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1978 Honda CX500
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Discussion Starter #21
Where is the bike now, Quin? I imagine it's nowhere near me, but there might be an experienced member nearby who can help you evaluate.
I'm in Morgantown WV. It's still out at my grandparents shop while working on it (about 20 minutes from me). I'm going to go out today to test some of the stuff everyone suggested then will report back!
 

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The people who have already offered you advice know what they are talking about so I don't have anything to add about getting it to turn except maybe if you have access to an endoscope type camera you might have a look inside the cylinders through the spark plug holes but if you don't I wouldn't rush out to get one yet.

But welcome to the forum. Please add your location to your profile and your bike's model and model year to your signature so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).

And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old has had none of the maintenance necessary to keep it safe & reliable for a long time so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. 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). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) 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).

The best advice anyone can give you about customizing any vehicle is to get it safe & reliable in more or less original condition and use it for a while before you start making any changes so it can tell you what changes it needs to make it do what you want/need better. That approach almost always results in something you actually want to keep and use but making changes based on style or on what someone else (who may or may not really understand how the changes affect the way it works) has done often results in a piece of expensive yard art that you can't stand sitting on for more than a few minutes and might even be dangerous.
 

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1978 Honda CX500
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Discussion Starter #23
You mentioned that you are new to motorcycles, but... If you've managed to take the front cover off, attach a 17 mm wrench and socket, and can see the crank rotating through the timing cover - then you've done great !!

You mentioned that this is a 1978 model, with low miles. These all had a recall due to the "Cam Chain" tensioner. Dealers resolved this as part of a recall. When they completed it, they punched 3 marks next to the Engine Serial Number (found on the left hand side of the engine):

View attachment 205682

The fact that you can rotate the crank a small amount would seem to indicate it is not truly "seized", if it is in neutral. It's not the "Gearbox" - if you can select 1st or second gear easily, which also rules out the "Clutch"..

A suggestion was made above to remove the cylinder head valve covers, this might be really helpful. If you do that on both sides, it exposes the "Inlet valves" (at the back of the engine, near the battery & air filter), and the "Exhaust valves" (to the front, close to the muffler down pipes). The valves are part of the 4 stroke cycle (suck - squeeze - bang - push) and are opened and closed as part of that, allowing fuel/air in and exhaust out.

They are controlled by the "Rocker arms", which are moved by the "Push-rods" - these are close the frame. They are moved by the "Camshaft" inside the bowels of the engine.

What you could be happening is as a result of a "Mechanical failure" of the Push-rods, a "dropped" or stuck valve hitting a "Piston". Worse still - it could be part of the internal moving parts connected between the "Crankshaft" and the "Camshaft" that moves the "Push-rods"., i.e. a damaged "Cam Chain" due to the tensioner as mentioned above.

If all appears to be OK, try removing the "Spark plugs", and use a small long wooden dowel. Rotate the crank again (slowly) and ensure the dowels move up and down. If they don't you might think they are seized - they could be. But it's also possible that the "Connecting rod" ("Conrod") between the crankshaft and the piston has broken.

If you end up having to do a rebuild, you will hear a lot on the CX 500 forums, click on the link to learn about the "Triple Bypass" (for the the "Cam chain" and tensioner/guide blades, the "Stator" and the "Camshaft" mechanical seal)..

There's a lot of help available in this forum, and everybody here will give you great advice. Good luck with your diagnosis and fixing it !!
Thank you this post made my morning! Super kind and welcoming and insightful advice! Luckily my bike does seem to have the issue fixed as there are the three little marks by the serial number. See my next post to see an update of the issue.
 

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Discussion Starter #24
When you turn it counterclockwise, do you see the fan and/or flywheel (inside the inspection port) turning? If neither turns, you are in fact loosening the primary gear bolt. If only the flywheel turns, you have a broken cam chain.
Good news! Ill post my full process for details and if anyone else has the issue. I went out and had some time today to work on the bike. Turning crank counterclockwise, from front of bike, right cylinder (left when riding) will rotate slightly under a full revolution from stopped point and stop right after TDC (used a dowel to see if piston was moving)

Left cylinder (right when riding) when going ccw (counterclockwise) or cw (clockwise) stops at TDC. Can do slightly under a full revolution in either direction starting from maxed out point on either side ccw or cw. Radiator fan will rotate each direction as well as fly wheel.

