Vintage Thing No.105 - Tarkus radial engined trike

The most amazing of Jake Challenger's trikes is for sale (Photo : Bonhams)

As I mentioned earlier, Jake Challenger created a series of special three wheelers named Tarkus after the ELP track and the last of the series (I'm tempted to say latest for you never know) is this device featuring a 3 cylinder radial engine of his own design that uses BMW R100 barrels and cylinder heads.

Stable as a very stable thing, if you're going to leap aboard Tarkus be sure you're wearing split screen goggles and a sheepskin jacket (Photo : Jake Challenger)

I had an e-mail from Jake this weekend to say he's selling it and having spoken to him again and found out some more details I can divulge that it's in Bonhams Motorcycle auction at Stafford on 29th April. Unfortunately, his wife Cynthia has had a knee replacement and can no longer get in Tarkus.

The standard BMW components look like they should've been made for use in a radial 3 cylinder engine (Photo : Bonhams)

The engine is what makes it so special. The crankcase is machined from solid and contains a single piece crank, all made by Jake in his extensive workshop. It uses three standard BMW barrels, conrods, pistons and cylinder heads so spares are not a problem. The bore and stroke of 94 x 70.6mm gives a cubic capacity of 1470cc. Because of the layout of the engine, Jake used a dry sump lubrication system featuring three (again) BMW oil pumps, two to scavenge and one to provide pressure. I remember him saying that on start up the two inverted cylinders burnt a little oil that had drained into the combustion chambers but this is just what flat twin Beemers do when you leave them overnight on their side stand.

There's something of a taxi-ing aircraft about this, the ultimate Tarkus (Photo : Bonhams)

Following on from earlier incarnations, this Tarkus uses a five speed Citroen GSA gearbox and the 15 inch alloy wheels are also from a GSA (the limited edition Pallas SE no less) but with the outer design machined off to resemble moon discs as beloved by salt lake record breakers in the fifties.
The chassis is an aluminium honeycomb monocoque and Jake made his own uprights for the front suspension. He designed the equal length wishbones to allow completely flat cornering with no roll and used a Watt's linkage on the front. Both sides compress a single horizontal adjustable Honda shock mounted behind the engine. Jake also incorporated fully adjustable front suspension geometry.

Tarkus has a generous luggage rack for overseas touring (Photo : Jake Challenger)

At the rear is a rising rate swing arm inspired by the geometry of big Kawasakis but single sided like a BMW to allow a common size of wheel to be used throughout. There are discs all round, those at the front being the standard Citroen inch inboard ones featured on the GSA gearbox.

Tarkus has a very comfortable leather trimmed cockpit (Photo : Bonhams)

This Tarkus is fully road legal and recently recommissioned, although not MOTed at the moment - Jake might put a ticket on it before the auction if he can. Jake has driven over 27,000 miles since he built Tarkus in 1997, most of it in extensive touring. Performance is best described as prodigious.

Another view of the unique but highly practical engine. (Photo : Bonhams)

Guide price is £5,000 - ridiculously cheap when you consider the sheer artifice in its creation.