Today I finished welding up the manifold. Nothing too tricky really. I did tack weld it with the mIG first to make sure everything was in the right position although since I had already made all the holes the only thing I really had to get right was making sure the plenum and the outlet port flanges were at right angles. I tweaked things until they were then MIGed them in place then brazed around the welds hence the couple of bumps in the brazing!
That’s under the plenum though so not really visible. I soaked it all in caustic soda to remove the flux but it still needed a lot of wire brushing to remove it all. I then filed all the mounting flanges flat then sanded everything smooth. I’ll pressure test it all by bolting on flat plates and filling it with water then pressurising it with air from the compressor. It’s the same way I have tested model steam engine boilers. You fill it with water first since water isn’t compressible (much) so if it does burst you don’t have a sudden release of a massive volume of compressed air. Hopefully that should prove it’s solid enough. To test for leaks I can just blow air into it (at low pressure) and put it in a bucket of water and look for air bubbles.
I did a test mounting of everything and it looks good.
The lugs on the blower also nicely mate up near some of the head studs so I can make an additional bracket to support the blower to the head via long studs.
With the downdraft SU on top there is about an inch clearance to the bonnet line. I’ll need maybe half an inch to make an adapter plate to bolt the carb to the blower so the bonnet will need a tidy little bulge right above the carb I think.
Next, back onto aluminium bashing. Drilling and tapping the plenum for a vacuum/boost port won’t take long.
I have done more on the inlet manifold. I completely forgot to buy a 31mm hole saw when I went to the engineering shop so I had to drill and file the outlet holes by hand. With that done I did a test fit of everything. I found that one of the bolts to bolt the blower on just wouldn’t fit through the hole past the outlet pipe. I could have fixed it by filing one of the flats on the head of the bolt as that would give enough clearance. I don’t like having specific fasteners in specific places though. Better if the four mounting bolts are all the same so it doesn’t matter how you put them in. Instead I filed out the holes and fitted a bigger diameter tube which gives me enough room now to drop the bolt in.
A test fit shows everything will work. I’ve started tack welding parts and tomorrow will braze it all together.
I also played about a little with making a new dial for my custom tachometer. The first was just printed on paper and glued on but for a recent project I played with etching brass. The results of that were so good I decided to try it on aluminium. The process is a little fiddly and needs nasty chemicals but the results are good. This was my first try and it’s good enough to use.
The etched one is on the left and the printed one on the right. The etching isn’t perfect so the face had a nice, old patina built into it. I wasn’t taking much care over it as it was just a quick test to see if it would even work. It is hard to photograph and looks better in person.
Once in the instrument panel with other suitably old gauges it shouldn’t look out of place at all.
Aluminium work, as always, continues slowly. Just some minor smoothing out to do now then I can re-anneal all the edges and we can try wrapping it on the tubes again.
Today I cut and shaped the little right angle inlet tubes. Joss noticed that my vice jaws were exactly the right height for one side of the inlet rectangle. So I just used the vice to squeeze the tube then a hammer to tidy up the corners. I eyeballed everything (measuring curved, round tube is hard!) and it came out fine.
The rectangular ends fit into the holes I cut in the mounting flanges of course so they bolt to the block. They are a nice, tight fit.
That’s the block I extracted these good tappets from being used for test fitting as it still has (long!) studs attached.
Those tappets will be reground on the end to the correct radius for my cam.
I drilled some holes to match the inlet studs on a piece of flat steel bar so I can hold the inlets in the correct position once I start welding everything in place. But you can see how the inlets will fit into the bottom of the plenum here. The tubes will be cut down so the plenum won’t be so high as shown here. After a weekend of hand filing I couldn’t be bothered making the holes for the tubes. I need to go to the engineering shop soon so will buy the correct hole saw. It’s all made from pretty heavy steel. I am waiting for someone to suggest drilling holes in it to lighten it!
I have also been working, on and off, on the horn I bought. We were trying to think of where were could get flat, spring steel to make a replacement spring. I was thinking piston ring compressors but Joss suggested these things:
I popped down to the local panelbeating supply place and got some of them. You get four in a pack and they are usually used for spreading body filler. I chopped and drilled one to make a replacement striker/spring piece. The steel isn’t as thick as the original so I made the metal weight on the spring smaller.