Decided to take off the valve covers and had a look. Unfortunately only the left hand one (when riding bike) can be taken off. A screw broke on the right cylinder and lower half is stuck inside so not sure how to tackle getting it off. Maybe a separate post or more research. So when I rotated the engine mechanically the amount I could (>1 revolution) I saw the exhaust valves opening but not the intake. Starting all the way ccw then rotating clockwise the valves close. Or vice versa if starting all the way cw. When going CCW from locked CW position valve spring goes up then stops with about half of the one revolution I can do left. So it stops moving then I’m able to turn another half rotation of the crank still. Assume this is just due to where the crank is stuck with respect to the process and nothing more. Not sure if this is just due to the amount I can rotate the crank or not. 4 stroke->two cycles-> roughly 1 rev of crank->piston going up and down then up again (exhaust portion of 4 stroke process) (if I’m right). Not very important just an observation.

So I imagine when the bike was able to turn over for a split second that was due to the engine rotating the amount it can then getting stuck after that one turn.

I also tried putting the bike in gear and rotating the crank manually. I could crank it as far as I wanted in either direction. Not sure how this freed things up. The intake ports on the valve cover I was able to remove did move but did a strange up and down motion for a duration of the rotation then stopped in the down position before the exhaust valves went up and down. I believe with the intake ports it’s just because I’m working against the springs, because when I held the crank carefully-still with the socket wrench they didn’t seem to move. The pistons, flywheel, and fan all rotated while doing this using the crank in either direction. Not sure why it'd rotate in gear but not in neutral. The wheel would not move at all when i would try to rotate that previously while in gear but was able to get everything to rotate freely with the crank.

This was without the clutch engaged. When pressing down the clutch and rotating the crank it’s the same and everything seems to rotate (pistons, valves, fan, flywheel). Back wheel also spins.

Decided to try to put the bike in neutral again and was able to rotate freely as much as I wanted in either direction. Not sure how putting the bike in gear, manually turning the engine, then going back to neutral freed it up past only being able to do one rotation of the bolt while in neutral...but it did. Put in the new solenoid, charged battery and it seemed to turn over fine. So I'm rather confused as to what would cause this to happen but luckily it seems fixed! Now onto cleaning the carbs....then hopefully it'll run.

If anyone has any ideas why this would happen this way it may help prevent it from occurring again in the future/make it a safer bike to ride feel free to weigh in. Thank you everyone for such excellent help and advice! Truly a great forum.
 

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I still believe it was your first thought on the matter, a little rust build up on one or both cylinders. I think it is just coincidence when you got the rust to break free. I don’t know this for a fact, just my hunch.
 

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Discussion Starter #26
The people who have already offered you advice know what they are talking about so I don't have anything to add about getting it to turn except maybe if you have access to an endoscope type camera you might have a look inside the cylinders through the spark plug holes but if you don't I wouldn't rush out to get one yet.

But welcome to the forum. Please add your location to your profile and your bike's model and model year to your signature so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).

And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old has had none of the maintenance necessary to keep it safe & reliable for a long time so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. 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). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) 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).

The best advice anyone can give you about customizing any vehicle is to get it safe & reliable in more or less original condition and use it for a while before you start making any changes so it can tell you what changes it needs to make it do what you want/need better. That approach almost always results in something you actually want to keep and use but making changes based on style or on what someone else (who may or may not really understand how the changes affect the way it works) has done often results in a piece of expensive yard art that you can't stand sitting on for more than a few minutes and might even be dangerous.
The people who have already offered you advice know what they are talking about so I don't have anything to add about getting it to turn except maybe if you have access to an endoscope type camera you might have a look inside the cylinders through the spark plug holes but if you don't I wouldn't rush out to get one yet.

But welcome to the forum. Please add your location to your profile and your bike's model and model year to your signature so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).

