The clutch on the Blackbird engine is hydraulic which complicates matters. The clutch itself is at the front of the engine (that is, the end nearest the nose of the car) but is activated by a pushrod which runs right through the engine/gearbox unit. The pushroad is actuated by a hydraulic slave cylinder. This is located to the left of the drive sprocket cover. The diagram below is a rough sketch of the drive sprocket cover and slave cylinder.

The first problem is the drive sprocket cover itself - it’s going to get in the way of the propshaft. There are two options, and which one you used depends on how you mount the clutch slave cylinder.

The main problem in doing the clutch is that once the drive sprocket is replaced with an adaptor to take a propshaft, there’s very little clearance between the propshaft and the slave cylinder - and in particular, between the propshaft and the banjo bolt on the slave cylinder if the slave cylinder is used in its original position. If the hydraulic system is kept it’s always necessary to move the slave cylinder away from the engine/gearbox block for clearance reasons - again, more details later.

There are (AFAIK) three options.

The first is to convert the clutch to cable operation. I’ve no experience of such a conversion but I can see that it shouldn’t be too difficult: it’d just need a cable-operated lever pressing on the clutch pushrod. If you try this, let me know - I’d be interested to know how you get on.

The second option is the one I was advised to use by Fisher. This involves binning the drive sprocket cover altogether. Then using (I think) two of the slave cylinder mounting holes, 2 lengths of threaded studding are inserted in the threaded mounting holes, spacers made of tubing are slid over the studding, and the slave cylinder is mounted on the 2 lengths of studding. HOWEVER, the slave cylinder is turned round 180 degrees so that the banjo connector, instead of pointing towards (and into!) the propshaft, is pointing away from it.

I didn’t use this technique as, as far as I can see, it’s fundamentally flawed since the mounting points on the slave cylinder are not symmetrical (as you can see from the diagram). This means that either the clutch pushrod is not going to line up with the slave cylinder properly, or the studding is going to have to be bent into place. I took the view that this would weaken the slave cylinder mounting and was likely to put lateral forces on the pushrod. No doubt an adaptor plate could be made up but I didn’t fancy going to those lengths.

I should add that at the time of writing I’ve never seen an install done in this way and it may be the dog’s doodahs. But it seemed like a bit of a bodge to me (and Ed Cane, fellow Birdista) so I took another course.

The third option is the one I’ve used. The problem with the drive sprocket cover getting in the way of the propshaft is easy to resolve: Mr. Drivesprocket-cover had a blind date with Ms Angle Grinder. It’s pretty obvious what needs to be cut off, but I’ve done a piccie anyway.

The remains of the drive sprocket cover and the slave cylinder need to be mounted on the gearbox, but as I mentioned above, they need to be moved away from it. This is how: the propshaft should be in place and (assuming it’s got a sliding shaft in it) the thinner end should be closest to the engine. Cut 3 or 4 lengths of 6mm studding (about 10cm long?). Put the drive sprocket cover and the slave cylinder (without the banjo bolt) in place where they would normally be mounted on the engine, and put the lengths of studding through the mounting holes on the drive sprocket cover (from now on this is the DSC, my fingers are getting tired) and thread them into the block. You can now slide the DSC along the studding. The best position is the one in which the thread for the banjo bolt on the SC (slave cylinder, OK? ;-)) is furthest away from the propshaft - you need as much clearance as you can. Measure the gap between the DSC and the gearbox. On mine it was 40mm.

Then make up 4 spacers from ali tubing, the same length as this measurement. Because the DSC and the SC are going to be further away from the g/box, the clutch pushrod needs to be longer. Some people have made up extensions using a tubing sleeve and a rod extension. I decided to merely make up a longer pushrod: it’s 8mm diameter, so I got some 8mm diameter stainless rod and cut a length 40mm longer than the original pushrod. THIS NEEDS TO BE ACCURATE: the effective travel in the clutch system is minimal. I then rounded the ends of the new pushrod off to roughly match the existing one.

The next bit is the trickiest bit, although it may not be necessary for all installations. I found that even with the maximum clearance between the propshaft and the SC, there still wasn’t enough room to fit the banjo bolt and banjo connector on the hydraulic hose. BTW, I got the hose from BGC motorsport again - send them the Blackbird banjo bolt and they’ll make one up. Mine was 49cm long, end to end.

So, I ended up grinding down the faces of the banjo connector with the angle grinder, and griding down the head of the bolt. Lots of this meant that I had 3~4mm clearance even with two copper washers in place. The first time I did this I didn’t do it accurately enough - it turned out that the ground faces of the banjo connector were not parallel by about .25mm. Although the clutch worked there was a slight leak: when you pressed the clutch pedal a very fine spray of fluid came out.

With the aid of vernier calipers I’ve made them parallel so *hopefully* they’ll now work. At the time of writing I hadn’t tested the new version but I’ll post an update when I know how it’s gone.

I’ve heard some complaints that the clutch pedals on bike-engined-cars are very light. This is not the case with the Furrybird! There’s not much travel but it’s certainly firm enough.

This document maintained by Dan Bromilow webmaster@danstuff.info.
Material Copyright © 1998 Dan Bromilow