I’ve just been given 1948BSA Single 600ccand would love help restoration,either as a trike or back to normal it is painted military green ,
Any body got any thoughts or an any body help?
                                                                                                                                                                             

worth a lot more put back how it should be                                                                                                                                                                             

have a word with the vintage bike club                                                                                                                                                                             

If it's the M21 side valve model. I had one over 40 years ago. VERY reliable. I chopped it. Big mistake, leave it original material..                                                                                                                                                                             

You could do worse than PM GHW. He's a bit south of you, but knows his BSA stuff.

There are several BSA specialists in the midlands...parts are easy to acquire, and support for the whole range is immense.
                                                                                                                                                                             

Don't paint it don't polish it just get the motor sorted with correct parts and running right. Brakes and bearing on the wheels and steering head and correct tyres. The rest leave as is.                                                                                                                                                                             

Please don't trike it! 🙏                                                                                                                                                                             

Wotcha.

Sorry about the delay - just got back from France ( and eye surgery yesterday )

BSA M21 eh. Speed, power, economy, braking, . . . you'll have none of those. What you will have is reliability. Count on having to grind the exhaust valve back in every couple of years. You'll know when to do it - the bike will get slower and slower. Engine and gearbox bits are easy to get, tinware not so much.

Riding it will teach you how to leave a good braking distance from the vehicle in front. Don't be alarmed if the exhaust port glows red at night - they all do that sir. I'd probably change the carb if you intend using it a lot - a 26mm Mk.1 Amal Concentric works well.

In short - ride it and enjoy it.

Have words with Peter Tipping at Mersey Motorcycles in Bootle. Old-school corner bike shop of a type that's rapidly vanishing, and what he doesn't know about ex-WD British bikes isn't worth knowing.
                                                                                                                                                                             

Absolutely leave it as is where possible , as said leave the age on the bike once removed it's gone and never replaced.
M21 are very reliable but make sure you use a good mineral oil like Silkolene Donnigton 40 and change regularly. It will spit from the crank breather onto the chain area especially if left to wet sump.
If stood one thing to really check on a 48 would be the forks. They have a number of grease points and check carefully for play in all of the cross bushes they should pivot under brake loading but not lock or knock. If bad it will be like riding a kangoo hammer
Be careful of rear stand also castings can break on the back of the frame.