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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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i have a starter if you need one
the bottle breather on the 650 as i was told in a honda class (there is a service bulletin about it have seen it ) was to relieve extra crankcase pressue
caused by our higher speeds and more prolonged distance riding
the higher crank case pressure would force oil by the weaker oil control rings (due to increased piston rock) and cause oil consumption and oil
building up to quickly in the breather catch can so we fitted the kit to twin the vents to all the gl650s and cx650e we sold in canada

that was my understanding of it
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.

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.
the bad part of that is you don't get the honda OEM rad fan switch IMO the best way of controlling the fan all else is fiddly and does not work as well or as long as the direct control switch in the 650 rad or the gl 4 cylinder direct contact controller that is designed to handle the full amperage draw of the fan for years and years
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right. he sells the correct intakes for each motor. since the 500 intakes fit the 650, i will be using them, which will keep the carbs straight instead of pointing them towards the single spine.
the 500 intakes do not fit the 650 they are way different i don't make 500 intakes YET i am beta testing 3d printed ones in nylons 12 right now for stock carbs
for the mikunis the 500 and 650 intakes are the same
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