I had my engine overhauled last year and only have about 10 hours on it since I got it back on the airplane a few months ago. I have been fighting a vibration issue ever since, so I thought I would bring it up here. My 100 series manual says for a 172 with the O-300A witch is what I have to have the #1 cylinder TDC on compression stroke but the guy I had overhaul the engine said to put #6 TCD on the firing stroke. If I use #1 TDC this puts the timing marks on the bottom of the crankshaft not the top. My problem is where do I put the prop? The 100 series book does not address the placement of the prop in regards to #1 blade. I assume that #1 blade needs to be @ the 1 o’clock position with #1 cylinder TDC, this gives me some vibration. I want to make sure I have the prop in the correct position before I start trouble shooting anything else.
Anybody got any advice as to the proper timing and prop position. By the way the mag timing is great and the engine runs good just this vibration.
Engine timing.
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n2582d
- Posts: 3013
- Joined: Mon Apr 29, 2002 4:58 am
Bill,
It sounds like your prop is mounted correctly. The information is on page 45 of the Cessna 170 book. With the # 1 cyl. at TDC your prop should be at the one o'clock position as viewed from behind.
It's interesting to read the "chatty" way service newsletters were written in earlier times:
DATE: 7-8-53
SUBJECT: 45' Advance of 170 Props
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' 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.
It sounds like your prop is mounted correctly. The information is on page 45 of the Cessna 170 book. With the # 1 cyl. at TDC your prop should be at the one o'clock position as viewed from behind.
It's interesting to read the "chatty" way service newsletters were written in earlier times:
DATE: 7-8-53
SUBJECT: 45' Advance of 170 Props
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' 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.
Last edited by n2582d on Sun Feb 17, 2008 9:31 pm, edited 1 time in total.
Gary
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GAHorn
- Posts: 21295
- Joined: Fri Apr 12, 2002 8:45 pm
Bill, there's been some confusion on this matter over the years due to terminology. The "1 o'clock" position is intended as if viewing from the cockpit.
The anecdotal commentary from the old Cessna Service Letters was a reference to the user's erroneous placement of the #1 blade in the 1 o'clock position when viewed from the front of the aircraft (as if when hand-propping the engine. This actually placed the blade in the 11 o'clock position when viewed from the cockpit.) Rotating the #1 blade to the 11 o'clock position (moving it forward 45-degrees as the commenter suggested) actually placed the #1 blade in the correct 1 o'clock position when viewed from the cockpit. That's why he experienced improvement in the vibration problem he had. As you know, this is vibration situation is due to the position of the prop versus the power-strokes versus the dampers on the dampered crankshaft. (The early engines were not dampered. If your engine's serial number has a letter "D" in it's sequence, it should have a dampered crankshaft. If your crank's prop-flange has a 1/4" hole drilled between prop bushings thru it's flange, it is un-dampered. None of the C-125 cranks were dampered, and a couple of C145 engines have reportedly been found with incorrect C125 cranks in them. They were underpowered, of course.)
The #1 CYLINDER is also the correct timing mark reference. It does indeed place the crankshaft timing marks (prop shaft marks) at the 6 o'clock position, where they may be compared to the crankcase-split halves, which is the witness-reference location for reading those marks. Your mechanic's suggestion moves the marks to a more readable position perhaps, and is probably not any practical difference, but is technically incorrect. However, that technique should not be used when mounting the propeller.
The anecdotal commentary from the old Cessna Service Letters was a reference to the user's erroneous placement of the #1 blade in the 1 o'clock position when viewed from the front of the aircraft (as if when hand-propping the engine. This actually placed the blade in the 11 o'clock position when viewed from the cockpit.) Rotating the #1 blade to the 11 o'clock position (moving it forward 45-degrees as the commenter suggested) actually placed the #1 blade in the correct 1 o'clock position when viewed from the cockpit. That's why he experienced improvement in the vibration problem he had. As you know, this is vibration situation is due to the position of the prop versus the power-strokes versus the dampers on the dampered crankshaft. (The early engines were not dampered. If your engine's serial number has a letter "D" in it's sequence, it should have a dampered crankshaft. If your crank's prop-flange has a 1/4" hole drilled between prop bushings thru it's flange, it is un-dampered. None of the C-125 cranks were dampered, and a couple of C145 engines have reportedly been found with incorrect C125 cranks in them. They were underpowered, of course.)
The #1 CYLINDER is also the correct timing mark reference. It does indeed place the crankshaft timing marks (prop shaft marks) at the 6 o'clock position, where they may be compared to the crankcase-split halves, which is the witness-reference location for reading those marks. Your mechanic's suggestion moves the marks to a more readable position perhaps, and is probably not any practical difference, but is technically incorrect. However, that technique should not be used when mounting the propeller.
Last edited by GAHorn on Mon Feb 18, 2008 1:07 am, edited 1 time in total.
'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.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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1SeventyZ
- Posts: 253
- Joined: Mon Aug 11, 2003 2:08 am
Somehow my prop was reinstalled out of index after being reconditioned 2 years ago. I was experiencing some vibration too. After reading some posts on here and deducing the correct index position (#1 blade at 11 o'clock when standing in front of the spinner looking backward, TDC mark on prop flange at 6 o'clock) I reinstalled and it smoothed out considerably.
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