the important areas as the 400/4 frame, then you'd be good to go.

 

[Nessism]

Just buy a bigger bike.

 

[scratch]

the 550 front sprocket alignment on a 400 twin frame would give you a good puzzle...

Buy a 550, they are cheap and f'n awsome.

 

[Rob S.]

Remind us, this 400 is your very first bike? So you've got maybe a couple thou total two wheel miles under your belt?

Ride it. There's definitely something cool about a 400cc bike ridden by someone not afraid to use the throttle. Want more power? Redline it.

Just please be safe.

 

[scratch]

I just looked at a 450 and a 550... the sprocket offset difference isn't actually as bad as I thought, perhaps 1/4" further out..

 

[Ziggy400gs]

I've got about 700 miles on it this past month. I like projects that's all

 

[Chuck78]

The difference in the weights of the two bikes is primarily just in the heavier engine in the 550 or 650E... A slight bit of the weight difference is in the extra exhaust pipes and the larger tires and wheels on the 4-cylinder that would be required for the power upgrade. So really, you would only be saving a few pounds once you have the four cylinder exhaust on it, and swap to the 550 swingarm and rear wheel...
and you would probably want to add dual disc brakes to it, so that adds a little more weight on top of...and the spindly 33 mm forks are not up to the task of a bike any heavier than the stock 400, they can't even do a good job holding up the stock 2 cylinder configuration when REALLY pushed.

It is obviously not worth the massive amount of work to overcome the engineering deficiencies of the smaller bike when applying a significantly more power to it, especially considering the chain lines are in different positions on the engine (the 4-cylinder bikes will have the chain further out by about ~12mm+ from the center line of the bike), so the narrow swingarm and the VERY skinny rear wheel will need changed out, the chain may rub the frame then, & the even bigger issue, the exhaust pipes are very unlikely to clear the front frame cradle tubes, they are spaced for a GS twin, not a 650E or 550 4 cylinder. major structural areas of the frame are not something that you really should go into re-engineering without having a proper frame jig and great skill at welding...

No offense, but you would more than likely just ruin the bike in the process and be left with a pile of parts to sell off.

 

[Chuck78]

It would be very much more advisable just to perhaps buy a spare GS400 '77-'78 engine or a spare set of cylinders and head, have the cylinders bored out for 2 Wiseco K844 pistons (you can buy them individually, but they are generally sold as a set of four, to punch out a GS750 up to 850cc), & buy those from forum member Big Jay @ APE Racing Products, he does not have them advertised but sells them with a custom Cometic head gasket for the larger than standard bore size.


Then have the cylinders bored and honed and the deck resurfaced. Send the head out to a proper motorcycle engine machinist like Rapid Ray etc, and have a Serdi type valve job done on it, & if you really want some extra power packed in, have some Web Camshafts grind #110 camshaft profiles ground on your spare cam cores for some extra potent punch...
Install a 2 into 1 performance exhaust and rejet the carburetors accordingly after a full rebuild.
MegaCycle Cams also sells nice performance grind cams for the GS twins.

this is much more straightforward work than attempting to re-engineer an entire bike and then leaving it sit in pieces forever, eventually destined for the scrap yard... but this will set you back the cost of another used bike without a doubt ($1200-1500), but will get you about the fastest GS twin that you can reasonably attain without dropping a fortune on it, and it will be a GS twin that dreams are made of... And you will still have your first bike, and it will be a prized trophy piece at that point, at least mechanically...

You will then require some very grippy upgraded tires, and upgraded front brakes at least, I would go for upgraded forks to GS500 models mounted in 83 GS1100E triple clamps, & the GS500 brakes with a 98-99 CBR900RR rotor with the bolt holes enlarged from 6mm to 8mm, using a drill press. GS850/1000/1100 axle, axle spacers, speedometer drive.
Hagon or YSS shocks for the rear, & RaceTech gold valve cartridge emulators for the GS500 forks.
Get the GS500 OEM (or aftermarket) fork brace and use it to mount a fender to (old Honda VF750C I believe can be modded to work well in this configuration).

That will be the recipe for you to keep your first bike that you love so much, but make it significantly faster & improved in nearly every way.




As you can see, shopping for a GS650, GS550, KZ550, GPz550, KZ650 would definitely be the easier route, but then that bike likely will still need better tires, a lot of maintenance caught up on, and upgraded brakes... And probably a carburetor rebuild and valve adjustment. And regulator rectifier upgrade, ignition relay added, wiring harness issues investigated with a few upgrades made....


You know what you have now, but the 448cc (449cc?) upgrade I recommended is the most power you'll get out of it, however you could have the cylinder head ported as well, that will give you a bit more extra power with a mild street porting job... It will really surprise you how much that will wake it up boring it out 50cc, adding high-compression pistons, and adding high performance aftermarket camshaft profiles. But still, the 73hp of the GS650 will leave it in the dust on the wide open roads.... BUT... 30lbs bike weight difference is significantly noticeable when leaning the thing over in corners, so this is where the small twin will really excel with all of the modifications that I recommended for you...


I am building a similar bike, but going to great lengths and putting a lot more money and major parts upgrades into it. I would not recommend my path (of going even further than I recommended for you) for the faint of heart, you need to be a really serious tinkerer and have some more in-depth mechanical skills and knowledge. Mine will be near 500cc with more chassis mods and GS1000 hubs with aftermarket wider rims...among other mods.

 

[scratch]

and... that may have been the most awesome set of good advice posts I have ever read