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650 on a 500 frame

5480 Views 92 Replies 12 Participants Last post by  SirFoxx

Just wanted to start a general discussion about the thoughts, or personal experience of a cx/gl650 engine swapped onto a 500 frame. I've got a cx500 standard that I rip around every now and then, and I think the extra power from the 650 would be nice!

I've talked to murray about it several times, and I know he loves the extra power the 650 has to offer, even with the slightly longer gears.

What got me going on wanting to do this is, I picked up two GL650 engines from an estate sale for $100. One has the end of the camshaft snapped off, where the water impeller goes, and the other is complete. I need to stick my endoscope into the complete engine and see how the cylinders are, make sure the complete one is in decent shape and not blown up from lack of oil. Makes me curious why the PO was trying to take apart the other motor, and how hard he was prying at the impeller to break the cam.

I've been trying to get a 2nd starter as neither engine has one so I can also crank them over and listen for anything funny, but it seems they are becoming hard to come by and rather expensive. I'd use the one off my cx500, but I'd rather not drop the engine just to borrow a starter...

(if anyone has one they'd sell to me cheap I'd really appreciate it~)\

I think I have everything mentally written down that I am going to need / do for the swap:

Rae-San ignition, timing jumper to aggressive
12v coils
murray mid-pipes
rejet murray carbs
modify cx500 engine hangar
gl650 radiator + efan wiring
swap output shafts
inspect cam chain, replace mechanical seal while swapping output shaft
Swap over HD clutch springs?

I don't think I'm missing anything..but I probably am. If the cam chain tensioner isnt stretched to the max, I am going to leave it. No reason to change good parts. Same with the stator.

Only thing I have ordered right now is the 650 radiator, mainly because it was in great shape, came with the efan and the shroud for $70 shipped!

I may make a build thread once I get this project going. The hardest part will be modifying the engine hangar, but theres a video on youtube doing it, and its pretty easy if you have a welder (which i do lol).
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If I wanted to convert it back to a manual tensioner, will my 500 case work on the 650, and if so, will the same rae-san v4 module fit the 500 case? If I remember correctly, the v4 module will work on all motors...

Just curious, what do you mean convert it back to a manual tensioner? afaik, none of the 650s had manual tensioners?
Just in general, why shy away from the auto tensioner? I've come across a couple other threads on doing this to the CX500s and the general consensus seemed that it wasn't worth doing. I thought the auto works fine as long as it's monitored, and the manual will require your attention just as often.
according to murray, the manual tensioner, when serviced correctly, will get you almost double the life out of your chain vs the auto tensioner.

Yeah I remember that point, and the point of them breaking when left unchecked.

I have a turbo 500 case (with a severed water pump end as well) and a 650 motor, hence my interest in that part of it.

Someone here was making parts for the auto tensioner that made the plunger part against the guide thicker, giving you a bit more range out of it. I think the same guy making new water pump impellers. Never did see anyone say they tried it though.
You MIGHT make the CX rear cover work, if the Rae-san kit will work with the CDI ignition cover, and you can modify the crankcase venting. Easier just to get a GL500 rear cover.
Use the 650 water pump impeller and cover.
You'll need a specific thread adapter to host the tension adjuster lock bolt. I know of one seller on Amazon with the correct adapter. I posted the link in a similar thread within the last month or two.
I've been running a manual adjuster on Nimbus since I reassembled it last summer.

That Nimbus is a 650 motor, right? If it's not terribly difficult to do I might be tempted. My problem would be sourcing a manual tensioner, I don't see any on ebay and I think the Turbo 500 I have is automatic.

@SirFoxx I'm putting my 650 into a 500 Turbo frame. I think the 650s drop into a GL frame with modifed GL650 hangers but on mine I may be fabricating completely new hangers because I hate the stamped sheet metal ones. What are your engine hanger plans looking like? If you've caught Murray's attention I'm sure he's discussed it with you I'm just curious.
the 650's, cx or gl, will drop onto the 500 frames with a modified 500 stamped steel hanger. you cannot modify the gl hangers as they are cast.

there are 4 bolts that hold the hanger to the motor. I believe the lower set needs to get modified--you cut the collar that the bolts go through off the mount, get new collars and move them down like a 1/4" and reweld them. its a very simple process. the reason for doing this is because the upper part of the mount that bolts to the frame is very different between the 500's and the 650's.

I know all that stuff, I meant with your bike, I thought you had an older CX500 frame? I didn't know what CX500s that worked on ^
Why can't you modify the cast hangers? They're just cast steel, not hardened or anything. They take a weld bead just fine.


In my case? It's just a preference to have something more attractive. And welding any cast is not something most people can do at home; I'd say the average guy has a mig welder and knows how to melt metal just well enough. The GL500 hanger that's sheet metal was just the easiest solution I think.
you're not supposed to weld to cast do to its porosity. You can braze to cast, though I wouldnt trust a brazed cast piece on something thats keeping the engine secured to the bike.

