A Twin Cam called Ratty Part 9

Tyre fitting at Dawsons, Bedford

At last, after two years work, Ratty’s back on its wheels again. I had been dragging my heels for some time trying to decide which tyres to buy and finally made my choice after talking with my friendly tyre expert at Dawsons Tyre and Exhaust Centre in Bedford (01234 341585). He gave me some sound advice and was very helpful in sorting out the best product to match the Twin Cam performance and the depth of my pocket!

The factory would have originally supplied the car with Dunlop RS4 cross-plys but tyre technology has progressed dramatically in the last forty years and radially constructed tyres now offer improved safety, durability and price. I am told you can once again buy remanufactured RS4 tyres but they are quite expensive and I decided that value for money and safety were more important than originality in this case. As I intend to use the car for touring both in the UK and on the Continent safety is an important consideration.

Potentially the Twin Cam can cruise at well in excess of 100mph and therefore tyres have to be selected with a “T” rating to suit continuous speeds up to 118mph. With a National UK speed limit of 70mph it could be argued that this is academic because attempting to use the full Twin Cam performance on the public highway will probably cost you your licence. If a vehicle has the potential to cruise at a given speed however the tyres must be compatible to its top performance. Circumstances may arise where top performance can be legally used, for example on a track day at one of the racing circuits. When the red mist comes down out there on the track it will be comforting to know that the tyres will cope with the car’s top speed!

The size of radial tyre to match the wheel rim was 165×15 and quotes were obtained from three major suppliers. I found that Firestone, Continental and Michelin had tyres in this size and speed rating but the difference in price was staggering. The least expensive tyre, fully fitted and balanced was £50 supplied by Firestone. The most expensive, supplied by Michelin was £78. By choosing Firestones I made a saving of £140 on a set of 5 tyres and they also had the tread pattern which most suited the age of my car.

I have been using Dawsons for many years and find their staff has a very sympathetic attitude to owners of older cars. They take a great deal of trouble to avoid damaging the rims when fitting the tyres and can also successfully balance unusual wheels. In the past they found a way to mount and balance the large 19-inch wheels fitted to my 1929 MG18/80 and the difference to the feel of the car afterwards was amazing. The Twin Cam wheels also presented the fitter with a challenge when he tried to mount them on the balancing machine. They are a centre-lock, peg-drive design made by Dunlop and were only fitted to a few types of car in the 1950s. They are therefore a rare sight today for the average tyre fitter. They were not put off however and quickly adapted the balancing machine to mount the wheels as shown in the photograph.

Back at home it took only a few minutes to fit the wheels and at last it was possible to roll the car outside for a photographic session. It was a great moment for me and it made all the hard graft over the last two years seem very worthwhile. However this was only a morale boosting exercise and there was still much to do so the car was put back and work continued.

In the last article I reported that the engine machining by ‘Dick Turpin’ was well under way. The machining has now been completed and the parts have been reworked as follows;

1. Engine sleeved to standard bore.
2. Original 8.4 to 1 pistons bead blasted and machined to accept thicker piston rings.
3. Crankshaft main journals reground minus 0.010 inches. The big end journals were unworn and only required polishing. New bearings supplied.
4. Half speed shaft bearings supplied and fitted.
5. Pistons and connecting rods weighed and balanced to be within 0.1 grams.
6. Crankshaft, flywheel and clutch dynamically balanced.
7. Valve seats re-cut with multiple angles to improve gas flow and valve seating.
8. Inlet and exhaust valves and new valve guides supplied and fitted.
9. Steel inserts fitted for the spark plugs.

This is quite a comprehensive list and I was not surprised to receive an invoice for £800 for the above work. On the plus side there was not much else to purchase to finish the engine rebuild, only a new camshaft chain and four new tappet buckets from Bob West which added another £100 to the total.

Cleaning the oil ways. Note old plug removed and new replacement ready to fit	Fitting crankshaft and main bearings. Note shiny areas on crankshaft balance weight where material has been removed for balancing
Removing plug from oil way	Getting ready to install the first piston and connecting rod. In this photograph you can see the new piston ring set and big-end bearings

Dick returned the bottom half of the engine while he continued with the work listed above on the cylinder head. Every time I have any machining done by Dick I get the same lecture about cleaning the parts before assembly and quite rightly so. Too many newly restored engines are ruined in the first few seconds because of inadequate cleaning of the oil-ways before assembly. Dick insists that it is a waste of time to clean the inside of the engine if you don’t also clean the oil-ways using special long reach brushes as shown in the photographs. I purchased those shown in the photograph from Frosts (the catalogue car accessory suppliers).

This cleaning process is not straightforward on the ‘B’ series engine because you need to remove seven brass plugs at the end of each oil-way to allow the brush to do its work. The photographs show one of the larger plugs drilled and tapped being removed with an improvised puller. This particular oil-way is 0.5 inches in diameter and once the plugs were removed each end the brush was used to thoroughly flush out years of accumulated sludge. The sludge of course is a wonderful medium for capturing any particles from the machining process so it easy to see how on first start up oil would carry them straight to the bearings.

