GS550-650 Head Swap. Both Ways?

[Guest]

So I currently have both bikes and I'd like to see what my options are. To my understanding, I need to take the 650 cams, and put them on the 550 sprockets and chains. But can I do the reverse and still have two complete engines?

[cornishgs]

Why would you fit 650 head onto 550 cylinders and pistons they have different combustion chambers 650 head will fit on 650 cylinders onto 550 cases easy ish but you have to open crankcase to enlarge a bit for 650 cylinder liners. but to try and and fit 550 on 650 why!! It should be possible to fit 550 pistons cylinders and head onto 650 cases and use 650 cam sprockets!!

[TxGSrider]

I should stay outta this as I know nothing about these engines... but... wouldn't it be easier to swap the entire engine and use the extra cc's?

[steveb922]

Most 650s are shaft drive, so wouldn't be easy to fit in a 550 frame. But the main advantage is that you end with a 674cc (if memory serves me correctly), with a 6-speed gearbox and chain drive. The 650E (i.e chain-drive 650) is a 5 speed, and a tad heavier than the 550.

[illeatit]

Hi, sorry for the late reply. Apparently I can only log in when I'm in incognito mode. Weird.

So yea, I guess l was using the wrong terminology when I said heads. I meant the whole top end, cylinders, pistons, etc.

The 550 is my current bike, I picked up a non-running 650E for $200, I couldn't say no.

I'm going to do the top end swap with the 650 and some 1mm oversize pistons, which should put me close to 700cc.

I would still like to get the other bike running though. And I think it would work both ways. I could put my 550 top end on the 650 case using the 650 cam sprockets.

Either that or just part it out, I might actually save more money doing it that way...

[Steve]

Personally, I would just put the 650 top end on the 550 cases, then part out the rest. Why would you want to go through all the effort and expense of downsizing the engine in the heavier bike? You would certainly have a hard time selling it because everybody wants "bigger, better, faster".

I'm going to do the top end swap with the 650 and some 1mm oversize pistons, which should put me close to 700cc.

Doing the math, you would end up with 695.8 cc.

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[Chuck78]

Aaaaaawwwwww man..... you have a GS650E basket case?!?! The GS650E is a hard to come by model that a lot of people would really kill for. The rare chain drive 650!
I have no remorse parting out junkyard shaft drive GS650G engines to build up chain drive 550's into a 673cc, but a GS650E is definitely a more rare model. It is not necessarily worth much more money than other GS models, but definitely much more highly-regarded to those who are fans of chain drive - the more performance-oriented.

I'd advise (urge) you to leave the 650E as is, and pick up another GS650 cylinder and head off of eBay Etc

But yes, you could make it a 548cc GS650E simply by just dropping on the 550 cylinder and pistons and head and carburetors.

Sixth gear is fairly redundant on a high performance build GS550, 5th and 6th are very close together in ratio, the six-speed is just to give the smaller engine a bit more mechanical advantage. A 700cc engine does not really need the six-speed, but it is a nifty thing to have when you build the hybrid engines. No real advantage, however. Unless you are able to change the gear ratios to a wider spread

[Chuck78]

And yes, the camshaft gears should stay with the crankshaft. Not the cams. Although the 650e may not use the same camshaft gears or crank gears as the 650g, perhaps it could be the same as the 550, but I would not chance it. Do they have a different number of teeth?

[Steve]

Although the 650e may not use the same camshaft gears or crank gears as the 650g, perhaps it could be the same as the 550, but I would not chance it.

I don't know how they compare with the 550, but I can guarantee that the 650E and 650G have different tooth counts on the crank and cam sprockets.

I was working on a 650G that had been over-revved (not by me), had a 650E engine to harvest some parts from. The E cams looked a bit better, the manual said they had the same specs, so I just moved them over. I noticed a little more room around the cam chain at the top, but didn't think much of it. Rotated the engine SLOWLY BY HAND after assembly, only made it about 1 1/2 turns before hearing a CLUNK and the crank stopped NOW. Pulled the cams, starting the crank/cam timing procedure again, got the same results. THEN I paid attention to the extra room around the cam chain. The E cams have fewer teeth, so the cams were turning faster than they should, which put them out of time, into an interference situation. I swapped the sprockets, installed the cams a THIRD time and eventually got the engine to run.

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