The trigonometry of timing

The Chummy has no visible timing marks unless you remove the “bacon slicer” starter motor that lives in the passenger compartment on top of the bellhousing, it’s heavy and it’s dark down there so not easy to do a quick timing check. Luckily the head has the spark plug holes in the right place to allow a dial gauge to check top dead centre (TDC) so if I knew what 8 degrees of crank rotation was in piston travel it would be good.

The App

I was a terrible student, what I did retain was lost soon after the exams but I have been saved by technology, firstly spelling and now trigonometry as they say “There’s an App for that” and on my Android phone I use a free app called aptly “Right Angle Triangle”

To cut a long story short, literally working on the back of an envelope there are 2 triangles in this calculation, the first one has a hypotenuse of half the stroke and the angle is 8 degrees, using my trusty triangle app I get the adjacent and opposite measurements. The second triangle is stacked on top with an hypotenuse of the distance between centres of the big and little ends on the conrod and the opposite side is the same as the first triangle’s opposite side from that we get the adjacent measurement. Lastly add the two adjacent measurements together and subtract them from the sum of distance between centres of the big and little ends on the conrod and half the stroke and bingo we have 0.46 mm.

The Envelope

So I zeroed the dial gauge at TDC disconnected the low tension lead to the distributor and connected my multimeter across the distributors LT terminal and earth, then cranked the motor (with the handle) and on the compression stroke the buzzing stopped at 0.45mm before TDC.

A bit of a letdown really as my original guess was  just about dead on so no easy jump in horsepower so back it tracking down the oil leaks of which there are many.

As an aside this is the internet where everyone is an expert so feel free to shoot down my mathematics.

Posted in Austin 7 Chummy | 7 Comments

A post-war pre-war carburettor

Over the weekend a group of us went on a pootle down to Wilson’s Promontory as we Regionals can, it was a lovely weekend but I think the businesses down there need the return of the Melbournites as we were the sole occupants at the motel.

While we were away during one of the many group male huddles around an open bonnet, it was noted by Colin Cheesman that I had a Grey Fergie tractor carby, this was news to me.

Then I stumbled onto a great article on why this is so, basically in the UK after WW2, old cars were being recommissioned as all the new ones were being sent overseas. A particular problem with late vintage cars was the use of Mazak instead of brass for carburettor bodies. As you probably know Mazak was a really crappy alloy that was used for all sorts of things but it corroded, so this left a whole lot of useful cars with useless carburettors, Zenith who was already making an updraught carby for the grey fergie tractor made a special one for the Austin Seven and that’s the one on my car.

This is the link to the article: http://www.ba7c.org/technicalArticles/carburettorZenith%2024T2.html

From the article I found out the things to look out for with these units, mine is a picture book example of what happens after 70 years of wear, corrosion and neglect.

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Covid fuel contamination

I took the Chummy for a run into Warragul today, first stop the petrol station, filled up then realised that I didn’t have a mask on as this car has not been used for months, bugger so paid and went home. After turning the car off I got out and stood waiting to see if the rear main leak had been conquered only to find fuel pouring out. Hmm. turned fuel off (gravity fed) removed carby and emptied the contents of the fuel bowl into a container this is what was in it:

Watery mud/rust

The float bowl had a fair bit of rusty muddy water amongst the fuel. The car came from South Australia so red dust can be found throughout and the fuel cap seal was non existent so that explains the red dirt, it is amazing it actually ran.

After a bit of reading it seems that the amount of water fuel can hold is temperature related so this car was filled with summer fuel, it has sat through a cold winter with the water separating and rusting the tank. The obvious answer to this is use your car and if you can’t because you are in lockdown, drain the tank and use it in your everyday car or even the mower.

I will chuck some metho in to hopefully suck up whatever water is left but usage should fix the problem or I may end up fitting one of those glass bowl water separators but for now fingers crossed.

Lastly here is a shot of the carby fuel inlet:

Posted in Austin 7 Chummy | 4 Comments