The International Cessna^® 170 Association

What is the proper placement of #1 blade when the TDC mark is at 6:00?

Tom Downey wrote:What is the proper placement of #1 blade when the TDC mark is at 6:00?

Tom,

According to the book "Timeless Classic The Cessna 170" looking at the prop flange from in front of the aircraft the number 1 blade center line should pass between the bolt at 12 o'clock and the bolt at 10:30. This information was a change from the original position for the number 1 blade that was between 12 o'clock and the bolt hole at 1:30.

I have to add here from Bruce's signature, this information is only worth what you paid for it.

To be clear, that's one bolt hole advanced from the vertical.

I ask because that is where I installed this one and it has a vibration in that position, and the prop passes the static balance checks.

I'm wondering if I could get a few of you good folks to actually look at your installations and see where they really are.

have you checked the track of your prop? If you double check your installation and can't find any problems you may need a dynamic prop balance.

Tom, I didn't want to remove my spinner but perhaps this'll help in your survey: My prop has one blade exactly centered by the BTC range (24 thru 32 degree hash-marks) marked on the prop flange. This places the trailing edge of that blade almost exactly at the T|C mark. (I have no idea which number blade that is, ... as I didn't remove the spinner, but I'd bet it's the No. 2 blade.) This would correspond to the other blade (presumeably No. 1) being at approx. the 11 o'clock position from the view of someone hand-propping the engine...if the T|C mark were at 6:00 o'clock.
To add additional confusion, my engine is an O-300-C with 6-bolt flange and an EM series prop, but I believe that's not important in this instance.
Hope that helps.
George

Years ago my friend Mickey's 170A had a vibration. His prop was not in this 11 o'clock position, when he made it so the vibration went away. I seem to recall posting about this, and Tom, as I recall you said you had oriented the prop on yours every possible way & it made no difference re: vibration.
According to Jeff Burns, if the prop is not tracking true it can result in a vibration even with a good (balance within spec) prop.
The there's always the dynamic balance option if nothing else helps. Paul Nyenhuis at KAWO has the equipment to do this. I recall that Bela had this done to his about a year ago, and although they had to add a lot of weight to get it right, it really smoothed things out.

Eric

Yeah, Eric's on the right "track" (sorry for that. Couldn't resist.)
One advantage (which I know Tom and Eric and most others of their experience knows) of a dynamic balance is that it not only balances the prop, but it also balances out everything else in the engine. PLUS....when the dynamic is performed...a good balance-man will recognize a bad cam with flat lobes which can make an engine shake and dance (as can worn damper bushings, etc.) Yep. A dynamic balance is a good thing.
I plan on doing mine someday even tho' others who have flown my airplane frequently comment it's "smooth running"....I sometimes feel it's not as good as it could be.

Yup, what Eric said.

The logs on my airplane previous to my ownership have numerous
entries where they sent the prop out to a prop shop for static balance /
redress, only to repeat the same thing a number of times.

The way it was explained to me, once you start messing with
a prop (filing out dings, profiling blades, etc.), you can have
a situation where the prop will statically balance, but one
blade moves more air than the other. Dynamically balancing
my prop/engine combination was the best $175 bucks I ever
spent on an airplane. I just might do it again, as the DP-90 flat
black paint is a bit worn on the back sides of my prop, and I thought
I'd spray another 2-3 coats on, and if it doesn't continue to run
smooth, my wallet gets opened back up for another "fine-tune"
dynamic balance.

In my opinion, even for an engine that's apparantly running
"smoothly", the benefits of removing whatever ips vibration
you can tends to make the whole FWF package last longer (less
vibration, less stress / cycles on all the components.... Exhaust,
brackets, hardware, mounts, wiring.... the list goes on and on).

Tom

On my C-145-2 with an undampened crank it seems to make no difference between the old and new position.

I'm currently running my prop in the new position as John Ebb described.

cessna had a service bulletin about this, mabe I can fid it.

A dynamic balance is something I have been considering. Does anyone have a recommendation for a good prop shop in Northern or Central California.

Thanks guys I got it fixed. I removed it set number #1 as described, and reinstalled it at 11:00 /05:00. one bolt hole advanced from vertical. and retorqued and saftied it and it runs smooth..

Yes it was tracked

It's on a new overhaul by me, and runs great. but it did have shudder at all RPM.

Tom Downey wrote:To be clear, that's one bolt hole advanced from the vertical.

I ask because that is where I installed this one and it has a vibration in that position, ...................................

I thought that's where you earlier said you had installed it?(see above)
Did you turn it 180 degrees and re-install? Or was it not in the recommended position after all?

Eric

That's exactly right. I took it off looked it over, replaced it, and now it is go to go..

I don't know what was wrong, and hate it when I fix something and don't know what I did to fix it.