A binding question

[onetenor]

I have an OS40. in really good condition. In fact too good I know glows are a bit tight over TDC but this one is so tight I can't flick it over and even loosens the prop unless really torqued up Anything I can do to ease it?

 

 

 

 

 

Edited By onetenor on 17/10/2018 02:57:26

[Piers Bowlan]

Have you run the engine in the past or have you just bought it second hand? Will it turn over with the glow plug removed? Just wondered if the bearings are corroded or something is physically stopping it from turning over TDC, rather than it just being tight? If it is so tight it loosens the prop be careful you don't bend the con-rod.

Hopefully someone more informed about engines than me will be along soon to help you. Good luck.

[Dave Hess]

More often than not, it's because the cylinder has too much fuel in it. Angle the motor so that the exhaust port is downwards and turn over the engine a couple of times so that it ejects all the excess out of the exhaust. Sometimes you'll see an unbelievable amount come running out. I'm not sure if it happens when the exhaust pipe/silencer gets so full that the fuel flows back into the cylinder instead of coming from the carb.

Edited By Dave Hess on 17/10/2018 15:42:55

[J D 8]

A more info would help,as in is in an aircraft and which way up is it mounted and when was it last run if ever ?

[onetenor]

No fuel in Less tight with plug out but still pretty tight Plug in a few threads but not screwed down so not fouling piston tight again. Not in plane not run for some time. Could be ring of dry Castor I suppose Or maybe carbon.

[Martin Harris - Moderator]

You might try pre-heating the engine to see if it loosens a little with expansion. If so, it may just be that the piston and cylinder are at opposite ends of their manufacturing tolerances and particularly tight.

If this is the case, start it while still nice and warm and run it up to working temperature quickly, running on a reasonably small prop to avoid loading it too much. Run for a couple of minutes just slightly rich of peaking and vary the revs. Stop, allow it to cool and repeat the exercise several times and it's likely that the engine will then turn over more normally and start from cold.