Engine Trouble

[huntaero]

Glad you made that landing successful. Ive never seen the cyl base studs crack on a lycoming like these and I have years of maint experience on lycomings. Because it is a narrow deck eng make sure when you are reinstalling the cylinder hold-down plates to use use shims as per the manual attached.

[Nev]

Thanks for that - very much appreciate the advice.

[Bissetg]

Hmmm … red RTV rings a bell, as does a blocked oil gallery and a wreck bought off the insurance company of a plane I once flew. Be careful.

[svyolo]

Looking all over the engine, the only place it was visible was the accessory case. Vacuum pad and one other I can't identify off the top of my head. Oil sump, case, etc not visible.

[Nev]

Finally got my Bearhawk home today. My engineer Kevin and I got an early start at 5am, drove up and removed the sheared studs, and replaced the two cylinders. We changed the oil back to straight 100. Also found several very loose nuts and bolts on the engine - the vibration had taken a toll, and we spent a while checking everything once it was back together. I've started running the cylinders in on the way home. Once thats finished we will clean the remaining 4 cylinder flanges and complete an annual on the aircraft.

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[Steve W]

Congratulations Nev on a good all around job getting it down safely without any incident and getting it back to base after repairs.
Because of some recent cylinder trouble, I have been researching engine/cylinder break-in procedures at length, and cannot find anything concrete on gospel power settings quoting a reliable source. I am only asking this for the purpose of educating myself and for no malicious reasons. I see a power setting of 28” and 2300 rpm on the efis. I gather that is wot and a low prop setting at 1300’. I would like to know if there is any supporting documentation to use these numbers. I have walked away from the computer with the idea I had the right numbers of 25” at 2500rpm below 3000’ with variations on either side for proper initial ring seating. Friends of mine with recent OH engines have been told by the shop to set up their ground adjustable props for 2200 static rpm and run it at wot. Again I can’t find anything that supports this but looks similar to what your doing. I’d appreciate any help here. Thanks

[Nev]

Thanks Steve. Yes it was WOT at 2300 RPM. Those settings are not based on anything Gospel or scientific, just lots of reading and chatting with others, and my previous engine run-in went well. I think my engineers words were "don't baby it - best to give it some abuse on the way home".

First time around for run-in I used ROP and around 2400 RPM. Normally I cruise LOP at about 26" and 2200 RPM. Yesterday I wanted to keep the ICP relatively high, but without the cylinders getting too hot. It seemed easier yesterday because the other cylinders are already run-in and so I was able to keep cylinders 4 & 5 below 210c (410f).

The chart below from the Lycoming manual shows that the power setting is within the recommended envelope. The red dashed line is for my normal cruise operation, and 28.5" MAP is on the edge of the envelope at 2300 RPM.

There's others on the forum who might chime in here with a lot more specific experience than I have.

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[TJ_Slice]

Nev,

As someone who will be sourcing an overhauled IO-540 next year, thanks for posting all of this!

[Battson]

Because of some recent cylinder trouble, I have been researching engine/cylinder break-in procedures at length, and cannot find anything concrete on gospel power settings quoting a reliable source. I am only asking this for the purpose of educating myself and for no malicious reasons. I see a power setting of 28” and 2300 rpm on the efis. I gather that is wot and a low prop setting at 1300’. I would like to know if there is any supporting documentation to use these numbers. I have walked away from the computer with the idea I had the right numbers of 25” at 2500rpm below 3000’ with variations on either side for proper initial ring seating. Friends of mine with recent OH engines have been told by the shop to set up their ground adjustable props for 2200 static rpm and run it at wot. Again I can’t find anything that supports this but looks similar to what your doing. I’d appreciate any help here. Thanks

Based on research we did dozen years ago, for a Lycoming -540 engine, we arrived at 75% power (or more) for engine break-in.
Given the elapsed time, I can't recall where we sourced that from, but we have it documented in our test flying procedures. I thought it was authoritative, but I can't be sure sorry.

