Clutch woes

After being laid up for a few weeks with drive-train problems, "ABW" is now back from the local garage and trundling around in the Autumn mist.  The lengthy time away was a result of a total and catastrophic failure of the clutch.

The clutch on the MG Midget can only be accessed by removing the engine... typical!  In most old cars the gearbox can be dropped to get to the offending item.  Being an engine out job, I determined that this was a little too much to take on myself (at least in an acceptable time-scale).

The clutch itself is quite a simple single dry plate affair.  It has a single drive plate with friction linings attached by rivets.  The centre (hub) of the plate slides on spines machined on the gearbox output shaft.  Drive from the plate to the hub is transmitted through springs to allow a cushioned take up of power.  The plate is sandwiched between the rear face of the flywheel and a spring-loaded pressure plate carried inside a cover bolted to the flywheel.  Drive is disengaged when the pressure plate is drawn backwards against the force of the thrust (pressure plate) springs.  This movement is activated by levers inside the cover, ultimately connected to the clutch pedal hydraulically.

Clutch components, 1275cc MG Midget

When the clutch pedal is pressed down, the clutch master cylinder forces hydraulic fluid through hydraulic pipes to the clutch slave cylinder.  A piston in the slave cylinder is connected to the pivoted clutch release arm by a short pushrod.  As the hydraulic fluid pushes the piston out, the release arm moves and the forked legs at the other end of the arm move forward against the clutch release bearing. The release bearing contains a carbon (graphite) block, that stands proud of its housing cup. This carbon-faced bearing pushes against the release bearing thrust plate.  The thrust plate actuates the three clutch release levers radiating from the hub which are pivoted so as to move the pressure plate backwards, so by releasing the clutch plate.  When the clutch pedal is released, the pressure plate springs force the pressure plate back into contact with the friction linings on the clutch plate and at the same time force the clutch plate against the flywheel (in the pressure plate - clutch plate - flywheel sandwich).

It was the carbon release bearing that failed in this instance.   The garage tells me that lumps of carbon fell out of the casing when the gearbox and engine were separated.  When the bearing failed the slave cylinder that actuates the other end of the clutch release arm over-extended, causing the piston to leave the cylinder and the clutch pedal to lose resistance and go to the floor.  The slave cylinder was replaced.

The failure came as a bit of a surprise, and occurred when Mrs C was driving the car. The clutch was a little noisy, but no more than the gearbox, or what one might expect from a car of this vintage. There were certainly no nasty squeals when changing gear,  a tell-tale sign of of a badly worn clutch release bearing.  However, I did start to get strange noises from the starter motor just before the clutch failed. This could have been caused by bits of deteriorating carbon bearing becoming stuck in the teeth of the flywheel and the starter motor pinion. The starter motor has been now been checked and seems okay.

We've now done over 1,500 miles since buying the car, in around six months.  Whilst this is not much by modern standards, it is still quite a lot for an old girl and a lot more than she was used to before I got hold of her!  Wear of the clutch release bearing is accelerated if the clutch is ridden or held down for long periods in gear whilst the engine is running.  Note to self:  remember to put car in neutral at traffic lights and junctions!

Thanks to Alan and the team at Darley Dale Garage for getting "ABW" back on the road.

Shakespeare Irregulars

Early September saw “ABW” take part in her first historic road rally:  The Shakespeare Rally, organised by A La Carte Rallies, and took place in the heart of England, near Stratford-upon-Avon,.

This was a regularity challenge over two days, designed to test each crew’s ability to maintain a precise average speed over a route requiring complex navigation on public roads. The idea is to provide a competitive event, without encouraging high speed driving.

Participating cars included Jaguars (E-Type, XJS, and Mk1), Porsches (356 and 911), Triumphs (Stag and TR4A), Austin Healeys (3000 and Sprite), Lancia (Fulvia), a Corvette, and of course an MG Midget!

Lined up, ready to go.  Le Mans start not necessary!

The target speed was 24mph (apart from a couple of slower narrow lanes), designed to maintain safety and protected cherished, and in some cases valuable classic cars. That’s the idea!  Sounds slow... perhaps a little tedious? Unfortunately, as soon as you’ve made a mistake or got delayed, you’ve got to try and make up time. Crews are being timed to the nearest second through several intermediate time controls on each stage, sometimes with secret controls located out of sight. At the end of the event, the team that has visited all these controls and who has the fewest early or late penalties overall is the winner.

