Vintage Thing No 139.1 - Raven 4WD

The Raven 4WD in action

I was strolling nonchalantly round the paddock at Wiscombe the other day...

No that's not right. Let's start again.

I was running round the paddock at Wiscombe in an over-stimulated state of febrile excitement caused by all the amazing rolling sculpture when something stopped me dead in my tracks.

It was a Hillman Imp gearbox. Not only that, it was upside down and attached to some wheels. This could mean only one thing - it must be in some sort of mid-engine device.

As my senses struggled to take in what they were seeing, I realised it was connected to no Hillman Imp engine This was no Vixen! Instead, there was a crossflow Ford running twin 40s.

Then things started to get really weird. There was an extra alloy case on the back of the imp box that ran to the nearside and sprouted a shaft that ran forward. My mate Pete Low was quicker on the uptake than I was.

"It's got four wheel drive," he said. "Look, it says so on the airbox - Raven 4WD!"

In all the excitement it seems that I'd forgotten how to read.

Unfortunately there wasn't anyone to ask about it so on that occasion all I could say about it was this.

When I went to Wiscombe this year I was hoping that the Raven 4WD would be there again and that I would have the chance to speak to its owner/driver/creator.

It was and I did!

James Dean (no not that one) campaigns the Raven 4WD these days but it was built by his father, David Dean, in 1970 for use on their local hillclimb of Gurston Down. The Raven 4WD was put away in 1973 with a jammed drivetrain and left for many years. By the time James was in a position to revive it, some parts had gone missing and David had died. Consequently, some technical details on the family's heirloom were sadly lacking but it was essentially as we saw it with a square tube frame, home made suspension and a 1600 crossflow Ford sporting a pair of DCOE Webers.

Look! It says Raven 4WD on the side

James told me that the original layout was front engined and two wheel drive before becoming mid engined with two driven wheels at the back. Four wheel drive required a radical re-work and a whole new range of development issues.

Note the Imp box and the transfer case on the back end

I asked him to take me on a guided tour of through the drivetrain and he obliged. The Ford bellhousing is mated to the inverted Imp gearbox that initially attracted my attention last year.

More Impishness goes on up front

Drive is taken from the back of this box via a transfer case that powers a propshaft that runs forward along the left hand side of the powerplant and cockpit. This connects to a second Imp box at the front that drives unequal length dirveshafts, as a consequence of the box's offset positioning. Mini hubs and discs are mounted on home-made suspension arms featuring inboard shock absorbers.

Here you can see the gearchange mechansim. The driveshaft is hidden in this view by a square tube chassis member

He found the transfer case on Imp box number one contained out of mesh gears and described the original sheet steel affair as a "biscuit tin"! The extra casing simply wasn't rigid enough so he made a new one out of solid alloy and new 1:1 gears to live in it. He also had to get a special final drive ratio sorted out for the front gearbox. Now that the same sized wheels all turn at the same speed, the handling is much better...

Home made front wishbones

When he dragged it out of its resting place, the Raven 4WD had smaller Mini wheels at the front but it now sports the same sized wheels all round. This ensures that all wheels turn at the same speed - James discovered that initially the front wheels turned more quickly than the the rears.

In fact, most of it was home made and made well

Another improvement was to remake the adaptor plate between the ford engine and the Imp box. James discovered that the old plate put the engine and box out of alignment, which caused copious tears of EP80 to flow. A new plate that lowered the input shaft for the inverted Imp box got the alignment right and cured the leak.

Two bright spots on the diveshaft show how close everything is

The front box still retains synchro so James can select four wheel drive on the move if he so wishes but on a hillclimb there's usually enough entertainment in the cockpit of the Raven. Running in just two wheel drive yields 15 bhp more than when in 4WD so, depending on conditions, he usually chooses one mode or the other before setting off.

No rubber doughnuts on the back

His latest mod is stronger rear drive shafts. In four wheel drive, the old ones behaved but in rear wheel drive only they span within their collars - although not enough for any serendipitous friction welding.

Under power, the propshaft flexes and touches the clutch bellhousing but only slightly and not enough to worry about.

However, at the front Imp rubber couplings provide drive and articulation. 

For me,  it was fascination at first sight with the Raven. The Imp box hasn't wilted under the strain as you might think and the car must take a certain amount of technique to drive effectively.

Quoth the raven, "Never more!"

 

So perhaps now you can understand why I was "raven" about it so much as soon as I saw it...