I have my 59 straight tail in annual at present and IA found a crack on the spinner bulkhead. This is the second one in my 9 years of ownership. Found the first at the first annual in 2008 and replaced the entire spinner with one from Wicks Aircraft (I believe). Also in the intervening years replaced the prop with a new 8 bolt (I think it was a MDM7653). My engine is a C-145-2 from a 170. That was done back in the 1960s. I have never had it balanced but it seems to be very smooth. However, that is just a seat of the pants assessment.
I have a couple of questions here. Any reason why this engine would crack a bulkhead on the spinner in 400 hrs (estimated hrs in 8 years)? And anyone know where I can buy an untracked bulkhead? Or is that not done and I need to buy an entire spinner?
Pete, there may be several reasons for the cracking, including pushing/pulling around on the prop to move the aircraft, leaning on the prop spinner (perhaps even by bystanders with an arm draped across it) or insufficient or infrequent tightening,.... but a real common reason is lack of dynamic balancing.
These six-cylinder Continentals are smooth and lead many to skip balancing, but consider this... dynamic balancing gets rid of all sorts of vibrations you may never notice in the cockpit.
I'd certainly eliminate that possibility after you get the spinner repaired.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
What type of spinner do you have? Is it the one with a rear bulkhead and plug that centers it using the hole in the front of the prop hub? How much play is there between the plug and the hole in the prop. If it has play and can wobble, that could cause a crack. Most likely you have a dynamic prop balance issue as Gahorn described. How long and in what area is the crack? I see no reason that it cannot be repaired by welding, It is made of 1100 aluminum and easily weldable.
What type spinner? Gee, I didn't realize there was more than one type. The bulkhead has fillets and threaded plates that are riveted on the backside of the back flange. The spinner itself has a center plug. When we installed it we wrapped a 1" strip of duct tape around that plug to make it fit tight with the prop central hole. I have nylon washers underneath the screws holding the spinner on and periodically check the torque to ensure tightness. The spinner has a polished finish so nobody touches it (at least not in my presence ). I do push on the prop to move the plane but recently purchased a tug. When I move the plane, my hand is adjacent but not on the spinner.
One thing that I noticed which may be relevant - the tape around the center plug of the spinner was black as though it was fretting/moving. Something has to be causing that and if there is movement, that would explain the crack (i.e. metal fatigue). Correct? But the question then is what did we do wrong in the installation or what is causing the relative motion?
As always thanks for the replies, it helps that we are all in this (the joys of aircraft ownership) together.
Your spinner may not be tracking true. Block the plane up in flying position so the spinner is parallel with the ground. Remove a set of spark plugs so the engine can be turned easily. Put a ladder, pole , or whatever that you can attach a mini-felt tip pen to and center it so it is just barely touching the point of the spinner. Turn the engine over carefully by hand and see what kind of trail the pen leaves. Obviously if it draws a circle instead of just leaving a dot, your spinner is not tracking straight and is slightly wobbling.... Going to crack bulkhead sooner or later. Also possible the spinner assembly is slightly out of balance. A good dynamic balance would probably fix that.....just my thoughts and experience.
With someone in the cockpit holding brakes, or with the airplane tied down/chocked etc., and engine idling, you can stand aside and see if the spinner wobbles.
But wobble is not usually sufficient to cause cracks.
The black tape residue indicates vibration. Get the prop/engine combo dynamically balanced, IMO.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
I intend to have it balanced by either the vibration specialist in our company or my IA. I work for a large electric utility and we have a guy who specializes in vibration analysis/balancing of rotating equipment. He has told me that he could do this. My IA also has the ability to balance the prop.
Next question - any idea on the best price/place to purchase the new spinner? I have an 8 bolt C-145-2 in the plane. Just do an internet Google search? Thanks.
