OS Max 15 LA help please

[Tim Donald]

I have this OS Max 15LA that is supposedly brand new and never run.  When I turn it over there is click as the piston gets to the top (just before the compression pop).  See attached video. Is this normal?  My other two stroke doesn't do it and I can't remember any of my old ones doing it back when I was all glow fuel.  If it's not normal,  any suggestions as to what could  cause it?  Does it with the plug in or removed. 

Thanks.

[Tim Donald]

Can't get the video to work so trying another one

[dave windymiller]

Brand new engine with lapped ABC pistons (ally piston chromed brass cylinder) often do this.  Its the piston getting tight in the bore. As the engine runs, it expands and the tightness reduces.  As it runs in, the tendency to click or even squeak reduces.    

[Tim Donald]

Thanks Dave,  that is good to know.  I didn't want to put fuel in it and try it if there was a chance it would get damaged but sounds good to go then.

[David Ovenden]

I cant see your video. But from your description it could possibly be the prop driver "clicking"against the D shaped drive on the crankshaft. Slight play between the prop driver and crankshaft. Does it still make the noise with a prop fitted and really tightened up?

[J D 8]

Funny thing, when one clicks to go off the no show video it appears for just a second or two.

[Tim Donald]

Thank you David,  I don't think it's prop driver.  It does it when that is removed.  I have been told by somebody that used to sell these engines that it is as Dave Windymiller suggest - just the piston being tight at the top due to the engine being new.  Normal apparently for ABC engines.

Not sure why that happens with the video JD8.  I can go to my attachments and download it but not from the post.  Maybe it's too big (but it's under the size that it said was the maximum).  

[Graham Bowers]

See the manufacturer's instructions "Engine construction" box on page 1 that makes a statement about the tightness at tdc.  The running in procedure is on the second page. Must admit, I usually do the first 4 or 5 runs on the test bench, however stick exactly to the recommended throttle and needle positions. The old softly-softly running in procedures of ferrous pistons and cylinders are to be forgotten as it's important to get heat in to these to expand the cylinder liner.

 

https://www.os-engines.co.jp/english/line_up/engine/air/aircraft/manual/15_25la_eg.pdf

[Engine Doctor]

• As per Graham Bowers post 👍 .It's perfectly normal for ABC type engines to be tight at TDC, something would be wrong if it wasn't.  Run it in in short bursts tuning it to run at high revs but but just slightly rich, not max revs but near  to max .Run for a couple of minutes to allow it to get up to max temp then stop it and allow it to cool down fully . Repeat process a few times but don't run it at low revs yet or you risk damaging the con rod or crank . After a few cycles of running and cooling tune for slow running as well then put in airframe and fly it. Use a good quality synthetic based fuel. Once the tightness over tdc eases its run in  . Even when run in you should still feel a slight tightness at tdc.

Unlike older generation engines the modern engine of this construction doesn't take very long to run in .

Edited November 17, 2022 by Engine Doctor

[Tim Donald]

Thanks Graham and Engine Doctor.  I'm going to set it up on a test bench to run it in by the method you describe.  It's all good learning for me.  I will read the manual too 😀.