Hi Alan,

This is perfectly normal. These engines are made up from an aluminium piston, brass liner which is chrome plated and this is known as 'ABC'. The ringless piston is usually made from a high silicon content ally which has a low thermal expansion rate. The cylinder liner is very slightly tapered with it being narrower at the top such that when it gets up to running temperature, the hotter top end of the cylinder expands more and the piston / liner clearance is perfect all the way down. When new, piston / liner fit can be very tight indeed but after running in, it will free up a bit but even then, some engines will still have a very tight top end when cold.

Simon

The advice above is spot on – its an ABC set up and definitely should not be run in as a conventional piston and liner set up. As Tim says let it rev fast but sightly on the rich side.

Depending on the pitch the 12" prop should be okay – 4 r 5" is ideal – a 10 x 6 on a 46 is a bit on the small side. I run 46's in aerobatic control line models and they use 11- 12 diameter x 6 or 5 pitch respectively.

I have quite a few '46's' with ABC set ups but one in particular, a Ukrainian 'Stalker 42', despite considerable use, has a very tight piston liner set up. It will often 'seize' at TDC when flicking it due to the squeeze on the piston It takes considerable force with a high degree of tortuous sound squeaking to free it. Heating it with a hot air gun is an option if that happens – not always available on the flying field though!. Flicking it backwards on to compression is much the better way to start it. Apparently all the other engines in that specific batch were similar so not a one off. A very powerful and consistent runner I should add that I never use any form of starter motor – just hand flicking.

A pic of the engine would be nice – most usually have some indication of makers name – maybe we can identify this one for you.

Tug