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It runs! Gs550/650 Top end swap w/pics

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Well guy's... It's done. I have successfully took a gs650 shafty, and swapped the top end, including the pistons and cylinders, onto my gs550 chain drive motor.

This project took 2 full days, working at a slow tedious pace. I ended up pulling the motor to just make things easier.

Bought the 650 motor off ebay for $5. It was somewhat local. Compression before starting was 155 across the board.
Bought a gasket kit off ebay for $50.
Bought new piston's wrist clips through bike bandit for $8.
Bought a used set of carbs off ebay for $60 shipped.


Used alot of engine build lube, and took my time. There is grinding to be done on the block, but it's soft aluminum and it was just tedious. That took me a few hours. There's hardly any to grind, but i wanted a smooth fitment. All i have left to acquire is a exhaust. Found out the hard way that the 550 exhaust will not fit the 650 head!



It runs, and idles like a kitten. Trying to track down a 650 exhaust, so haven't rode it. But can't wait. Another guy on this board did this swap, Neobro, and he helped me a ton. It wasn't easy, and this was my first time ever even cracking open a valve cover, let alone taking it down the the crank.

I hope that other 550 riders that see this and want 14 more HP and 124 more CC's will be able to follow in Neobro's and I's footsteps.

Enjoy the pic, i'll have more up later.

Here you can see both engines on their stand. 650 on the left. My empty frame in the background.
 
More pictures:

Here's the cams of the 650. (you can barely see the 550's in the background)


650 engine


Here's the pistons. You can obviously see the 650's are bigger.


Here's me grinding with the trusty dremel. Notice all the rags stuffed in the crankcase.
 
Very interesting.

The 550's carbs don't work?
What is the problem with the old exhaust? Header heigth?

Congratulations on a successful job!
 
The carbs are the correct body's and everything. Instead of ordering a jet kit and researching to find out what jets i need, i just decided to run it all stock, and picked up those carbs. Just a little bit easier. But you can use the 550 carbs, just have to rejet.

The 550 header "fits" but the header holes on the 650 block are a larger diameter than the 550's. The header it's self is loose in the holes. The distance between the holes are fine, they just don't seal. I ratcheted the bolts down to see if i could get them to work temporarily, but it still sounded like a harley on steroids.
 
One other question: How did you handle the endless cam chain? Could you find a master link? I was under the impression they couldn't be reassembled once taken apart.

OK two questions.:? :-D
 
i was really worried about that too, until i drew it out on paper.

You use the stock 550 camshaft sprocket, and the 550 crankshaft sprocket. So you naturally just use the cam chain from the 550. Don't have to break it. Had no problems timing the engine. Just followed the book.

That's what both of us did. Neobro was the one who advised me on it.
 
YEY, someone else has done it! :-)

The 650 carbs have heavier springs in them so there will be more vacuum as well. I think this leads to a more progressive feel, though slightly less horsepower all told.

I understand brveagle will running with the airbox, so using the 650 carbs straight up should be just fine.

As for the differences between the 550 and 650 carbs. They have different air jets, pilot jets, main jets, needles, springs.............. So short of the actuall carb bodies they dont' share much.

In my case, to save more trouble... I went ahead and put the dynojet stage 3 kit on mine.

Brv: your exahust problem is becuase you need new exhaust gaskets. The outlets on the 550 and 650 are the same. the gaskets are $8 on ebay. Pick up a set. And.. it's neRobro. As in Brother of Nero. Neo came... some 20 years after nero did.
 
can someone post the pics of the bike again? i would really like to do the swap and yes the war sucks, but can we have the swap pics back? thank you, have a good day
 
This thread had been dead for 16 years. I'm not seeing any pictures that were in those posts. brveagle hasn't been active since June 2021.
 
Suzuki_Don had a pretty involved writeup after his initial 673 build. The title of the write-up was more of a troubleshooting thing trying to figure out a noise after the swap, which led him to discover the deck heights were different and a 650 top end on a 550 required thicker head gasket or thicker base gasket, otherwise the Piston will be tapping the head slightly, especially at higher RPMs when the engine is warmed up.
 
Gs550lkid said:
can someone post the pics of the bike again? i would really like to do the swap and yes the war sucks, but can we have the swap pics back? thank you, have a good day
Click to expand...
I .. believe I lost my images. I'll see what I can find. The pictures aren't a lot of help honestly. "the parts fit" You need to relieve the case a little so it will sit.
 
Chuck78 said:
Suzuki_Don had a pretty involved writeup after his initial 673 build. The title of the write-up was more of a troubleshooting thing trying to figure out a noise after the swap, which led him to discover the deck heights were different and a 650 top end on a 550 required thicker head gasket or thicker base gasket, otherwise the Piston will be tapping the head slightly, especially at higher RPMs when the engine is warmed up.
Click to expand...

I'm... Not sure that's right. Using GS750 pistons you do need to do some work. But I had no head clearance issues with my GS650 top end on my GS550 bottom end.
 
Different engines are machined at slightly different tolerances, you might find some that have barely enough clearance to not have noticeable interference, but Don and I have measured several engines, and it's quite uniform that all 650 top ends on 550 engines need a slightly thicker head gasket than the stock offerings in order to have proper piston to head clearance.

750 pistons require massive work to run in a bored out 650 cylinder with a 1980+ GS550 2-valve per cylinder head. Not compatible at all with a 650 head unless you ruin the advanced design of the 650 head transforming it into an old school hemi had like a 1980 550 head. But the valve pockets on a GS750 piston aren't spaced properly for 550 or 650 head, you need to set them up on a milling machine to use a fly cutter to adjust the valve relief locations.

A 673cc conversion with a tight piston to head clearance, K&N filter(s), aftermarket high flowing exhaust, & precise jetting will be more efficient and make more power than a stock bore 748cc GS750 or 740cc GS550 with 750 8v pistons. It's not worth it to lose the swirl chamber combustion chamber shape and advanced design
 
Ecampolo said:
Planning on mounting above the rear tire with a fan to pull air from the area where the air box used to be. Not sure how much pressure will be lost pushing it through a larger volume cooler. Looking to avoid running lines around the cylinder to the front. I have enough to build 2 bikes plus so getting [NODE="1"]Home[/NODE] done first, been collecting parts for years.
Click to expand...

The air up front will be much cooler than that coming off the back of the engine.
 
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