YS120NC

[KT So]

Thank you Troy for the information. In the past, I have heard about the term
ring gap but didn't really what it means. I probably have had replaced some
engine parts unnecessarily.

I am curious to know what would the the normal ring gap for a smaller
engine, say .32 or .40 ? And is it possible to use the ring gap of a new
ring in a used sleeve to decide if a new sleeve is needed if there is no
abnormal scratch marks.

You also mentioned that the piston may need to be repaired. How do you
decide on this issue?

Your insights would be most appreciated.

K.T. (Hong Kong)








----- Original Message -----
From: "Troy Newman" <tanewman at qwest.net>
To: <discussion at nsrca.org>
Sent: Friday, August 23, 2002 8:31 AM
Subject: Re: YS120NC


> The YS 4 strokes sometimes don't seem to have much compression..I think
its
> a function of whether the motor is dry and also other conditions like temp
> and humidity...
>
>
> When they get running they heat up and develop good compression.....so its
> not really anything to be worried about. You might look into a new piston
> ring. Usually these things go on the 140's at about 300 flights..An easy
way
> to tell is to take it all apart and take the cylinder and put the ring by
> itself in the cylinder make sure everything is aligned properly and the
ring
> is sitting just like it would if it was on the piston. Do this at about
the
> top dead center point inside the sleeve....you'll know where it will have
> wear marks in the sleeve. Then measure the end gap of the ring.....with
> feeler gauges...A new ring is about 0.004-6" and a worn one that's starts
> loosing power is around 0.011-12" they are cheap at about $20 for a new
> ring. Upon doing a new ring look a the cylinder is its still crosshatched
> and pretty even that's good if it has large scratches  or is smooth
> especially up at TDC use a brake cylinder hone and clean up the inside of
> the cylinder...Note this only works if done properly and usually you can
> only do it once. The next time a new sleeve is in order.....Check the
piston
> for round with a micrometer....If the motor has been run a ton and is
pretty
> worn then you could do the whole piston, sleeve and ring trick.....This
will
> make it a like new motor and will cost you around $150 for the parts. My
> guess is the ring by itself will do the trick....if its suffering on
power.
>
>
> If its not suffering now then keep an eye on it with a Tach.....once the
> power loss comes it tends to happen in less than a gallon or so...today
its
> great and by the end of tomorrow's flying it just doesn't seem to have the
> power. Then the day after its down about 4-500 rpm but seems to still be
> running well just getting tired. This is classic ring replacement time.
>
>
> Good Luck
>
> Troy Newman
> ----- Original Message -----
> From: "Ron Sonderegger" <ronsond at erols.com>
> To: "NSRCA-Discussion List" <discussion at nsrca.org>
> Sent: Thursday, August 22, 2002 5:07 PM
> Subject: YS120NC
>
>
> > I've got a YS120NC in a Prophecy that pulls the plane very good,
> > powerfully,  through the Advanced Sequence.  Recently I've noticed it
> > has almost no compression but it continues to put out lots of power.
> > Anybody know what is going on here?  -----  Ron
> >
> > =====================================
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> >
> >
>
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