Augusta progress

[Mikenoangelo]

I’ve fitted an Air Fuel Ratio gauge to sort out the peculiarities of the Weber 30DO carburettor of our Augusta. The device reads a sensor unit attached to the exhaust pipe as it leaves the engine compartment and shows the ratio of air to fuel, the ideal ratio is in the region of 13 to 1 by weight. I also fitted a temperature gauge, an electric version to avoid the need for extra holes in the bulkhead. Both gauges fit in a panel below the dash under the steering column, attached to the bracket for the upper bearing of the steering column.

I had earlier improved the running by fiddling with the only manual adjustment (as opposed to changing jet sizes) on the Weber but felt it was still not right. I read an article

(http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm)

which explains a good method of setting both the slow running mixture screw and the slow running stop for the throttle and followed these with an immediate improvement to the slow running. However the instructions indicated that the setting of the slow running screw which had to be screwed down to ¾ of a turn to get a smooth tickover suggested that the mixture had been far too rich and that the slow running jet was too large. The ideal setting of the idling screw is between 1.5 and 2 turns. The jet is the correct 0.55mm bore (marked No. 55 - jets are marked in 100ths of a millimetre so for example a 105 jet  would be 1.05mm bore) so how could the mixture  be so far out? It looks as though the conical tip of the jet which seats in a sharp edged 2.5mm hole is worn, along with the seating and since the jet controls the flow of fuel from a passage linked to the float chamber a poor fit of the jet to its seating would provide a by-pass route for excess fuel to get into the slow running mixture. So another machining exercise is needed.

[Mikenoangelo]

Firstly to sort out the worn seat for the slow running jet. Tricky as it is 30mm down a 10mm diameter hole. To recut the seat flat and axially true can be done using a small slot drill, a milling bit which cuts a flat face, the hard part being to ensure that the slot drill is held vertically and central to the 2.8 mm bore of the seat, 30mm down the hole. I made a brass insert with a 0.25 inch bore to guide the slot drill and with a 10mm external thread to screw in place of the jet. (photo 135)The thread  on the jet holder which appears at first sight to be M10 x 1mm pitch curiously turned out to be 10mm by 24 turns per inch for which obviously there are no dies available. Luckily the aged Harrison lathe can do Imperial TPI as well as metric, although it needs the drive gears to be swapped around so that was possible if difficult because I was cutting a thread to the measurements of the male thread of the jet but not able to try the female thread on the guide. A small amount of thread chasing with a fine triangular file finished the job.

The brass guide and slot drill were next used to recut the seat. It is very hard to see the result as the recess is deep and hard to illuminate but using a camera was the best method. I rotated the slot drill by hand with very little pressure and frequent inspection until the seat looked clean. (photo 136 and 137)

The tip of the slow running jet can be pulled out of its holder and machined to the correct 45 degree taper, being very carefully centred in the lathe with a dial gauge.

As a final check I fitted the tip of the jet back into its holder,  blued the tip of the jet and inserted it into the carburettor then removed it, leaving a trace of engineer’s blue on the seat. The jet was cleaned and reinserted and - bingo- picked up a complete even ring of blue on the tip. (photo 138)

Hopefully this should result in a proper seal between jet and seat.

[Kari]

Amazing how Mike is performing open carburettor surgery. I am sure the Augusta soon will be running satisfactory with the Weber 30DO.
In my Augusta I am using a Weber 30DO for 10 years now. It never failed in several 10'000 Km's. At installing I made sure that all the jets and other parts are at factory specs.

For those not familiar with this carburettor type, I made a display of parts from a Weber I bought in bits and pieces. The figures shown are the factory specs. Although the most parts are bronze, brass or aluminium, there are a few bits from Mazac and amost impossible to get as spares. Its the diffusor (4,5), the choke tube (19) and the arm which attaches the bowden cable for the starting device. I am looking for the right needle valve, it looks as I will have to adapt a modern one, as I have not found a spare one sofar.

Regards   Karl

[Mikenoangelo]

I ran the engine to see whether my slow running jet clean up had made a difference. It has and the response to twiddling the slow running (mixture volume screw) now is much more sensitive than before although it still needs to be less than one turn open. The Air Fuel Ratio gauge reading now makes much more sense and small adjustments of the slow running screw have a marked effect on the reading. The gauge seems more sensitive than it needs to be as there is a fair range of oscillation of the reading even with a steady throttle. I’m not sure if this is inherent to the gauge or if it is detecting the variation in exhaust composition due to minor but frequent changes in combustion while ticking over. The true result will only come when I can drive the car to put a bit of load on the engine.

