Technical Matters .............. Float Levels - Zenith 22FZ There has been much discussion over the years regarding the setting of float levels of the up-draught Zenith 22FZ carburetter. ( That's Zenith's spelling not mine - I favour the final 'O' myself ! ) Recently I rebuilt one of these delightful little carbs, and had to manufacture a new needle and bobbin. The difficulty comes when you fit the bobbin - where do you set it? The Zenith manual prescribes that the static fuel level should be 3 millimetres below the top of the main jet cover. But how to arrive at this condition? My solution to allow setting it up on the bench was to produce a small header tank made out of a 'pop' bottle, connected to the normal petrol pipe union on the side of the float chamber by a flexible tube. Thus you can fill the float chamber by elevating the tank, or drain by lowering it. Removal of the two brass bolts securing the butterfly and choke assembly allows this to be removed. It has no effect on the fuel level, and its removal exposes the main jet cover. Also remove the main jet but securely replace the access plug and washer below it. Now for the fun bit! Douse all naked flames! Now half fill the pop bottle, and raise it so that the petrol runs into the carb. Watch the jet cover, and if the petrol starts to come out of the top then immediately lower the bottle to drain the carb. The level is too high, so the raise the bobbin up the needle. If the petrol does not come high enough up inside the jet cover then lower the bobbin. The correct level is 3mm below the top of the cover - ie just about visible. Try a using a match for a dipstick. The bobbin needs to be fairly tight on the needle, perhaps needing some bruising with a pair of pliers. When the correct position has been found then run a little solder around the top of the bobbin to secure it.
Ian Morecraft has kindly allowed me to use the
following article which first appeared in the Association Magazine.
It shows another and simpler method than mine (not difficult) and also provides
you with a useful little gauge for your tool kit.
A better way to set the petrol level of your
Zenith FZ up-draught carburettor: Following the Zenith instructions, first
remove the carburettor, the plug, and the main jet (F); then put back the
cap and rig up a gravity supply of petrol. Then you look down
the manhole, past the throttle (as thick as a manhole cover) to check the
correct level; 3mm. below the top of the main jet cover.
You see nothing - and the FZ is very finicky about getting this right. Instead, with the carburettor removed, do the
following ................ Use a piece of straight 2 - 3mm. wire and make
a 90' hook on one end. Slip this past the butterfly and rest it on
the main jet cover. Measure the distance (1) to the top face of the
carburettor flange (50.3mm.). Now remove the slow running
device (C&B) and measure (2) top flange to top hole (13.1
mm.). The petrol level must be (1) minus (2) plus 3mm. below
the top of the slow running tube housing - in this case 40.2mm. Next take a piece of clear plastic tubing as
used for pneumatic controls ( 5mm.OD
x 3mm.ID), if necessary straighten
it by inserting a rod, immersing in boiling water and allowing it to
cool. Make a washer approximately 3mm. thick to fit tightly on
the tube. Set this on the tube with the lower face at the above
calculated dimension plus 10mm. above the bottom end. The length
above the washer should be enough to hold with two fingers. Push the tube into the housing of the slow
running tube as far as it will go, and feed petrol from the gravity
supply. When the float chamber has filled, seal the top of the
plastic tube with a finger and withdraw it. There should be a
10mm. column of petrol in the end. Next time, you can do this
without removing the carburettor provided you have noted down the dimensions. Afterthought: Take care of your FZ,
especially the early bronze type which is a beauty. The design is METRIC, so use
the correct spanners; 6 and 10mm. for the small nuts and 18mm. for the jet caps.
Brake Cable End Caps ... Recently I had
occasion to remove one of the end caps from the front brake cable on my
Chummy. Having cleaned all the paint (and crud) away I was a little
horrified to discover that there was a split to one side of the slot, about
level with where the ball would sit. Imagine my dismay, also, when
on holding it up to the light I found that I could see daylight through a small
rust hole.
