2 stroke glow engine

Picked up an aircraft engine at the weekend as it looked like it could do with new home!

No manufacturer name on it, the only marking is '46' which I understand is it's capacity in cu inches (7.5cc)

Guy said it has never been run and it looked new, it came with a 12 wooden prop.

Definitely never been run upon inspection but I notice that when turned over the piston gets tighter at the top of it's stroke. Popped the head off and could remove liner and all appears to have super finished piston and bore.

Reassembled with a spot of synthetic oil and on flicking it over with the prop fitted as it passes through TDC it is tight enough to squeek.

I've read about clearances getting tighter at the top of the bore but?

Should I motor it with a view to easing it in?

Alan

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

It,s probably a generic Chinese engine if it has no makers name on it. yes it should be tight at TDC if it is a ringless piston known as ABC for aluminium (piston),brass(liner),chrome(plating of liner) although the materials may have changed these days. I would break it in with a smaller prop say a 10 x 6 glass filled nylon to keep it lightly loaded with a rich mixture to start with but let it rev. Short runs of about five minutes and let it cool down in between.After four or five runs like that it should be good to go.

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

Thanks guys (I didn't really want to lap it out!) Will give it some runs and see how it goes. Undoubtedly of Chinese origin but seems quite well made with some decent sized bearings on the crank. I have bought 'non runners' before as projects usually having to replace crank bearings as they have corroded and I will try and totally remove any remaining fuel and swamp things in oil to prevent a recurrence.

Alan