I took the plunge and bought a new rubber cover for the gearbox from Cigognani in Italy to replace the perished original. Ordered Wednesday last week, it arrived today Tuesday, a remarkable service. It is not quite as good a fit to the shape of the gearbox and looks a bit bloated, however I think I can improve this with a bit of silicone used as glue. Not cheap though at 110 euros plus local TVA and carriage.

Mike

[DavidLaver]

The recent book on classic engines and modern fuels has a lot to say on how much variation there is with combustion.  

https://www.amazon.co.uk/Classic-Engines-Modern-Fuel-Solutions/dp/1787115909

A lot of the content is here, but there may be more online and more in the book (I've a memory, as always with me quite weak, of the book mentioning a blog and maybe a forum).

https://www.mg-cars.org.uk/imgytr/paulireland/paulireland.shtml

[lancialulu]

I wrote somewhere else on this forum re this book. Although a bit repetitive it makes some good points:

Summer fuel better than winter.... Less front end components, less volatile, less gumming

Modern fuel works Better with about 5 deg more advance mid range (argument for programmable distributors??)

I could go on.

[Mikenoangelo]

Thanks chaps. I had seen the MG website but now I should buy the book.

As soon as I get and fit the new propshaft fabric discs and we get a reasonably salt free road I can get out there and test the carb and hopefully find no more vibrations.

Mike

[Mikenoangelo]

New fabric propshaft discs arrived from F Tooms. They are very accurate and were easily fitted, if lying on the floor for an hour or two is easy!

Photos 139 and 140 show the two new discs which are 11mm thick (7/16 inch) as was the thicker of the two which were on the car which looks like an original. The yellow one is obviously a more recent replacement and is only 8mm thick. The new discs after fitting remain absolutely flat with weight of the car on the axles whereas the previous discs always looked a bit wavy. They are very stiff compared with the earlier ones but whether this matters only use will show. Was the vibration a FLOPPY DISC problem?

Mike

[Mikenoangelo]

Finally a dry enough day after days of rain (good as it washed the salt away) I was able to try the car to see the results of the  last month’s fettling.
First the carburation and the Air Fuel Ratio gauge. Success - the gauge works and interestingly has confirmed that the A/F ratio with a steady throttle and load is in the region of 13 to 1 as I hoped. This is with the standard jets in the Weber 30D carburettor and the slow running volume control set as advised in the link I quoted previously. The ratio does fluctuate by one unit or so but generally does make sense. I’ve evidently got the slow running correctly set as it ticks over reliably and very slowly and evenly. It was far too rich previously but went very weak when slowing downhill to a halt so tended to stall. It no longer does that.  I have not yet played with the economy setting of the choke (pulled halfway out the control acts as an extra air valve for economy) or pulled the choke fully out with wide open throttle to richen the mixture to climb an Alp.

The radiator shutters work fine and I can now maintain an engine temperature of 70-80 C with the shutters about half open.

Now to the subject which has been bugging me all along - the vibration, propshaft or not?
It has changed after fitting new discs U/Js but not gone away. Damn it!!

The propshaft was balanced last year and after fitting the new Hardy discs I checked whether the propshaft runs true using a depth gauge from the centre cruciform of the frame. It does, the variation of the reading as the propshaft is turned was only 0.5mm which represents 0.25mm out of true which may even be ovality of the tube rather than wobble, and I think is of little consequence.

On the road there is still  a vibration at 2800 to 3000 rpm in top gear. It does not occur at the same revs in the lower gears and continues even if the car is put into neutral and the engine revs dropped to tickover. It does not occur at these revs in the lower gears so it cannot be related to the engine. So still a mystery. However it is less intrusive than before and not enough to spoil the enjoyment of the car which I must say now that the carburettor is properly set, goes amazingly well and energetically and is great fun to drive. I suppose the next move must be to put it in a rolling road to see what is going on. That will have to wait until Spring.

Mike

[Mikenoangelo]

Today some real progress on the vibration. Rather than wait for the rolling road I decided to jack the car up on four axle stands and run it to observe what is going on. I was a bit nervous about running it this way but I needn’t have been, it worked perfectly and did not feel in any way unsafe.

I could use the hand throttle to run the engine through the range of revs in top gear and see exactly what was going on. The vibration followed exactly the pattern I’d found on the road, coming in at 2600 up to 3000 rpm and continuing as the transmission slowed down when I knocked it out of gear and let the engine slow so, as I thought, is unrelated to the engine, clutch or gearbox. The propshaft runs absolutely true as do the new Hardy discs but the off side rear wheel has a wobble.

