650 head on 550 engine?

[Guest]

Just noticed this after an embarrassing amount of time working on the bike. Can anyone easily spot why this might look like this? Did some PO put on another head or what are your opinions?

[1948man]

http://www.thegsresources.com/_forum/showthread.php?201784-Finally-getting-around-to-the-550-699-project

650 on 550 builds are not uncommon and yield increased displacement while retaining the 6 speed transmission. I've never done one and don't know if they would mate up like in your picture. Maybe they used the wrong 650 jugs.

[Nessism]

The 650 cylinder/head has an extra bolt in the front center of the engine to reduce cam chain tunnel oil leaks out the front of the engine. The early 550 cylinder head doesn't have this feature though.

[11csive]

http://www.thegsresources.com/_forum...50-699-project

650 on 550 builds are not uncommon and yield increased displacement while retaining the 6 speed transmission. I've never done one and don't know if they would mate up like in your picture. Maybe they used the wrong 650 jugs.

I've read a little bit about them, and I was wondering if this might be something like that.

The 650 cylinder/head has an extra bolt in the front center of the engine to reduce cam chain tunnel oil leaks out the front of the engine. The early 550 cylinder head doesn't have this feature though.

So what you're saying is, if I don't get you wrong, that this looks like a 650 cylinder with a 550 cylinder head? If so, that's quite interesting..

[1948man]

So it's kind of a sandwich? 550 head, 650 jugs, and 550 bottom?

[Steve]

Might be.

Look at the bottom front of #1 cylinder to see what the displacement label shows.

.

[tom203]

Here's my 81 650 in that area. Yes, it's dirty- it just got stuck in my basementimage.jpg

[11csive]

So it's kind of a sandwich? 550 head, 650 jugs, and 550 bottom?

Hopefully we will find out, I just need a little bit of advice here

Might be.

Look at the bottom front of #1 cylinder to see what the displacement label shows.

.

I will have a look tomorrow when I get back to it - Wouldn't mind some 650 power on it

[tkent02]

What's odd is that the 650 pistons won't work with the 550 head. Totally shaped wrong. You may have some custom parts in there... Like 750 pistons and a 650 cylinder bored to fit them? Not sure, post a picture of the end of the engine showing both the head and cylinder?

[11csive]

What's odd is that the 650 pistons won't work with the 550 head. Totally shaped wrong. You may have some custom parts in there... Like 750 pistons and a 650 cylinder bored to fit them? Not sure, post a picture of the end of the engine showing both the head and cylinder?

Won't work as in will bend the valves? I've changed a valve in the head because it was bend. This is getting weird.

As soon as I get to the bike again tomorrow I'll post some pictures.

[tkent02]

No, the 550 pistons are completely the wrong shape for the 650's combustion chamber. The 550s are the old shape like all of the previous GSes, the 650 had new shape which was much better for making power, the 650 is 73 HP where the 550 was 49. That's a 49% power increase for only a 23% displacement increase. The fact that the 650 makes it's power in a broad range and the 550 only makes power at a very high RPM is just icing on the cake.

I'm curious to find out what you have.

[11csive]

No, the 550 pistons are completely the wrong shape for the 650's combustion chamber. The 550s are the old shape like all of the previous GSes, the 650 had new shape which was much better for making power, the 650 is 73 HP where the 550 was 49. That's a 49% power increase for only a 23% displacement increase. The fact that the 650 makes it's power in a broad range and the 550 only makes power at a very high RPM is just icing on the cake.

I'm curious to find out what you have.

I'm a little disappointed right now. Just went to have a look at it. The displacement label on the cylinder says 549cc. But as you guys said, the front end on the 550 doesn't have that extra screw hole. I snapped pictures from some different angles and hopefully someone on here can recognize the build. It's in a basement with bad lighting and a little cramped up, I hope they are usable though.

[nejeff]

The 550 DOES have the extra hole up front at least in the 80s, not sure what that head is but looks like a 550 to me except the squared off, no hole front. Maybe newer model cylinders with original head. I don't see any 650 components.

Edit: Yes, original 70s head with later model 550 cylinders is the correct answer, no gs650 stuff here

[11csive]

The 550 DOES have the extra hole up front at least in the 80s, not sure what that head is but looks like a 550 to me except the squared off, no hole front. Maybe newer model cylinders with original head. I don't see any 650 components.

Edit: Yes, original 70s head with later model 550 cylinders is the correct answer, no gs650 stuff here

Thank you for making this clear. Any difference between the two cylinder blocks that I should be aware of, besides the extra hole?

[tkent02]

That's about it. You may have a complete later 550 engine, not just the cylinder. Does your bike have the kickstarter?

The good news is the 650 top end will fit!