I guess it varies alot on condition and if its marinised or straight out of an old bus, quite often they appear on ebay and boats and outboards, I want a Gardner single to have in the workshop as a generator!
How old? I worked on a large yacht fitted with a Gardner 6LX in the 1980s when they were still standard on double decker buses and our local bus garage sold all the spares. Don't recall a 5 cylinder version. The 8LX was similar to the 6LX, just a couple more cylinders.
I have a Gardner 6LW in my fishing vessel. Still all original except for the water pump and generator. Don't see many 5 cylinder versions about although I looked at a fishing boat 15 years ago I was considering, and it had the 5 cylinder version. There are a few large yachts about with the 4 cylinder version.
Locally there is a 6LW with gearbox for sale for 1500 dollars. See them and 6LX for sale occassionally. Parts are available but things like nuts in Whitworth thread are hard to come by.
A marine 72 hp 5LW would be worth a goodly sum. If you wanted to find a buy-in trade value call Paul Gardner Engineering; nothing to do with the original company, just a family connection. Perhaps the word "just" is "unjust".
As a complete guess I'd say a good marinised second hand engine with a gearbox seen running might be £5k, but it is only a guess. Rebuilt must be double that. However boatsandoutboards currently showing a pair of 6LW marine engines with gearboxes at £2,500 each, a wreck the same for £500, and a 3LW for, (WAIT FOR IT), £6,500. A tad ambitious perhaps.
Thanks, John, I actually hadn't realised that they did 5 cylinder engines.
The reason I was asking was that I had been looking at an old fishing boat that had one and was trying to give myself reasons to go ahead and buy the boat. The amount/cost of work needed on the hull and the availability of suitable hard-standing locally has pretty much put me off now.
Regrettably many of those remaining exist in Africa and Greece now! where they make bits and somehow manage to keep them going!very much favoured there.