New spinners are available from Wag Aero for $369. I have been contacted just last weekend by a guy who has what he describes as a good spinner he'd like to sell. The spinner coming from a reseated fellow pilot. Money going to a scholarship in his name. I'll send yo contact info via email today.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
It would appear from looking at the Wag-Aero catalog that it may be possible to purchase vrs components for a C-170/172 spinner rather than having to purchase the complete spinner? While the text for the components 1-108-100 shows to be for a C-170 and the complete spinner assy 1-949-000 is for C-170's & C-172's I am not clear if the former one is "legal" on an early 172. Might be worth checking it out before committing to purchase a new one should the one Bruce referred to doesn't work out. Lot of difference in cost! Yrs ago I too had a cracked spinner bulkhead and at that time, as I recall, one could purchase a complete spinner assy for a 170/172 with one having a Wag code 3 and the other one a code 4. The two items were identical except that the code 3 did not have the FAA's PMA/STC blessing. Our more studied associates can likely shed more light on this.
ptporebski wrote:I intend to have it balanced by either the vibration specialist in our company or my IA. I work for a large electric utility and we have a guy who specializes in vibration analysis/balancing of rotating equipment. He has told me that he could do this. My IA also has the ability to balance the prop.
Next question - any idea on the best price/place to purchase the new spinner? I have an 8 bolt C-145-2 in the plane. Just do an internet Google search? Thanks.
Regards,
Pete P.
Pete, does your company's vibration specialist have authority to alter an airplane spinner backing plate? (A&P minimum) It's a rhetorical question, no need to answer...only wanted to mention it. Props are usually balanced by placing weights/washers onto the spinner backing plate. Many folks who do dynamic balancing are not A&P's, therefore they do not provide logbook entries, yet FARs require any work be logged. Who will log it?
The Wag Aero spinner might be less expensive but it is reported to be almost incapable of being polished, if that is what you desire, because it is "spun" a bit rough.
The Univair unit is much better finished, but much more $$$.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
Could we do this? How's about an owners mx logbook documenting mx tasks completed by the owner and inspected by an IAand When sufficient tasks have been completed based on a 100hr the owner is issued a A&P limited to that aircraft only.
You make a good point. Our vibe expert has been doing only vibration analysis for over 20 years. He is really a subject matter expert on this specific field and routinely balances all sorts of rotating systems (pumps, steam turbines, combustion turbines, motors, etc...). However, he does not typically do prop-recip engines and is not an A&P. So my IA would have to sign off to be legal. That being the case might as well have him do it.
I have contacted the gent that has the used spinner - haven't gotten a reply yet. I really only need/want the bulkhead as I already have 2 spinner domes (present and previous spinners). You are also correct about the Wag-Aero being difficult to polish. I polished the existing one (a Wag-Aero replacement) using our EAA tech counselors equipment and under his guidance (he has a polished Swift). I will never do that again. I looked like a Nubian when done, and SWMBO (i.e. my wife) made me strip and hose down in the garage.
I will contact both Wag-Aero and Univar and see if they will sell only the bulkhead. My IA signed off the last Wag-Aero replacement, so as the owner that works for me. (I once went down this path with a flight examiner that didn't know the maintenance FARs when I went to take my instrument practical. But that is another story...)
OK.
And another thing to consider is that an experienced (aircraft-specific) dynamic-balance person can reveal all kinds of things another (non-aircraft) person may miss. For example, a cam-lobe that is badly worn will impart a harmonic that will show up and be noticed by the non-aviation guy... but the guy experienced particularly with aircraft props/engines will likely pin-point the problem because it fits within his special area of expertise. There are other sources for vibration than the prop. Just, FYI.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
This is the second one in my 9 years of ownership. Found the first at the first annual in 2008 and replaced the entire spinner with one from Wicks Aircraft (I believe). Also in the intervening years replaced the prop with a new 8 bolt (I think it was a MDM7653). My engine is a C-145-2 from a 170. That was done back in the 1960s. I have never had it balanced but it seems to be very smooth. However, that is just a seat of the pants assessment.