I had previously checked that the tyres run concentric to the hub and had the wheels balanced when the new tyres were fitted. but had not found a good way of seeing whether there was any swash-plate like wobble. Running jacked up like this, a wobble was very obvious. I then swapped wheels around which showed that the problem is with the wheel not the hub or half shaft. The offending wheel was demoted to spare and with a reasonably dry road I had a test run which showed a significant improvement, with far less vibration. In fact on country roads at 45-50 mph it is barely noticeable and even at 55-60 not intrusive. Freed of this dominating vibration, I can now feel that the engine itself is free of any major vibration period and hope that the remaining lesser vibration is due to smaller amounts of wobble in the other wheels.

The problem now is to see whether the wobble can be rectified which will mean finding a way of measuring it and putting it right. The wheels are made of fairly thin gauge steel and I suspect easily distorted by kerbing or a blowout, indeed some of the rims show signs of this. The wobble however may be caused by distortion of the supposedly flat inner face which the wheel studs clamp tightly to the hub/brakedrum. The offending wheel can be slightly rocked when laid on a flat surface. I can imagine that careless tightening of the wheel nuts as the wheel is fitted could be responsible. I think I can find a way of truing this mating surface relative to the main pressing of the wheel, either by pressure or a light skim, although there is very little thickness of metal to play with.

The Augusta has those very attractive  pressed steel wheels of the style which used to be called “Easyclean”. They also are unfortunately of the Michelin rimmed variety, a style introduced to get around patents on the "Well Based rim". The Michelin wheel has a well to assist fitting of the tyre but the well only extends around 60% of the rim which introduces an imbalance, corrected by the factory by three pieces of steel welded to the inner face of the wheel spokes or as on one of my wheel with weights fixed by three studs.  I hope that the minor dints in the rims and the alignment of the rims with the hub turn out to be of less consequence as welding new rims to the spokes would be very difficult as the spokes of the Michelin rim vary in radial length to fit the strange profile of the rim.

There is a small possibility that the wheels could be dynamically balanced to minimise the effects of the wobble. When the new tyres were fitted the balance weights which are plentiful(!) were all fitted to the inner side of the wheel so as to invisible. It is common practice when balancing wheels to put balance weights both inside the centre line of the rim and  to the outside to eliminate wobble. I shall speak to Longstone for their expertise.

So I think I know the problem, I just have to find how to sort it out. In the meantime though the car is now perfectly usable, very pleasant and great fun just as I hoped when I chose it.

Mike

[DavidLaver]

If efforts to balance fail would you be able to source another wheel?

I was also wondering about "hit it with a stick" type rectification, but I've not got a solid sense of what the motion is. 

[Mikenoangelo]

I haven't thought about replacing the wheel yet but will see how I get on straightening it. The wobble is like a swashplate - the rim is running on an axis which is at a slight angle to the halfshaft. I would call it SWASHBUCKLING.

I think the stick approach might be a bit brutal and dint the rolled edge rims. I well recall my son's Delta Integrale regularly suffered bent alloy rims due to the very low profile tyres and the excessive local supply of potholes. He carried a lead sash weight to beat it back into shape.

Mike

[GG]

Have seen this problem of wheel wobble in Aurelia and Appia wheels: the inner flat portion of the wheel distorts over time, likely due to sitting in one place for extended periods. I have a set of Aurelia B20 early wheels with this problem - at one time, there was a guy in St. Louis, MO, who would straighten them - he did the Appia wheels which had the same issue. Such people are very hard to find.

Possible fixes? Not sure. Have heard of people cutting out the section and remaking the surface from the wheel rim to the hub. Probably easier to source some untroubled wheels - I was able to find a set of Borrani steel wheels for the Aurelia that were in decent shape. Oddly, they weighed just the same as the originals - 18#, but seemed a bit better and didn't have this problem.   

[JohnMillham]

I would bet that the problem is the balancing of the wheels. I spent a lot of time on mine getting them dynamically balanced and it was worthwhile. It seems that static balancing isn't good enough with sliding pillar cars as they seem to be more sensitive than other forms of suspension. Keep up the good work.

[Mikenoangelo]

Just in from the shed having spent a couple of hours looking at the wheels and measuring wobble etc. Yes John I think dynamic balancing is the right way but will now wait until the New Year if we are allowed out. It looks like there is only one which is significantly out of truth and fortunately the car has two spares so it can be the emergency get you home  wheel for two punctures. I think the main problem is with the edge of the rim which seems vulnerable to being dinted. My original suspicion about the wheel centre is probably wrong as the distortion there is very slight.

I have another question  - has anyone found an ingenious modern electronic method to reduce the shock to the starter Bendix when running a 6V starter on 12V or do we just get it rewound and if so by whom? I doubt a resister would help as the voltage drop would only happen once the load was applied and would be too late for the Bendix.

Mike