costin Costin Walker F3/F4/FJ Imp Rebuild

[Mark (smokey mow)]

5 minutes ago, DIY-Si said:

It's looking good, and about as safe in a side impact as an XI!

 

For the wiring, do you need any lights at all? Would it be worth allowing for a rain light or something like it?

thanks, yes although not originally fitted to the car I would need a rain light for racing so was planning to run an extra wire in for one.

[Mark (smokey mow)]

Getting through the jobs slowly. New wiring loom made and loosely assembled then once I was happy with the routing everything was bound in loom tape.

 

the spare tails are for the rain light switch and an oil pressure light if I decide to fit one.

 

 

[Mark (smokey mow)]

In other small jobs I’ve been trying up spacers for the shocks on the lathe, 8 done and another 8 to go.

 

[Mark (smokey mow)]

One of the difficulties of old race cars and particularly those that are prototypes is that there’s very little information or anything to copy when it comes to some of the technical details.

 

Shock length was easy enough to calculate from the geometry and there was four old Spax dampers that came with the collection of parts which supposedly were from the car. All good so far but then comes spring selection. I had twice as many springs as there were shocks so little idea as to which were for this car so somehow I needed to work out the spring rates. The obvious way would be to physically test them but as they will need to be replaced and the budget needs reining in a bit I opted for the mathematical route.

 

Those that know the maths can skip ahead but for those of you that don’t the spring rate is calculated from the following parameters:

 

L = Free Length of The Unloaded Spring (m)

G = Shear Modulus of Rigidity of Material

d = Wire Diameter (m)

D = Mean Diameter (m)

N = Number of active coils (an active coil sweeps one full circle)

 

For spring steel the shear modulus would be around 79,300,000,000 Pa and the Mean Diameter = Total Spring Diameter – Wire Diameter

 

These parameters are then entered into the following formula.

 

Based on the dimensions of my on springs this gave me spring rates of 83983, 98620, 33196 and 42766 N/m which equates to 478, 562, 189 and 243 lbs/ins in old money.

 

Now I know the spring rates the next task is to determine which of these were fitted to the car and for this we need to look at the wheel rates and suspension frequency. I won’t type it all out but this guide from Koni is what I’m working from.

 

The published data for my JW4’s was much better and these had a suspension frequency of 3.5Hz which seems consistent with racing cars so I will stick with this but I’ve had to estimate corner weights for the Costin since the car is nowhere near complete. I’ve taken an educated guess at 85kg for the front wheels and 125kg rear again based on the same F/R bias as the JW4 but allowing a bit more for the heavier engine and chassis.

 

By way of a comparison I found these figures online for various different types of cars. 

 

0.5-1.0Hz Passenger cars, typical OEM

1.5-2.0Hz Rally Cars

1.5-2.5Hz Non-Aero racecars, moderate downforce Formula cars

2.5-3.5Hz Moderate downforce racecars with up to 50% total weight in max downforce capability

3.5-5.0+Hz High downforce racecars with more than 50% of their weight in max downforce

 

Plugging the different spring rates into the formula I found the 189lbs/ins springs at the front gave a wheel frequency of 3.6Hz and the same with 240bs/ins on the rear.  Conversely the heavier springs would have given a wheel frequency of 5.5Hz so clearly wrong for this car.

 

So based on these results and what’s available from Faulkner off the shelf I’ll be fitting 175lbs/ins springs to the front and 250lbs/ins on the rear as my starting point.

and that’s how to loose several evenings and not make it look like you’ve done anything 😀
 

[Mark (smokey mow)]

Fitted the brake bias valve today.  It needed a bracket making to mount it to the chassis, I got a price from Fractory but they wanted over £200 so I thought I’d make it myself on the mill.  Total cost £6.73 for the aluminium so quite a saving.

 

 

and all mounted in position.

 

 

[DIY-Si]

I do enjoy being able to do something that gets quoted as expensive for peanuts.

[Mark (smokey mow)]

A trip across the country this weekend to collect the gearbox fresh from its rebuild. 
 

To recap, when I first got got the box it looked like this, caked in oil and dirt and in parts rusted right through from neglect.

 

 

after a lot of graft from @windy it’s been transformed and totally unrecognisable from before. Blasted clean, new bearings, seals and pretty much a brand new box. Now looking even better than the day it left the factory over 50 years ago. 
 

[Mark (smokey mow)]

Meanwhile the engine is away for a partial rebuild. The engine was overall in good condition and had been checked and serviced prior to me buying it at the start of this year but to run it in the Costin requires a few mods to be made.
 

In the Hillman imp the engine is laid flat but for the Costin it runs at 20degrees past vertical so it needs a few extra oil drains to be drilled in the head. After speaking to one of the specialists they advised that this is something I could do myself but the risk of hitting one of the coolant galleries didn’t fill me with confidence so we made the decision to send the head off to the specialist for them to carry out the work. 
 

 

 

 

[DIY-Si]

That gearbox is very shiny. My inner magpie approves!

[Mark (smokey mow)]

The cylinder head is finally back.

 

This has now had extra oil ways drilled for the upright orientation and a few extra jobs whilst it was away.

 

Bronze valve seats fitted.

Colsibro valve guides fitted

Skimmed and Wills ring groves recut 

New valves and competition springs 
 

now to get it all put back together again.

 

 

 

 

 

[Glen_I]

Looking good!

 

Something about shiny metal.....its a 'Man thing'!

[MR.C]

The engine was way ahead of its time...

[DIY-Si]

That looks so much like my Climax it's a wonder they're different engines!

[Mark (smokey mow)]

Finally some progress and a long overdue update. After an extended wait as my engine builder was busy preparing for the start of the racing season the engine is finally back together again.

 

first job is fitting the new clutch. As the engine came with a flywheel machined for an F3 clutch when i bought it, I decided it would be a sensible upgrade for the standard imp clutch that the car originally ran as these are a known week point. I didn’t however factor quite how expensive this upgrade would be!

 

 

The AP clutch also  meant that I’d need  a custom made clutch release bearing to suit and some minor mods to the gearbox to fit a spring to support the bearing and stop it rubbing on the unit shaft.

 

[Mark (smokey mow)]

With the clutch fitted I could finally move on to fitting the engine.

 

Despite the sales brochure for the car saying that it had been designed so the engine and box could be fitted as a single unit my trial build last year showed that this definitely was not the case, not least because the clutch fork needs to locate one side of a chassis rail whist the slave cylinder and the casting it mounts to on the gearbox is the other side of the rail.  I forgot to take a photo of this so I’ll try and remember tomorrow.

 

Not wanting to damage the paintwork the chassis was liberally wrapped in corrugated card and the the gearbox could then be slotted in to position. This is the originally gearbox from the car and this is the first time since 1972 that it’s been in the car as I used a scrap box for the trial build.

 

 

The big job came next of lifting the engine in, this needed to be stripped of all the ancillaries to stand any chance of squeezing into the engine bay.  The mounting flange on the engine for the box is actually larger than the aperture in the chassis so to lift it in the engine has to be orientated vertically with the crank pulley pointing up and then once through it needs to be laid down horizontally.

 

 

Once in the engine mounts, water pump and starter motor could then be fitted before finally bolting it up to the gearbox. This whole process took the best part of two hours to get the engine and box in.

 

At this stage one job I needed to do was make a nylon bush to support the gearbox. The original got destroyed trying to get it out when the chassis was stripped for Powdercoating and I’d not made this before as I needed everything assembled in the chassis to work out its length.