Practice Day and Gale Hall (sort of)

September 22nd 2017

I didn't post directly after the Practice Day.

It went pretty well. I went without John, my regular passenger, who was out of the country.
As a sole driver I managed to grab a few experienced drivers to sit in with me. Robin Jager was the first victim. He drove it as well and thought the engine swap a great success. No issues to speak of except the starter refused to co-operate a few times. Then it would be fine. Blew a lot of fuses as well but a word with Martin Grimwood determined that I had gone overboard on the use of fuses. Don't need most of them. As I use the fuse block as a distribution board as well, I decided I would just stick 40 amp fuses in each slot.
The ECU is fused separately.

Andrew Woodhead had a ride and a drive as well and found the throttle response was much more gradual than he had expected it to be. His passenger, Karen, rode with me for a while and we overcame some technique problems, but one particular post was beyond reach. More of that later.

The site was just outside Kendal and was brand new. It was great. I enjoyed it. I hope we'll have an event there next year.

Robin advising

Sorting fuses

Karen passengering

This was the problem post

The day was very enjoyable with none of the pressure to keep on going that you have during a trial. Very relaxed.

A good thing was that the oil pressure was absolutely fine (you never know with a "used" engine) and the cooling was well up to scratch. As it was a warm day and the car was repeating hills over and over, this was a good test.

Anyway, after the event I sorted the fuses and got another terminal block to replace the bullet connectors I had used

(I never trust them).

I took the starter to a sparky in Penrith who found it was getting red hot when just whizzing over without load.

It was a scrapper purchase and I reckon it was a Chinese copy and not up to much.

I went and got a genuine Bosch starter from the same place, hoping this one will be more reliable (new ones are £80 or so). You could say I don't learn, but let's see.

Robin did mention that the exhaust was quite high and a marshall could easily burn themselves on it. This was a good point, so I made a shield from an old bit of alloy chequer-plate and a section of a Laser dinghy mast that I had lurking in the garden.

Back to that number 4 post that I couldn't get around.

The coil/shocks at the rear are Hagons and mounted well outboard of the chassis. They are outside the body just behind the wheel. This means that, as they have a limited stroke (about 3") the wheel travel is very limited. I began to suspect that the wheel with the lightest load is actually being lifted and spinning when really it should still be in contact with the ground.

The post I had trouble with was a climb up grass without a run at it and then pivoting around the post to return down. The problem was that however I approached I could never nail which wheel was going to lose grip. Which one did, every time. But it wasn't predictable.

I decided that the limited axle articulation was slightly lifting a wheel, enough to lose grip, when it should have allowed it to stay on the ground if there had been more travel.

I noticed that Richard Sharp's car has very soft rear suspension with a lot of suspension movement when you rock on it. Yes, it's independant and has the central shocker with a rocker mechanism, but it pointed the way to me. I need more compliance and more travel.

I decided to move the coil/shocks inboard so that there was more leverage on them which would effectively lower the spring rate. (although I had an issue with the car bottoming-out as well, which would be a bit worse if the spring rate is effectively lower). It would also allow a bit more vertical travel at the wheel.

Moving the coil/shocks would have a second advantage in that the Hagons are small diameter and if I wanted to fit AVOs or similar with 1.9" springs I would have to replace some frame tubes to make room if they were still outboard. Inboard there is loads of space.

So I mounted the shocks further inboard. Nearly about 1/3rd of the distance from the wheel to the diff.

This immediately made the back end softer with more roll. 

I was entered for a trial at Melmerby where I could try this out. Things conspired against me. John fell off his bike and injured his neck. Luckily, as he fell on his head, there wasn't too much damage.  I had a deadline for the paper I edit to meet on Sunday, to get it off to the printer. Whilst Sunday was out, I could manage the Saturday so went to help Andrew and Martin set out the Hills.

This gave me a chance to see if the changes had had any effect.

Whilst it did seem better, the effectively softer spring rate meant the rear was bottoming-out more. The back axle also seemed to be tramping when I was travelling at a steady speed over the fellside.

The top end of the rev range was poor, in fact it died if I tried to use full throttle. Absolutely perfect at lower revs though. Martin thought the throttle seemed to be less gradual than I had thought and that it seemed to snatch a bit.

