Singer Owner November - December 2008

Roadster Repairs - Wheel Arches Part 2 / Dwell Angle

Ashley Crossland

So Part 2 of how to make wooden rear wheel arches (click here for Part 1). If you've all got your bendy ply, then we will begin.

As you can see, the wooden rear wheel arch here on the jig looks a bit sad - the question is do you try and repair it or do you replace it? I have found that the worst wheel arch will tend to be on the gutter side of wherever in the world you happen to drive. The gutter side accumulates more water and dirt that is all thrown up when you drive through the potholes. All 50-year's worth of doing it isn't kind to Singer's wood. Anyway we decide we need a wheel arch so we will proceed.

The picture shows the wheel arch jig that I borrowed from the previous owner of this car, Graham Smith. Graham devised and built the jig so I can't take any credit for that. The finished wheel arch is a complicated shape width-wise, but first I will describe the jig so that you know how to make one.

Essentially, the jig consists of some welded-up angle iron brackets screwed onto a backing board. As you can see, you first offer up the remnants of your side of the body / wooden rear wheel arch, and then match the brackets to suit the curve, and then screw the brackets to the board. Quite straightforward but ingenious! The jig will make a parallel sided wheel arch that can then be adjusted to fit either side of the car - hence you only make one jig.

The jig uses 9 brackets - you could use more if you want, but 9 seem adequate. You can either clamp the plywood to the brackets, or conceivably drill the brackets so that you could screw into the wood and thereby fasten them to the bracket. I have always used G-clamps. The 9 clamps will hold the ply to the curve, but you are best advised to keep the laminations squeezed together between the brackets by using extra clamps and some wooden spreader pieces. Thus you need the 20 G-clamps that I told you to get in our last article.

So what you need to start with is: At least 20 G-clamps, ideally with deep jaws. Bendy-ply ready cut into 7" wide full-length strips. Waterproof glue, and a brush to apply it with. A roll of masking tape.

What's the masking tape for, I hear you say? Well it's simply to stop you gluing the wheel arch to the jig when you lash on all that glue. Just stick some of the masking tape along the line of where the wheel arch will sit, and that ensures that the wheel arch will come off the jig. The standard thickness of the bendy ply is 5 mm so laminating up three layers comes out just about spot on for a Roadster wheel arch, but stick one layer at a time - i.e. don't try and stick the tree layers together in one go. Start at one end and work the ply to the jig taking care to keep the layers together as best you can. Then, once laminated up, leave the thing on the jig for as long as you can, e.g. a week, so that the glue properly sets, and the wood is happy taking on a permanent set. The three plies once glued together do become rigid, and any resemblance to bendy ply disappears.

Now to try and describe the shape. The inner side of the arch (i.e. the side closest the back seat and boot lid) is straight apart from a triangular cut out which is about 17" long and 1 " wide. (Sorry, but this bit of wood was missing from the photo. Also there is a cut out at the front but we will omit the fine details.) This triangular cut out matches the triangular bit that goes at the side of the rear seat pan - lift the back seat and you will see what I mean. The triangle starts at the bottom of the lap joint that I mentioned in the previous article. Now, if you look at the photo, the inner side of the arch is uppermost and this is "level". The bottom side of the wheel arch is sloping away from the backing board of the jig.

The outside edge is virtually one complete straight taper to the rear, and whilst I can give some dimensions it's best to tailor the wheel arch to suit your car and your aluminium bodywork, trying to make the left hand and right hand wheel arches mirror images of each other. The widest point at the front is about 6.3/4" (except it would be if it weren't for some notches. Thus the 7" wide wheel arches we have made allow you a bit to straighten up the sides.). Then 6.1/2" wide nicks in to 5.1/2" at the triangular notch, then its 5.3/8" at the lap joint, and 5" at the highest-most part on the car, getting narrower at the side of the boot opening. You get the idea? So basically, the outer edge forms a straight line to the rear, then it rounds off round the tail, but perhaps one thing to note is that the edge of the wheel arch is not square - it has a slight bevel to it which matches the angle on the aluminium body. When I'm feeling creative, I will try and produce a drawing, but meanwhile don't hold your breath!

Now a bit of a diversion onto setting up distributors. One of our members asked me if I had the figure for setting up his distributor using the dwell angle scale on a multi-meter. I might as well share the information, just in case anyone else is interested.

Firstly let me say that these early engines were fairly tolerant of dwell angles, but Singer's figure was 60 degrees +/- 3 degrees for the 1500 cc engine, and the same setting for 9hp Roaster engines after 1951. For earlier Roadster engines the dwell was specified at 49 degrees +/- 4 degrees. "Dwell" is the portion of time that the contact breaker points are closed, and therefore during this time the coil is getting charged up in readiness to make the spark at the spark plugs. If the dwell is short in duration, then not as much charge goes into the coil, and then a weaker spark results. Adjusting the gap at the contact breaker does the job of setting the dwell angle, but by reading the multi-meter scale you are measuring the effect directly, and not just inferring it from setting the points gap. Technically it's a better method to measure dwell and it compensates for a worn cam in the distributor. However, I must say that I get by with feeler gauges even though I have a meter with a dwell function on it. The dwell is altered by changing the points gap, but this alters the firing point which then needs the distributor readjusting. Whichever method you choose, once you have set it up, it should then stay "in tune" if you are consistent with your method.

Note that I have mentioned Singer's published data and not tried to match up to the part numbers of Singer's distributors, which again is a job for another day. I don't know if Singer's stock control was all that good - i.e. they might have put new distributors in the front of a bin leaving old ones at the back, and so they didn't get used up in sequence. This was not really a problem until there was a change in spec, and then new cars would appear to be getting the wrong distributor. Still, there's plenty more mysteries of Singers to write about in a new year.