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650 on a 500 frame

5479 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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The starter can be removed with the engine in place. See FSM.
Ill do that. With how tight it is against the spine of the bike i wasnt sure you could get it out or not.
Some pics of the motors and my cx500 standard~

edit--looking at the auto adjuster on the motor with the busted cam, the chain is toast since the hole on the plunger is exposed. Might be why the PO tore it apart. Prolly means the internals are good on it.


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i have a starter if you need one
how much do you want?

Also, question--

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?
Honda converted it to an auto tensioner. I'm going to convert it back 😁
The rear covers are different-no hole for the tensioner bolt on the back of the 650 and the water pump and cover for the ignition are different too...
right, but if i use my cx500 back and the rae san ignition, that wont be an issue.

how is the water pump different?
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.
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.
CX CDI to 12V coil Conversion Kit | Rae-San Electronics

that solves the ignition issue

this isnt something ive thought about in awhile--doenst the crankcase vent come out from the middle section of the motor, not from the back cover? what issue do you see with the venting?

do you still have the link for the thread adapter?
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 ^
I do. '78 standard. first year babyyy!

im not well versed on every flavor of the 500's, but the modification of the stamped steel 500 hangar should work on any of the us derived cx500 bikes. I am not sure about the gl500's, cx500e's, or the turbo bikes. i do know that it will work on mine as murray used to offer the modification service, but since stopped, but gave me advice on what to do, as well as finding a video on how to do it.
Why can't you modify the cast hangers? They're just cast steel, not hardened or anything. They take a weld bead just fine.

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 have a diesel heater for when its get nipply if I need to work in the garage lol
I've watched the video on it a while back, I thought they only had to do the top left one, my mistake.
ill have to go back and watch it lol. all i remember is it needs to get modified (currently at work and cant view YT >.< )
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.
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 mean, thats fine with me. it doesnt seem that hard to do.
Depending on the year of the engine the crankcase may be vented through the cylinder heads, CX500s, through the pulser cover, GL500 and others, and through a bottle breather at the timing inspection port.
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.
Note that these are M6x1.0 to M8x1.0. The common adapter is M8x1.25.
ok, so it needs to be m6x1.0 to m8x1.0? just want to make sure
@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.
nope. the engine got scrapped about 6 years ago.
Bottle Breather and the vented pulser cover.
The bottle on the inspection port is really to increase condensation of vaporized oil before it passes to the reclamation system. It's a secondary vent, at most.
reclamation system..?
OIl vapors and moisture from the crankcase are directed to a collector under the air filter housing. The volitiles are pulled in with combustion air and burned. The heavier junk, including water, is retained and drained at each oil change (if you're doing your proper maintenance.) The GLs have a more elaborate separator and reservoir. I believe the bottle is intended to help separate the oil vapor and return it to the crankcase.
oh. my cx500 is just venting to the atmosphere lol. i think i have one of the hoses still hooked up tho.
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