LOP dilemma

[Treekiwi]

Howdy all,
Looking for feedback from folks who actually overhaul engines for a living.
My engine has just had a full overhaul, and the shop says never run LOP.
This is based on their experience......LOP causes deformation of the cylinder walls, and they lose their choke and become bell shaped. It doesn't become a valve issue, according to them, but a ring issue.
He said while CHT's may be lower, the other areas can experience higher temperatures which causes the damage.
He said LOP makes him a lot of money, and recommends 100° ROP.
Now, I have always been an LOP guy, but maybe the savings are not really worth it in the long run. I've also had to do 2 top end overhauls on engines I've run LOP. Hmmmm?
I realize many so called gurus recommend LOP, but is it possible they've had it wrong all this time?
Tangible evidence is encouraged.
Cheers
Stephen

 

[rocketman1988]

Howdy all,
Looking for feedback from folks who actually overhaul engines for a living.
My engine has just had a full overhaul, and the shop says never run LOP.
This is based on their experience......LOP causes deformation of the cylinder walls, and they lose their choke and become bell shaped. It doesn't become a valve issue, according to them, but a ring issue.
He said while CHT's may be lower, the other areas can experience higher temperatures which causes the damage.
He said LOP makes him a lot of money, and recommends 100° ROP.
Now, I have always been an LOP guy, but maybe the savings are not really worth it in the long run. I've also had to do 2 top end overhauls on engines I've run LOP. Hmmmm?
I realize many so called gurus recommend LOP, but is it possible they've had it wrong all this time?
Tangible evidence is encouraged.
Cheers
Stephen

Look at the data. I would love to see the supporting data on "cylinder wall deformation" and "losing their choke". What other areas are going to be "hotter" and what is going to make those areas "hotter"? Running LOP at power levels below ~65% actually reduces internal temperatures as well as CHTs and fuel flow.

Is it possible that your mechanic is wrong and the "so called gurus" are correct?

What was the specific reason for the top overhauls? (Running LOP isn't a valid answer)

 

[Ironflight]

I don’t build engines for a living, but I have built them for my own (and a few for others) use, so take this for what its worth.

Tangible Evidence…..

RV-8: 2280 hours - all of it (except take-offs) LOP
RV-6: 2,000+ hours - all of it LOP (except Take-offs)
RV-3 : 980 hours - all of it LOP (except Take-offs)
Dream Tundra: 450 hours - all of ti LOP (except Take-offs)


There are many, many old wives tales out there, and many folks will tell you things that they think are true but can’t back up with data. Most engine shop employees, builders, and owners don’t fly….they just work on engines. They’re not dumb - they just have no first-hand experience how engines are actually operated in aircraft. Many will say “Lycoming says don’t do it!” But they are actually refering to the boosted Lycomings not our normally-aspirated motors.

Good reason not to run LOP? You’ll get a biut mnore power and speed - and if your coolign system and wallet are happy there, then run at peak or ROP. But we find with our tightly-cowled motors in the hot high desert, we go LOP as soon as we reduce power below 70% (which is generally right after take-off) and leave it there until shutdown.

By all means, fly the way you are comfortable - but don’t be afraid of LOP because one shop told you to be….

 

[lr172]

I have built my own and a couple others, so not necessarily what you are looking for. As paul said, you should just ignore that. I am sure they see all sorts of issues but have basically no data or info on what led to those outcomes. Most of these guys understand the mechanics of engine assembly and machining. They are not engineers working on dynos and running engines to destruction in various different conditions to understand cause and effect. I would far prefer the opinions of local mechanics that see an engine every year and understand how it is run and how that behavior results in issues. Overhaulers only see the carnage, with absolutely NO appreciation for how it got there. Be sure you accept opinions from those with the credentials to support them.

LOP operation are not damaging. Every auto engine built in the last 35 years runs lop in light load conditions, even the air cooled porsche boxer engines, which are very close to a lyc. I have one.

You will find many engines that don’t make it to tbo with messed up cylinders; some will have run lop and others always rop. There are countless variables in play beyond mixture and absolutely no way to isolate just mixture as root cause in these cases. Cylinder wall deformation can cone from various different issues, but mixture is not one of them.

My 320 has 1600 hours and i never run ROP beyond take off or climb and sometimes climbs are done lop. Cylinders look great and make good compression.

 

[blaplante]

He said while CHT's may be lower, the other areas can experience higher temperatures which causes the damage.

So,
Seems simple enough. Lets instrument the barrel of a cylinder at multiple points, then run it ROP and LOP, and get the data showing where some part of the barrel becomes hot/hotter. In fact have the shop tell us where they want the probes.

 

[plehrke]

The reality is that there are very few people/shops/companies that have enough data to make definitive claims. This includes most gurus and local or internet experts that are on both sides of the LOP/ROP discussion. Of those with enough data there are probably only one or two that need to be right or face financial liabilities therefore are very cautious in what they say.
You need to make up your own mind between those opinions with little or no data and the few that are experts but have financial risk that maybe too conservative.

 

[Treekiwi]

Thanks for the comments. Mostly pretty much echo what I have learned over the years.
Paul's real world example numbers are quite persuasive.
I agree there probably isn't great data to back up the shops claim. They have been in business for years, and have rebuilt many 1000's of engines. I can only presume they have asked owners how they run their engines, and then observe what the issues are. That is not very good data, of course. How many owners with cylinder problems routinely operated in the red box due to lack of training? That right there could very well cause the issues observed by the shop. And, they most certainly are very conservative and have a financial incentive to be so.
LOP was probably misunderstood by pilots for awhile until the red box and big pull concept came into the light.

If any engine shops want to comment on their real life experiences, that would be great. Absent that, we are left to make our own decision based on figures and experience.

Tangible Evidence…..

RV-8: 2280 hours - all of it (except take-offs) LOP
RV-6: 2,000+ hours - all of it LOP (except Take-offs)
RV-3 : 980 hours - all of it LOP (except Take-offs)
Dream Tundra: 450 hours - all of ti LOP (except Take-offs)

These numbers are a very good start.

 

[rv8ch]

I hope the Savvy guys expand the amount of data that they gather, like fuel type, oil type, spark plugs, oil filter type, ignition type and timing, when consumables are changed, when cylinders are changed/honed, sticking valve cleanups, regular maintenance, etc. If they do, in about another 10-20 years, they will be able to tell us definitively if LOP is bad or good. Until then, we have to process all the data we have consumed, and make a decision. Personally, I run as lean as I can depending on the speed I want to fly. If not in a hurry, I lean it to just before roughness.