Member postings for Old School

Model engineering seems to be building and running steam powered loco,s and traction engines and this is the basis for a lot of model engeering clubs. Other interest seem not to be catered for. I stuck it out at my local ME club for two years but the clubs focus was making sure they could do the public train running. With little or no interest in anything else. The hobby needs a wider focus that covers all model types, I like things that go fast currently tether cars but are they model engineering the people who race them build and maintain the cars but are not members of the model engineering community. The old Eastern Europe has junior teams that compete with tether cars and have access to work shops to build and maintain cars. So the hobby is still alive and growing.

Neil you are correct the amount of interference is controlled by measuring the liner lift. This is done with the piston and bore oil free as you turn the engine over as it nears the top the stroke you measure how much the liner lifts out of the crankcase.

Thanks for all the responses food for thought, Nick Hulme last suggestion seems within my capabilities.

I have followed Jim allens what he has achieved in his home workshop is outstanding model engineering building these racing engines.

Tether cars and there engines are designed to do a flying 500metres as fast as possible piston life is measured in minutes. The modern 10cc (0.60cu in) engines are developing around 8bhp at 32,000 rpm a liner piston will do about 9 sprint runs before it needs replacing. Being able to determine if the liner is reusable by fitting a new piston is a significant cost saving and an interesting engineering challenge.

Oliver

MichaelG, never seen those before and look interesting but I am after a value for roundness the liners have a tapered bore about 0.003" over the length and I only want to check the liner above the exhaust port. The engines are two strokes so it's an area of about 8 to 10mm. Oliver

Emgee, thanks for your reply I am making pistons to fit the liners and as a last resort will lap it in but prefer to turn them. The thing is some go faster than others and I am trying to determine why measuring and having a value is key to this process. As you know the difference between a worn out piston and a new one is not easy to measure with a micrometer.

Edited By Old School on 15/03/2017 08:55:14

The bore is nominally 15mm the silicon content is 25% from memory Dispal 226. I have made the pistons they are oversize at the moment and will be machined to fit the liners. I just want to check the used liners are still round after being used I have not been able to do it but fit/feel. The piston when finished will have a 0.75 degree taper starting about 2.5 MM. below the piston top. Oliver

Edited By Old School on 14/03/2017 22:20:16

The piston we use are round, no piston rings.

I used a hard insulation board that sounds like yours you could drill and tap it was tough on hi speed steel cutters it was called sindanyo not sure about the spelling.

Chris thanks for the suggestion, I am after a number so I can pick the best ones to use and see what the limits of out of round I can use. The Stelling tether car engine is a high performance engine it does around 40,000 rpm when flat out the piston life is measured in minutes.

i am making new pistons for my 2.5cc tether car engine, the liners are brass with a chrome plated bore. As they have been used and the original is worn out I would like to check that the are round. Does anyone in the midlands have the test kit to do it and would they check 6 liners.

To late to silver solder once you have had a go with soft solder you cannot get it clean enough to silver solder.

Not only records but also the documented quality systems and procedures, training records, goods inward inspection are a few of the things that will be audited annually.

Upvc solvent cement from a plumbers merchant.

Forgot to say also use this oil in the saddle and the bed etc.

I use Machine/slide way oil 68 from Arceurotrade

Richard. I have used the warco D13 backplates on my 254s you just have to make the studs. I use cap head bolts with a plain shank and thread it M10x1 to fit the backplate use a good die to cut the thread the bolts are tough. The register in the warco and a cast iron back plates I have used is correct.

If it was me I would see if I could get what I wanted elsewhere and if they could when I wanted. Then cancel if they cannot give you a delivery date that suits.

I also use brake cleaner in 5 litre cans it also comes with a spray dispenser but it's a few pounds more than the basic cleaner.

Surely you can scale it from the picture and then draw it up to check that you got it right.

Do your drawings in metric so much easier to work with. I draw in metric and machine in imperial it sound daft but it works for me. Most model engineering drawings are not toleranced mine certainly are not but I know for my application what fits are required from a performance requirement. Also I very rarely do a complete drawing just put on important centres and dimensions, they would not make much sense to anyone else.