I’ve been playing with replacing the electromechanical contacts with electronics and so assembled the horn so it was physically arranged how it was with the top spring contact but without worrying about all the electrical gubbins. Instead I am using a small circuit with a 555 timer and a MOSFET to electronically switch the coil directly. With a little tuning the thing is working. It makes a god awful noise. More a rattle/buzz than a beep. I realised I don’t actually know what a vintage horn like this should sound like. It’s not one of the Oogah ones. With the electronics you can tune it a little but it still sounds awful. I get a headache just imagining it now.
I found a suitable tin to use as a temporary back cover. I should probably make something better or paint that one. But I kind of like the cows.
Today I finished filing the inlet manifold port by hand as it seems the regulator on my air compressor is playing up.
I also started making the backfire valve. This is a spring loaded valve that’s there to vent pressure if there is a backfire in the engine. I tried to find out some guide to sizing but there is nothing out there. Some US sites sell different sizes of valves (really just a plate and springs) and the smallest is only a few inches across. They are running much bigger engines/blowers though. I think mine should be large enough for a little Austin 7. I just drilled 6 holes that are covered by a 5mm thick steel disc I machined up.
It will have a gasket of course so it can seal. The spring there is a valve spring. The other thing I did today was start stripping the old blocks Joss has. Mainly so I could get a good set of cam followers I can re-radius. I managed to extract a set and cleaned them up in some kerosene, removing the little rust on them with a 3M pad. There was also that valve spring so I am using that for now. I will machine up some little end caps to hold the spring in place. The bolt is an 8mm one. It’s just bolted through for now but when I braze everything up it will be welded to the inside of the manifold sticking up as a threaded stud. I don’t want nuts or anything inside there to come undone and drop into the engine!
When the chamber is all done I will bolt temporary plates to the blower inlet and the outlet ports and pressurise it with some air to see at what point the plate lifts. The area of the holes is about 1.2 inches.
It all fits neatly behind the blower.
Today I did moer aluminium bashing. Joss came over and helped me put the skin on the frame which makes it easier to work on. It’s pretty close to ready for attempt two at wrapping it over the frame soon. One thing about all the aluminium work is you end up looking like the tin man in the Wizard of Oz with all the aluminium on your hands.
I also started work on the plenum chamber/inlet manifold. This is just rectangular steel section. I cut it to length then cut two end plates from 3mm steel. They are a push fit at the moment. Later I will bevel the edges so I can braze them in place. The blower mounts to the top of this. It is mounted by 6mm bolts, normally passing through the flanges in the outlet manifold piping. I am bolting it to the plenum so in order to pass the bolts right though the chamber I cut short sections of tube which will be brazed in place though the plenum.
That way the bolts pass through it but the chamber is still gas tight. It also means you can easily unbolt the blower any time. The hole matches the outlet of the blower of course. I drilled then cold chiseled that out then filed it as best as I could.
Of course you can only use short strokes on the file and for some reason that caused everything to become magnetized. You really have to resist the temptation to try to brush away all the little flecks of metal with your hands. it may look soft and fuzzy but every piece is a tiny little razor and you end up picking the damn things out of your skin with a scalpel. Guess how I know!
Tomorrow I will finish making the hole with the die grinder. Was a bit too late to start messing about with the compressor tonight. Eventually under the plenum will go the pipes to the inlets on the block.
They’ll sit up higher that than in practice so that the plenum isn’t too high up. There are two inlet pipes of course and one of them is directly opposite the blower outlet but I don’t think that should matter. The whole point of the plenum is to build up an area of positive pressure and even out the flow to the inlets.
I also still need to make the sneeze valve. That will go on the top of the box and will just be a flat disc of steel that covers a series of holes. A spring will hold the disc closed usually (perhaps a Mini valve spring?) but if there is ever a backfire in the chamber the valve opens to release the pressure rather than blowing up the supercharger.