Time for new ones I thought!!! Much the same 'think' as when a wheel nut stripped. Items like this I categorise as 'insurance' and put them in the appropriate column; steering arms are another example. The problem is that it is well nigh impossible to get 'correct' new ones. If they are not made the original shape, and without the proper radius on the end they can foul on the back plate. Also, I am told, there are some about that do not have a long enough slot for the ball end, and thus they try to decapitate the ball. Very embarrassing this, particularly if it happens during the annual test! Thus I set about making some new ones. Material is 5/8" BMS bar. A suitable length was chucked in the ML7, and the end turned to a dome with a form tool. Reversed in the chuck, then centre drilled, pilot drilled at 5/16", and drilled to depth at 1/2". This was followed with a 1/2" domed end mill to give a final thickness to the domed end of 3/32". The open end of the cap was faced off to finished length.
To perform the cross drilling and to machine the slot I made up a small jig. This carries the cap firstly for the drilling operation, and then having inserted a 17/64" peg to keep the register the mandrel is turned through 90 degrees for the final operation of milling the slot. A quick de-burr is the final operation, though I have dunked the ones I made in Frost's Metal Ready zinc phosphate 'stuff' to give a degree of rust prevention. Some may query the use of BMS but the forces are not tremendous, and the wear rate is not high. It is easy to machine, and now that I am set up if I do manage to wear them out in my lifetime I can make some more!!! Incidentally,
I discovered a part number on the one I removed. It is BA 185.
Spanner. September'05 .
Fuel Filters again ...
Halogen Lights A recent topic of conversation was that of halogen lighting. I promised to put up the details of Paul Goff from whom I obtained my own bulbs.
There is some good gen on Paul's site, particularly see 'History' and 'Bulb Types' These are at the very top of the 'Car and Motorbike Bulbs' page. (be warned, there is no 'go back' - thus go to the bottom of page and re-enter!) Spanner June '05 . Steering Arms Steering arms have become a hot topic in the Solent Club it seems. There was an amount of discussion last summer when I changed mine for one of the new 'high tech' offerings. My argument (to myself) was that if I put the cost into the column marked insurance it would not appear that I had spent such a lot of money on the car! Now the subject has reared it's evil head again. There has been a recent incident in the Forge car park when John Pike had the arm on his Ruby part company with itself. Fortunately there was no collateral damage on this occasion. However, it could have been very nasty since John had just towed another member for several miles. The grapevine tells me that John's arm had been cracked for some time as there was evidence of corrosion on a part of the broken surfaces. I am hoping that I will be able to get a sight of the pieces, and to get a photograph for display here, if only out of interest. By a quirk of fate I had my old one in the glove locker and was able to let John have it as a get-you-home. So far as I know it is a sound unit, and has been completely cleaned of paint. There are no 'obvious' cracks but it is bent, and has NOT been crack tested. Thus I asked John, for safety's sake, to only use it carefully and short term. Dave Cochrane has written an excellent article on this very important subject for the Association Magazine. It was he who was responsible for bringing these up-rated steering arms to the market place to the benefit of us all. The article appears on pages 6/10 within volume 2004B. I have been in touch with David Cochrane < A7C@ingineur.co.uk >. He has advised me that although the first batch of arms has already been sold, there is a new batch in production. He hopes that these will be available later this year, and is happy to accept orders now. Contact details are
as follows ............
David Cochrane A7 Components
Ltd Bridge Farm Rugby CV23 9RB To place an order, send a cheque made out to A7
Components Ltd, in the sum of £75. This includes delivery, and comprehensive fitting instructions.