All pistons and bearings fitted.	Oil pump and front engine plate fitted	Sump and timing gears fitted

I remade the brass plugs with a very slight taper of 0.001 inches and replaced them when I was happy that all the sludge and debris had been removed by brushing and copious flushing with white spirit. The same treatment was applied to the oil-ways machined into the crankshaft and once again a lot of sludge was removed. The inside surfaces of the cylinder block were also cleaned at the same time and it was surprising how good the internal surfaces looked after the cleaning fluid dried off.

Building up a newly machined engine is pleasant work using the standard approach starting with the block upside down on the bench and the main bearing shells placed in their machined recesses. At this point it is perhaps worth mentioning that I once rebuilt an engine with one bearing shell supplied by the manufacturer 0.010 inches smaller than the rest of the set. The engine went together satisfactorily, although it seemed hard to turn, and it was not long before the journal with the wrong half shell damaged the crankshaft. This experience has made me very cautious and I trust nothing unless I have checked it for myself. I now adopt the following build procedures to ensure this kind of problem is avoided.

Engine with cylinder head, the first trial fitting	Setting the tappet clearances. Note small spacer discs on top of the four tappet buckets	Trial fit of timing case. It is a large alloy casting and it must be checked for flatness to ensure an oil tight joint

I place the crankshaft in the bearing shells with plenty of engine oil to lubricate the journals, followed by the bearing caps with the bearing shells fitted. I tighten the bearing cap nuts by hand first and check the effort required to turn the crank over. Then as each bearing cap is tightened according to the manufacturers torque setting I ensure that the crankshaft can be turned without any increase in effort. Any sudden change in the torque required to turn the crank indicates that there is a problem somewhere which must be investigated before going any further. The most common problem is usually a minute speck of dirt between a bearing shell and the cap but the effect if left unattended will be disastrous.

The next stage is to fit the pistons to the connecting rods ensuring that any numbering of rods and pistons set up in the balancing process is preserved. Each piston and rod is pressed into the engine from the top of the block using a piston ring compressor. I knew Dick would have checked and set the piston ring gaps but I still needed to measure them for myself. My advice is, always trust nobody but yourself when rebuilding an engine. By connecting one piston and rod at a time to the crank it is possible to detect any tightening which may occur as the big end journal is assembled. As each piston is fitted there will be more effort required to turn the crank because the piston is being driven in the bore but it will still be obvious if there is a fault somewhere in the bearing journal.

Cylinder head showing polished hemispherical combustion chambers and new valves	Restoring cylinder head studs and nuts using tap and die set
Original wiper motor and replacement. Note the replacement was new ‘old stock’ with some missing parts which were recovered and cleaned from the original	Wiper motor installed in the bulkhead

Once the main and connecting rod bearings are fitted and locked the last task at the bottom end of the engine is to fit the oil pump. I fill the pump with grease to help the pump start and deliver oil as soon as possible. The sump is then fitted to avoid any dirt particles entering the critical bearing area.

It is worth noting that I have ended up making all the gaskets for the engine despite managing to obtain a new-old-stock set at an auto-jumble. When I came to use the set I found they all seemed to be too small and I think they may have shrunk over the years. By using gasket material and good quality hole punches it was not as difficult as you might think to make new ones, especially with the original as a pattern.

With the engine standing up on the sump I fitted the flywheel next and then the front engine plate on which the chain drive to the camshafts is fitted. Careful checks were made of all the components involved and this revealed a blocked lubricating jet. If this had not been discovered it would not have been a disaster but the timing gears would have been noisy and a source of irritation when the car was up and running.

About the time I finished assembling the bottom half of the engine Dick rang to say he had finished the cylinder head. The twin cam set up on the MGA engine is straightforward to assemble if a little fiddly. The tappet gaps are controlled by small precision discs which were originally supplied in a range of sizes varying by increments of 0.002 inches. To set the correct gap it is necessary to assemble all the valves, springs, tappet buckets and camshaft and measure what gap is present. Theoretically any correction involves selecting a larger/smaller spacer to adjust the clearance. It is job that requires a lot of patience and several attempts were needed to achieve the correct clearance of 0.014 to 0.015 inches. That just leaves the fitting of the timing chain and checking the valve timing and I am working on that at the present time. I will report on the finished engine in my next article.

I have also considered the possibility of fitting Ratty with a five-speed Ford gearbox instead of the standard MG unit. A company called Hi-Gear supply a complete kit to carry out this modification and I have been impressed with their approach and engineering. It is not cheap but does come complete with everything you need, including a new prop-shaft and alloy bell housing. You can choose which gearbox suits your needs including an overdrive 5th gear to improve fuel economy and noise reduction for motorway cruising. It seems an attractive option but needs more thought and I will report on my decision in the next article.