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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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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.
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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.
do you still have the link for the thread adapter?
Note that these are M6x1.0 to M8x1.0. The common adapter is M8x1.25.
@Randall-in-Mpls So @SirFoxx could order these and they'd be a bolt in solution?

No. He's not using a GL500 frame. He needs to modify the hanger that fits his CX500.
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ok, so it needs to be m6x1.0 to m8x1.0? just want to make sure
I know the gl650's that i have use the bottle breathers.
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.
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.
I hope it doesn't vent directly to atmosphere, or you're sucking in dust and contaminating your oil.
If you have hoses, but no collector, you're leaving a trail of oil drips somewhere.
I've seen designs using a T-connector. Up to a small pod filter, as Charles described. Down to a capped tube extending past the swing arm pivot, similar to the stock airbox drains. It's long enough to function as a reservoir, if it's emptied frequently.
I haven't tried them on the 650, but I suspect HD takeoffs might be a good replacement.
Usually a pair. Older Dynas are a good choice, but getting harder to find.
Used with the stock h-box, too free-breathing isn't a concern. Might need re-jetting with the mid-pipes.
im trying to do the opposite lol. im putting a 650 in a 500 frame.
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;
You're in new territory, there.
@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.
According to the respective FSMs, both the GL650 and '78 CX500 use 35mm carbs. My first attempt will be to mount a pair from a '78 CX. I think it was Charles who said the CX500 stock isolators can work on the 650 engine. Maybe I'll need to adjust the brackets and transfer pipes a little. I think that would be easier than straightening and spacing the 650 carbs. It might be easier still to 3D print custom intakes, assuming the ASA I'd use could take the heat.

And the radiator return area is different on the 500 from 650. Was there more?
I'm tempted to use the CX500 radiator with a GL1200 cooling fan (the one with the flat motor) that I have on hand. That would mean less modification to the engine hanger. I'll need to mock that up before deciding.
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