And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old has had none of the maintenance necessary to keep it safe & reliable for a long time so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. 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). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) 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).

The best advice anyone can give you about customizing any vehicle is to get it safe & reliable in more or less original condition and use it for a while before you start making any changes so it can tell you what changes it needs to make it do what you want/need better. That approach almost always results in something you actually want to keep and use but making changes based on style or on what someone else (who may or may not really understand how the changes affect the way it works) has done often results in a piece of expensive yard art that you can't stand sitting on for more than a few minutes and might even be dangerous.
Thanks Bob this is great advice and things I think most people wouldn't think about till they were done. I'm definitely worried about the safety of things and want to make a checklist of things to do before I deem it "road-worthy" If you know of any checklists or anything similar it'd be great to know but it sounds like the factory shop manual you suggested would have most everything I could need. Thanks again and best
 

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Discussion Starter #27
I still believe it was your first thought on the matter, a little rust build up on one or both cylinders. I think it is just coincidence when you got the rust to break free. I don’t know this for a fact, just my hunch.
The only reason I may believe that this wasn't the case is because when I was attempting to rotate after letting the oil/diesel mixture sit for a few days it didn't want to budge at all, nor would it today. When I put it in gear and turned it manually it moved instantly and with practically no resistance. I could be wrong but just my observation!
 

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Unfortunately only the left hand one (when riding bike) can be taken off. A screw broke on the right cylinder and lower half is stuck inside so not sure how to tackle getting it off.
If a valve cover bolt is broken, it won't hold the cover on. Remove the other bolt, and give it a tap with a rubber mallet. It's probably just stuck on by the seal. Then, replace that bolt.

So when I rotated the engine mechanically the amount I could (>1 revolution) I saw the exhaust valves opening but not the intake.
In a 4-stroke engine, the crank makes two revolutions per complete cycle. You won't see the intake and exhaust valves moving during the same revolution of the crank.

The intake ports on the valve cover I was able to remove did move but did a strange up and down motion for a duration of the rotation then stopped in the down position before the exhaust valves went up and down.
That's normal. All valves are closed during the compression and ignition strokes.

Not sure why it'd rotate in gear but not in neutral. The wheel would not move at all when i would try to rotate that previously while in gear but was able to get everything to rotate freely with the crank.
I suspect you started out in gear, then shifted into neutral. First gear is at the bottom of the shift range. Neutral is between first and second.

This was without the clutch engaged. When pressing down the clutch and rotating the crank it’s the same and everything seems to rotate (pistons, valves, fan, flywheel). Back wheel also spins.
The clutch is disengaged when you squeeze the lever, as it disengages the drive train from the engine. It's engaged when you release the lever, sending power to the rear wheel. If there's oil in the crankcase, there will be some amount of hydraulic friction in the clutch, which can cause the rear wheel to turn. This happens even when running the bike in neutral on the center stand, especially with cold oil.

I wonder if the hangup you were encountering isn't just the combination of valve spring tension, drive train drag, and cold oil in the crank case.
 

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BTW: When referring to parts of any vehicle it is usual to refer to left and right relative to the operator's position. In other words, the brake lever and brake pedal are on the bike's right side and the clutch lever and gearshift are on it's left side. Even when the engine is removed and you are looking at it from the front the cylinder that would normally be on your right when sitting on the bike is still the right cylinder.
This becomes important when you do things like adjusting the valve clearances and need to adjust the left ones when the L (left) timing marks are visible in the inspection port.
 

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1978 CX500, 1982 GL500 Silverwing Interstate, 1980 CX500 Custom
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BTW: When referring to parts of any vehicle it is usual to refer to left and right relative to the operator's position. In other words, the brake lever and brake pedal are on the bike's right side and the clutch lever and gearshift are on it's left side. Even when the engine is removed and you are looking at it from the front the cylinder that would normally be on your right when sitting on the bike is still the right cylinder.
This becomes important when you do things like adjusting the valve clearances and need to adjust the left ones when the L (left) timing marks are visible in the inspection port.
All good stuff, and perfectly true.