Which settings you choose, to achieve your desired power setting, are surely dictated by the Lycoming operating manual, the engine's performance (temperatures mostly), among a range of other factors. Some of the main considerations are the need to keep the engine below the redline CHT, and the maximum allowable difference in MAP and RPM.

I see you've heard people using 2200 RPM and WOT. That would be pretty close to the allowable limit, depending on the MAP the specific configuration is achieving. In my aircraft, that would be beyond the allowable limit at 1,000ft and just within the limit at 3,000ft. If engine temperatures allow, a lower MAP and higher RPM may be a lower risk option.

[Battson]

Lycoming's Operations Manual might be worth a look, in terms of reference material.

[Nev]

Just to add to this, I couldn't find anything in the Lycoming Manual about running the engine in, however there is a Lycoming Bulletin on the subject attached in post 41 below.

[Steve W]

Thanks Nev. That’s what I needed to see and hear. I am so old that when I hear high over square numbers I cringe! Have about 3000 hours sitting behind Conti 520’s and it was beaten in to my skull by the company engineers “square for climb and one inch off in cruise rpm. Helped take two engines to tbo without a cylinder change. Also no leaning below 5000’. These were factory OH engines but of course, Continental. Different beasts.

[jaredyates]

Reconfigure the manifold pressure to show hectopascals and the remainder of your oversquare concerns will be gone.

[Steve W]

Yup mind over matter. That will work!

[svyolo]

There are a few IO540 powered aircraft that are rated at 235 hp (Maule and Cherokee come to mine) that limit HP by limiting max rpm. Off the top of my head I can't remember the exact rpm, but 2350 or 2375 comes to mine. So seal level MP and those max rpm seem to be OK.

[Gerhard Rieger]

2500 RPM if I remember correctly

[kestrel]

Our RV-4 barely exceeds 2200 rpm on take-off and climb out. ...WOT, of course. Need to get above about 100 kts to get the rpm higher.

[Nev]

Here's another version of the chart posted earlier on this thread, showing that the lowest RPM for operating at 28" is 2200 (noting it's actually for a carburetored engine).
Below that is an excerpt from the Lycoming website. Link to the full webpage HERE.

Link to Lycoming service bulletin on how to run the engine in HERE.

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[Nev]

Sky Ranch Engineering Manual

We learned a few more things today. My engineer Kevin dug out an old manual that he had and found the section titled "Paint and Broken Cylinder Studs". It appears that it is a known issue, and definitely a no-go item in the aircraft engine industry. Needless to say that finding this information stated so clearly in an old aircraft engine manual has raised some serious questions in our minds.

It appears at the very least that we will need to replace the remaining 5 studs on the #4 cylinder, which necessitates removing both #4 & #5 again.



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[DBeaulieu]

Interesting read, thanks for posting!

[svyolo]

Was the paint/sealant just under the base of those plates, or also at the base of the cylinders themselves?

[Nev]

The paint was under the hold down plate - between the hold down plate and the cylinder flange. We haven't found any between the flange and the crankcase.

[John Bickham]

Thanks for posting Nev!
I have been negligent in not checking into the BH Forums as much as I should. Too busy flying and having fun doing it. To be completely honest, I was was enjoying being ignorantly bliss!
Now I have been educated a bit and need to determine best path forward. This is my first Lycoming engine and I have learned a lot but have a long ways to go. So if you offer advice, type slow so I can understand.

I basically have the same engine, just no "I" (carbureted). One of Bob's engines. Has been in service 4 years now with 670 hours. Just started to notice small oil weeps around cylinder bases on mostly #4,#5,and #6. When I consult more experienced Lycoming guys, the basic response is that the "L" in Lycoming stands for leaks. I have been very successful at keeping the inside of the cowling spotless so I notice even the smallest weep.

