OldRookie

My Feedback: (13)

I have a YS 140 L that only has had about 3/4 gallon of fuel through it. I am running Wildcat 20/20 YS fuel, with a Xoar 17 X 8 prop, and an OS F glow plug. This was a NIB engine before running.
I have 5 YS engines, and am very confident in my tuning of these engines. I am now getting 8300 RPM WOT, and when dropped to idle (2000 RPM) it stays within 200 RPM.
I have read where the 140 L engines had some problems with surging, and there was a process of drilling holes in the piston ring groove to eliminate this problem.
Does this seem as if this is what this engine needs? If so, is this something I can do, or is there more to it than just hole drilling? I have been a machinist for over 35 years, and am more than capable of doing this if I know the drill size, how many holes, and hole location. Like 3 holes at 120Ëš, or 4 holes at 90Ëš.
I really can't think of anything else that could cause the surging. The surging is anywhere from 1/2 to full throttle, and usually starts after any maneuver after take off. It doesn't surge on the bench or at take off..

Thanks in advance,
Greg

petec

My Feedback: (58)

I have had quite a few 1.40L engines and don't remember any of them having a gas ported piston. Gas porting the piston to the ring land is used to improve sealing. Surging is usually a function of lean mixture. You say it doesn't act up on the ground or at take off but will in the air. Is this in a tightly cowled installation? I have run into tuning issues where the cowling was causing airflow issues once airborne. Could you give some more specifics of the issue and perhaps post a few pictures of the installation?

OldRookie

My Feedback: (13)

The installation is in my DP Ultimate.
Anyway...There was one other symptom I noticed that I didn't mention before. when advancing the throttle to wide open, the engine would only hit about 7600 rpm sometime, otherwise it would hit 8200 rpm.
I included pictures that show about everything. Notice that the cowl opening to direct air over the cylinder, is the only one that is open. I blocked the other one.
I noticed that I didn't open up the air exit from the bottom of the cowl. I was going to do that but forgot about it. The exit at the back of the cowl is about 6-1/2" wide X 1/2" high at the largest gap.
It didn't seem as if the engine was going lean. There was no detonation noise, or lack of smoke from the exhaust. The engine didn't seem hot upon landing.
As long as I have the cowl off, I think I'll fly it again without the cowl, and see what happens. This thing really barks with that shorty pipe.

Greg

petec

My Feedback: (58)

Please let me know what you find with out the cowl. It looks really nice but I think it needs a little more airflow to be happy.

OldRookie

My Feedback: (13)

I got out last night to try how the engine ran without the cowl.
It was actually worse, and still intermittent, but never good.
Next step is to start pulling the engine apart to check for foreign material in the fuel system. Another person at my club field is having about the same problem with his YS 140.
I thought this was a manufacture forum. Unless petec is the YS representative, where is the support? I would like to get some input on the piston modification. Like I said, I can do this if I had the specifications. It has been stated that all of the 140 type formats use this type of piston, so there must be an advantage to it. I would like to hear more about it from a factory rep or service person.

Greg

David Bathe

It's a classic older YS problem. Changing the ring was the only cure that worked for me. They started gas porting the piston/ring groove, never tried it my self.

OldRookie

My Feedback: (13)

I talked with Richard at YS Parts and Service, and he thought it sounded like the piston modification may be in order.
I am going to check the piston and cylinder for any irregularities like out of roundness, or taper in the cylinder. Maybe a new Bowman ring.
I'm going to send it in, have the piston modified, and see how it works out.

Greg

David Bathe

Try and new ring first, should work in the short term, if after some short time the surging returns, it's the liner. Probiuld where quite insistent claiming YS, being a small company had problems with quality consistency back then. There are some article here/pattern form maybe, showing the gas porting process BTW. Not difficult.

OldRookie

My Feedback: (13)

David,

I was just guessing with the 17 X 8. I use a 17 X 6 on my 120FZ and interpolated up for the 140L. It turns the 17 X 8 Xoar wood prop at 8300 rpm.
I haven't had a decent engine run, so it is difficult to tell how much more prop I could put on that engine. I had a 17 X 10 APC prop that I tried, but it seemed to bog down the engine too much. I am using the 140L in a Dave Patrick Ultimate, this is a big draggy bipe so maybe getting in the 18" prop size would be better. Maybe 18 X 6 or 7?
What would you use? How about wood vs composite (heavy) prop?

Thanks in advance,
Greg

David Bathe

Yes that sounds about right, I ran a 16-8 on the 1.20. The prop of choice for the 1.40 FZ was 16-10. Fantastic for me (pattern) spot on. Third many different, this was great.

Dave Harmon

Hi Greg....
The gas porting of the piston will improve the ring seal for sure. It made a big improvement on my 140L.
"It does not surge on the bench or takeoff....."
Don't laugh....replace the throttle servo and make sure the radio is not going into fail safe.
This very thing happened to a friend of mine on every flight for a year thinking it was the engine....until it crashed...of course I was flying the thing when it went into the LA harbour!
Had to swim for the damn thing.

DH

OldRookie

My Feedback: (13)

I just got done taking my 140L apart, and was surprised that there was no noticeable wear on the ring or cylinder. The hone marks in the cylinder were like new. I would have thought there would have been some sings of breaking in after one gallon.
I set up a bore gage to check the cylinder for roundness and taper. There was less than .0001 throughout the whole cylinder, so at least the cylinder is good.
I'm going to send my piston into YS Service tonight. I also ordered a couple of 140L rings from Frank Bowman. I replaced rings in two DL engines with Bowman rings, and it was like a whole new engine.
We will see what happens when I get everything back.

Greg

Salander

I had a leaky gasket on the valve cover give me something similar once, until eventually it got so bad that it wouldn't throttle up beyond half throttle without throwing a (BIG) wobbly. Might be worth checking out.

Dave Harmon

Greg....the YS engines are a bit finicky on the ring end gap.
When you get the parts back....put a new ring in the cylinder (not mounted on piston) then bring up the piston from below to square the ring in the bore, then measure the end gap.
If the gap is more than .006....expect problems such as surging....however, the gas ports will help this a lot.
A new ring should be about .002 or so.
Also...the gas ported pistons will wear the ring quicker due to the vastly increased ring pressure on the cylinder.
Make sure to always use at least 20% oil.

Dave