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I suspect the answer is no but can you get enough room to change the o ring without engine out of the frame? The bike is a 40 Jupiter

Thanks

Mike

Typo 450 Jupiter

Yes, the cylinder head can be removed without removing the engine from frame.
It's a nice thing about our bikes.
The 4 long cylinder/head retaining bolts will pass upwards, either side of the main frame tube.

Care to not alter cam timing when doing this though, to avoid more work to re-time.
Suggest move the piston to TDC of a compression stroke, so no tension on valve springs.
Then remove kickstarter, to avoid accidental movement of crankshaft while working.
Tank, seat, exhaust system, maybe carburettor are taken off first.
Lift head off complete with bevel shaft tube, when you'll see the semi-circular coupling.
When replacing, don't trust the O-ring in the lower housing to keep oil inside, even if renewed. They don't work, vibration defeats it, as you'll likely see by the fretting at the bottom of the tube. Clean with petrol, dry and apply a sparing amount of clear silicone sealant on the tube as you assemble, then wipe off excess before it goes off. You won't get any in the engine as long as you don't use too much sealant.
This can all be done within an hour.

Thanks for that I was hoping not to have to remove from frame to change a 40p part!!
Cheers Mike