costin Costin Walker F3/F4/FJ Imp Rebuild

[Mark (smokey mow)]

The other job for this month was trial assembly if the engine and transaxle in the chassis. Some time later in the cars history it was fitted with a Honda S800 engine so before the chassis goes to paint I wanted to be sure that the engine mounts were still in the right place for the imp engine. For now I'm just using a scrap gearbox and an old engine till something more suitable is built.

 

In the advertising literature for the car it was stated that the engine and box could be fitted as a single unit to ease assembly.  Encouraged but this news I set about trying to squeeze everything into the small engine bay but there was just no way it would fit from any angle.  Disassembled again the transaxle was slotted in first and the engine dropped in and bolted into place.  All the ancillaries and manifolds were then fixed into place to check for clearances.

 

 

 

 

 

[Tom-225]

One day when I'm closer to retirement i can dream of picking up a nice historic project like this to restore!

[Mark (smokey mow)]

This last month I’ve been getting to grips with a few smaller jobs when time has allowed.

 

I’d picked up some replacement brakes for the rear a while ago as these were in a slightly better state than my originals. Even so they still needed a good clean up and rebuild. Everything was stripped down and the back plates were dropped off for powdercoating.

 

 

In the end I found both the adjusters and the wheel cylinders to be rusted solid do these were all replaced when reassembled. 

 

 

[Mark (smokey mow)]

I was slightly worried that the sump might not be salvageable and I even went as far as to buy a replacement to modify but after a good dousing of degreaser and the old glazing paint had been stripped off I was pleasantly surprised to see that we metalwork hiding beneath was actually in remarkably good condition. A quick check was made for any leaks and then it was ready for paint.

 

[Mark (smokey mow)]

Continuing the theme of refurbishing parts I dug out the box with the pedals in for a look and set about stripping them down for a good clean up.

 

like so many of the the parts they’re covered rust and a thick covering of body shop dust and overspray from storage.

 

half hour on each pedal with the wire wheel got them back top bare metal. Lovely to see the braided joints.

 

 

then a couple of coats of tough satin black to finish.

 

[Mark (smokey mow)]

Also fabricated a couple of parts that were missing from the boxes; A clevis for the rear suspension as I only had 3 of the 4 needed and a pair of upper wishbones.

 

 

[Mark (smokey mow)]

Last weekend the car went off to the exhaust fabricators for the new manifold and silencer to be made so Although there’s a lot of jobs to get done there’s not much to do without a car.

 

luckily I had a delivery in the week from the laser cutters with the parts needed to build the new rear uprights so I set to work by first folding and then tack welding the final assembly.

 

 

 

[Mark (smokey mow)]

You’ve gotta love eBay, sometime you just get lucky with what you find on there.

 

 

[Mark (smokey mow)]

For those wondering about the lack of progress, we’ll the truth is there has been very little.

 

a few weeks before the Coronavirus lockdown kicked in I’d trailered the car to the exhaust fabricators to get the manifold  made and unfortunately it’s been stuck there ever since. So I’ve been doing what few little jobs I can without a car in the garage.

 

one of those tasks was the final welding on the rear uprights.  The parts I’d tacked together were boxed up and posted down the road for them to be welded, and then returned again a few days ago all nicely TIG welded.

 

 

 

 

[Mark (smokey mow)]

Good news at last, the Costin is back home again from it’s holiday on the Norfolk coast. keen to resume progress I decided to pay a transport company to collect it for me rather than wait till the restrictions of this lockdown have been lifted.
 

maybe the size of the lorry was a bit bigger than needed though 

 

 

 

Other than a couple of photos over the last few days this is the first time I’ve seen the new manifold in the flesh.  Very pleased with the results and well worth the wait. 
 

 

 

 

 

and just a reminder of what this replaces 

 

[Kevin Pullen]

Lovely piece of work but the can is mahoosive Mark

[ludo]

should be a bit of an improvement on old one 😄

[Mark (smokey mow)]

12 hours ago, Kevin Pullen - WSCC Treasurer said:

Lovely piece of work but the can is mahoosive Mark

it’s not as big as it looks, it’s just that the car is so small! The can is only 6” dia x 14” long.

 

that problem is that in period these cars ran unsilenced with a straight through pipe so it was always going to be a bit of a problem with packaging.  In reality we wanted to make it longer to ensure there are no issues at scrutineering but the MSA regulations limit the rear overhang to maximum of 600mm from the centre of the rear axle. The lengths given to me by the engine builder for the primaries and secondaries very much dictated the overall length and given that we’re aiming to extract as close to 100bhp as we can from the tiny 875 engine I didn’t want to compromise anywhere at the expense of power.

 

 

[ludo]

what about moutning the silencer accross the car rather than longitudinally?

thinking of something along the line of a BMW M3 E46 but all on single pipe:

[Mark (smokey mow)]

From the point of packaging a long exhaust system it’s a good idea and you can see why it’s used on road cars, however the design is far from efficient. 
 

Each bend will introduce a pressure loss within the exhaust system which will correspondingly impact on performance.

 

The tables below were written for calculating losses in fan ducting but the same mathematics and K-factors is relevant when looking at pressure losses in the design of exhausts.

Looking at a very complex subject quite simplistically (and ignoring scavenging for a moment) you would try to design for the lowest pressure possible in the exhaust manifold as any pressure in the system would reduce the amount of gas that could be ejected from the cylinder into the exhaust branch when the valves open.