Air Cleaner Modifications and Installation

Today I took the opportunity to do some work on the Air Cleaners.

The first thing I did was measure the clearance between the engine hood and the top of the new Air Filter assembly on the centre carb.  As you can see there is about 6.5mm clearance (approx 1/4″).  A good start.


I have been pondering if the strap across the base plate actually adds and value.  Considering that the carb takes all of the Air Cleaner retention load, I decided that they did not.  I therefore removed them as it will improve the flow quality into the carb throat.  I broke them off by tapping them with a hammer – they were easy to break off as they are a low pressure castings.

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I really want to maximize air flow, so I did some Googling and found some American made filters in two heights (1 3/4″ and 2 1/2″) at Allstate Carburettor & Fuel Injection.  The filters do not require oiling and are washable.  I have dealt with Allstate before and found them to know their stuff.

In order to maximize the air flow into the carbs I decided to modify the bases by cutting the front and rear down.  This will allow me to use the 2 1/2″ filters on the ‘dumpers’ and an 1 3/4″ filter in the middle.  The smaller filter in the middle is because the choke housing prevents me lowering the filter enough to use the taller filter.

I conservatively measured and marked where I wanted to cut.  I only lowered them just over 1/2″to start with as I can always remove more material if needed but I can’t put it back!  The hacksaw cut through the alloy base quite easily.  I repeated this for the second base and then spent some time filing the bottom face flat.  A lathe would have made this many more times easier.

Dennis O’Brien at O’Brien Truckers (where i bought the filters) told me to be careful when reducing the inlet height because the taper might make the hole larger, however what I found was the taper went the other way and the opening got smaller.  I therefore had to spend some time making the hole larger so it would fit the carbs.

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I also spent some time with my large electric die grinder and a carbide burr smoothing the inlet where the straps were removed.


I now turned my attention to the finned tops.  I want to paint them similar to the rocker covers, so I started by using an allen key and a rag soaked in methylated spirits to clean out the grooves and remove any buffing compound left behind.  A little bit tedious, but very necessary.  Once complete I masked the tops up to prevent everything being painted.

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I then blew on some light coats of VHT Cast Iron Engine Enamel.

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Once it had started to cure I removed the masking tape.


I then soaked a rag in acetone and carefully removed the paint from the tops of the fins.  This is much easier when the paint is still a little wet.  The result was pretty excellent!

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While the tops cured I had another look at the bases and found all of the handling had scratched the outer polished surface a little.  I gave the surface a rub with P800 wet & dry sandpaper, followed by P1500.  This gives a nice satin finish, however I need polished.  I used a buff wheel in a drill and polished them back to a full gloss.

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A little later I assembled the air cleaners on the carbs.  As you can see there is still plenty of clearance between the base and the choke housing, so I could lower the centre base if needed.  Measuring on the carbs, I expect I will need to lower the front and back bases another 5 or 6mm with the higher filter elements in order to have the finned tops all the same height.  I decided to leave the new filters assembled on the car using the supplied filter elements.  Already this is a huge visual improvement on the 4″ round filters, with a significant increase in filter surface area (more than double).

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As a final check I put a piece of Blue Tack on the centre filter nut (the highest point.  I closed the hood carefully, and gave the hood a bit of a push over the filter when it was fully closed.  the result was about 3mm clearance.  Keeping in mind that there is a sound absorbing damper under the hood over the carbs, this should be fine however I will lower the centre carb another 3mm in the future just to make sure.  I have a friend with a lathe which will make the process much easier next time.



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