So. 
Back home I thought through these things and decided that either the electronic ignition was giving bother or the SU needle that had been in the Imp is just not rich enough for full throttle.

1040cc versus 1600cc, but with the same carburation. That makes sense.

I logged some runs in the car in the timing software and did a timing wheel data log. I emailed these to Dave at Canems (it's a Canems ECU) to see if he thought anything showed up as suspicious. 

He thought they were perfect.

The carb needle needed altering then.

But first

I needed to look at the shockers.

I took them off and removed springs  This gave me the chance to check their poundage (130 lbs per inch). Without the springs on it was obvious the damping effect of the units was minimal. They were in fact, knackered.

This explains the bottoming and the pattering of the axle over rough ground. I'm surprised it hadn't occurred to me. They are probably over 30 years old! But from inside the car you don't see what would have been obvious on a video. Lesson to learn there.

I found some 2 year-old Hagons for £50 in Carlisle and got those. (AVOs are nearly £300, including springs. I'm not made of money!)

I took the springs off and checked the dampers which were nicely firm. The springs are 150 lbs per inch, which probably means the extra leverage created by using mounts inboard is compensated for.

These have slightly less travel, but as the springs are a bit stiffer I don't need to apply any pre-load, which should mean they droop more (don't leave the ground as soon) when the car rolls or drops a wheel into a dip.
It sounds an odd concept, but I found a tutorial on coil/shockers on Youtube in which the bloke explained the theory of preload and damper rates. Everything a track car needs is the opposite of what we need.

I had to move the brackets to the top of the axle as these shocks are a bit shorter, so took the whole thing off the car off this time to make sure I did a proper job. I put two holes in the bracket so that I can fit a cantilever bracket over the back of the axle tube, should I go for longer shocks in the future.

Back to the carburation.

I have a farm track behind the house which I can use. It's half tarmac and half grass. 

This is the first run after fitting the engine, before the Practice Day.

I found that if I open the throttle with the original needle in the carb, as long as I do it gently the revs will rise to about 4/5000rpm before, cutting out. If I open the throttle quickly it cuts out earlier. I did a run with the laptop plugged in to log the various readings and also to have a rev counter on screen.

I found a website with a graphing display for all SU needles (there are hundreds) which would compare needles.
I've not messed with them before but it's fairly easy really. You measure the diameter at 1/8th inch intervals (they call each a "station") for this particular site. Another database I found measured stations at 1/10" intervals. 
Nothing like a bit of consistency. And this was nothing like it.

It turned out that my existing needle was virtually an ABT.  I decided to try narrowing down to better match a CP4 which had a much richer top end.

The bottom line is the ABT needle.

I did this by putting the needle in a drill and spinning it slowly whilst gripping some wet'n'dry on the narrower end of the needle. By measuring it as I was progressing I could get a pretty accurate idea of how much it was reducing by.

It occurred to me that I would be stuffed if I was wrong, so tried the needle on the car, on the farm track, before I removed too much metal. It was a lot better, but still wouldn't rev right out, and would die if I tried.

So I found a number 6 needle on ebay and bought that. This would be almost perfect according to the graph, having a thinner (richer) top end. If not I would have an idea which way was producing the more promising result.

When it arrived I fitted that and off I went again. 

This time it was nearly spot on. Just a little fluffy at the top end but great pull when snapped open. The bottom end was still as torquey as it had been.

Back on the internet and I decided to get a CP4 needle which is richer still at the top end. This time I went to the SU Company and got a brand new one. (about £8)

After trying this it seems as close as I need to perfect.

It's not like racing where you are at full throttle for most of the time. A blast would only be about 20/30 seconds if that, you either don't make progress or you do. I do have a bit of video of a member at a particularly slimy Southwaite event with his throttle open for about half a minute. 

This was the wet event at Southwaite, Carlisle. (my car was running a 1040cc Imp engine at the time)

But let's face it. If it's too weak it won't run and if it's too rich it doesn't really hurt, as it isn't for very long. It won't even destroy the planet!

Next event is at Firbank near Sedbergh. When I lived in Central Lakes that was just a 20 mile run. Now that I live up near Penrith it'll be a long run (at least 35 miles). I don't know how I'll cope.