Leyland Car Owners -

: Some time ago now I had a problem with my V8 engine. It was idling erratically and seemed unable to rev freely so I finally decided that I should really do something drastic like giving the poor old thing a tune up.
: After purchasing new plugs, set of points and capacitor, I tackled the job one Saturday afternoon thinking that this should only take an hour. I actually finished in less than the hour but when I started it, I couldn't notice any difference. An inspection of the dizzy cap and rotor revealed that they were really second hand so after shopping around, I finally located a cap and rotor (the cap at that time cost me $24 but by this time the price is probably over $30) and duly fitted them. Guess what? The mindless thing still didn't show any improvement! Now, I don't know about you but I don't like being beaten by something that is supposed to be fairly straight forward so I decided to get serious.

: Off came the air cleaner. Check Carby butterfly shaft for any sign of wear or play - OK. Run the engine and check all the inlet manifold joints with Aerostart - no change in the engine, so no manifold leaks. I'm now convinced that the problem is in the spark department.

: This time I pulled the dizzy off the engine (should have done that in the first place). When stripped down and cleaned I'm confronted with a miserable mess. The main drive shaft was so sloppy in its bearings that it must have rattled and the centrifugal weights had been so clogged with gunk and so badly worn that there is no way that they were working.

: To get myself mobile again I dug out my spare dizzy and stripped and cleaned it and then examined it fairly carefully. It too, was showing signs of wear but not enough to radically impair its performance so I reassembled and lubricated it and then put it back on the engine. No surprisingly, the engine ran better than it had for a long time.

: Some time later when I had some spare time I sat down with all the dizzy bits and had a good look at the whole set up. I wanted to have it reconditioned to use because the spare fitted to the engine wasn't in good condition either and I wasn't confident that it would last very long. I found that parts were hard to get or just not available. Bearings for the main shaft were available or could be made with little difficulty but I was unable to get a cam assembly or any centrifugal weights. Further to the parts problem, I decided that I didn't like the design of the dizzy at all. The plate that the points are mounted on does not turn concentrically about the centre shaft but is pivoted off to one side which means that when the vacuum mechanism moves the plate, the dwell angle changes. Great design Lucas!

: I then looked around for alternatives. The Rover dizzy appears to be suitable without too much trouble but is expensive, parts are expensive and it's still (yuck) Lucas. If you get the impression that I don't like Lucas stuff, you're right on, but I'll qualify it by saying that I don't like stuff made by Lucas Australia or stuff made by Lucas U.K. since 1960.

: I found that Bosch Australia used to manufacture dual point dizzy's suitable for Australian engines for Repco who marketed them as an after market performance item under the brand name 'SCORCHER'. I understand that only a few were made to suit the P76 so if you are ever luck enough to acquire one, treasure it!

: It is possible that there is an American dizzy that is easily adaptable that could be used but 1 didn't pursue this because initial price is high and availability of parts doubtful.

: One day at a wreckers yard while looking for something else I found an eight lead dizzy lying on the ground. It was a Bosch unit and the dealer told me that it came from a Holden. It looked close enough to warrant a try at adapting so I purchased one from a 308 Holden engine for $20.

: With the two dizzy's in pieces along side each other it was easy to see the differences. Both drive shafts are the same diameter but there is no tang on the Bosch unit to drive the oil pump. The drive gears are different but the Lucas one will fit onto the Bosch shaft. The Bosch housing is a fair bit different but is fairly simple to modify by a competent fitter and turner. The Bosch points plate rotates around the centre shaft concentrically - much better! Another great plus is that you can buy parts like dizzy cap, points and capacitors at the local supermarket - the last time I bought a cap it cost me $9.50 at Big W.

: So let's see what is involved to get up and running with a Bosch dizzy.

: First get a dizzy from the wreckers to suit a Holden 253 or 308, preferably in good condition so that you don't have to replace bearings, and completely dismantle it. Throw away the drive gear 'cos you'll be using the one from the Lucas unit.

: Dismantle the Lucas dizzy - preferably a spare one because this will take more than five minutes - and throw away everything except the drive gear. Actually, better keep the main body because you will need it for some measurements.

: The bottom section of the Bosch body has external ribs and this need to be turned off in a lathe and an alloy sleeve made to fit tightly over it - see fig. 1. This sleeve incorporates a flange at the top end to match the mounting flange on the dizzy body. This is necessary to raise the dizzy high enough to clear the water pump. The outside diameter and shape of the sleeve should be made to match the body of the Lucas unit. The only other critical dimension is the distance from the bottom of the mounting flange to the centre of the drive gear to ensure that it meshes at its centre. The sleeve also needs a slot to take the 'O' ring seal and a small oil access hole to match that of the dizzy body. Well that's about it for the body, now for the drive shaft and gear.

: The drive shaft requires a tang to drive the oil pump and a hole drilled across the shaft to retain the drive gear. Before this can be accomplished, the shaft must be annealed or softened - that's right, it's hardened and tempered. This is no big deal and your average fitter and turner should be able to do this as well., It is done by heating it to a bright red colour and cooling it very slowly. I did this by burying the hot shaft in a bucket of sand. The shaft may now be drilled to take the drive gear roll pin and the tang for the oil pump can be either machined or filed to match the Lucas one.



: The dizzy can now be assembled and will actually work quite well but will be better if you have the centrifugal advance curve changed to suit your engine. Incidentally, I believe that the centrifugal advance function is the most overlooked and least understood aspect of engine turning. If you haven't had your advance curve checked during the last couple of years then the only place your engine timing will be right will be at idle where you set it, but it won't be right between 1500 and 2500 RPM where most engines do the most work. The original distributor curve specifications are not optimum now for a standard V8 engine nor are they optimum for an engine that has been modified. This is due in the first instance to changes to the octane rating of petrol since 1974 and in the second to changed engine requirements due to engine modifications such as increased compression ratio and changed camshaft timing. The only way to have your dizzy set up properly is to find someone who has both a dizzy graph machine and a dyno. With this equipment a competent operator is able to determine the advance requirements of your engine and then set the appropriate curve up in the dizzy.

: One member of the Brisbane clubs knows a fitter and turner who has modified several of these Bosch dizzy's for our club members (machining only for about $90) and as far as I am aware all users are satisfied with the result.

: Bosch also markets a breaker-less ignition system that just bolts on for this dizzy. It uses a Hall effect switch and a different rotor assembly that has a toothed metal cup attached to pass through the switch and a small outboard alloy box that contains the electronics. This is a very reliable system that has been used by hundreds of taxi cabs Australia wide wince the early seventies. There are other electronic ignition systems that may be used with the Bosch dizzy but I feel that this subject really deserves a separate article.

Leyland P76 Owners 2005

Technical Information

DIZZY DYNAMICS

by Peter Rose for 1990 South Australia National