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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
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 ;-)
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.
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.
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.
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
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 ;-)
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.
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.
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.
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