This is a question I hope Dave will be willing to answer.

I've had 6-7 YS engines in the last 10 years. That includes the original 120SF, 120AC, 140FZ and the 140L. They have all been put to hard use in pattern planes.

I've been very pleased with the overall performance and handling of these engines. However, they've all had a gradually performance degradation that I think is starting after about 80-100 flights.

After break in, the compression is usually excellent. After about 80-100 flights the compression is reduced and it is possible to hear the engine leaking when turned over slowly. In my opinion this is due to leaking valves and not the piston ring, as grinding the valves seems to be the only cure.

The valves in Saito and OS engines seems to last much longer than this. I've heard that the newest YS heads has aluminum valve seats as opposed to the typical brass inserts.

Can anyone (Dave ?) comment on this performance degradation and the longevity of the valves and seats?

Oistein, NORWAY

I think the problem lies with the fact that since the YS engines make such big power, everyone wants to load them up with huge props which keep the noise factor down for pattern flying. This in turn makes the engines run so much hotter which takes a toll on engine life.
We have field reps who have 300 plus flights on a couple of the DZ engines with virtually no changes in performance. Admittedly, these guys are experts who know how to set engines and seldom have leans runs.
I believe that running less load will make any of the engines last longer. Maybe you ought to try it.

Good Flying,
Dave

I would have to agree with that, have a 120SC that has 100+ flights on it using a 18x6 carbon fiber prop. This lets the engine turn up about 9,300 to 9,400 on Wildcat 30/18 Fuel. The only problem this engine has had was a broken valve tappit, which was fixed using a metric anlan head screw. Very surprised to see that that screw has lasted for 40+ runs.

Hmmm... Dave, you've got me wondering now.

Even though it shows absolutely no sign of overheating (even back in August), do you think I'm loading up my 91FZ too much with that 16x6 APC? I'm getting 8700 on the ground, with a distinct but not too heavy smoke trail in the air.

Steve

Hey Steve, wondering will get you in trouble!!

If you're satisfied with the way the prop works for you, trim 1/4" off each tip and pick the rpm up just a tad. I like the 91 at between 9000 and 9500. Some of the racing guys run them over 11000 with no problems, but they crash before the engine has time to self destruct!

Good Flying,
Dave

Ditto to what Dave said on overloading these engines, you can really roast a motor in a hurry with a lean run/overheating during flight.

What I found for propping is that it is really dependant on your altitude. I used to live at about 1000' asl now I live at 3500' asl. I spent a long time learning that the props that worked for me at low altitudes were way to much for me at higher altitudes. Although they seemed to run fine on the ground once in the air they were obviously loading the engine down too much. Now that I have it figured out I have no problems with my motors. I now dont get too worried about the rpm the engine is running but how it sounds in the air during a flight. If the engine sounds like it is working hard then it is and smaller prop will give you better performance and longer engine life.

So just be carefull about using props that others recommend as your location may not be that suitable for that particular prop, and you may be loading your engine down too much.

On a side note I have seen and experienced valves (exhaust specifically) that would be covered with buildup enough to affect the seal, but this should take far longer than 80 flights to occur, more like 400.

<<...between 9000 and 9500...>>

Okey dokey. I'll just put that 16x4W back on there. I loved the way it did, but was afraid it was letting the engine turn up too much. It was right at 9500 on the ground.

Steve

Hey Steve, that ought to be just perfect for the kind of flying you are doing!

We at Mesa AZ run the Graupner 14x7 prop and the engine turns about 9500 on the ground. They run, cool, and perfect for many hours. See RCENGMAN on this site for more data. He is the best YS Engine repairman I have known. He can "soup them up" also. Changes the timing, lap surfaces etc. for a fee of course.

You can buy the 14X7 p/n 1316/36/18 Graupner props from Central HObbies or new creationsrc in Texas at a good price. This is the prop Graupner recommends for YS91 engines. Try them out! Just my .02cents worth.


dickj

I totally agree that these engines should not be loaded down with too heavy props. With one exception I've always had my 120-140 engines turn in the 8500 rpm range.
The exception was my 140FZ which I flew for about 500 flights with APC 16-12 turning (I think) about 8000 rpms or slightly less. This didn't give maximum performance but as Dave correctly commented very low noise. This engine, even though it was heavy loaded, ran very consistently.

When I say performance degradation I meant a slight degradation of say 200-300 rpms compared to the engines "best period" peak, not an engine breakdown needing rebuild.

Maybe I am too focused on minor details, I just want my engines to perform at their best ... :-)

I still think that the valve/seat seal is very important to the performance. What is the reason that YS has changed the design of the head, using no brass inserts in the valve seats ?
Is it just a cost issue ?

Oistein, Norway

Dick, I agree that Graupner props are second to none. But their size selection is quite limited. I have a 14x7 and 16x8.

What I am looking for here is a combination of pulling power (as opposed to speed) and braking effect. The airplanes I'm flying have super light wing loading and lift ratios; in no wind, they are difficult to get on the ground without spoilerons. The lower the prop pitch, the better.

In fact, that 16x4W is amazing. When you throttle back, it is like throwing out a drag chute. You can SEE the model visibly slow down as if a brake was applied on a car. But it makes an eerie howling noise at full throttle, and that concerned me. It sure sounded like the engine was overspeeding.

Steve