550/650 hybrid or 673 build thread(s)?

[Scott S]

I searched and came up empty.
Is the 550/650 (and/or a 673) build documented on the site anywhere? Maybe in someone's build thread?

I'd love to see some pics, details, instructions, parts lists, etc., on this conversion.

[dorkburger]

Heres one.....

http://www.thegsresources.com/_forum/showthread.php?201784-Finally-getting-around-to-the-550-699-project&highlight=

[Scott S]

Wow, there's a lot of information in that thread! I'm really intrigued by this combination. It looks like it's a little bit involved and might take a bit of time and money to collect all the parts, though.

I saw this mentioned in there, too: "A note: And Air/Oil cooled GSXR 750 will fit the old 550. And with a re-sleeve, can go up to 955cc's.".
Can anyone elaborate on that swap?

[Yozzer74]

I'm trying to find one too .want to find out if I can use the 550 ignition electronic not points .also seen something about base gasket thickness but what should it actually be .

[dorkburger]

Chuck78 is very knowledgeable about swapping parts between different GS engines for building power / more CCs.

[dorkburger]

Wow, there's a lot of information in that thread! I'm really intrigued by this combination. It looks like it's a little bit involved and might take a bit of time and money to collect all the parts, though.

I saw this mentioned in there, too: "A note: And Air/Oil cooled GSXR 750 will fit the old 550. And with a re-sleeve, can go up to 955cc's.".
Can anyone elaborate on that swap?

I cant add too much, other then fabricating new engine mounts is required. The oil cooled range is not as long front to back as the older air cooled GS engines, plus the need to fit an oil cooler, and possibly fab or modify an existing exhasust system, etc.

[Nessism]

More threads http://www.thegsresources.com/_forum...-673cc-project

Member Suzuki_Don did an epic rebuild on his 550 converting it to a 700. Can't find a build thread though. Can't remember if he made one but don't think so. He has lots of posts in the archives discussing his project though.

[Scott S]

You've heard of the snowball effect, right?

This search led me to a mention of the GSXR 750 swap (and the 1100). Then there was mention of the Bandit 600. And Turbo may have popped up.
Now ALL the gears are turning!
Too. Much. Information.

[Chuck78]

Clearancing the crankcases for the 650 sleeves, and either using a custom head gasket at 1.5mm or 1.6mm+ (+ if decking the block), or running a custom 0.8mm base gasket is what you need to get the deck height correct. I think both Suzuki_Don & mlinder (?) Have documented the deck height extensively. Mlinder discussed it on a "GS550 Performance" thread on dotheton.com, although the off the top of his head measurement I recall being incorrect.
Don discussed extensively his mysterious "top end rattle" (those words were in the title of his post which ended up being like eight pages) at which point he discovered the deck height difference, he was only running about .025" piston to head clearance and was getting interference, i.e. piston hitting head making a funny knocking sound.

You'll need to fabricate up a way to center the exhaust head pipes in the 650 head if you are using a 550 exhaust still, and Don had a nifty part number for a GSXR exhaust gasket that works perfectly to mate the two, 550 exhaust, 650 head.
As could be expected, you will be better off with the 650 carbs, but the 550 carbs can be made to work assuming you have in 80-81 CV carb 550. The 550 carburetors will require a lot more tuning and shimming and rejetting, and potentially different needle jets, which means you are better off just getting the 650 carbs.

This combination can give a very fun and adequate amount of power to a bike that still isn't terribly heavy for its size and era, which will translate into an incredible all-around bike that handles very well on twisty roads and is easy to manage due to it's lighter middleweight status, but packs a pretty darn nice punch, power-wise.

I have two of these here myself in the works. I built a 610cc GS550 last June, and it was nice ripping around on that thing! Noticeably lighter than my substantially lightened 465lb(with 1gal fuel) 77 GS750.
I just hooked up another friend with a fairly stock 78 GS550, so I assume I will be doing yet another 673 top end in another year or less on that one.

[Chuck78]

http://www.thegsresources.com/_forum/showthread.php?164443-Camshaft-Top-End-Rattle&p=1295188#post1295188

That is the beginning of Don's figuring out about the deck height discrepancy between the 550 and 650 top ends, starting with Billy's suggestions and observations in post 128, which I believe is the third page. That link should take you directly to Billy's first reply post on the topic

Also, one last important detail - you absolutely cannot use the camshaft sprockets off of the shaft drive 650. You must use sprockets the same size as the ones on your 550, which would come on any 550 8V 77-81, or a gs650e chain drive engine (rare).
The crank sprockets are different between the 650G and the chain drive versions of 550 and 650

Also with the thicker base gasket, you will want to do some minor alterations to open up the oil passage in the bottom rear corners of the base gasket, but you will need to allow the egg-shaped o-ring that seals the oil pressure to smash up against the paper gasket, since they don't make these O-rings in the added thickness needed. This was Don's method, and he had no trouble whatsoever with it.
Also I noted that the GS 1100 G base gasket egg-shaped oil pressure O-rings order of the correct thickness, but the diameter was slightly larger, and may or may not work if you were to try and trim it out of the base gaskets so that the O-ring was metal-to-metal. It would be tricky and a close call because the O-ring would want to jump out of the recess in the crankcase and get sandwiched where the base gasket is, which would cause problems.

[Scott S]

Honestly, at this point, I think I'm either going with a stock rebuild OR swapping in a GSXR750 engine.

[Chuck78]

Then it's not a GS!!!


The 673cc hybrid will pack a potent punch with aftermarket exhaust, slightly milled head for more CR, K&N filter, and a DynoJet kit... you will be surprised. And it's all nearly a bolt-on
The GSXR SACS engine will be a ton of fab work on engine mounting and exhaust, & the engine is a lot shorter front to rear and wouldn't really realize the potential of that design unless you slammed it as far rear as possible to get the countershaft sprocket as close to the swingarm pivot as possible - the intent of that design (well, intent was to move the swingarm pivot forward for better chassis geometry, but that's too much engineering and frame jigging).


673, my vote, very advanced closed chamber combustion chamber and piston design, raised intake ports to further advance the flow. The 673 engine made 1hp more than the hemi-chambered GS750 8V, 73hp 8v 673cc closed chamber head vs 72hp 748cc 8v hemi head... great **** there... & why I keep snagging 550 project bikes & 650 parts bikes!!!!