Props
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When the engine was mounted by Sylva I had asked Jeremy to keep the sprocket as close the to centreline of the diff as possible and with the flanges parallel. This had compromised the location of the engine slightly by making it sit very far over to the nearside, actually slightly over the chassis rail. However, this was one area of the car that needed to be done absolutely right as I didn’t want to start getting vibrations that result from excessive or unequal prop angles.
I took some measurements and found that the flanges were offset by such a small amount that the prop angles would all be no more than 1-2 degrees, which is ideal.
I had decided that I definitely didn’t want a mechanical reverse box and that I would see if I could manage without reverse before deciding whether to add an electric reverse to the car. With no reverse box this meant that I would need a 2-piece propshaft with a centre bearing. On the advice of others from the bike-engined-car list I had decided to use some kind of cushdrive in the drivetrain as they are considered to make trailing throttle much smoother and also quieten things down a bit. There were two ways on doing this, the first being an Allens cushdrive on the engine and the second being a torque resilient tube in the rear prop. Perhaps the best solution is the Allens cushdrive. This means that you use one less UJ on the front prop because it runs at 0 degrees to the sprocket output and is probably a bit lighter. On the downside I couldn’t see how I would achieve equal and opposite UJ angles with this setup and on a more practical note the 0 degree front prop meant that I was running dangerously close to the underside of the transmission tunnel. I therefore decided to use a more regular 2 piece prop with torque resilient tube in the rear section and UJ on the front section connecting to a sprocket flange. This also meant that I could mount the centre bearing at 0 degrees to the line of the props between sprocket flange and diff (effectively making the 2 props seem like one prop) which would achieve the ideal equal and opposite angles horizontally and vertically to absorb the vibrations that arise from the yokes accelerating and decelerating as the rotate at an angle. With the small angles that I am running on the props then this seemed like the ideal solution for smooth, vibration free operation.
I ordered the props from Bailey Morris, from whom others on the bike-engined-car-list had had good service and from whom Mark Fisher buys his props. I had purchased a prop adapter from Mark and he gave me the part number for the front flange that I would need to fit onto it (FY1.6). I had a choice of centre-bearing between transit old style and new style. Most people use the old style centre bearing but I decided to use the new style one as the cage is an omega shape with flat mounts, which makes it easier to secure than the old, which has legs sticking out of it at ’10 to2’. I ordered the props with 2” front section diameter and had to use 2 ½” rear section because of the torque resilient tube. I also specced a slider in the rear section to allow a little margin for error in the measurements and allow me the option to fit a sprocket into the drivetrain at a later date for electric reverse. The props were ordered by specifying the operating length, type of centre bearing and location from the front flange, front and rear flange types (rear is sierra FY1.1).
The prop arrived 2 days later from Bailey Morris and was not quite as I was expecting. Firstly it was 1” too long as they had made it to the operating length with the slider fully closed. This was no good because I couldn’t then fit a sprocket in anywhere for reverse. Secondly they had used the transit old style centre bearing rather than the new one I had asked for. This was no big deal apart from making the thing harder to mount. Finally the FY1.6 front flange didn’t fit onto the sprocket adapter. This was because the R1 uses a big nut to hold the sprocket on. It is 42mm outer diameter and was protruding by 4mm from the mounting face. I had checked with Bailey Morris that this would fit inside the FY1.6, but it didn’t.. I called them to explain the problems and they were great. It seems that the chap who took my order didn’t usually deal with orders for bespoke propshafts and that he had assumed that I really wanted a ‘fireblade’ style prop like they make for Fisher Sportscars rather than what I had asked for. Fortunately the specifications in their system tallied with what I had ordered and not the length that I had received also. They were most apologetic and set about making me a new propshaft to my spec to same day, which arrived the next day and was exactly right. The FY1.6 flange had been relieved slightly inside to clear the sprocket nut, it was the right length and had the new style transit centre bearing. Being able to compare the old and new style centre bearings was quite useful actually. This confirmed that the new style was a better mount in my mind because it was far simpler to mount in the chassis but more importantly the bearing is located in a big rubber donut which allows it to be moved by a degree or two without putting any strain on the bearing. This would allow me to mount the cage to the chassis and run the props through at 1-2 degrees off dead ahead without putting any strain on anything. The one downside of the new style transit bearing is that the cage is slightly bigger diameter than the old style because of the bigger rubber donut.
The distance from the centreline of the prop to the mounts on the centre bearing is 58mm. With this figure is was then able to determine the height above the gearbox mount that the centre bearing needed to sit at (42mm from memory). I got a simple mount fabricated from a 2” length of U with a flat plate welded on top, in aluminium of course to save a few ounces ;-)
It was necessary for me to relieve the sprocket adapter quite a bit in order to get it to attach to the front flange, which was a complete pain in the arse but actually the first bit of messing around that I have had to do with the build, so I probably shouldn’t complain.
The props were secured in place with
locking spring washers and more importantly green loctite threadlocker, which is
the stuff used for permanently securing fasteners as I don’t really want these
coming out. I did have a brief moment when doing up the bolts on the front
flange when the threadlocker started to go off with the bolts half out. This was
because the engine, and thus flange, was hot and the stuff was curing faster
than I could do the bolts up as access was very limited. Luckily I was able to
back them out before they became permanently fixed.
With the props secured I was able to drive the rear wheels round for the first time, which would be a good test for the prop phasing, the new oil seals in the diff and the new tripod joints on the halfshafts. I stuck the car up on axle stands and ran it up to about 80mph. Everything was nice and smooth and no leaks. With the car back down on the ground all I needed now was a clutch cable and I could get the thing to move under its own power.