Speed tables are used to accurately re-calibrate the speedo in the car, based on a precisely measured circuit (so in our case we were using 23.9 mph tables for this rally). Mrs C was navigating and checking average speed – the tables giving us exact times for precise distances (to the 1/10 mile).

Arguably more important is navigation. The rally used a series of ball and arrow diagrams to describe junctions where a deviation from “the ordinary course” was required, supplemented by clues and instructions that are not always obvious. The diagrams are usually referred to as tulips; not because they look like flowers, but because they first came to prominence in the Tulip Rally (Tulpen rally) of the 1950s. Getting the route wrong makes you hopelessly behind on the average speed, hence the importance of navigation.

“ABW” and the crew came a credible “not last” in our first taste of this type of event. This was despite missing one of the first turns and getting hopelessly off course on the first morning. Gradually we improved our accuracy and reduced the penalty points – even scoring a near-mythical zero on one section (completing the section to the nearest second at average speed).  The winning Jaguar MK1 team scored only three hundred penalties over the whole weekend; I think we managed that on one stage!

Approaching a control point

More importantly we had a great time, met some new friends and fellow classic car enthusiasts, and had an excuse to clock up a couple of hundred miles in the car. The navigating and regularity driving was mentally challenging, but good fun. Fortunately there was time to relax and recuperate each evening.  To top it all navigator and driver are still on speaking terms.

A great event that was excellently planned and executed by A La Carte Rallies. Bring on the next challenge!

Dizzy distributor

Some tweaking in the workshop last month, resulting in a new distributor cap, left me hopeful that misfiring issues were firmly in the past. Then last weekend the tell-tale lurch of a mild misfire reared its unwelcome head! Was it electrical or was it fuel? Nine times out of ten the issue is electrics – points, distributor rotor, distributor cap, plugs, coil, condenser, HT leads…

“ABW” is fitted with a Luminition optical ignition system, ruling out points issues. But last time the problem was the distributor cap – burnt out by the fitment of the wrong coil by the last owner. Next to check is the plugs and HT leads, but no obvious issues are apparent; spark is good on each cylinder.

So what about the distributor rotor arm? I’ve read plenty of bulletin boards bemoaning the quality of replacement rotor arms. To my surprise the rotor arm doesn’t look like a regular MG Midget item. What is going on?  Examining the existing rotor results in more questions about MG Midget distributors.

Firstly which distributor should be fitted? From 1961 to 1974 MG fitted the Lucas 25D unit to the Midget; from then to the end of production in 1981 the Lucas 45D type was fitted. Both were fitted to MGBs and other Austin Morris vehicles. So, being a 1972 model, “ABW” would have originally had a Lucas 25D type.

Lucas 25D distibutor

The 25D unit is considered to be a reliable unit with an abundance of spare parts. The mechanical advance mechanism is generally reliable and dependable, with original components of high quality hardened steel. The use in multiple engines, and multiple applications of the A Series engine in particular, means that many advance and retard curves are available.

The main alternative is the 45D unit fitted to the later MG models. Not only are second-hand items widely available, but many brand new reproduction units are available.

Lucas 45D distibutor

Reports suggest that the quality of some replacement units is variable, with lower quality bearings (though not always an issue for low mileage classic cars).

MG Midget ignition rotor arm Lucas 25D4 type 1961-1974

MG Midget ignition rotor arm Lucas 45D4 type 1974-1981

The existing rotor arm looks similar to that fitted to the 45D type distributor.

Of course, the engine doesn’t know whether it is being serviced by a 25D or a 45D distributor; no more than it knows whether the distributor is electronic or has points. All the engine is interested in is that a spark of the right strength is delivered as the right time.

What exactly does the distributor do – beyond delivering the spark? The most important function is to place peak cylinder pressure at 17º-20º above top dead centre (ATDC) by advancing the ignition spark as engine speed increases. The difference in crank speed between idle and maximum engine speed is about an order of magnitude. However the rate at which the fuel burns is relatively fixed in comparison. That means that the mixture needs to be ignited earlier and earlier as the revs are increased. Igniting the mixture too soon drives the piston down before it has reached the top of the stroke – “knocking” which will damage the engine. Leaving it too late reduces power. Not surprisingly, car manufacturers are incredibly conservative, preferring low power rather than warranty claims!

The stock ignition curves that MG used when “ABW” was manufactured never envisaged the engines would be operating 40 years later, let alone using lower octane unleaded fuels or coping with engine, carb, or exhaust modifications.

