YS 91SRX Tuning Help

[mdu6]

That's what I always do - OS or YS - Magnum bushing in 3 engines - one of them has 3 years +600 flights and still going.

[Heli$]

MDU, did you send your engines to Buzz or did you just order the rear bushings?

[mdu6]

No - you need to send to Buzz - usually he is pretty quick - about 1 week turnaround time (unless he is away).

[Rob43]

Heli$,

On the OS bearing, I believe the reputation of short lived bearings is mostly from those with experience with the 50 Hyper, running exhaust pressure. The YS bearing should hold up fine, running crankcase pressure.

It does sound like you need to maybe enrich the high needle. I've learned to go three clicks at a time to see the difference, and then, adjust closer. Don't worry about the mid until you get the high sorted. Then adjust it so it will smoothly hold rpm loading/unloading (like tic tocs).

[Heli$]

Thanks Guys, I'll wait to do the bushing mod until my new bearings go out. I think buzz is away right now anyways.

Just waiting on a new fan and shroud and I'll be up and running again. Weather is kinda wet out here anyways. I'll richen up the high 3 clicks and I'm also gonna try to richen the idle a wee bit.

[Heli$]

Update, I have flown several tanks in the last 2 days trying to get the engine perfect but still no success. I feel I'm getting closer though.

My power outs look good with a puff of smoke after I unload at the top. Big power loops and full throttle forward flight look good. Engine runs well inverted circuits. Back plate temp is always just warm after basic stuff.

But, tic tocs look good with smoke until I finish the maneuver and hover. The engine starts screaming and the smoke decreases significantly. I immediately come back to land and the back plate is very hot. Head temp 120-130 F though? Same thing happens with continuos flips. The glow plugs also get blackened and stop working sometimes.

My idle is 1 turn open. Any richer and the engine won't idle unless I bump up the throttle.

My mid is 2 turns open. 1.75 open is the rich side according to the manual.

My high is about 1.4 open. 1.25 open is the rich side according to manual.

Tank pressure is great and I replaced all fuel lines except inside the tank.

No bubbles in fuel supply line and no foam in tank. There are small bubbles in the short fuel line that came installed with the engine. I replaced that line as well.

[Heli$]

I replaced the MOAS and fuel line in the tank. Will give it another shot tomorrow. If tomorrow is no good, I'll overhaul the engine.

[Rob43]

Sounds like it's hanging on the pipe. Mid range too lean?

[Heli$]

It was hanging on the pipe but the mid is way rich. I flew again today and had tons of smoke with a kicking tail cruising around and then after tic tocs, the engine would start screaming a little. Blew out some glow plugs.

I'm going to take the whole engine apart and see what the heck is wrong. I ordered a new piston, ring, and liner just in case.

It seems that the mid isn't taking over after the tic tocs and the engine starves of fuel.

[Heli$]

In the past, the engine would do tic tocs and never hang on the pipe. This only started recently with much richer settings. Something has to be going on in the engine.

[Rob43]

Okay.

[mdu6]

Be careful - these signs do NOT equate to be running rich - YS are deceptive (compared to OS) with the smoke level

kicking tail cruising

the engine would start screaming a little

Blew out some glow plugs

[Heli$]

Mdu, spot on. This engine has kicked my butt.

I'll tear it down and see what I can find.

[Heli$]

Bingo, took off the rear plate and saw pieces of metal. sections of the rear bearing cage are missing. Doesn't look good at all. I'm sending it in for warranty.

This bearing must have been going out gradually over the last month since that's when it started burning more plugs and terrible to tune. The idle has been rattly but I have the low pretty rich and the rattle would stop at head speed. I also looked at the rear bearing a couple weeks ago but didn't see anything noticeable.

replace your rear bearings if you're burning plugs or you hear any kind of rattle! I have only 6 gallons thru this engine so it can happen early.

[mdu6]

Interesting - when I posted about my choice of sending the YS for a Magnum bushing (from new) - I had a couple of reply saying early bearing failure on the YS 91 did not happen

[Heli$]

That's what I thought after people telling me the same thing!

[Rob43]

I've not had any bearing failures with mine. I've seen my bearings damaged from metal particles caused by other problems. I had detonation of my piston in the YS 60sr last season. Then, had a wrist pin retaining ring come out and make shrapnel of the top end (my fault for re-using a wrist pin retainer, as I dropped a new one, and couldn't find it). Kind of unforgiving in nature, these beasts.

[One_eye]

Originally Posted by Heli$

Bingo, took off the rear plate and saw pieces of metal. sections of the rear bearing cage are missing. Doesn't look good at all. I'm sending it in for warranty.

This bearing must have been going out gradually over the last month since that's when it started burning more plugs and terrible to tune. The idle has been rattly but I have the low pretty rich and the rattle would stop at head speed. I also looked at the rear bearing a couple weeks ago but didn't see anything noticeable.

replace your rear bearings if you're burning plugs or you hear any kind of rattle! I have only 6 gallons thru this engine so it can happen early.

Heli$, that's what I told you in my earlier post.

[Heli$]

One-eye, I inspected it earlier but obviously I should have replaced it. It was hard for me to believe that it was already failing.

Oh well, live and learn!

[Rob43]

It's all good learning experience. Main thing, in my opinion will be to get everything very clean before reassembly. Regulator is the concern I have. I had metal particles from a piston giving me tuning problems. I started having tuning problems again last fall, and found my rear bearing was going from a prior incident.

So, it definitely does follow that a new tuning problem might be the first symptom of a rear bearing problem.