Well itís the New Year already and I must admit I have not spent much time in the workshop working on my tether cars, other things have taken priority, but before we know it the racing season will be upon us.
This is the head from my 2.5cc car long with the print out showing the acceleration of the car and it cutting out with a blown plug. Most of the season I have been burning out glowplugs and having a shot blasted finished chamber in the head. I have been reducing the compression but it has made little difference. I put the pictures along with some key data onto one of the controline web pages, it was suggested that I was running the engine lean to compensate for the low compression, I have never had any bad advice from this guy so I am going to try the compression ratios he has suggested and other 2.5cc car drivers use.
On the right is my head volume device that I copied from Gabor. Itís accurate as long as you get all the air out of the glowplug. I use an insulin syringe which measures small volume this one does 0.3cc and they are cheap off EBay.
Back to making heads, you have probably seen this before but itís a slightly different way of doing it. Still using a D bit cutter to form the taper seat for the glowplug, and a tapping size hole for the thread. The second picture shows the grooving tool I use to cut a recess at the top of the taper so the plug seats well. To the right parting off the part finished head blank, five blanks ready to have the chamber cut in them. More on this next time.
Making pistons for my 3.5cc engine not done these before and itís a new material but the same silicon content as the other material. It machines very well.
The 3.5cc piston is not a standard collet size. 5C collets have a small size range, but you can buy emergency collets that can be machined to size.
The three pins hold the collet open
while you machine it
and when done you pull them out.
The finished collet and
it holding the blank for the start
Still on with collets, this time ER32 collets to fit the bigger 3.5cc piston. I use a collet chuck which come with 3 hold down bolt holes whilst my rotary table needs 4.
Drilling the extra holes and then
clocking up the collet chuck so
that it runs true on the rotary table.
Milling out the inside of the pistons itís a slow process on a manual machine. Got 5 insides done 5 more to do.
More on machining the pistons next time got to put a couple of holes in them and machine the skirt. Plus a little more tooling.
I put this picture up last time. I am led to believe that the Maserati is a Vega casting, anybody know where I could get some tyres from? They will be around 90mm diameter. If you know of any tyres let me firstname.lastname@example.org
The Moore car no 12. I can get the parts that I need and I can fabricate a gearbox. The other Moore car on the right of the picture I am unlikely to build as in my eyes itís not a pretty car.
Thatís it for this month, hope to get back into the workshop and carry on the preparation of my 2.5 and 3.5cc cars.
Could be held up a little with the FEMA rule translation to English and any rule changes needs to be complete for the race in Kapfenhardt.
I have had a bit of a break from making pistons. My old laptop has been slowly dying, so I bought some software that would sort out its problems and make it go faster. That finished it off. I spent a few days sorting out my Windows 10 laptop and loading all my files onto it, so this is the first Ramblings on my new machine.
The batch of pistons ready to
have the circlip groove machined in. Easy to do once you have set up the bed
for the distance in, and set the zero on the cross slide for the depth, you can rattle through them.
To get the right amount of nip at the top of the cylinder bore, I set the engine up with the amount of exhaust timing I want. Measure the height from the top of liner to top dead centre using an old piston and then to this dimension I add the distance from the top of piston to the sealing band and the amount of liner lift I want (how tight you want it). That gives me a dimension to use when I fit the piston to the bore.
The wrist pin hole is checked
to ensure it is parallel to the base of the piston if not the base is altered
until it is.
Then the piston is fitted to a mandrel ready for final turning to size
The cutting lubricant is
cleaned off the piston with solvent and then dried, the liner is also cleaned,
you slide it over the piston for measurement it comes to a dead stop and you get consistent results.
The first picture shows the taper being turned on the top of the piston the blue is just so you can see what you are doing. The other picture shows the tooling being set up using and old piston. The collet is a design that I saw on the internet being used by Andriy Yakymiv for machining pistons works very well.
The jig in action shaping the
piston skirt, the blue dot on the scale is so I can find my stop positions
The finished goods ready for this season.
I needed a break from pistons and found this tin plate car on eBay already got the engine and tyres, the engine will fit, just.
Removing the inside of the car is not a precision job, the engine will fit. Just going to need some fancy wheel nuts. Should be a fairly quick build as it will be similar to the Cobra car I run at Great Carlton.
Well next month more pistons for the 1.5cc engines, hubs and wheels to make for the 2CV. I have really got to get to work on the FEMA rule changes that I have received.
No joy with the plea for some tyres for the Maserati, so thatís going on the back burner until something turns ups.
Thatís it for this month. Get to see all the UK modern car racers for the annual scrutineering session in early March.
Workshop Ramblings March 2018
I was given four boxes of Model Engineer magazines and this was the only one with any tether car information in it. It describes us modern tether car racers as fanatics.
It's normally a challenge to find a new home for magazines, but rather than send them for recycling I advertised them on the local Facebook for sale page. I had five people wanting them, they went to a nine year old boy who collected them with his mum.
A while ago I made some head blanks for the 2.5cc engines. Below is the finishing off process, I cut the combustion chamber with a ball end mill the fixture has a stop in it so it goes to the right depth. I then put on a shoulder, a little bigger than the bore of the liner, this lets me measure the head volume.
On the first picture I am machining the squish band, I use 3 degrees. You will see in this picture that I am using a micrometer saddle stop. This lets me take accurate cuts so that I can get the head volume I require, during the process I take the head off and check the volume as I go. The second picture is the head finished to fit liner and at the right depth to give me the squish clearance I want. All it needs now is a polish of the combustion chamber.
Sometimes you get the mental arithmetic wrong. Pistons for Aaron 1.5cc engine
Back on with the 2CV project. The engine is a
little too wide but the front bearing is well recessed
|Parting blanks||Band sawing through||Machined wheel blanks||Milling tyre groove|
Cutting wheel blanks for hubs for two of my twinshaft engines. The first machining operation done. I have always turned the groove for the tyre to go in, but someone suggested milling them in, certainly an easier way to do it.
Left: Finishing off the hubs and boring the fixing taper on the engine side of the hub. Mandrels and soft jaws make the process very repeatable and quick to do.
Right: The new wheel and the one that came with the Temp engine. The new tyres I got from a friend in Lithuania. I struggled with the original Temp tyres the kept coming out of the hubs the rubber has probably gone soft. We will see how they perform this season at Great Carlton.
The 2CV is not going quite as planned. It's sitting a bit high off the chassis, the picture on the right shows the fix. Put on the back bench while I decide its future.
My projects are coming to an end as I am struggling for bits for the castings I already have, but I have a new Russian car kit being delivered at one of the races. Itís a junior 2.1cc car but of modern design and for a modern engine, should be interesting.