Cheques will not be presented until dispatch. 'Steering Arms' An article reprinted from the Association Magazine by kind permission of David Cochrane and Ruairidh Dunford Towards the end of 2002 I became aware that the topic of replacement steering arms was cropping up fairly frequently in magazines and on the internet. As is often the case, there was quite a lot of chat but very little action! Talking to various people made me realise that the problem was rather more serious than first thought; none of the usual suppliers were selling these arms, and the stockists of used spares were finding it very difficult to get hold of any that weren't cracked. Wayne Rushin (Midshire Sevens) and Tony Betts (County Sevens) were most helpful, and examined several batches of steering arms which came through their hands. They managed to crack test a total of about 60 arms, and found that the average failure rate (i.e. cracks present) was around 70-80%. A typical cracked arm is shown below
For those of you familiar with failure analysis, the traditional "bathtub curve" illustrates how some kinds of failure occur early in life, then the failure rate drops; whereas other kinds become more and more frequent as the vehicles get older, i.e. the failure-rate graph rises up again. Fatigue failures belong in the latter category, so we might expect a lot more of these failures as time (and mileage) goes on. Several people told me that they had had them fail; Nigel Coulter of the 750 Brooklands Centre wrote: "On a fine warm spring day I had been out for a lunchtime pint with a friend and we were returning home. Coming into Liphook we started to turn right at a tight roundabout. This needed a fair wrench on the steering wheel and just as we started to turn, the wheel suddenly became free and we carried straight on into a flower bed on the far side of the roundabout. Fortunately there was no other traffic near the roundabout at the time. Being an Austin 7 it took but a moment's effort to remove it and park it safely by the roadside. Half an hour later having got a lift back home I fitted a replacement arm and we were on our way. Immediately before the steering arm finally broke there may have been some early warning in the form of an increased springiness in the steering. Otherwise there was no reason to believe there was anything amiss. The arm must have been cracked for some time but it was the hard pull at slow speed (thank goodness) that caused the eventual failure." Other accounts usually ended with something along the lines of "Thank heavens there was nothing coming the other way". Obviously it would be a very useful service to get some replacement parts made. A metallurgical analysis had been carried out a few years ago, and Steve Jones kindly supplied me with the results. This suggested that the material used conforms to EN16B.
Looking at the various arms produced by Austin over the years showed that there had not been any significant redesign until the Big Seven came along. This arm is much heavier and the radius of the bend is not so severe, but there are several other differences: it has no flat on the flange, there is a keyway on the shaft, and the arm does not curve back as far as the earlier type. However, to my knowledge, none of this type has ever been known to fail, so it was decided to use this arm as the basis for the new ones. It seemed justifiable, in this case, to break from usual practice and make these parts to a later design.
Assuming that techniques in mechanical engineering and production have moved on somewhat in the last 80 years, I thought that improvements should be possible in both design and manufacture. Given the safety-critical nature of this component, it was decided that a professional quality regime should be observed at every stage of the project. A conversation with Geraint Owen in the pub after the VSCC Derbyshire trial was extremely useful, and he put me in touch with Hartham Technology, an engineering & technology consultancy near Bath. They undertook to analyse the existing design and use computer modelling and analysis techniques to improve the life of the arm. Part of their brief was to retain the aesthetic appearance of the arm as far as possible. Dave Williams of the Austineers kindly allowed them to inspect and photograph a rolling chassis so that they were able to understand the way the arm was fitted and used on the car. They produced a very comprehensive report, which included finite element model generation, analysis, results and life estimates. They also provided drawings, manufacturing recommendations and advice on material selection for the re-designed steering arm. The stress distribution in the bend for the original and redesigned arms is shown, from which it can be seen that the maximum stress is much lower than before, as well as being far less concentrated (the peak stress denoted by the red in the right picture is about half the value of the peak stress denoted by the red in the left picture).
The overall improvement in life of the re-designed arm is significant. From the stress results calculated by finite element analysis, it can be shown that the life has increased from several thousand to several million cycles (assuming an indicative loading for comparison purposes – this does not give the actual life). For instance, looking only at the stress in the bend, under the assumed loading conditions the original arm would fail in this region after approximately 6 thousand cycles. With the re-designed arm there is a reduction in stress of 48% and this effectively takes the stress below the recommended endurance limit for EN16B steel. Hence the life is likely to be greater than 10 million cycles (at the indicative loading). Whatever the actual loads, this represents a large increase in the life of the steering arm at this location. Hartham Technology also looked at the choice of manufacturing techniques: casting, machining from solid or forging. Each has benefits and drawbacks, but in terms of the steering arm the biggest considerations had to be strength and fatigue resistance. Casting would require complex heat treatment to restore the material structure and properties and was therefore discounted. Machining would only weaken the material slightly (due to cutting through the structure), but to create the steering arm would take a significant amount of time on a CNC mill as well as produce a large amount of material wastage; hence this too was discounted. Forging is the most suitable simply because this will maintain or even enhance the strength and fatigue resistance of the part. Once the forged part has been produced, only simple machining processes are required to finish the steering arm. They recommended that EN16 steel should be used, as it gave the best match for strength and fatigue resistance.