Got a condition inspection on the near horizon and looking for some advice on how to proceed and make sure I understand all the information shared so far.

Given the "Experimental" tag on our engines and this information shared by Nev, I think it would be prudent to remove the baffles and other interfering components and do a torque check of all the cylinder base nuts. If they all meet the Lycoming torque specs, smile and put it back together. Probably should be done every 500 hours?

If even one is loose, then what? If I have a correct understanding pre-stressed vs load stress from the info shared in this thread then re-torquing a base stud nut or through bolt may even accelerate a failure. If I find a base bolt not to torque is the answer to pull all the cylinders, clean the bases of any RTV and reassemble? I think this is what I understand to be Nev's course of action. Does that sound reasonable? On the bright side, this would be an excellent opportunity to ream the exhaust valve sleeves and lap the exhaust valve seats. Just to clean things up.

There is a delicate balance in being proactive and not inflicting further harm. Interested in any advice, please be gentle.

Nev, on that suspected governor oil leak. If you haven't located the source of the leak, check that plug bolt on the nose of the engine for the governor drive shaft. Use the borescope, it is deep behind the starter ring. I had a gasket leak there that needed to be replaced due to a developing leak. Gotta pull prop and remove starter ring to access.

Also I do have a question Nev. You mentioned pulling an opposite cylinder to replace damaged through-bolt. Isn't there an o-ring seal at the case split that can only be accessed by splitting the case? Any concerns there? Are through-bolts routinely replaced when cylinders are installed without splitting the case?

[Battson]

I had a similar experience with onset of oil leaks as the engine ages. I suggest finding the source of the oil leaks and resolving them, or at least determining whether they are cause for concern.

Common places for oil to escape are the pushrod cover seals, cylinder head gaskets (often comes loose, tighten screws), oil return lines (both ends - search for my earlier post about the shoddy flares I found), etc.

Oil isn't supposed to leak out of the engine... rather than accept it and move on, I think it's worth pursuing. P.S. I have never heard the "Lycoming's leak" comment. Sounds like an easy excuse

[John Bickham]

Battson,
Could you give me a better lead on the post for the oil return line leaks. I've done a few searches and come up empty.
thanks

[Battson]

I have posted explicitly about it in the Maintenance section, a new post.

[Bissetg]

I agree with Battson. Finding the source of the leak and making an informed decision on how to manage it is critical.

This has been a great thread from a learning point of view for those of us with limited knowledge.

[John Bickham]

Thanks. Agree with all that. The challenge I face is to listen CAREFULLY when the plane is talking to me. It is easy and often the initial response to rationalize away an issue. Been guilty of that. I have a couple of suspect pushrod shroud cover gaskets. A suspect oil return line. My head gaskets are good. I check those and tighten screws every oil change. I want to emphasize that I'm just in the weep stage mostly. Nothing that I would classify as a leak. I've got a few of the cylinder base bolts that look like the source of some weeps.
Today I did check of few of the cylinder base bolts that I could access with a torque wrench and they were at least Lycoming torque spec.

So my current plan, so far just thinking about it today:

1. Document and ID all weeps, seeps, and leaks with pictures. Most will be borescope pictures.
2. Clean all weeps, seeps, and leaks.
3. Fly and monitor every 5 hours. Document with pictures.
4. Take action as needed to eliminate leaks.
5. If I reach condition inspection, remove baffles, exhaust and any other hardware to check the torque of each cylinder base bolt per Lycoming spec.
6. If any nut/bolt less than Lycoming torque spec, remove cylinders to inspect, clean, re-gasket and reinstall.
7. if the cylinders come off, I'm gonna lap the EV seats and ream the EV sleeves. Just to clean 670 hours of lead off.

If the cylinder base nut/bolts are the source of the weeps, I don't know of any remedy except to remove the cylinder and clean the metal face flanges. Any other recommendations on that?

Open to any and all suggestions. Fly safe!