Engine RPM

[PaulSA]

I'm not sure the advice you are getting is 100% correct. On a ground static run, you should NOT achieve max RPM. The RPM should be limited to around 50-75 rpm less by the fine pitch stop. Then, as you accelerate on take off, the RPM should increase to rated and be limited there by the governor as the blades come off the stop.

[Battson]

Paul - what about this option makes it better than setting the fine stops for the engine's limit?

[Nev]

Right, that makes sense. Thanks Paul.

[PaulSA]

Battson - because if you set it on the limit, you are not sure if it's the fine stop or the governor that is limiting the the RPM initially. This is the way the MT manual tells you to set up the prop.

[Nev]

I've had a couple of niggling prop governor issues that I never fully resolved. Today I rang Hartzell. I explained that on the first flight the initial RPM was a bit higher than expected ( after a low RPM during the static ground runs), and that also when running the engine up, the prop wasn't cycling reliably unless I increased to about 2000RPM.

Turns out that the governor I have (S-1-15) is for a wide deck engine, and I have a narrow deck engine. (Someone might explain the difference for me). Apparently these symptoms are exactly what you'd expect to see.

The Hartzell technical rep explained that the easiest fix is to make an adjustment inside the governor which I'll get done in due course. I'm adding this post in case someone else sees similar symptoms.

[Tyler]

I’m glad I read this. I have the same situation. I got an s-1-15 governor like most, and my Bob engine turns out is a narrow deck 540…and I’m having the same symptoms you described above. Looks like I’ll be flying up to the Hartzell service center sometime later for them to adjust mine internally. Meanwhile it flys so I should be able to keep testing the plane and just manage the nuances of the governor.

[Chris Werner]

Glad you have this figured out. There is a difference in governor drive ratio between the two engines. This is a quote from a Lycoming service letter... Propeller governor drive speeds are slightly faster on wide cylinder flange -540 model engines than on standard cylinder flange engines. If the engine upgrade is made to a wide deck from a narrow deck engine, the customer must also change the propeller governor. The gear ratio is .947:1 versus .895:1. Refer to the propeller manufacturer's instructions.

[robcaldwell]

Interesting... My prop won't cycle unless I take it to 2000 rpms. I assumed this was because my Hartzell Trailblazer carbon fiber prop was too light to cycle at the slower speed. I'm not certain, at the moment, if my IO-540 Thunderbolt is a wide deck, or narrow deck.

[Mark Goldberg]

The newer, smaller Hartzell governor will not cycle below 1900 - 2,000 rpm. Regardless of whether it is wide deck or narrow deck engine. Mark

[Nev]

Mark, do you have a model number for the newer governor by chance ?

[Mark Goldberg]

Most of the governors for 540 powered Bearhawks are S-1-15. MG

[jaredyates]

Interesting... My prop won't cycle unless I take it to 2000 rpms. I assumed this was because my Hartzell Trailblazer carbon fiber prop was too light to cycle at the slower speed. I'm not certain, at the moment, if my IO-540 Thunderbolt is a wide deck, or narrow deck.

I would bet half a quart of used brake fluid that yours is a wide deck Rob. Generally the wide deck is the more modern design.

https://generalaviationnews.com/2009/10/07/ask-paul-wide-deck-vs-narrow-deck-engines/

[Battson]

I understand the way to check WD vs ND engine, is how the cylinders attach. WD has bolts through the cylinder flange only, no other parts. ND has so-called "banana plates" which sit on top of the cylinder flange and the bolts go through both the banana plate and the cylinder flange. The banana plate is supposed to be used with a barrel nut with an internal star / torx drive head, whereas the WD normally has standard hex nuts, however given we are experimental I would not count on that.

I am not an expert, but that's what I have been advised.

Sounds like the PCU-5000X governor will cycle much lower than the Hartzell compact - both are a similar size / weight. Mine will cycle the Hartzell Trailblazer two blade at an RPM down as low as 1,400 on a good day, always at 1,600.

[Pbruce]

I think all the narrow deck engines have “banana clips” on them. My last plane had them, since it was a 1950’s engine from an Apache. These are 2 brass-coloured curved metal plates covering most of the circumference of the cylinder. They are about1/2” thick. They provide a more robust mounting than just bolting the cylinder flange onto the case. (Like a big washer) The cylinder bolts protrude though the banana clip, the cylinder flame, and the case. The wide deck engines don’t have the clips and so the bolts go only through the case and the flange, which is wider, hence the name “wide deck”. I have no technical expertise in this. It’s just what I was told about my engine. In short, if it’s got the clips, it’s a narrow-deck. If it has a wide flange it doesn’t need them.

[Battson]

The banana clips are often painted too, such as on a Bob engine.

[Chris Werner]

Some extra reference material to identify wide vs narrow deck. Both visually and with serial number.

https://www.lycoming.com/sites/default/files/Wide%20Deck%20Cylinder%20Configuration%20on%20Lycoming%20Engines.pdf

[robcaldwell]

Well there you go. Looks like anything after 1987, except O-235, is a wide deck. Thanks for this!

[JimParker256]

Today, after many years of frustration about this, I leaned through this forum that there is an easy-to-spot visual difference. Narrow deck engines (older style) have "banana clips." I doubt I'll ever be confused again!

Thanks to all who contributed to this discussion...

[marcusofcotton]

I don't know about narrow deck O-360s but I understand narrow deck O-320 150 hp (low compression 7:1) didn't use banana clips but the 160 hp (high compression 8.5:1) did.

[Chris Werner]

I believe you are correct, low compression narrow deck used the same internal hex nuts without the plates.

[JimParker256]

Dang it! Now I'm completely ignorant – again...

[svyolo]

Well there you go. Looks like anything after 1987, except O-235, is a wide deck. Thanks for this!

Rob, if I remember right you bought a new engine. I wonder what percentage of engines are wide or narrow. Most certified light aircraft were built before the mid 80's, and most of those engines are probably still around.

[Battson]

Some steel recyclers still use a process that is over 50 years old, because it works. That said, 50 years ago was 1972 so that's not that old... I hope!
I wouldn't bet the Lycoming factory has changed much, given all the certification required for any changes. I would be interested to know, if anyone does know.

[robcaldwell]

Very true. I still would think that machining and other processes have been improved. Also, since my engine comes from the Thunderbolt line, which didn't exist way back when, it was hand assembled. I would like to think there is a benefit to that compared to a case swinging down an assembly line.

[AKKen07]

Rob I got a new engine as well, though from Continental’s Titan line (formerly ECI). Before it shipped I flew to Alabama to tour the factory and I thoroughly enjoyed seeing how the magic happens. One thing I learned was that, at least at Continental, every engine, Titan or not, is basically hand assembled. Each one has a set of perfectly organized set of parts that a technician then builds into a new shiny power plant per a spec sheet on his or her table with the parts. I bet Lycoming is similar. And I know for a fact that the technology in the construction of current Continentals didn’t exist 50 years ago. Anyway, my point is - be proud Brother! I am sure excited to run my new engine this year.