Suzuki GS 6/550 Yes, 672 block and pistons on a 550 cases..

[Old Colt]

Hi Don,
That is the info i needed.
I have shaped the combustion chamber to clear the 750 pistons, that part is easy. The small chamber will be giving a rather high compression. That should be fine as long as the center cylinders cool well.
I have thought of opening up the chambers but it is easy enough to go in later and do that.
One of the hold ups I ran into is the 550 engine I have has adapters on the intakes that position the smoothbores for straight ports that are quite downdrafted compared to the original. The stainless screws do not want to come out of the adapters and will need to be drilled out so I can transfer them to the 650 head to do the porting. Being that I want to ride the bike a bit this fall I chose not to do so.
Plus the 650 exhaust ports are a larger diameter at the pipe so I will need new headers. My old Kaz Yoshima pipes are not real pretty now but they still function although a bit loud buy todays standards. I think a new header will be in the works.
Here I am rambling about my project on someones elses thread, Back to it.

The 750 pistons are a 3mm overbore for the 650 block. It is just the lower section of the sleeve that is down in the cases that looks to be a bit tender. I think I will just run it and if it cracks a sleeve I will then epoxy the case to give support for the sleeve.

 

[Suzuki_Don]

Charlie if you have 550 headers they will fit the 650 head if you use the 650 exhaust port gaskets. They are bigger than the 550 gaskets and will seal much better and not allow exhaust gas to escape.

On the 650 head Suzuki offsets the intake and exhaust valves in the combustion to create the swirl effect required for more efficient combustion. The standard 650 compression ratio is 9.4:1

 

[Old Colt]

Not having measured I am expecting this compression up about 11:1. Bit high for an air cooler.

The exhaust may just get a sleeve over the pipes for the first running, but This header is 1 3/8 tube and I am looking at going down to 1 1/4 tube for the primarys.
I have always used 11K as a shift point on this 550 but do not expect the 750 to pull up there.

 

[Suzuki_Don]

My next challenge is to try and fit 26mm VM carbs to the 650 head. But I have to find intake boots that will fit the 26mm carb throats and with the correct bolts spacing to bolt to the 650 head. The bolt spacing for the 650 intake boots is 68mm apart from centre to centre. I would be interested in receiving replies from anyone who has a 750, 850 or 1000 with 26mm VM carbs to give me the measurements off their intake boots. To see if they will fit the 650 head.

 

[Old Colt]

I use KZ1000 boots on mine with an aluminum adapter to set the spacing and angle. I think Sudco or someone has a bunch of the mount information posted.

 

[Old Colt]

Here is how mine are setup. This was built back in 1980.
There are no starting circuits in the carbs since these have accelerator pumps. The carb tops are not back on yet since they were just serviced and not setup yet.

 

[Guest]

Hi Don,
That is the info i needed.
I have shaped the combustion chamber to clear the 750 pistons, that part is easy. The small chamber will be giving a rather high compression. That should be fine as long as the center cylinders cool well.
.

So how did you do this may i ask? This is the problem i ran into?

 

[Old Colt]

Using clay, electricians dum dum actually.
Assemble the bottom end up through the block. I work without rings on the pistons so it spins freely.
Put some clay on top of the pistons where you intend to work and with the head set in place, not bolted since it will be on and off a dozen times.

Rotate the engine to compress the clay a bit. lift the head off. This will allow you to visualize where you need to remove material.
I use a lubricant like WD40 when cutting the aluminum and it reduces the clay from sticking to the head.
You can start with just one piston mounted if you choose, just tape cardboard to the other rods so they will ride nice in there bore.

Keep your gasket thickness in mind as you get close and are setting your squish areas.
If the pistons rock in the bore keep that in mind. I have wrapped tape around the piston to reduce rocking but have not needed to in a decade or two. Pistons fit more snug today the they used to.

When you get close you will want to bolt the head down to be more accurate with the squish. I myself run the squish much tighter than standard but you need to do so cautiously.

Final check is with rings on the pistons.

 

[Guest]

Great work! I did the opposite. I just put a base spacer in, which dropped the pistons in the bores. (didn't work so well)

My plans are to continue working and researching my gs740 design. Sounds like you're gonna have a more efficent motor running before I will.


Thanks for the input.

 

[Old Colt]

I was curious when you wrote about a low compression. But a base plate would explain that.

The chamber work can go pretty quick depending on how well you visualize what the clay is telling you. Plus these heads have allot of material in them, you cant really go to far.

I would sure love to get some larger valves in this but I do not see that happening.

 

[MrZufall]

Awesome project guys! I'm going to give it a shot next winter!

I've got an 81 gs550l- Got any advice on where to start? I read the step by step break down and it seems pretty comprehensive. Thanks for that!!!!

Do you have any advice on what year/model of 650 I should start looking at to pull the top end off of?

Thanks,
Matt

 

[DCrippa]

This sounds ridiculously awesome and labor intensive. Any pics?

 

[Suzuki_Don]

__________________
'77 GS 550 (was an L I think)... cafe racer - work in slow progress (hopefully will be bad ass)

There was no "L" model in 1977. It was just a GS550B.

 

[DCrippa]

Thanks for the clarification it's been confusing me as to what I have - it must be a '79...

 

[Nerobro]

any 650 block will do. I'll rehost the pictures at some point.

 

[Stahlgrau333]

I'll rehost the pictures at some point.

Looking forward to this.

 

[240punk]

Id be interested in these pictures as well.

 

[TyFerris]

so i would like to know why you are doing this. is there something special about the 550 bottom end? seems like an awful lot of work when you could just get a 650 in the first place right?

 

[240punk]

Because if you already have a 550 why would you buy a new bike when rebuilding as a 650 is the same price?

 

[TyFerris]

frustration, time, frustration... and im not saying buy a whole bike im going with if you are already buying the head block and pistons why not just buy the whole motor and throw it in a 550 frame? so just to make sure there isnt something the 550 bottom end has that the 650 bottom end doesnt?