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Oliver Monk

  'Workshop Ramblings'

2017

 

January 2017

This is my NSC 2.5cc tether car, now on its fourth engine. The best speed I have managed is a few laps at 260kph with the second engine. It has been named the "British Brick" by Michael Schmutz who had had the misfortune to have horsed it on a regular basis. For the last race of the season in Tallinn I changed the pipe length, the wheel diameter and head volume plus put a new liner piston in, and I nearly forgot, a new shape head and top hat glow plug. The first run showed a bit of promise but it died when accelerating, turned out to be a glowplug seal failure. The second run was 256kph and if I hadnít been greedy it would have done 258kph, not the best speeds but a significant step forward for me. Michael also said it horsed OK, just like it should but itís still going to be called the brick.

This is my second 2.5cc Stelling engine. I have wanted one for years then two turn up. This one needs a bit of remedial work as the clamp ring head has been modified, so I am making a new one as standard.

Parting off the head, then into the chuck with soft jaws. I bought a new 3 jaw chuck so I could use soft jaws. This is the second job, so much easier to hold thin parts securely. The final picture is counter boring the hold-down holes on the rotary table.

The engine came with a Zimmerman disc intake system and used a remote needle valve, unfortunately the overall length is too long and the venturi is almost touching the tank. I am told that it was made by Lothar Runkel. To make it fit the car I am going to make it shorter using a conventional needle valve assembly.

Start of the new Zimmerman back plate
First picture show the disc housing machined in and parting off for the next operation.

Seemed to have missed a few pictures but it was only straight forward milling. The picture on the left shows me centring up the back plate prior to coordinate drilling the mounting hole, this was the easiest way of getting the holes in right place.

The picture above is prior to drilling the holes and on the right the new back plate and head are bolted to the engine. Some more work still to do on the back plus a new needle valve assembly.

About 14 months ago I was contacted by the Society of Model and Experimental Engineers and asked if I would do a talk on tether cars and the engineering that I do. On a Saturday at the beginning of January I went down to London by train to their headquarters, had a tour of the workshops etc. and taken for lunch at a local cafť. The cafť has a list of meeting dates so they can put on extra staff, the place was full of model engineers. The talk went well, I had taken some cars and lots of bits for them to look at; some of the members had built and run cars when they were a lot younger. Spent a quite a time talking to people afterwards apparently this is a sign of a good talk. Didnít get any takers to run model cars though.

Well thatís it for this month only about four months to the first race in Hanover need to crack on with the second Stelling engine. For a change I am building a couple of model aeroplanes, one a control-line model from my school days and the other is a coupe de hiver rubber powered free flight model of modern construction using some carbon fibre. I am allowed to build these in the house much warmer than my workshop.

 March 2017

More work on the Stelling 2.5cc, continuing with the back plate, milling the intake slot and in the centre picture it's ready in the vice for blending in the two different shapes using a Dremel. On the right, Removing surplus metal from the back plate.

Installed in the car with the needle valve assembly on top of the intake. It just didnít look right, thought it might give fuel feed problems so on with plan B.

Machining up the venturi using my new 5c collet chuck. Should have bought one years ago.

 Drilling the hole ready to fit a more conventional needle valve assembly in the usual place.

Here it is all finished, and with a bit of milling to the car's pan it now fits and an elongated hole in the body I can use this Zimmerman valve or the drum valve. I had deliberately left enough metal on the underside of the venturi to give me this option.

Back making piston blanks for the Stelling engine, the metal is free machining but wears the HSS tooling out quickly. For turning the bar I use a carbide inset design specially for aluminium, the drill is HSS.

Eight pistons on the way, all gudeon pin holes drilled, ready for reaming to size.

 Bottom of the piston having the surplus metal milled out.

Two pistons with the bottom all milled out by plunge milling using a carbide cutter.

Blanks being cut in half to form 2 pistons, again a carbide tipped cutter.

Eight new pistons

The last operation before fitting the pistons to the liners, putting in the circlip grooves.

Final fitting of the piston to the liner taking tiny cuts and measuring the amount the piston moves up after every cut, so you can put the taper on the top of the piston and have enough liner left to give the required "nip".

In the latest version of the Retro Racing Club's newsletter is an article on a car called the Shadow designed by Ian Moore. I had slowly been collecting all the parts to build it and they had been sitting in a drawer. The article prompted me to get the bits out. The engine is an original Oliver Tiger but needs a rebore. Also it will make a change from working on modern cars, especially pistons.

Holding the pan was going to be a challenge as there is nothing straight that I can work from, so it was down to see our local tig welder who welded on a piece of plate so I can hold it. While he was doing that I got him to weld on a new smaller diameter connector as I am modifying a 3.5cc pipe to use on my 2.5cc car.

Thatís it for this month, one 2.5cc car is ready to race, the other one is close, just need to make some stingers for the pipe. The 3.5cc car needs a new piston so hopefully I will get that done before we go to Hannover for our first race this year.

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