SNL 7-8-53 Propeller Installation

[53B]

Gentlemen,

In my quest to obtain a field approval for the 1A175DM propeller for my taildragger 172, I find that a copy of SNL 7-8-53 would be beneficial to my data package for the FAA. If someone could forward me a copy of the actual document it would be greatly appreciated.

msfullen at gmail dot com

Thanks!

[GAHorn]

You would be shocked to see how the official Cessna SNL 7-8-53 reads.
It reads like an anecdote.

----------------------------------
"Date: 7-8-53
Subject: 45-degree Advance of 170 Props S.N.L. (7-8-53)
"Had a chance to fly a '54-170 and what a suprise. Among the several improvements in the '54 Model is the noticeable improvement in engine smoothness. It's been accomplished by advancing the prop 45-degrees or one bolt hole in the crankshaft. Engineering reports as much as 50% reduction in the amplitude of vibration, whatever that is, but it sure does the trick and can be done on earlier 170's in the field.

All 170's beginning with 26110 have the prop advanced."
------------END----------------

No kidding! That is the official verbage from the Cessna Service Information Summary distributed by Cessna and reproduced/distributed at the Kelowna Convention MX Seminar.

[Bruce Fenstermacher]

Mark I'm curious is your plane suppose to have a 1A172DM? What advantage is the 1A175DM?

[53B]

Hi Bruce,

My airplane currently has a 1C172/MDM propeller. The 1A175/DM is the seaplane propeller approved for the 170 by STC. I'm looking to gain some added climb performance and I'm willing to trade some cruise speed as most of my trips are under 200 miles. I do a fair amount of camping in the summer and carry a lot of gear for my friends that have Luscombes', T-crafts', etc. I have no first hand experience of the performance difference but from what I have read on this forum it is the best mod, short of a horsepower increase, to help climb performance. Hopefully the added performance will open up some new camping destinations.

Everyone is welcome to confirm or deny the performance increase as based on their experience.

Thanks!

[Bruce Fenstermacher]

So Mark why don't you have your current approved prop repitched to a climb pitch. Perhaps you already have this and I'm missing something else. Is the 1A175/DM a longer flatter prop?

[53B]

Bruce,

My current propeller is a 7653. The 1A175/DM is available in 8040 and 8042. As I said, I have no firsthand experience with the seaplane prop, but I hope all of the trouble is worth it. If I got another 100 - 200 fpm I would be quite satisfied.

[Bruce Fenstermacher]

Ok yes now I remember other folks talking about it. Just didn't recognize the model number and associate it with an 80/40 or 42.

[marathonrunner]

It makes a difference. You will like it

[drewcaughlin]

Sounds like you have put your prop on and off several times recently. I took my prop off a while ago when doing some other maintenance and the alignment marks I made where wiped off. I see there is a service bulletin for advancing the prop 45 degrees to help smooth out vibrations. Unfortunately I have not found anywhere where the step by step instructions are for crank placement (TDC ?) It was 20 years ago the last time I had the prop off. (this is the second time I've owed this plane) Any suggestions? Thanks.

[Bruce Fenstermacher]

Drew it seems you found a few places to ask your question after all. But it is not necessary to find a topic similar to you question in order to ask it. simply start a new topic. Of course we do appreciate the effort to try to keep similar material in the same place.

The answer to your question is you place your engine with the #1 cylinder at top dead center on the compression stroke, then place the prop as the diagrams describe.

To do this you need to rotate the prop or crank as part of the process so make sure to observe all safety precautions as turning the prop could cause the engine to start. Ground the mags manually and or remove at least a spark plug from each cylinder Before continuing.

To set the #1 cylinder to TC remove a #1 spark plug. With your thumb or finger over the spark plug hole, slowly rotate the prop until you feel pressure building indicating the start of the compression stroke. Then looking at the seam of the engine case halves under the crank, line the TC on the crank up with the seam.


You may have to temporarily install your prop to the point you can use it to turn the crank.

[GAHorn]

Whenever removing/reinstalling the prop, consider the use of new hardware. Some of those bolts and self-locking nuts can be quite old and worn, not to mention the loss of plating.

[drewcaughlin]

Thanks for your reply. That is what I thought but its always good to check. The manuals (and I have several) can be somewhat sketchy.