Bonnet & Clutch

2nd June 2010

Still lots of different things going on, which I'll try to write down in a logical fashion!

I bought a new clutch master cylinder, one with an integral resevoir. I like the idea of having the brake and clutch circuits separate, just in case I need to dismantle one to work on it. Not fitted it yet, but it's there.

Also managed to source an s2000 clutch. And the result iiiiiiiis....it doesn't fit. Oh so nearly, but it's just a bit small, by 10mm or so - the friction area on the flywheel is too far out, and the inside of the clutch disc overhangs the inside of it. Luckily it only cost £40, so at least no great expense.

Alfa on the left, the (very slightly) smaller honda on the right

So, that's Plan A gone. I moved directly on to Plan B, which was to get a custom flywheel made up which would have the friction area in the right place. I liked this idea, because it means that the clutch, release bearing etc all stays standard. But I went off it when I got a couple of quotes for doing this, which were in the region of £1500.

Which leaves Plan C (trawl through clutch catalogues in the hope of finding parts of the right size from which I can cobble something together) and Plan D (get a custom clutch made up). In both of these cases, I may no longer be able to use the standard clutch release bearing, arm and slave cylinder, and may need to use an aftermarket concentric release bearing.

So that leaves The Bonnet.

For some time, I've been toying with how to secure the bottom edge of the bonnet (which should "just" hook under the front of the chassis, but doesn't look very secure on mine), and whether to make it pivot.

I like the idea of having a flip-front bonnet - it's all very well taking the whole lot off and lying it on the floor at shows when it can lie on the grass, but what if I need to get in the engine bay by the roadside? I don't fancy having to lay my easily-scratchable nosecone on tarmac if I can avoid it. So I thought I'd try to design a pivot that would let the bonnet tip forwards, and hold the nosecone securely in place when it was closed.

I was advised against sticking bolts through the side of the nosecone, as this apparently often causes the GRP to crack; plus you have to unbolt them to take the bonnet off completely.

After a fair bit of thought (and much experimenting with cardboard cut-outs, I came up with a pivot system which would let the bonnet tip forwards, then when it was roughly vertical, be simply lifted off. This consists of a pair of hooks which fit to the nosecone, and a pair of pivot pins welded to the front of the chassis:

  

Left is the pivot pin, one is welded to each side of the chassis. The hook on the right fits over the pin (red circle). It's shown in the "closed" position, pivoting it backwards by 90 degrees (arrow) rotates the slot into position, so that it can be lifted off and away from the pin. Nice and simple.

Below shows it all in position, with the hook hanging on the pin. It's all stainless so I don't have to worry about rust. I had to releve the bottom of the nosecone by about an inch to allow it to pivot, and then it works pretty well:

  

Although the hooks are bolted to the nosecone, it's also bonded on with wurth. The bolts are only really for setting up - the wurth should spread the load better, to avoid the risk of the bolts cracking the GRP.

It's much, much easier to put the bonnet on with this set up, because it locates positively at the front. The hooks also hold the nosecone solidly in position when it's closed, which is the major point.

What it's not is stable like a production car bonnet - not so much because of my handiwork, but rather that the whole nosecone/bonnet assembly is very flexible, by nature of its lightweight construction. It's fine in the garage, might have to be careful in a breeze though! I'll need to attach a cable stay to prevent it falling open, (which would probably break something) and I may also fit a solid rod like on a production car - that should help with the flexing issue.