No. More likely worn guides, or valve stem seals. Smallbore heads didn't have proper valve seals, but 1275 ones can be fitted. Replacement guides have grooves fo seals.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

a head rebuild is probably a good idea, but blue smoke at idle can be caused by glazed bores and worn out oil scraper rings. Even though compression is good, it can still have worn rings

Try checking your compression first thing in the morning, and then again after the engine has been driven

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did I tell you that I won a trophy?

Would a wet and dry compression test achieve anything ?

only the seats... when modifying a head for unleaded the machinist bores out the valve seat area and fits a hardened insert

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did I tell you that I won a trophy?

You have to take the head off and have a look

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Lillee - 1969 Morris Mini K

Or take out a spark plug and use a $20 endoscopy camera on your phone.
Way easier and cheaper. Also good for finding the TV remote under the couch.

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Too many cars, and too little time.

I have a $7 ebay endoscope for my phone. It works well for checking bore and piston condition but you need a good mirror attachment on the end to see the valve seats.

especially when they're covered in soot & buildup - seat inserts are really hard to see unless you know what you're looking for and they're clean...

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did I tell you that I won a trophy?

I was going to say, endoscope, you guys make it sound so easy! When my head came off the exhaust valve, seat and port was completely covered in 1/2mm of black soot. There's no way you're going to be able to spot a hardened valve seat insert... unless your endoscope comes with a scraper attachment to scrape some carbon buildup


Coincidently a new head gasket is about $20

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Lillee - 1969 Morris Mini K

The machined edge of the insert. The trouble is, a standard head is often machined there and looks similar.
You really need to pull the valves to check inside.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Yeah I thought of that but in theory you could turn the engine over I gear so the valve is open and stick and endoscope in there to see the seat, but as I said it would be covered in carbon as the OP's engine is already blowing blue smoke, it would caked up big time

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Lillee - 1969 Morris Mini K

Don't believe me? Here's only a small portion of what came off my head and mine wasn't blowing any smoke or even using up oil.

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Lillee - 1969 Morris Mini K

Here is a before and after of a 12G940 I did on my last car.




Here is a close up of the inserts for the exhaust valves. The seats standout when it all cleaned up but you need a good eye if there is carbon and soot.



I would be looking at pulling the head. It is a pretty easy and cheap job on a mini and you can get so much information about your engine condition from doing it.

But getting back to your original question your valve guides are probably worn and the valve guide seals have probably gone hard and are not holding tension on the valve stems.