Gn Thunderbug -

PaulSands · 27 Feb 2006, 13:47 (Ref:1532511)

The Mark Walker GN Thunderbug combo has to be one of my favourite at the moment. How somebody can throw what effectively looks like a boat with wheels around like he does amazes me. I noticed how rapid he was at the Birkett Relay and he showed it again at the Pomeroy Trophy this past weekend. Full on commitment , brilliant stuff

**John Turner** · 27 Feb 2006, 14:06 (Ref:1532524)

I'm with you all the way on that, Paul. Great picture (that's clipping the apex alright!) of a car and driver combination which provide great entertainment value. No action, I'm afraid, but one taken at the VSCC Silverstone, April, last year, showing a bit more detail of this extraordinary machine:-

robert77 · 27 Feb 2006, 15:43 (Ref:1532569)

Great photo Paul.

I've done a small write-up about a few of the GN cars as part of a chapter in the book I'm writing at the moment, but this is one I've never seen before.

Chris Roden · 27 Feb 2006, 16:38 (Ref:1532597)

Agreed, Mark and Thunderbug are huge value.

IIRC, the engine is a 2.1 litre V twin based on an early Riley and, being long stroked, you can hear each cylinder firing independently, hilarious

Mark usually drives the car to and from events as well, takes a special breed to do that, particularly with the temperatures we had on Saturday.

Mark is just as entertaining in his Grand Prix Peugeot too.

robert77 · 27 Feb 2006, 16:49 (Ref:1532599)

I know from seeing Spider, Spider 2 and Wasp what the V-twin J.A.P. engines sounds like. It's amazing to think how fast they still are even though the aformentioned are over 70 years of age and still manage 70mph plus up Shelsley Walsh.

relativtortoise · 27 Feb 2006, 17:56 (Ref:1532630)

Mark built the car about three years ago from as Chris says a Edwardian Riley V Twin engine but then added cylinders barrels from an aero engine to increase the capacity enormously judging (correctly) the Riley bottom end could cope.

The principal Walker racer is a Panhard and not a Peugeot and that one is a real original as opposed to the Monarch and Thunderbug which are newer creations from his motorhouse.

RT

**John Turner** · 27 Feb 2006, 18:07 (Ref:1532637)

Yes, indeed, Thunderbug is now 4.2 litre, and in fact that is what it says on the yellow banding on the side at the front.

robert77 · 27 Feb 2006, 19:18 (Ref:1532671)

4.2 V-twin in a little thing like that!!! Bloody hells bells I bet that shifts somewhat.
Bet it don't do the old eardrums anygood either.

PaulSands · 27 Feb 2006, 22:29 (Ref:1532772)

It looks like it shifts like snow off a hot shovel, I was constantly amazed during the Birkett juts how often it appeared and the amount of cars it juts blasted right past. I think the way its driven helps, on Saturday every time it entered the Luffield complex it was right on the edge, always looking like it was going way too fast, especially for such spindly wheels. I love the idea that its a one off home creation...very Caractacus Potts

johnh875 · 27 Feb 2006, 22:30 (Ref:1532773)

Wow that looks impressive, it always great to see cars of that era with unfeasibly large engines! I mean, it looks like a Morgan but has an engine 4 times the size - fantastic

I was reading about a 1908 Benz that used to live here in Melbourne many years ago, it was a variation on the GP cars with an engine over 18L capacity, and only 4 cylinders. The mind boggles!

ranoff · 27 Feb 2006, 23:11 (Ref:1532809)

The crankcase is from a c1909 Riley, the cylinders are from a WW1 era radial aero engine. There are adaptor plates under each cylinder to couple up the somewhat different fastener circle diameters and sizes. With only two forward gears at the last count its not too quick off the mark but pulls forever. Mark will drive the beast to a meeting. Its not the only lunatic machine the Walkers have been involved in building from period parts. My favourite is the GN Vitesse Cyclecar that they fitted with a Curtis OX5 V8 aero engine of around 8 litres. Duncan Pittaway drives this with enormous verve edging towards inspired lunacy. Then there is the similarly powered Monarch, the Parker GN with a large 4 cylinder De Havilland or Blackburn Cirrus aero engine and the list goes on. The Walker speciality is to build or rebuild a car so you cannot tell its been touched. They must have a shed full of old paint, stacks of previously used aluminium sheet and various bits of GN cyclecars and chain gang Frazer Nash. Mark has been seen out shopping for bits in Rugby in the Thunderbug.

johnh875 · 28 Feb 2006, 03:56 (Ref:1532938)

There is a 1927 5000cc Cirrus-powered car out here too ranoff, it also looks very authentic although I understand it has also been built more recently. It normally appears in regularity events rather than races.

relativtortoise · 28 Feb 2006, 07:59 (Ref:1532995)

The Parker GN is diiferent in that it is a period constructed car. Mark acquired it roughly as you see it now from David Thirlby he told me. It had not run with that engine in it though and Mark discovered that the only way for the clutch to operate involved the whole gearbox moving backwards!

BTW I am not sure that it was vintage or PVT period constructed.

RT

jamesholland · 28 Feb 2006, 12:45 (Ref:1533204)

I believe the Parker GN was built as a special pre war, but I stand to be corrected on that.
David Thirlby owned it for may years and it was his idea to fit the Cirrus aero engine and mark Walker finished the project making it the very effective racing car it now is.

The cylinders on the Thunderbug are from a WW1 Salmson radial.

Chris Roden · 28 Feb 2006, 14:43 (Ref:1533277)

Quote:

Originally Posted by relativtortoise

Mark built the car about three years ago from as Chris says a Edwardian Riley V Twin engine but then added cylinders barrels from an aero engine to increase the capacity enormously judging (correctly) the Riley bottom end could cope.

The principal Walker racer is a Panhard and not a Peugeot and that one is a real original as opposed to the Monarch and Thunderbug which are newer creations from his motorhouse.

RT

Quite right, Mark's Grand Prix car is a Panhard, apologies

zefarelly · 1 Mar 2006, 10:38 (Ref:1533836)

The car runs nearly as much positive camber as Peter has managed to squeeze negative from his Capri!

BugEyed · 7 Mar 2006, 19:59 (Ref:1539769)

Quote:

Originally Posted by ranoff

The crankcase is from a c1909 Riley, the cylinders are from a WW1 era radial aero engine. There are adaptor plates under each cylinder to couple up the somewhat different fastener circle diameters and sizes. With only two forward gears at the last count its not too quick off the mark but pulls forever. Mark will drive the beast to a meeting. Its not the only lunatic machine the Walkers have been involved in building from period parts.

That Mark is a hero of the VSCC is beyond doubt. As you say, Mark has "created" a number of very enjoyable specials. However, myths have grown up around the source of some of the parts. The crankcase, crank and rods in Thunderbug aren't original pre-War (except Iraq!

) parts whatever the rumour may be.

Mark's latest creation (a pastiche of a 1914 GP Mercedes) has yet to find the performance of his other creations, but like the others appears ready patinated.

Duncan

Chris Roden · 8 Mar 2006, 08:52 (Ref:1540083)

Quote:

Originally Posted by BugEyed

The crankcase, crank and rods in Thunderbug aren't original pre-War (except Iraq!

) parts whatever the rumour may be.
Duncan

So come on Duncan tell all, where do the bits originate?