The distributor contains a cam and two springs. Under the cam are a pair of counterweights that fly out as speed increase and cause the cam to advance. Different cams can be used to adjust the maximum advance figure. The cam opens and closes the points… and is increasingly becoming obsolete with the introduction of after-market electronic systems! However, the principle remains the same. The other item that can be adjusted is the springs. The length and rate of the spring can also be manipulated to change the advance curve.

“ABW” is fitted with a performance distributor from Aldon Automotive (http://www.aldonauto.co.uk), a long-established supplier of performance parts in the West Midlands. Aldon have been successfully modifying distributors for many years, supplying its own make of performance distributors amongst other items. Their units that are based on Lucas and Bosch distributors, with a modified advance curve to suit the engine specification. It appears that “ABW” has an 100AR series Aldon unit. A quick call to Aldon has a replacement rotor arm sent, arriving next day – excellent service.

The rotor arm is definitely the same as that used on the later 1500cc Midget unit. Reassuringly, Aldon sent me Bosch rotor – hopefully of good, durable quality.

Aldon AR100 distributor

Classic car, classic ads?

MG had a history of producing classic advertisements for its cars. "Safety Fast!" became a slogan synonymous with the brand.

According to the various fundi on the MG forums, the origin of the slogan was George Tuck, who was the publicity manager for the MG Car Co Ltd in the 1930s. The story goes that Ted Colegrove, the original Sales Manager of the company at Abingdon was driving behind one of the new buses in Oxford. The bus had a big red triangle on the back and words "Safety First!" painted through it, to indicate that they were fitted with four wheel brakes which was a novelty then. Ted thought that if the "ir" was replaced by an "a" it would make a jolly good slogan for the MG, so he went back to Abingdon and, with George, sold this idea to Cecil Kimber, one of the founding fathers of MG. From then onwards it was the only slogan for MG! It was still being used into the 1960s. For example, it appeared on a 1962 MG Midget advert - "Safety Fast motoring is the safest of all".

Now my interest is more at the other end of the decade.  The MG Midget was still trading on its sporting heritage in the sales brochures for the Mark III model.  "Sport the real thing" became the slogan for both Midgets and MGBs. I've been hunting around on eBay for bits of memorabilia and picked up a framed original, fittingly featuring a glacier white Midget similar to ABW.

1970 MG Midget sales brochure

The time around 1970 is widely recognised as the nadir of MG advertising, although it has a certain period charm. For a while "Your mother wouldn't like it" was the banner on many ads - though it was never clear whether this referred to the car or the driver!

Of course, the driver was inevitably a man, even though a reasonable proportion of owners were women.  Some of the copy must have seemed quite dodgy at the time; it seems downright sexist now!  An example was the "You can do it in an MG" slogan... very Carry On!

My favourite period advert tried to address the question of the manliness of the MG Midget; it carries the slogan: "85% of Midget owners are men". In marketing terms you might describe this advert as "suggestive".  It features a scantily-clad young  lady fondling the handbrake!  The copy is even better, reminding you that "lots of girls will be relaxing in our new, thick contoured rake adjusting seats."

MG Midget advert, 1970 

Mrs C was horrified when I purchased this one on eBay; "Not in this house" or something similar! Some of the other copy on this advert is open to challenge too: "Magnificent high speed cruising."  Whatever you might say about the MG Midget, it is not a high speed cruiser.

How different these adverts are to those that were used just 10 years earlier to advertise the Austin Healey Sprite.

Austin Healey Sprite brochure, 1958

 Ahhh!  Halcyon days!

Oselli 1293 Fast Road Stage 2 Engine

In an earlier article (Oselli and the MG Midget A-Series Engine) I discussed the history of Oselli and its links with the MG Midget.  Since taking delivery of ABW, I've been able to do a lot more investigating into the tuning that had been carried out on the car.

ABW was tuned by Oselli in 1998. The engine was removed , reconditioned and rebuilt to 1293 Fast Road Stage 2 unleaded specification. But what does this mean?

The 1293 Fast Road Spec claims to gives 95 horsepower, but retaining good manners for town driving. Fuel consumption remains good at cruising speeds and there is lots of low speed torque (see previous article on towing with MG Midgets!). Oscelli strengthened the bottom end considerably to provide a reliable unit able to rev up to 7500 rpm and able to last over time.

