Locost 7 4×4 Front Propshaft

OK, so it’s been a while since I did anything in the garage. During the last 7 months, the only thing that has happened on my Locost 4×4 is dust and rust. Part of this was down to declining health and being out of work. Most of it was because I knew the next few tasks were going to be real nightmares.

Whilst making the stainless headers, it became obvious that the front propshaft arrangement might need some serious attention. What I had mocked up a couple of years ago, now wanted to occupy the same space as the starter motor, the engine mounts, the steering, the brake pedals, the gearbox, the exhaust
…. well you get the picture.

Locost 4x4 Front Propshaft

Locost 4×4 Front prop shaft

It was probably because of this particular, possibly disastrous blunder that I had not felt like doing much on the car. However, a chance bargain internet auction had returned several 1960’s Volvo Amazon prop-shafts.  There were various lengths for less than £10, so I felt like experimenting.

The main body of the gearbox is from a 4×4 Sierra Cosworth, whilst the bell-housing is from a Rover 3.5 P5B automatic. On the Cosworth there is a single short front propshaft linking to the front differential. The differential is mounted low down on the side of the original 2Lt sump.

Locost 4x4 mt75Locost 4x4 Sierra-Front-Propshaft-CAD

Building a 4×4 Locost is not easy, I wouldn’t recommend it to anyone.

Due to how low slung this car is, the 19″ rims and the positioning of the wheels relative to the engine (50/50 weight distribution). The differential on my car is 1metre forward and 30cm up compared with a Sierra. This means the propshaft needs to be in 2 pieces, with a central UJ to allow it to travel around the engine.

On the standard Sierra, one UJ is solidly bolted to the front differential, where as the rear is a splined shaft that slides in and out of the gearbox as the transmission moves and rotates.

This is where the problems start. My new central UJ needs to be solidly fixed to the chassis. The front section does not need the ability to adjust for length as the front differential is solidly mounted, but the rear does.

Suitable Donor cars

With several prop-shafts as donors, I began to cut them up, using a band-saw and the lathe to remove all the UJ’s and mounts. I ended up with a selection of  different UJ’s, that I could push into the cleaned up tube ends (with a mallet). There is a local company, that balances prop-shafts and has made several for me in the past, so I knew this was an OK route.

shortening-front-propshaftturning-front-propshaft-yoke

Although they shared the same flange bolt pattern, the diameter of tube and the thickness of metal of the Volvo items was less substantial than the Sierra items. Unfortunately, there is very little room in a Locost 7 for a Rover V8 and 4×4 system and the Sierra UJ’s are a little large. I therefore began to play with various Volvo joints and only the gearbox spline from the Sierra prop.

Locost 4×4 Front Propshaft Mock-up

Where I had originally mocked up the propshaft was no longer viable. It also needed to be solidly mounted where it was previously on sliding joints. It’s hard to see in the pictures, but in order to travel around the engine, there needs to be a ‘kink’ in the propshaft. In it’s original ‘mock up’ position this kink was approximately 14degrees. The maximum the UJ would take without fouling was around 16 degrees. I had never been happy with this.

After a lot of mocking up and head scratching the central joint has moved backwards approximately 30cms. The rear section of the propshaft is now 8cm shorter than the standard Sierra item. The front propshaft is roughly 5cm shorter than the standard Volvo item. The propshaft travels as close the the engine and gearbox as I dare (roughly 25mm). Rather than one UJ taking all the ‘kink’, moving the central joint backwards has effectively put all the UJ an even 5-6 degrees out of line.

locost-7-front-propshaft-2

 

Locost Rover V8 Starter Motor

On most Rover V8 starter motors the solenoid sticks out the side. This would be directly in the path of the propshaft. I had been planning on using a starter from an SD1 or P5B Rover where it sits tucked in above. However these starters have a longer motor, this extra length now means that the prop-shaft only just clears by 5mm. Therefore it looks like I’ll be spending a couple hundred on one of those fancy compact high torque after-market motors.

locost-7-front-propshaft-1

With the propshaft tucked in  a lot closer to the engine, I can now take some of the kink out of the steering linkage. Some of this kink was deliberate as having a one piece solid steering shaft with no kink could be lethal in an accident. However, it doesn’t need to be quite as much as I had. By adjusting a couple rose joints and cutting a few millimetre of the steering shaft I can straighten it quite a bit.

I finally think a Locost 4×4 with Rover V8 is a viable option. – I think? maybe…

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