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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.

 April 2017

This was not the start I wanted to the 2017 racing season. After a day of unsuccessful training and then two rounds of the competition without a run I finally found the problem.

Out of 10 glow plugs that I had bought loose one was a cold plug the rest were hot. With a plug change to a hot plug for the last round it went accelerating nicely and into the mid two hundreds, then the deathly quiet with Manu the horser slowing it down to reduce damage.

Anyway more later.

 Milling the top surface of the pan flat and  the start of boring out the casting for the back axle.

Boring out the hole for the axle bearing housing. The boring head I rescued from the scrap man when they closed the workshop at work, itís very accurate even though it looks pretty battered and doesnít have a name on it. The casting is not that easy to hold so I made a split mandrel to hold it to mill the housing face flat.

The third photo shows the start of machining the back axle that has a flange in the middle to bolt the crown wheel to, for some reason this is the only picture I took of the process. This end was left oversize the material pulled out for the side of the axle and all then machined to size.

Checking the bearing fit in the housing The bearing housing nearly complete Bearing housing being parted off

Facing of the finished bearing housing. The rear axle assembly all complete and fitted into the pan. No pictures of drilling all the holes in the milling machine, sure you have seen enough of those?

Just to make things interesting the engine is held in the pan by the front housing and the back plate plus it is sloped forward 5 degrees. To get the angle right I used a thin angle block under the casting. The picture on the right shows the front engine mount, the paper is there so that when itís finished you have a bit of clearance to tighten it down.

This is not the most rigid set up but it worked, the milling cutter is the only one I had that was long enough itís a roughing cutter but the finish was OK.

I had nearly finished the Ramblings and thought they all might make a bit more sense with a drawing. OTW added a couple of photos of Ian Moore's original car from an earlier article.

This was the damage to my 2.5cc car when the rod let go, it also bent the bottom of the liner so I could not pull the liner out through the top, it came out enough for me to saw the top off the line and get out through the bottom of the crankcase.

I have some new wheels on order but just in case they donít arrive I have machined the flat off, machined a mandrel to fit the boss in the wheels and held them in place with a revolving centre, save drilling and tapping holes to hold them in place.

Thatís it for this month I am hoping for a bit more luck in the next race at Kapfenhardt in the Black Forest, a good race and a nice social event.

 June 2017

The Shadow coming along nicely. The top has proved to be a tight fit but no real problems. The fibreglass version is a lot easier to make than carving a wooden one and a lot more durable. I am sure Ian Moore would have used fibre glass if it was available when he built his car like it is now.

The blue foam plug prepared as close to drawing as I could get, the other picture end on, its thin.

The glass I use is 28g a square metre and is bias cut i.e. at 45 degrees across the grain, this make it easy to work with. I covered the whole body with one piece of glass. First I give the plug a coat of epoxy resin then put two layers of glass on and let it cure, then rub it down until it's smooth. Another 4 layers and let it cure and rub down until smooth and so on. This body had 24 layers of glass from memory. It takes about 30 mins to rub down and put on 4 layers of glass.

Digging the blue foam out of the finished part. The last few bits of foam can be washed out with solvent.
On the right, starting to fit the body to the pan.

Start of the work on the gears, setting up to bore the hole in the gear to fit the axle. The other picture, the split aluminium cup to hold the gear for metal removal.

The pinion gear with its collet to go onto the engine, the crankshaft has been shortened.

The crown wheel having the mounting holes drilled, and the challenge of drilling and
tapping of the mounting flange on the axle.

I drilled some mild steel rod and Loctited the drill and tap in. Note the crown wheel being used as a guide for the drill. After the first hole was drilled it was tapped and the crown wheel held in place for the next two holes.

The gears in the chassis. Somehow I have got to get a flywheel in there.
On the right, setting up the cylinder fins for thinning down.

By the time I had removed enough metal to get the top on I didnít like the look of it so decided to make a new bit, more work to do on it.

That is as far as I have got with the Shadow this month. Got some wheels and tyres for it now. More next month.

I am not having a particularly good season with my 2.5cc cars. Have broken engines at both the race meetings I have been to. Been busy in the workshop making pistons but youíve seen that process, I seem to have finally cracked machining the pistons to size without having to lap them. I will find out how good they are when I go to the European champs in Stryi. I should be having some new liners and pistons delivered there as a backup.

Thatís it for this month, off to Hannover, last race before the European champs.

July 2017

I am a member on a control line model aircraft forum. One of the topics is Engine Development so I put a picture of my timing device on. This is the one that Barrie Lever built, itís a bit good.

Most of my time recently has been spent preparing my cars for the European Championships. I am racing one of the 2.5cc cars and my 3.5cc car, all four of the engines have had fairly major rebuilds. The gearboxes have also been stripped and cleaned and new ball races fitted.

More on pistons:-

One of the important things when making pistons is that the gudgeon pin hole is drilled square to the piston body. I bought a "V" block that fits into the lathe tailstock and added a micrometer to aid positioning the piston. First trials are promising.

A while ago I made some piston blanks for my 2.5cc motor but somehow I managed to turn them undersize. I was able to rescue some of the material to make pistons for Aaronís 1.5cc Kapu.

Making 1.5cc pistons required some new tooling to be made. The first one is a mandrel to hold the piston for final machining to size, the top hat type thing is for holding the piston while machining the circlip grooves. Once this is set up it is quick and easy to do.

I put a steel rod through the gudgeon pin holes, and on a surface plate I check the height of each end of the rod to ensure the holes are square. The other picture shows the set up for the circlip groves. I buy the cutting tools and the smallest I can get is 0.7mm wide. For the 1.5cc engine it had to be reduced to 0.35mm wide.

For a change Aaron and I went up the Barton Model Flying Club to see the jets fly at the speed weekend. They are fast and loud, itís very tempting to build and fly one.

Got a busy August racing cars, I doubt I am going to get much time in the workshop other than for cleaning cars. I will probably start work again on the Shadow car in September with a bit of luck.

Photo by Richard Grindley

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