Power curves from Oselli brochure, 1998

The work done by Oscelli:

• engine stripped out
• parts checked, tolerances measured, and prepared for machining
• engine rebuilt, clearances checked, cam timing set up
• engine bored out to 1293cc
• crank, flywheel, clutch, pistons and conrods all balanced
• tufftride treatment to crank, journals repolished, alignment checked
• heavy duty bottom end main and thrust bearings fitted
• flywheel lightened
• cylinder head modified to large valve OE62 Rally Spec
• A600 camshaft fitted, cam follows set
• high capacity oil pump
• miscellaneous new seals and gaskets
• performance distributor

According to the May 1990 catalogue, the specification of the Oselli A600 camshaft is: 37/71/71/37, 288° duration inlet/exhaust, 0.360" valve lift with std 1.25 rockers, 0.016" tappet clearance, 107° inlet valve full open for timing setting (data from Richard Wale, 2009). It was a slight de-tune on the 1293 'Rally' specification (for which the Kent 286 camshaft was standard).

Close-up of ABW's "Oselli tuned" engine

Some months later Oscelli tuned the SU HS2 carburettors, fitting ‘AF’ needles – the standard specification being ‘AN’. The new needles offer better performance with the K&N filters, tuned exhaust, modified head, and fast camshaft fitted to ABW.

ABW's engine bay

Standard Midget engines are quoted at 65 bhp. I'd be amazed if ABW is giving anything like 95 bhp – but she seems eager!

ABW gets a grilling

With old cars there is always a question as to how original one should keep the specification.  Purists would say you should try to keep the car as close to the factory spec as possible.  In the case of ABW that means Rostyle wheels, vinyl seats, navy trim and an MG steering wheel; rather than the alloys, leather, black interior, and 13 inch steering wheel.

Personally, I rather like the upgrades, particularly when they are period-style accessories.  The thing that attracted me to ABW was all the upgrades, small and large, that have been lavished on her without losing the period essence – which is after all why we buy classic cars.  I've already fitted a Smiths cigarette lighter that I had knocking about the garage.

Now the grille was causing me some concern.  I discovered, on close post-purchase examination, that the fitted part was close to disintegration.  This was the standard Mk III black “egg g box” item fitted from 1969 to 1974 when the rubber bumper Midget was introduced.  The grille is an alloy mesh, painted black, with a stainless steel trim and an octagonal black and red MG badge fitted centrally.  

Standard Mk III MG Midget (GAN5) grille

The options were to go with the standard black or perhaps fit the slightly plainer, polished alloy version from the Austin Healey Sprite, fitted from 1961 (Sprite Mk II) to 1969 (Sprite Mk IV).  This is similar to the MG grille, but without a centre badge and the stainless steel detailing.  

Standard chromed “egg box” grille fitted to an MG Midget

An even more radical idea was to fit the vertical slat grille from the earlier Mk I and Mk II MG Midget.  This is of a rather complicated construction, with a black and red MG shield-like badge towards the top centre of the grille. 

 Mk II MG grille

Cost inevitably becomes a factor, with standard grilles costing around £150 or more and second-hand examples often bashed and bruised and little better than the one being replaced.  A final option was to look to something sportier.  For a while Ashley Hinton has been manufacturing stainless steel components for Midgets and Sprites.  A snazzy grille caught my eye – retailing at a very reasonable £75 including badge at the Midget 50 show.  The quality was excellent. (Ashley Hinton website: http://www.mgcars.org.uk/ah/)

Fitting was simple; a straight replacement and a fitting kit was included.  The new grille fitted snuggly inside the existing aluminium surround finishers that are riveted to the body work.  However, to my eye the finished job looked a little too plain; perhaps too much like a racing car or special.  The solution was to take the stainless trim off the original defunct grille and mount it to the new item.  Finding some suitable fixings was a challenge, but eventually it all came together.

 New Ashley Hinton grille fitted, with additional stainless trim

I’m rather pleased with the final arrangement.  No doubt the purists will shake their heads!

Alternator aggravation

So a couple of days into owning ABW and already the gremlins are starting to attack!

Engine cutting out on deceleration when hot (probably fuel vaporisation in the carbs), a soaked floor under the driver’s seat in heavy rain (small rip in roof), a disintegrating grille and an annoying misfire (yet to be diagnosed).

The latest problem is the alternator.  Originally ABW would have had a dynamo, but at some stage (fairly recently, judging by the cleanliness of the components) she has had an alternator conversion.  Whilst trying to discover the cause of the misfire, I noticed the alternator was loose, only to discover cracks fore and aft in the mountings.

A quick bodge with some penny washers to keep things going, whilst I sort out a new alternator and bracket. This seems like an unusual place for the failure of a fairly new component, so I must investigate any root cause.

Old cars, don't you love 'em!