Unless you happen to be working on a British bike (and maybe some from other countries too), as before 1975 the gear shift was on the right, and the brake pedal was on the left (when facing forward...) :) Also true for some east European bikes...

It's very confusing to me, as my muscle memory takes over in some circumstances when riding, and I go to shift gear - but find I am braking!!

Cheers!!
 

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If a valve cover bolt is broken, it won't hold the cover on. Remove the other bolt, and give it a tap with a rubber mallet. It's probably just stuck on by the seal. Then, replace that bolt.


In a 4-stroke engine, the crank makes two revolutions per complete cycle. You won't see the intake and exhaust valves moving during the same revolution of the crank.


That's normal. All valves are closed during the compression and ignition strokes.


I suspect you started out in gear, then shifted into neutral. First gear is at the bottom of the shift range. Neutral is between first and second.


The clutch is disengaged when you squeeze the lever, as it disengages the drive train from the engine. It's engaged when you release the lever, sending power to the rear wheel. If there's oil in the crankcase, there will be some amount of hydraulic friction in the clutch, which can cause the rear wheel to turn. This happens even when running the bike in neutral on the center stand, especially with cold oil.

I wonder if the hangup you were encountering isn't just the combination of valve spring tension, drive train drag, and cold oil in the crank case.

Randall, Based on what I read, I would say the starter or starter clutch bound up. Doing the steps he did, especially with the transmission freed it up. If so, The issue could have just been temporary, or he may see it intermittently again from time to time. He may want to pull the starter and quickly give it a lube or hit it with wD40 or silicone spray. I had this happen on a Merc 175 EFI. After hitting the moving parts of the starter with some silicone spray, no further issues.

I have not seen pics, but sounds like he may have a nice low mileage cx.

Glad you guys were able to work through it. It was fun to read the thread.
 
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The starters on these bikes don’t have much in common with an outboard motor. Definitely less moving parts. Not sure what part you would be spraying a lubricant on. The end of the starter is constantly lubed with motor oil, that’s why there is an o ring on there.
 

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All good stuff, and perfectly true.

Unless you happen to be working on a British bike (and maybe some from other countries too), as before 1975 the gear shift was on the right, and the brake pedal was on the left (when facing forward...) :) Also true for some east European bikes...
I was referring to the bike he actually has.
 

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Randall, Based on what I read, I would say the starter or starter clutch bound up. Doing the steps he did, especially with the transmission freed it up. If so, The issue could have just been temporary, or he may see it intermittently again from time to time. He may want to pull the starter and quickly give it a lube or hit it with wD40 or silicone spray. I had this happen on a Merc 175 EFI. After hitting the moving parts of the starter with some silicone spray, no further issues.

I have not seen pics, but sounds like he may have a nice low mileage cx.

Glad you guys were able to work through it. It was fun to read the thread.
I had thought of the starter being full of rust, but forgot to mention it.
Then, we got onto hand cranking. If the starter impedes that, the problem will be in the starter clutch in the flywheel. Could happen with old, thick oil, I imagine.
 

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Discussion Starter #38
Randall, Based on what I read, I would say the starter or starter clutch bound up. Doing the steps he did, especially with the transmission freed it up. If so, The issue could have just been temporary, or he may see it intermittently again from time to time. He may want to pull the starter and quickly give it a lube or hit it with wD40 or silicone spray. I had this happen on a Merc 175 EFI. After hitting the moving parts of the starter with some silicone spray, no further issues.

I have not seen pics, but sounds like he may have a nice low mileage cx.

Glad you guys were able to work through it. It was fun to read the thread.
Thanks for insight. If problem presents itself again I'll start there or go ahead and hit with some lubricant anyway! Only 1500 miles on the bike :)
 

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Thanks for insight. If problem presents itself again I'll start there or go ahead and hit with some lubricant anyway! Only 1500 miles on the bike :)
What are you going to hit with lubricant? The gear on the nose of the starter? That won't accomplish anything except maybe introducing a lubricant to the motor oil that will cause your clutch to slip. I would be surprised if your motor locks up again anyways so maybe a mute point.
 
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