Hello
I've got two webra 1.20 engines, same muffler, same prop, same glow plug, same fuel but one runs fine a 17x6 prop, the other one has problem turning a 15x8.
I don't know what to do to have both at a fairly same power.
I went all the way down from 17x6 to 15x6 to know which one fits the best the engine, 16x8,16x6,15x8,15x6.
When I opened the engine, the ring was half "welded"to the cylinder so the compression was poor, actually when you flip it by hand you barely could notice when the piston went all the way up.
After noticing this, I loosened the ring from the piston so it could have more power, in fact I felt more compression when flipping it but the power in the air remained pretty much the same.
I did not break-in this engine, I bought it used so I don't if the engine overheated at some point and "welded" the ring
I am thinking about getting a new ring for this engine just to see if it could improve its performance.
By the way about the other engine I could not feel happier
Any feedback or shared experience would be highly appreciated.
Regards
Omar

The Webra 120 uses an L shaped ring that has little tension. They do not often make the best seal unless the engine is turned rapidly.

I think a new ring might be a good idea to get the compression back up to
where it needs to be. Be sure to de-glaze the cylinder wall, so the new ring
will seat properly.

FBD.

I've got 3 of them. Extemely happy with all. Do just as flyboy says. De-glazing is very emportant especially sence the engine has probably been overheated. Also make sure the piston and ring grove are real clean. Dykes rings suffer from the malady of getting carbon or other junk under them between the top of the piston and the top of the ringand then things can go bad in a hurry. Also use no more than 5% nitro. Mine won't even tune on 15%. They're all over the map tryin to run with 15%.

Denis

Hey
Thanks all for the input
I'll proceed to first de-glaze the cyulinder and then change the ring just to make sure I have the same comparison basis to notice whether it does affect performance or not ( aimpositive it will).
Just to make sure I copied you right, de-glaze means removing carbon from cylinder? Sorry for my english...
Regards
Omar

Omar....deglazing means cleaning up the cylinder wall, and preparing it
for a new ring, by leaving a scratched surface to rub against the new ring.
This rubbing will allow the ring to "break-in" in a short time, and will make
it up to full compression as well.

You can use 180 grit dry sand paper as I have done here. Use your thumb
with the paper, and make an "X" pattern on the cylinder as you work around.
When you get it all done, wash it out with some spray brake, or parts cleaner,
and put some fresh oil on the cylinder wall.

Put some fresh oil on the piston and the ring when you put it back together. [sm=thumbup.gif]

FBD.

Be careful if you use a coarse grit for scratching the cylinder. If its excessively rough then too much material will be scrubbed off the ring before it wears in. Usually 400 grit will work for model engines and provides a greater level of safety for untrained hands.

Yup I've never had the nerve to use anything more coarse than 400. Just fear.

Denis

Denis....not to worry,

....deglazing stones are 180 grit, and are used in electric drill motors. Once you
have cleaned and scratched the surface, like I have shown in the picture, you
are done. The cylinder is made of very tough material, you cannot hurt it.

You could use 400, or 600, or 800, or 1,000, or 20 million grit paper to
"deglaze" your cylinder....every time you go to a finer grit, you will spend
more time trying to get the ring to seal.

Don't believe me ? Find out for yourself.

FBD.

I agree Dave. I have run a 180 grit hone through many a cylinder ranging from lawn mower engines, motorcycles, Hondas and marine V8s but I'm still nervous about doing it with model engines so I use a finer grit, sometimes 280. There is also risk with a fine grit of not getting the glaze off all over and that creates problems but I still use a fine grit anyway and just spend more time.

Denis

True, Denis....as soon as you hit the steel with the 180, it breaks down
to a finer grit real quick. The 180 is the standard de-glazing grit, although
it does sound course. Too fine a grit just clogs the paper, and won't leave
the proper scratches on the surface.

The scratches on the surface is what retains the oil when the ring is seating
to the cylinder wall. The "rough surface" of the scratches wears off immediately
as the ring is sealing....this is the intention. There has to be some wear
between the ring and the cylinder, and you want this "wear" to happen as
fast as possible. This "wear" is only one or two ten thousandths of an inch,
an imperceptible amount....not enough to measure. This is part of a normal
seating procedure. Most Guys freak out over the scratches, they simply don't
know the reason they are there, and just assume the surface should be shiny
and smooth.

If the ring does not seal, then it will glaze up again, and the compression
will never get to where it's supposed to be.

FBD.