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Will A Blacken Piston & Liner Harm My Engine?

A question raised on our Message Board could be of interest to modeller, especialy newcomers who see their shining new engines getting dirty.

Whilst flying in a field recently, the prop did a lot of grass cutting and bits must have got into the engine (Irvine 46) and got burnt. As a result I have a blackened piston and liner - I assume this is a layer of carbon - that I can't seem to remove.

1. Will this do the engine any harm? - I haven't really noticed any loss of performance, but the engine seems to run a little hotter.
2. What is the best way to get rid of it and return to gleaming metal?
John C

I don't really think that grass getting into the engine will have caused much damage. Blackened piston & liners are usually caused by the accumulated carbon from the burning of fuel.

This will build up over a few years. Initially, it probably helps seal the piston and liner giving good compression.

However, when the build up becomes excessive, power will decrease noticeably. Only then contemplate removal of the liner.

You can then remove the deposits with very fine wet and dry paper lubricated with machine oil. Move up and down the liner in a figure of eight action. But gently does it.

Carbon on the piston can be removed n the same way. Clean all parts thoroughly. You don’t want any swarf to enter the engine!

Reassemble the engine, but don't be afraid when the compression is awful. You will have to run a few tanks of fuel though it before the piston & liner bed in again.

So, to conclude I don't think your engine has come to any harm. It seems that what you are seeing are the natural effects of normal engine running. You shouldn't unnecessarily take your engine apart and most defiantly not try to return the piston & liner to the gleaming example you had when you bought the engine.

Only contemplate the above procedure when there has been a very noticeable loss of power that cannot be attributed to anything else. This usually happens on quite old engines.

I recently revitalised an old HGK45 in this way. But then this engine was 18 years old!

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