E-225-8 Rough in mid-rpm range

[455 Bravo Uniform]

My 92 year old hangar neighbor has a G35. His engine runs rough from about 1300-1800 rpm. He says it feels like it’s going to shake itself apart.

Mag check is fine, no difference. Idles fine, clears up fine at higher rpm. No induction leaks.

I only know automotive carbs. Some have an intermediate circuit, or transition circuit, for midrange rpm. I suggested if the carb on his plane has any similarities in the fuel circuitry that there might be dirt or possibly old “gasketry” (I made that word up just now). Is that plausible with this era engine?

Anyone else have other ideas to check?

Thanks.

 

[William Pete Hodges]

My 92 year old hangar neighbor has a G35. His engine runs rough from about 1300-1800 rpm. He says it feels like it’s going to shake itself apart.

Mag check is fine, no difference. Idles fine, clears up fine at higher rpm. No induction leaks.

I only know automotive carbs. Some have an intermediate circuit, or transition circuit, for midrange rpm. I suggested if the carb on his plane has any similarities in the fuel circuitry that there might be dirt or possibly old “gasketry” (I made that word up just now). Is that plausible with this era engine?

Anyone else have other ideas to check?

Thanks.

The short answer to your question is Yes this is plausible. My inadequate research says your carburetor is likely a bendix stromberg PS5C. You can download a free PS carburetor manual at CSOBeech.com. This carburetor controls fuel for idle to about 25%, cruise to about 65%, and full power to 100%.

I would download a copy of this manual and study it. I would also talk to my AI and seek his advice.

Hope this helps.

 

[flyingron]

Ah yes, the ps5c. It's full of rubber things and can get balky (especially with periods of misuse).

 

[mondtster]

Ah yes, the ps5c. It's full of rubber things and can get balky (especially with periods of misuse).

Especially if the carburetor has the older style diaphragms in it. They will get stiff as they age.

 

[455 Bravo Uniform]

He said the carb has new diaphragms in it. I said “yeah, but what, that was like a quarter century ago?”

Also, he only put 4 hours on it last year, and about the same the year before. He winterizes it every mid-fall. He takes it out of hibernation in late spring. He’s still trying to get it going before he stores it again in November.

 

[hindsight2020]

4 hours? yeah bet those pressure carb internals are ossified.

 

[Dan Thomas]

Might also be worn engine mounts, letting the engine mounting lugs contact the airframe mount and resonating at certain RPMs. I saw that in an old Tri-Pacer once. Sagging mounts. Made strange vibrations. Torque and thrust factor into it.

Ignition is a possibility, mag check notwithstanding. At certain RPMs the cylinder pressures might be high enough but the mag's speed low enough (and the mags tired enough) that the spark isn't hot enough, and plugs are missing. A check of the mags at the affected RPM should show something.

 

[odie451]

E-Series Bonanzas: Flying, Owning, and Maintaining a Classic | American Bonanza Society

By Lew GageFrom the Introduction: "This book is a collection of articles I have written over the part 21 years, that have been published in the ABS Magazine. They are mostly maintenance articles; however, there are some on other subjects."Item ID: B-13

american-bonanza-society.square.site

Don't know if your hangar neighbor has this book. It is written by Lew Gage who is considered the guru of the E-series Bonanzas

 

[Bell206]

Anyone else have other ideas to check?

Has someone pulled all the cowling and performed a good tactile check of the engine install and components? A harmonic due to a loose exhaust stack or cracked mount can also cause a similar affect especially if its as severe as he states.

 

[455 Bravo Uniform]

The short answer to your question is Yes this is plausible. My inadequate research says your carburetor is likely a bendix stromberg PS5C. You can download a free PS carburetor manual at CSOBeech.com. This carburetor controls fuel for idle to about 25%, cruise to about 65%, and full power to 100%.

I would download a copy of this manual and study it. I would also talk to my AI and seek his advice.

Hope this helps.

He has the hard copy of this. Thanks. He also has his A&P/IA looking at it as well.

 

[455 Bravo Uniform]

E-Series Bonanzas: Flying, Owning, and Maintaining a Classic | American Bonanza Society

By Lew GageFrom the Introduction: "This book is a collection of articles I have written over the part 21 years, that have been published in the ABS Magazine. They are mostly maintenance articles; however, there are some on other subjects."Item ID: B-13

american-bonanza-society.square.site

Don't know if your hangar neighbor has this book. It is written by Lew Gage who is considered the guru of the E-series Bonanzas

Yes, thank you. He does have a copy of this as well.

 

[Wrench978]

I would pull the strainer out and see if there is anything clogging it up. Does it run smooth once it gets past 1800 rpm? Or does it not get there?

 

[455 Bravo Uniform]

I would pull the strainer out and see if there is anything clogging it up. Does it run smooth once it gets past 1800 rpm? Or does it not get there?

I think he checked the strainer. Yes, it’s smooth once past the rough spot.

Unfortunately I haven’t had time to check with him lately, I’ve been working on installing an engine monitor while my plane is down for annual.