Tightening-up the steering and front camber

After a week of doing not much, I set to trying to reduce the vibrations I believe are coming through the front end as the situation is improved after cleaning off the wheels, but should be better. I started off with the steering column and seeing as I have not had much luck the replacement bushes you can buy I decided to copy Dave and make up some PTFE bushes, which are almost three times longer than the originals, so much better now.




Further down the steering shaft the joint was replaced with one from Bill at Rarebits.




The only problem was that the new one was 10mm longer, not usually a problem for a standard car, but I had moved the steering rack over to the right as far as possible to give more space for the exhaust. This meant there was not enough space between the suspension tower and the upper pinch bolt of the steering joint. I tried for a time to work out how I could reduce the diameter of the joint to make it clear, but in the end I decided to weld it on to the lower steering shaft. The assembly can still be removed from the car without destroying anything.




The front end vibrations have now reduced, but I have now tracked down slackness in the steering rack, so one of the next jobs will be to try and remove some of that slack by removing a shim or two, otherwise I shall pick up another rack and re-build that in readiness to drop in the GT6.

Following Johns suggestion I bought some 1/2" aluminium bar, cut it down to length and drilled it to suit the lower wishbone arms.




It does look a lot better now as there is a greater surface area contact between the wishbone bracket and the chassis.

Wheels and shocker mounts

For a while the car had been suffering from vibrations around motorway speeds, I thought it was something up front as I could feel it through the steering wheel, but after watching the rear wheels on the rolling road it was possible to see that the wheels are nut running true. Some time this morning was spent first checking the hubs for run-out and then the wheels. Spinning the wheel over by hand you can the the wheel and tyre more in and out, at worst according to a dial gauge, 2mm.
To prove the point, the standard steel wheels were fitted, they run much more true and do not give vibrations at motorway speed. I reckon when the alloy wheels were re-furbished they did not take into account the thickness of the paint on the area where the wheel mates to the hub, so one side of the wheel is further out than the other. You can see on the inside of the wheel that it has not been contacting across the whole surface area. I removed all of that paint so it will sit flat again. They were fine before they went in, but the new paint is much thicker and having done this the car felt a lot smoother.




Following suggestions on how to make the car drive and feel better, wheel shims have been added to the rear. I started with 25mm spacers, but the studs supplied with them did not leave enough spare thread as I wanted, so the spacers were reduced down to 17mm. This means the car has a slightly wider track width than the later Spitfires with their long driveshafts, filling out the rear arches much better and noticeably improving the handling in corners.

Image on left with spacer fitted




Then a couple of weeks ago I noticed that the shock absorber top rubber was trying to escape, correctly diagnosed by charlieb as being due to the way the springs are now supported, meaning that these rubbers are now taking the weight from the spring also.




To get round this I have for now at least, fitted some re-enforced rubber washers cut using hole punches. Hopefully these should hold up better until I do something like copying Daves top mount idea incorporating rod ends.

GT6 update, rolling road.

Hmm, news on the GT6 is getting a bit out of date, having got the PI system working as it should on the GT6, I wanted to go and do a rolling road run to help further tune the megajolt ignition map, see what sort of power/torque it is producing and get an idea of what further improvements could be made. So we went over to Maynard Ltd in Stroud to have a run up, the results of which are below

Power





Torque




The red run is with the complete exhaust system (GT supplied 6-3-1 onto standard centre pipe and back box), grey is with the rear silencer removed and black is with the middle pipe (from 3-1 collector back) removed. All figures are corrected back to the flywheel.

It seems to suggest at the moment that the back box has minimal effect, but the relatively small 48mm ID middle pipe is holding it back. So one of the next jobs is to get the constricted (48mm) output from the 3-1 collector opened out to 52mm ID

It was a good afternoon out and was interesting to record what the engine is pumping out on what is basically a standard MkII GT6 engine, but with Lucas injection and a proper exhaust manifold. I'm not that bothered about the absolute power figures (though they are a good improvement on the factory figures), more interesting to me is the shape of the torque curve, which is relatively flat compared to other GT6 engines I have seen, with bags of torque from lower engine revs. I'm pleased with the results and that's what matters to me ;)