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1980 Honda CX500
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Discussion Starter · #1 ·
I got a 1980 CX500 today. Not sure what I'm going to do with it, but it was essentially free. It is in rough shape, but its mostly all there.
I'd like to see if I can get the engine to run, maybe use it to build a "morgan-style 3-wheeler" with the V2 upfront.
Or just get it running to sell on to a new owner. With $6 gas prices, someone should snap it up if functioning. Far from it right now.

The key switch is all bodged up, left side spark plug is gone and the wire broken. I'd guess step 1 is to check/fill the oil, and spin it and see if it has compression,
how do I check the oil, and what is normal for compresson? Then see if it has any spark. I'm gonna need a wiring diagram, I found one on here.

Any other advice? I am not really a motorcycle person, but always enjoy learning new things, I picked up one of these V2 engines years ago for a project that I can't remember what it was..maybe to power my MG Midget, but went with a I3 motor instead. I was told this motor hold the land speed record for 500cc class.

Cheers, Jack
 

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1980 Honda CX500
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Discussion Starter · #2 ·
Oh here is a pic of it. Is there a way to turn over the engine not using the starter? Don't want the break or bend anything if valves or rings are stuck.

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Welcome-Download the fsm (factory manual) and do the full "inspection" (major service)...
Do you know when it last ran??..if its been years you might need some extra steps before attempting a start/engine turn...

If you look at the front of the engine just near the bottom of the radiator theres a cap that looks like the cap on the final drive that will allow you to rotate the engine/do your servicing-e.g. finding TDC

Always liked the Morgans
 

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'84 CX650E that is evolving into a GL500
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Welcome to the forum and welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old and may or may not have had all of the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature too) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.

While there are a few CX powered Morgan clones around and I understand they can be fun, I'd recommend trying it as a 2 wheeler before making any decisions as these bikes are addictive.

I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. If you decide to keep it as a motorcycle check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet).
It looks like your bike still has the original rubber brake line, which should have been replaced every 2 or 3 fluid changes (= 5 or 6 years) so I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid).
And don't forget things like the rad hoses and the boot between the engine and swingarm (they can crack on the bottom where you don't see it).
 

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1980 Honda CX500
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Discussion Starter · #6 ·
I'm thinking it might be best to just drop the engine out and take it apart and see what shape it is in.
Can you get new valves and pistons and rings without spending like the cost another motorcycle?
The speedo says 51,000 miles.

I'm liking the morgan-clone idea the more I think about it. A little research shows there was a kit sold to build one with a CX500 engine, and found a number of them built. I already built an electric three wheeler, but having the gas noise and a 5 speed looks like a fun ride in good weather.

Here is my electric three-wheeler. And I go another trike project too.

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I'm thinking it might be best to just drop the engine out and take it apart and see what shape it is in.
Can you get new valves and pistons and rings without spending like the cost another motorcycle?
The best way to evaluate the engine does not involve taking it apart. While some of the parts you mention are available they are not inexpensive.
 

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For ~free, that looks far better than the $25 special I picked up back in 2020. The left side exhaust looks perfect.

For any bike that sat for a long time and you're unsure about the pistons being frozen, I would always:
  • vacuum out any debris or dirt in the spark plug wells
  • Pull out the plugs
  • repeat the vacuum step
  • put some PB blaster, MMO, or similar penetrant in the spark plugs holes
  • let it sit overnight, then try to manually crank it using the bolt mentioned earlier in the thread

Aside from the usual valve check, at 50000 miles, the cam chain and tensioner probably need a good inspection.

Personally, I wouldn't mess with the morgan conversion, but to each their own.
 

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1980 Honda CX500
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Discussion Starter · #9 · (Edited)
It has sat outside for years without the spark plugs, so the cylinders may be all rusted up is my concern.
Seems best to just disassemble and rebuild it.
There is no title, so there is a big hassle to get it legal as a motorcycle, which makes the morgan tribute build attractive.
I have plenty of engines, including a twin-turbo rotary, i3 jetski motor, i4 outboard, couple V4 outboard motors, but the integrated trans/shaft drive is what really makes the cx motor a simple solution. The V4 two-stroke has a v8 hotrod sound to it, which I like much better than the v2 four stroke.

 

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If the bores are rusted enough to require a boring, oversize pistons and rings are hard to find. It may require getting custom pistons made. It is also possible to re-sleeve the bore and fit standard size pistons.

If you have access to a borescope, inspection through the spark plug hole may allow you to decide how bad the bore is and if it is worth progressing or not.

A good used engine will be less expensive than a rebuild of a severely damaged engine.
 

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Discussion Starter · #11 ·
So I got a borescope and looked inside the cylinders. Rust. Will it hone out I dunno, but it needs to be taken apart and see how bad it is. I created a 506ci stroker out of a 460 ford using olds 403 pistons and 455 pontiac rods..so perhaps I can find some other pistons that might work if it needs bored.
 

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Discussion Starter · #13 · (Edited)
Finally got to removing the engine and the cylinder heads to see how bad things are.
Was busy fixing and customizing a 2017 Yamaha Bolt among other projects.
For someone who's never owned a motorcycle, I now have two. lol

As the borescope showed rust, seeing it without the head on was rather depressing. Hard to image it much worse...btw how to remove the fan? It doesn't seem to come off.
Also maybe a tip for anyone removing the engine, as I messed up pretty good.
I was tapping out the long bolt in back, and was using a small diameter rod, which ended up jamming next to the bolt instead of pushing on it. Was a nightmare to get that undone.
Oh its always the 1 minute job that takes 2 hours. :(

In any case, not sure what to do next, suppose I will finish tearing it down.

My bolt:
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:sick: that cylinder... Yikes
 

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Discussion Starter · #15 ·

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'84 CX650E that is evolving into a GL500
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Assuming everything else is in good condition maybe. How badly corroded are the tops of the pistons? Did any water percolate into the crankcase and mess something up in there?

I think I'd have looked for another engine instead.....
 

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Also maybe a tip for anyone removing the engine, as I messed up pretty good.
I was tapping out the long bolt in back, and was using a small diameter rod, which ended up jamming next to the bolt instead of pushing on it. Was a nightmare to get that undone.
You wanted a tip to remove the engine you say?
CX500 Engine Removal with Randall
 

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Discussion Starter · #18 ·
You wanted a tip to remove the engine you say?
CX500 Engine Removal with Randall
Good video. My tip is where he says use a pin punch to drive out the long bolt, I would not do that, I'd use a thicker peice, like one size smaller bolt, so it can't slip off the end of it and then jam against the long bolt.
Now of course, my problem was it took too much pounding to make it move at first, so I keep at it when it was not actually moving the bolt. dooh.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Good video. My tip is where he says use a pin punch to drive out the long bolt, I would not do that, I'd use a thicker peice, like one size smaller bolt, so it can't slip off the end of it and then jam against the long bolt.
I used a 3/8" pin punch. A pin punch isn't tapered, so it can't become wedged next to the bolt.
 

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Discussion Starter · #20 ·
Just about done disassembling the engine, no water got past the pistons, so everything is "like new" inside the engine.
However, the pistons are not going to budge from the rust cocoon. However I came up with a plan...since I have a new crankcase, I can just cut away the exiting one and peel off the cylinders from the pistons. Brilliant plan IMNSHO. :)

On the other hand I'm really thinking to make it electric. I think it would be sweet to hide the motor, controller, and even some of the batteries inside the existing case. It would look 'almost' stock, but like a super bobbed out minimal one with some fake carbs, stubby exhaust pipes, etc. Can really fake up some real poser gas look with the EV hidden inside.
 
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