Vintage Motorbike converted for rail use

Do we have anyone knowledgeable about vintage motorbikes here?

What motorbike is the pictured rail vehicle based on?

The photo was taken a few days ago at the Welsh Slate Museum, Llanberis, by my colleague Andrew Waldron. It is not a new discovery, it has been known about for decades, but it occurred to me that we don't seem to know what machine it is based on. It was used as a runabout at the Oakeley Slate Quarry near Blaenau Ffestiniog. When the quarry closed circa 1972 it was rescued and has been in the museum since 1982.

There is a photo of it in the slate quarry here: https://museum.wales/collections/on...e2671ebf71ea/Oakeley-slate-quarry-photograph/

 

What a maginifcent contraption! Could that be a 2-stroke JAP engine (looking at shape of cyl head)? Those were as often found on lawnmowers as owt else. I wonder if the hexagonal tube is a toolbox or a fuel tank?

 

Royal Enfield. (Looking a bit Royal Oilfield!). Combined Petrol and Oil tank with (I think) manual lube pump. State of the art c.1914.
Pat

 

Ye gods .... a good 10-15 years older than I'd suspected.

 

1914 was a guess, 1st World War Triumphs were similar.
I don't know whether the crankcases tell us that it was a RE engine, or a. n. other with their logo. They used JAP and Motosacoche engines early on. (Unfortunately I'm no longer a member of the owner's club, so can't see all the good stuff on their website.)
Pat

 

I'm not a Royal Enfield expert but I think that engine to be from about 1925.
Is it not rather like this?
https://www.bonhams.com/auctions/21136/lot/342/?category=list

 

making due allowance for the 'customisation*', I think that you are right.
Pat
*Designed in a pub, built in a shed.

 

Thank you for your replies. Royal Enfield it is. I've been looking at such photos as I can find on line and cannot match that fuel/oil tank shape with that engine. So, a prewar fuel tank (and presumably frame) with a post war engine? A bitsa in other words?