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

[Nerobro]

Yes it is. That's what made me thing the project was going to be easy. It wasn't as easy as I thoguht. But it wasn't all that bad either.

 

[Nerobro]

It's been done.

Skreemer and I have made the GS650 head, block, and pistons fit on a GS550 crank and block.

There's a lot more involved than originally thought.

First, the block wouldn't fit down into the crankcase. The cylinder liners don't actually touch down in thecrankcase so it was a matter of trial and error to find out where the interferece was.

As you can see... some of the interference was pretty severe.

Look carefully and you can see where we ground casting flash off of the inside of bore 2, and Skreemer is working on bore 3

 

[Nerobro]

Super Scary... Skreemer with a dremmel. He's not quite the artist as I, but he's competant And look... I let him inside my engine with that thing.

It involved a LOT of grinding. none of it was all that deep, just a lot of it. If I did it again, I'd split the cases, pull the headstuds, and have a machine shop bore the crankcase. But that was well beyond my budget ;-)

 

[Nerobro]

Testfitting. This was probally our 4th or 5th fitting of the block.

This is one of our last goes at making clearance. An artist at work... you can't see the work. ;-)

Seccond, much to our chagrin, the headgasket is different on the 650 and 550. so I had to reuse the 650 headgasket. I will be buying 650 headgaskets from here on out. Here's the reason why... The 550 uses an o-ring to seal the chaincase. The 650 just uses the soft fiber gasket. the 650 headgasket also has integrated oil gallery seals. The 550 uses seperate seals.

Finally, the timing chain was a pain in the butt. I did not realize that the 650 crank has more teeth on the crank sprocket, so that the camshafts use larger sprockets as well. Well, thats' not the whole story really. Lets just say that the discovery process led to me almost bending a valve. And that's an "I hope" I didn't bend a valve.

 

[Nerobro]

We swapped the sprockets from the 550 onto the 650's camshafts. And after following the directions in the book, managed to sucessfully time the 6/550 motor.

As it stands, the engine is now in my 1980 GS550E, and will crank over. And makes spark. Attaching the carbs is anotehr story. The carbs I'm tyring to put on are the carbs that came WITH THE ENGINE, but appear to be almost 1/2" to narrow. We're chalking that up to time hardening the carb boots. And the boots appear not to match up well with the ports in the head. We're going to put my 550 boots on it and see if that corrects the problem. My 550 boots are also much softer and more supple.

We found out that the boots that came on that head. are NOT gs650 or 550 boots. We aren't sure WHAT they they really are. They're damned simmilar though.

 

[Nerobro]

If you can identify these, we'd like to sell them. They're in good shape if a little stiff. No cracks at all.

so.. yeah. You CAN fit a 673cc top end onto a 550 bottom end.

549cc piston versus 673cc piston

Aw.. .look It's all dressed up.

working furiously last night before we discoverd the carb boot issue.

 

[Ironriot]

Is it just me or did you fix all the pictures????? And as for those little rubber boots my 550 came with them also. They seem to be some sort of mystery becuase no really knew what I was talking about. You can't see them individually in the fiches but they come with the little intake flanges when you order them new

 

[Nerobro]

Yup, I did. As well as I could. I couldn't re-edit the original post because I can't have more than 4 images in a post.

 

[nisom512]

So what kinda power do you think your pushin now. i know it's been a year almost, but hows it running?

 

[Guest]

So what kinda power do you think your pushin now. i know it's been a year almost, but hows it running?

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.

 

[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?

 

[Guest]

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?

 

[Guest]

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.

 

[Guest]

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.

 

[Guest]

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.