I was fortunate in finding Mills Forgings, a local company in Coventry, who were ISO 9001 approved and willing to produce a small batch at an affordable price. They liaised closely with Hartham Technology to ensure that the re-designed arm could benefit from up-to-date forging techniques. All the arms are heat-treated and 100% crack-detected. I obtained quotes from several local machining companies, and selected C.K.S. Precision in Nuneaton, who were recommended for their good work on some vintage Delage parts and were also ISO 9001 approved. These new steering arms are intended for use with any standard Austin Seven, and the improvements in design, materials, manufacturing processes and quality should go a long way towards increasing the fatigue life of this component. They will be supplied painted and with a new nut and lock washer; comprehensive fitting instructions will also be included. Please contact me (A7C@ingineur.co.uk or see under Pram Hood Register on the back page) for price and delivery details. I would like to acknowledge the encouragement, help and advice from many people in the Austin Seven movement, in particular Rupert de Salis, Steve Jones, Nigel Coulter, Dave Williams, Wayne Rushin, Tony Betts and members of the PWA7C Midshires Group. The advice and assistance of the three companies used in this project have been to the highest professional standards. Hartham Technology Ltd www.hartham.com Mills Forgings Ltd www.millsforgings.co.uk C.K.S. Precision Ltd www.cks-precision.co.uk David Cochrane. March 2004
Trailer A trailer story .............. for those who are interested.
Filters
Side Screens How do you wear your sidescreens?
The Club Spares Scheme We have over 450 different items in stock to help keep your Austin on the road, or to finish a complete "nuts and bolts" restoration. Please contact Peter Hughes on 01489 784386 with your requirements. Spares may be collected from Peter any day from 10.00am to 20.30pm, but please telephone first. Alternatively, spares can be brought to Club Nights for collection. Most of the spares come from the Seven Workshop (our prices are the same as their's). Special orders may be placed, and we will collect on our next trip to Seven Workshop at Bradford-on-Avon. When you buy from the Club's Spares Scheme you not only save on postage and petrol, but you help the Club increase the stock. Members buying spares must produce a current Membership Card. No card - No spares! Peter. Rear Springs Rear springs - I have just changed the rear springs on my Chummy, mainly so that I should not go up the road with a fifteen degree list to starboard. Many tips on completing the exercise, and on the avoidance of pitfalls, came from all quarters and I am most grateful. Altogether a good job out of the way. Mike. Special "Austin Seven" Tools ..... Herbert soon found that there was a need to provide special tools to do certain jobs, as this made the operation much easier, and thus more speedy. There must exist within the club a version of nearly every tool that was ever on the list, together with many ingenious offerings made by the members themselves. Perhaps there could be a register of tools owned by accenting members to the scheme whereby tools could be loaned out. There would need to be an understanding in respect of damage or loss. Obviously this goes on now, and I am not suggesting anything other than that there be a list for reference so that the availability (from those prepared to lend their precious tools) was more widely understood. There might even be a case for the purchase of a few additional tools by the club when once the scene was set. Some one-make clubs do do this, and small charges are made to allow for wear, and sharpening, as well as to build up a small kitty for other purchases. Perhaps there is already a list, and I have not come across it. Perhaps the idea has been mooted previously, and rejected. .................Just a thought. :) Mike W. February 2005
| ||||||||||||||||||||||||||||||||||||
