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

[tkent02]

It's completely worth it. A little known fact is that by swapping to a gs550, you are increasing displacement from 549cc to 673cc's. A 124cc gain.

What would it be with 750 or 850 pistons? Would the cylinder bore go that far?

[brveagle]

What would it be with 750 or 850 pistons? Would the cylinder bore go that far?

Funny you should ask that. I just happened to have done just that. (The bore will not accept 850 pistons.)

I did modify my gs550 to run the gs750 pistons giving me 740cc's of displacement.

Couldn't quite get all the issues worked out, so i'm reverting back to my 650 top end.

[tkent02]

Funny you should ask that. I just happened to have done just that. (The bore will not accept 850 pistons.)

I did modify my gs550 to run the gs750 pistons giving me 740cc's of displacement.

Couldn't quite get all the issues worked out, so i'm reverting back to my 650 top end.

How was the vibration with the 740?
What issues, carburetion?

[brveagle]

How was the vibration with the 740?
What issues, carburetion?

No vibration. I couldn't get my squish area correct. Compression was too low.

[tkent02]

No vibration. I couldn't get my squish area correct. Compression was too low.

Piston shape too much different?
I haven't gone there yet, still looking for a decent 550 to tinker with.

[brveagle]

Piston shape too much different?
I haven't gone there yet, still looking for a decent 550 to tinker with.

Head is too small. 750 piston dome too large. You can't even hit TDC without modification.

[tkent02]

Head is too small. 750 piston dome too large. You can't even hit TDC without modification.

So custom pistons will be required.
Just like Burt Munro.

[Old Colt]

I have 750 pistons in a 550. I have not run the engine yet though.
The engine still needs final assembly but it has not been any issues getting it together.
The 650 cylinders will simply drop into some 550 cases but need some clearanceing for others as shown in this thread.
The 750 pistons will go into the 650 block but the liners are thin. Not sure if this will be an issue.
I had started this intending to bore a 550 block to accept 750 liners. At this time I do not think that approach is logical.
The 650 head needs chamber work to match the piston domes. The head I have setup has the small chambers and the compression might be a bit stupid for street use. I will measure it this winter before final assembly. I would like to find a 650 head with larger chambers as my early 550 heads have. I just do not know the 650 engine that well to know if the early ones had different heads. I think the two 650 heads I have here are around 82 vintage or so.
I also will need to send some cams out to get a different grind to make up for the now tiny valve size for a 750.

[brveagle]

I have 750 pistons in a 550. I have not run the engine yet though.
The engine still needs final assembly but it has not been any issues getting it together.
The 650 cylinders will simply drop into some 550 cases but need some clearanceing for others as shown in this thread.
The 750 pistons will go into the 650 block but the liners are thin. Not sure if this will be an issue.
I had started this intending to bore a 550 block to accept 750 liners. At this time I do not think that approach is logical.
The 650 head needs chamber work to match the piston domes. The head I have setup has the small chambers and the compression might be a bit stupid for street use. I will measure it this winter before final assembly. I would like to find a 650 head with larger chambers as my early 550 heads have. I just do not know the 650 engine that well to know if the early ones had different heads. I think the two 650 heads I have here are around 82 vintage or so.
I also will need to send some cams out to get a different grind to make up for the now tiny valve size for a 750.

Sweet. Although i must say, you have alot of work cut out for you. The piston to head contact and compression issues is what got me. Stay in touch.

[Suzuki_Don]

I have 750 pistons in a 550. I have not run the engine yet though.
The engine still needs final assembly but it has not been any issues getting it together.
The 650 cylinders will simply drop into some 550 cases but need some clearanceing for others as shown in this thread.
The 750 pistons will go into the 650 block but the liners are thin. Not sure if this will be an issue.
I had started this intending to bore a 550 block to accept 750 liners. At this time I do not think that approach is logical.
The 650 head needs chamber work to match the piston domes. The head I have setup has the small chambers and the compression might be a bit stupid for street use. I will measure it this winter before final assembly. I would like to find a 650 head with larger chambers as my early 550 heads have. I just do not know the 650 engine that well to know if the early ones had different heads. I think the two 650 heads I have here are around 82 vintage or so.
I also will need to send some cams out to get a different grind to make up for the now tiny valve size for a 750.

All 650 heads are the same. '81 and '82 are identical and the reason that other pistons wont fit is that the 650 is the only 8v with a squish head. It has the sides of the combusion chamber left in place to direct the incoming fuel in the right direction for more perfect combustion and greater filling of the cylinder. The combustion chamber is basically rectangular and not hemespherical as in the other 8v motors. This is why the 650 has the same hp as the 8v 750 and only a couple of hp less than the 8v 850. The '83 head is slightly different, but that is only because in that year they fitted a different rocker cover with an extra bolt hole cast into the head.

If the 650 cylinders are over bored by 1mm that takes the capacity out to 700cc. The hard part would be getting hold of 1mm o/s pistons. The pistons are still available from Suzuki at $78 a piece.

[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.