Quite a contraption...There have been various attempts at racing the Square Four, both in this and other early forms and the later '4 piper' versions...
One used to be campaigned with a supercharger fitted as well...
However, although quick the Four wasn't reliable when tuned and blown head gaskets were pretty common I gather (along with other problems)...
I owned a pretty much standard Mk2 for a few years and of all the bikes I've had and sold it's the one I really regret getting rid of...
Smooth, a beautiful sound and with genuine 10-100mph performance in top gear (as often quoted in Ariels publicity) it also has the additional interest of being a unique engine layout....
Below is a picture of my '53 example in the snow...I thought it would be a handful in these conditions but the exceptional pull at low revs and low center of gravity made easy work of winter conditions.....
Fitted into a featherbed frame the Mk2 certainly looks the part but the engine is best left unturned in my opinion....Ian
email (option): ian@wright52.plus.com
A friend of mine had a 1000cc square four with spare engine and parts, it wasn't all original. He offered it to me for £1000 years ago, I probably should have bought it 
I've never ridden one either.
I quite like the OHC on this ebay bike, someone's done a lot of work on the engine. It's a shame they didn't take the same care with the rest of it. I wonder what it goes like
email (option): horror@blueyonder.co.uk
The OHC Sq4 was reputed to be quite fragile, although I believe one at least was supercharged for Brooklands use.
I seem to remember that the mainbearings were a problem to replace being of some very weird size.
His memory is dodgy though, I dealt weekly with Pratts back then, who were not trading till the late 1970s, although there was a bike shop of the old fashioned kind there beforehand, which I also dealt with now and again.
Maybe it was him he bought it from, he sold tat.
Personally I think that bike is a good source of spares, nothing else.
chacun a son gout and all that.
I have a photo somewhere of an ohc Sq4 'chopper' in Spain which was rougher than this one.
But heres one I did earlier.................
This is the only wartime square 4 photo I could find, not doubt impressed from a civilian during the occupation.
email (option): stinkypete80@hotmail.com