It's a bitch and it can work you in circles when you run into issues, but done properly I'd trust it if it's just the one bolt hole on the hanger, as is the process for the GL500 sheet metal hanger. In my Turbo frame I'd have to cut and weld across the entire hanger on both sides and I wouldn't mind trying but I don't know that I'd trust it. For the aggravation some plate steel and tubes was my plan, and I can make it look nicer (relative to my tastes of course)

And now I actually really want to try it but it's 20 degrees in my work area so f that lol
its both lower bolt holes, not just the one. I'll post the video here shortly.
I've watched the video on it a while back, I thought they only had to do the top left one, my mistake.

He only specifies that one bolt out of alignment?
There's no need to modify the cast hanger. Both the GL500 and GL650 use a two-piece cast hanger with identical attachment to the frame. You can hang a 650 engine on a GL500 frame using a GL650 hanger.
The one-piece, stamped metal hangers are all CX500. I'm not sure about the CX650C.
Thats my problem, and I guess it was bad of me to jump into another's thread about it. I have a CX650C w/ cast hangers that are very different from the turbo hangers. I'm using a Turbo 500 frame; most don't. That might work for @SirFoxx

CXPhreak pointed me to the diagrams this morning; I was about to ask in the Turbo forum about the frames but this saved me from that post:

Line Font Auto part Parallel Engineering
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@Randall-in-Mpls So @SirFoxx could order these and they'd be a bolt in solution?

@Randall-in-Mpls @SirFoxx has a CX500 frame; they look different than a GL500 frame?
We should compile this info somewhere on the motofaction site 🤔
AFAIK, there's only one CX500 frame mount pattern across all years; I think Randall's talking about a GL500 frame which is different and doesn't require modifications. The Red Rocket was built welding a GL500 frame to a turbo rear I think, and I've seen at least one other instance of that.

For your CX500 frame I think you're stuck modifying an engine mount.
i think my cx500 is vented through the cylinder head, though i'll have to check. its been awhile since ive looked under the covers.

before you say the '78 didnt have X style, i had to swap an '80 engine onto the frame after i locked the '78 engine up...

I know the gl650's that i have use the bottle breathers.
@SirFoxx Do you still have the valve covers from the 78? @Molten Stenberg cracked one of his and was looking for a set. Any set really.
I haven't tried them on the 650, but I suspect HD takeoffs might be a good replacement.
Most harley's being over 1200cc, are you saying one muffler for both cylinders?
Those mufflers look very unrestricted lol
Bob was working with GL and Eurosport frames. They're close enough to identical that the engine was almost a direct bolt-on.
I believe it was Gerard who recently put a GL650 engine into his GL500. Here again, there was no CX500 frame involved, so it was almost a direct replacement.
It's the single- vs triple-spine frame that necessitates all the adaptation.

And I'm doing a CX650c into a Turbo 500 frame; both triple backbone frames, I feel it's the easier situation to be in.

@Randall-in-Mpls The only thing off the top of my head for @SirFoxx to worry about is the carb body issue; where the 650 carbs need the space the 500 frame takes up, the 500 carbs being spaced to the outside of that. And the radiator return area is different on the 500 from 650. Was there more?

@nolimitz I'm probably a catalyst in your confusion since I started in on the turbo stuff with my 650 into a turbo 500 frame. Probably should have stayed out of it. But like he said, general discussion lol
As mentioned in one of my first posts, I am using murray carbs. All I need to do with them is a rejet since they are not directly linked to each other.

I'm would guess Murray can or did give you directions, but the 650 carbs are pointed inwards towards each other to fit inside the frame, the 500 carbs are parallel and go to either side of the center tube frame...I'll admit out of pure laziness I don't want to go read back but I didn't recall what mounts you were using.

Even though you're using aftermarket mikunis, they're still mounting to some kind of intake, I wasn't sure if his kit came with the proper intakes, I know he sells them though.

The point I was trying to bring up is if you use the carb intakes from the 650 I would think they'd aim your carbs into the 500 frame especially with pod filters. Since you said these were just GL motors sitting around, I also didn't know if there were intakes with them or not. I wasn't sure if you had mocked that up or looked/check into it. I plan on welding up my own intakes. I might get lazy and just use OEM though since I'm sticking with a stock carb.
ive joined several cx650 / gl650 groups on fb, as well as made a post here, and am still having issues finding a reasonable priced exhaust...

As much as i dont want to pay the price...i might get these. the headers, chrome and mufflers appear to be in great shape. Plus, i love the magna style mufflers that are on these as well...

Honda Exhaust
If you're looking for an oem Style, I think that's a pretty good price and a decent-looking set of pipes.

I know I plan on a custom header but how long it takes me to get there I'm not entirely sure otherwise I'd sell you mine
someone mentioned that the 650 headers are bigger than the 500's? hence me trying to find a set

i am definitely going to use murray midpipes and ditch the hbox

honestly, while i know the HD parts are cheap and fit, id rather use honda parts lol.

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