Here's some information of vacuum advance which explains in detail how the unit operates. If you look at the original advance specifications for the BJ8, the mechanical advance of the distributor is 18º distributor. Add to that 8º vacuum advance equals 26º. Because the distributor turns at half engine speed you double this for crankshaft degrees, 52º and add the static advance of 10º and the total advance at 6400 rpm is a massive 62º. This is 2º more than one cylinder! Much too high and my only guess is that in 1966 it was important to improve the MPG.
The rev limit is 5200 rpm but even then its 58º total. The six cylinder engines are much better at 34 or 36º maximum plus 16º vacuum. You'll also notice on the graph that the vacuum advance is constantly moving in response to speed, manifold depression and the amount of throttle.
Yes folks now you CAN service Lucas vacuum units so don't throw them away.
It's not too difficult to repair them and many of you will be able to do this with a few simple tools and a bit of time.
There is the coiled spring type connection to the points-plate and the lever type connection. With the level type, drill out the rivet and remove the lever, noting its original position. You'll have to replace this rivet with a 3/32" one.
Roll back the folded edge of the housing. I use a pair of 5" long pincers, similar to nail removing pincers. One of the blades has been ground to a curved sharp edge and the other to a concave flat edge that suits the curve of the housing. By working around the edge 5 to 6 times the edge will be opened up enough to separate the housing and reveal the old diaphragm, hardened and split by petrol that finds its way there from the carby and down the vacuum pipe.
Remove the old diaphragm by drilling out the centre, save the retaining washer. This material is fabric reinforced neoprene and available from pump repair places of gasket makers. It is about .016" thick; (.4mm) cut two circles 2.46" dia. and with a leather punch a small hole in the centre for a retaining screw 1/8" or 4 BA. Drill and tap a hole in the control rod to take the screw and reassemble using a small amount of RTV silicone. Don?t forget the retaining washer.
Using a small amount of RTV silicone on the edges of the diaphragm, reassemble making sure the control rod is in its original position, and start bending the folded edge back into place with some pliers. Finally tap the edge down with a hammer and allow the silicone to set. " VOILA " a vacuum unit that now works.
On vacuum units most of you know what the numbers mean but I?ll repeat them for you. A 5.12.8 unit means the advance begins at 5 degrees of mercury vacuum is complete at 12 degrees of mercury vacuum and provides 8 degrees of distributor advance (that?s 16 degrees at the crankshaft).
Vacuum units for the BN1 is 7.18.12 for the BN2 5.17.10 and from the BN4 to the BJ8 5.12.8. Modified engines should be recalibrated using a vacuum gauge and test runs using light throttle at specific RPMs to optimize fuel economy and avoid early pinging. Using these figures you can try to find a vacuum unit that matches the modified engine or use one of the Hexagon head units and alter the spring rate and degrees of advance. A final coat of silver paint will improve the overall appearance.
If all this seems too hard then give you vacuum to Don Hardie or me and we'll do it for a modest fee of $40. More on vacuums next month (will it ever end?)
I've been asked to write some explanatory information on the use of the "Tefba" Radiator Filter.
What the filter does is simply to filter the hot cooling water as it leaves the engine, before it reaches the top of the radiator. Normally, without the filter, any foreign bodies such as rust particles, paint flakes, mud build-up etc would reach the top of the cooling tubes in the radiator, which could, depending on the amount of contamination, very soon become clogged up and reduce cooling efficiency.
On a new car, such a filter is not necessary, because presumably the inside of the engine and cylinder head are quite clean. On a 35 to 45 year old car however, such as our club vehicles, quite a lot of contamination can have occurred, and considerable amounts of debris can be dislodged, particularly if the system is disturbed by an engine re-build or even removing and replacing the cylinder head for a top overhaul. From personal experience I have been amazed at how much rubbish is captured in the filter after this type of work.
For this reason I strongly recommend the filter be fitted whenever possible, particularly when you figure that the cost of a filter is less than half of that of a radiator clean!
The centrifugal advance mechanism adjusts spark timing according to changes of engine speed, while the vacuum advance unit adjusts spark timing in relation to engine load. The two devices operate independently but the total spark advance is dependent on both.
An engine operating at 1500 rpm may be running under very light load with the throttle open only a small amount. This would be true if the car were being driven at a fixed speed on a level road. On the other hand, at the same speed, the engine may be under full load, as would be true if the car were being driven up a steep hill with the throttle wide open. In the first example, engine speed at 1500 rpm, engine under light load -the manifold vacuum would be high. This would operate the vacuum advance and the total spark advance would be the sum of the centrifugal advance plus the vacuum advance. In the second example, at the same engine speed but operating under full load, very little vacuum exists in the manifold. Because very little vacuum is available, the vacuum advance unit would return to its retarded position. Therefore, the total spark advance would depend on the operation of the centrifugal advance unit only.
Under any operating condition, the total spark advance is dependent upon the' speed of the engine and on the load under which the engine operates. Thee higher the speed, the greater the advance, and also, the lighter the load, the greater the advance. At any speed, the load on the engine may vary from zero to full load depending on the position of the throttle plate. When the engine is operating at high speed, the throttle will be open which results in low manifold vacuum. Spark advance is controlled entirely by the centrifugal advance mechanism at this time.
In any event, the total spark advance at any engine speed is the initial advance, plus the centrifugal advance, plus the vacuum advance.
Copyright 1967 Ignition Manufacturers Institute Printed in USA 197
Well, we all should know about vacuum advance and be able to repair them by now. Neil Thew at Kiama is putting a new diaphragm in his Healey right now, so he?ll be able to help out the South Coast Members. Just remember: it?s there to improve economy at light throttle, cruising between 2,000 and 3,500 RPM. Average fuel consumption should be between 23 ? 26 MPG. The formula to calculate your average fuel consumption is:
John Kent in his BJ8, with a 3.5:1 diff, big circumference tyres and a 22% overdrive was getting close to 30 MPG on his way to Albany. When Geoff Sherman and I went across to Perth, Geoff was getting 34 MPG with a 3.5:1 diff, big tyres and a 28% overdrive. With the vacuum advance system working correctly you?ll get a clean, efficient burn and clean plugs & cylinders. You can actually go up one grade colder plugs on a long trip.
At the last meeting we showed the TEFBA radiator water filter and I think these are a good idea and keep your new $800 radiator from clogging with krud. Flush it every 2 years. I refill with Nobles Ultra Pure Water and a bottle of tri-acid corrosion inhibitor such as Nulon or Wynnes. You do not need glycol or anti-freeze unless your Healey lives in the mountains. Glycol actually makes the cylinders & pistons run hotter due to fact that it is denser than water and slows down the heat waves escaping from combustion.
2017 Concours guidelines order form
The 2017 US Concours guidelines are now available for order from the US Austin Healey Concours Registry. Cost is $US 15, if you choose the electronic (dropbox) edition. Here are the Order form and the Contents and coverage information.
BN1 & BN2 Concours d'Elegance Inspection Form - download form
BN4 BN6 BN7 & BT7 Concours d'Elegance Inspection Form - download form
BJ7 & BJ8 Concours d'Elegance Inspection Form - download form