I am blessed with a cylinder head that has no broken fins. Unfortunately, it has a significant amount of rust and thinning of the fins. I am reluctant to blast clean or caustic soak it for fear of damage to the fins, even if I remove all the rust they may be too weak to survive much further rusting.
What is a good finish to stop further rusting and help prolong the life of the head? I was thinking of a phosphoric acid bath. Vincent

Bead or vapour blast might be a way forward Vincent, I had mine beaded before, did a nice job too

It's not an aggressive format compared to sand blast which can sometimes be severe on some surfaces

That or an old fashioned wire brush and a reprint is a option

Jo'b

email (option): Jonnyob1@googlemail.com

I did mine years ago with a simple steel brush en spraying heat resistant paint. Didn't even take it apart.
It will be all right as long as you dont't leave your bike out in the rain.

easiest way to get rid of any rust without removing metal is to use a solution of household washing soda (not caustic) a battery charger and a sacrificial anode (a lump of old iron).
mix up solution in hot water, in large plastic tub or bucket, immerse head and old iron making sure they do not touch one another then connect 12v battery charger negative to head and positive to anode and leave for 24hrs or more.
(make sure leads from charger don't go into solution otherwise they will rot away,i use some old welding rods to connect)
this method works every time,myself and Kent Shaun have done this on M20/1 heads and barrels (check out julys edition of real classic to see end result)after rust has been removed either coat in oil or paint with HT paint