Workshop Ramblings October 2023

At the European Championships this year I was asked if I had been ill and unable to write the Workshop Ramblings, I replied that I was OK, had managed to avoid covid so far but was struggling to find something new to write about. So here we go, over the winter I am going to build two Ian Moore No11 cars and one for the pattern maker who is in the process of making the pattern for the chassis and of course the other one is for me.

5cc Profi as supplied with the Picco car kits	Set up on the test rig

This is the engine from my 5cc Class 4 tether car, it appears not to be  the engine of choice for this class, the Picco and a turned round Novarossi are the ones. When I bought my Picco 5cc kit car this was the only available engine, its life did not start well, on its first gentle run on my test stand it went very tight, on investigation it was found the piston pin hole was not square. I made a new piston and the engine ran well in the test stand.

The first visit to the track in Hannover we got the car going round but the performance was not there, all sorts of advice was offered but no joy. Back at home I found the Zimmerman disc was lightly pressing onto the back of housing, when the engine was running this acted like a disk brake. Some paper gaskets between the crankcase and the Zimmerman assembly solved the problem.

Basel was the next event it ran better but the speed was still not there, Alberto suggested a little more compression that did the trick a run of 293 kph and a new British record. After the run I took the back plate off the engine, in the bottom of the engine was grey sludge, one of the tungsten counterweight in the crankshaft had come loose and had been hitting the bottom of the piston.

That was an expensive run, pistons are made from high silicon content aluminium, it had done a lot of damage. I ordered the new parts, put the engine back together. All this happened prior to covid and the car was left under the bed in its bag.

Expanding mandrel for machining big ends	Con rod on the mandrel

I had the opportunity to buy some Picco/Profi spare parts and on trying to determine which was which I found the conrods were slightly different size on the big end. The Profi one was about 8 thou 0.2mm thicker than the Picco ones. On measuring the Profi crankpin it was found to be shorter than the width of conrod big end, the pictures show the conrod being turned down to the correct width. No more paper gaskets and problem solved, I hope?

Equipment required for setting up motors	Lathe for machining heads

I am going to run through how I put together my tether car engines. The picture on the left shows the tools I use from left to right.

A digital timing disc for measuring port timing mainly the exhaust duration.
A digital dial indicator with a homemade foot on it.
A diabetic syringe for measuring head volumes.
Two syringes with one with ATF oil (automatic transmission fluid) and the other with Castor Oil.

The other picture is my lathe very useful.

For engine cleaning I use brake cleaner, it is not recommended for bearings with plastic cages as it may damage them. For those, I use methanol.

As a first stage, check the bearings in the crankcase, check that they feel smooth with no gritty feeling as you rotate the inner, next put the crankshaft in, fit the flywheel. Then spin the flywheel, it should spin freely and when it stops rotating it should rock backwards and forwards about 4 or 5 times, if it does then all is good. In the past I have written about fitting bearings can do it again if any interest.

Having assembled the engine using ATF oil for the bearings and crankshaft and castor oil for the conrod big and little ends and the liner and piston.

The exhaust duration wants to be somewhere between 190° and 200° the actual figure depends very much on the set up of your car and the length of the tuned pipe, also how powerful your horser is to get the car onto the pipe. A good starting point is around 195°.

Paper used to check the closure of exhaust port	Selection of head and liner shims

I use a piece of paper so that I get a positive stop when the piston reaches the top of the port this method gives a small error of 1° to 2° for me this is acceptable, it gives me a consistent method of measures and I make allowance for this error.

There are other methods of doing this, shining a light through the exhaust port or just doing it visually, choose your own method but stick to one.

You can adjust the exhaust timing by putting shims under the flange at the top of the liner.

Checking the height of the piston at TDC	Checking squish clearance

Next is the squish clearance, this is the distance between the top of the piston measured with the piston at top dead centre (TDC) and the bottom of the head. On this engine I am using insert heads.

You will notice the gauge reads the same value, this is telling me the piston will hit the head, this is not good; on this engine I am looking for a squish clearance of between 0.3 to 0.5mm. The head will be raised by shims to get the correct value.

Checking head volume	Machining combustion chamber in head button blanks

Finally, the volume of the head with the piston at TDC as a rough guide it wants to be between 0.7 to 0.8cc for a 10cc engine so for this 5cc engine I am looking at 0.35 to 0.4cc. This volume is to the bottom of the glow plug hole. The head volume is fairly critical, too low and you will not get the performance and too high you will get pre ignition, this looks like a shot blasted finish on the head and piston and may also get glow plug failure.

I find it easier to use a dummy glow plug when measuring the volume its easier to see when the chambers full and then just deduct the volume of the dummy plug, so much easier than peering down the plug hole.

Tether car racing is supported by a variety of people making and supplying parts for tether cars and there engines usually only available at tether car events and not always on a regular basis.

The head I used came from one of these suppliers and manufactured so that it could be adjusted to achieve the volume and squish required, this is where the lathe comes in. The price of the insert heads is good as they are CNC machined and its not worth me making them from scratch.

That’s a quick run through of setting an engine up, you won't know if you’ve been successful until you run the car on the track, the challenge is working out what you need to change. Most of the people running cars will give you advice.

Next will be the start of the No11 car, if the castings are not done it will be wheels and axles or the shut off.

One simply rule for glowplugs, find one that works in your engine and stick to that plug. Changing the plug type and manufacturer will affect the performance of the car. Tether car glowplugs are available at the European tether car meets from a couple of sellers and at the right price. I use drop in plugs in my 1.5cc car and 2.5cc cars. Picco plugs in 2.5cc car, slightly more consistent and the 5 and 10cc cars the O’Donnell. It may seem extravagant I use a new plug every run in competition, the last thing I want is a blown plug as you only get three minutes on the cable. The good ones left over are used in practice.

This is something I started to write for publication elsewhere but it's happening here instead. It's something to think about if you are running cars at Buckminster.

After the European Championships in Hannover I was talking to Torbjorn Johannessen who had just become European Champion and set a new world record. He wanted to know how I had got my car to go faster, I had made a jump of 16 kph and set a new British record. Nothing stood out as anything significant that I had changed other than a lot of little things. He agreed that was typical of getting a car to go faster.

In the early days of Buckminster, before we had timing systems we were just using stop watches. I was running my Russian schools car powered by a Temp diesel engine, it sounded really fast, the engine was revving like a good one. At home I sat and worked the speed out, very disappointing. For my modern cars I have a spread sheet for calculating wheel diameter, speed and engine rpm. Using any of the two parameters, you get the third. I knew the speed and wheel diameter so the calculated engine rpm was 8,000 ish. Now, I know the Temp is not the fastest engine but it should do 14,000. It was one of two things, wheel spin or bouncing.

More to come next time.

Also the start of the Ian Moore No 11 car.

If you want to contact me buckytcar@btinternet.com