Seized engine

[Ninjas4m83]

Has anyone tried this using diesel and mystery oil?
https://youtu.be/fxXEpRRj-fg

I've taken the heads off both sides and let it sit in Screwfix penetrating oil for days as well as doing the same with paraffin. I've also tried pushing it in neutral then popping it out into 2nd with no luck. I would have preferred to put it in 5th gear to do this but for some reason when I pull the clutch the bike stays in gear. I'm not sure why it's doing that? I adjusted the clutch cable to see if that makes a difference.

The engine wont turn during hand crank and it has a single click on the starter button (I've ordered a new relay). I'm planning to clean the kill switch and starter button contacts next. I've taken the starter motor off and cleaned up the contacts along with the earth cable. I'm using a brand new MotoBatt battery.

Before taking the engine apart to look at the starter clutch is there anything else I can try to free up this engine?
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1980 Honda CX500

[Easy-X]

If you're in a "ah! f*ck it" mood you could undo the bolts holding down the barrel(s) [are they two separate barrels or is it all one piece?] so you can create a little bit of "slack" with the cranks. See if can turn the gearbox a little bit (push in gear, turn clutch basket by hand, that sort of thing.) If the gearbox isn't completely seized as well then stick some bits of wood between the barrel(s) and the bottom end then see if a light tap (rubber or wooden hammer preferable!) on the top of the pistons will free them.

WARNING! High likelihood of bolloxing up the top end so budget for new cranks, barrel(s) and pistons before attempting drastic manoeuvres. Also, you'll probably need to take the engine out depending on frame clearance.

If the gearbox is also seized it'd be easier to do a complete engine swap.

What bike BTW?
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[martin734]

If it is seized then dismantling it is going to be needed anyway, but the method I have used to free seized pistons is to place a block of wood on a piston that is not at top or bottom dead centre and then hit it with a lump hammer until it starts to move, adding a few drops of 3in1 oil as it starts to move.
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Current bike: ST1100 "Big Red"

[Pete.]

[Riejufixing]

[Ninjas4m83]

Sorry forgot to say it's a 1980 cx500. It's a free bike I picked up from a friend in the hope of rescuing it. Not much history about the engine other than he suspected a possible faulty starter clutch but I think the starter clutch is probably fine. Apparently a symptom of starter clutch is the starter spinning but not engaging. My starter just clicks once.
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1980 Honda CX500

[stinkwheel]

So it won't turn with a spanner/socket on the end of the crank? Not at all? No movement either way?

Can you see any damage to the pistons/bore/valvegear?

Usually for a piston to be seized, there would either be a fuckton of corrosion in the bores or some sign of damage. That's where your diesel/oil/hammering blocks of wood would come in. That said, if it's seized a piston, you're looking at a full strip anyway. The barrels are integral on the cases on a CX as I recall so any bore work would involve crank removal and if the piston has seized, it'll need honing at a bare minimum.

I've never worked on one so not sure of stripdown procedure but if there is a seized piston, you might be able to unbolt the conrods and wiggle the crank out, then you could drive the piston down without risking bending a conrod. Bet it's tight as hell in there though.

If there's no visible corrosion/damage, it's unlikely to be a piston seizure so you then wonder if it's tangled a chamchain/bent a pushrod or somethings jammed in the primary. Only way to find that is to have a look. Be something pretty severe to lock it up totally solid.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[A100man]

I take it we're ignoring the YouTube clip on the basis that it's utter nonsense..
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[stinkwheel]

[Easy-X]

Ah well, disregard my advice - the CX engine is an entirely different beast to most bikes.

If the bike as a whole is in reasonable condition then it's well worth putting the effort in to get it going. Very interesting design, IMHO
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[stinkwheel]

We really need WD forte in this thread, he knows his CXs.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[A100man]

[Tankie]

I had a CX that the engine seized on a run one day, the then owner asked me to pick it up, It was then dumped in the back of his garage till after his death.
His widow gave it to me so I then went through it trying to find why it committed suicide , first all the timing tensioner rails were shot, second, all the internal o rings from the oil pump right through the crankcase had all gone brittle and hard , the big ends had failed and the pistons seized in the bores.
My conclusion was that the engine had bleed to death because of all the failing o ring joints resulting in a loss of oil pressure.
The pistons had to be driven out with a block of wood and hammer, the engine was rebuilt and the bike was sold off in a running condition
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Always learning, everyday is a school day