Engine Vibration

[azevedoflyer]

Guys,
When I bought my Pacer 4 years ago, the engine (O-320 150 hp) had 460h after a major overhaul. One cylinder (maybe number 1) was substituted by a yellow-tagged part, as the head had a hairline crack to it. A brand new piston, rings and piston pin went in with jug change. All other jugs have a yellow strip but this one has a green strip. This means something, I remember, but what I do not know. The prop was statically balanced some 2 years ago but has been subsequently removed and installed a number of times. My previous flying experience was in Cessnas (172/152). All of this as a preamble to my statement that I think my engine vibrates way too much. New rubber mounts actually aggravated this perception as the old ones were sagged and mushy, perhaps less hard and actually doing a better job of dampening vibration! The engine works like a clock. Never misses a beat, consumes oil at < 2 qt/25h, burns really good. I also developed a system that measures the "health" of the PCU (power cylinder unit - piston/rings/cylinder)by sensing the blowby gases and it tells me the engine is very healthy inside.
However, I still think it should vibrate less, but lack a reference to judge by...
Any thoughts on the matter by anyone?
Thanks,
Miguel
N8714D

[Hillbilly]

I dont know how much lighter it will be but youve got 3 .020 over cylinders and one .010, that could easily be a contributing factor, plus its probably not good for the crankshaft.

Lycoming uses the following color codes:
Orange - chrome barrel
Blue - nitride hardened steel barrel
White - rebarrel
Green - Plus .010 oversize barrel
Yellow -Plus .020 oversize barrel


Hope this helps-Hillbilly

[Steve Pierce]

Hillbilly, I didn't know about the green and yellow bands.

Miguel, I have never had an engine shake because of a low cylinder and I have found some in the 20/80s. Most of the vibrations I have seen are from the prop or prop indexing. My Dad and I recently swapped props. He noticed more vibration and I lost the vibration. Had Jim Fixx overhaul my prop and it is now smooth. I flew a Clipper back from WA once and it seemed to shake more than normal. I noticed when I shut it down the prop would stop at the 3 & 9 o'clock position. I re-indexed it to 1 & 7 o'clock and it smoothed out. I have done the same on several other airplanes. I have never seen a Piper document saying where to index the prop but have found it in Cessna manuals.

[Hillbilly]

I have no idea the difference in weight between a piston and one thats .010 larger or smaller, since my post Ive thought about it and the difference has GOT to be very small, Steve is the expert here if he thinks its prop indexing it probably is...
-Hillbilly

[Steve Pierce]

I didn't think about the weight difference. That could cause a vibration. Seems I remember reading a piston weight difference speck on some engines.

[Hillbilly]

I have never seen a Piper document saying where to index the prop but have found it in Cessna manuals.

I recall somewhere a Cherokee 180 manual that says 2and 8 o'clock (1 and 7 could be the same depending on the engine and viewing perspective)

[Hillbilly]

I didn't think about the weight difference. That could cause a vibration. Seems I remember reading a piston weight difference speck on some engines.

Course its not very relevant but I used to fool with some old German built V6 engines that were balanced with varying weight pistons, not really a problem till some unsuspecting schmoo started changing pistons... that thing would run like a magic fingers vibrating bed...

[Bultaco Jim]

Steve, I did see a prop indexing blurb on Pipers somewhere recently. Found it on the internet. Now you're going to make me start searching for it. Jim

[Bultaco Jim]

Hey, that did't take long.... I found the indexing info in the SWPC useful info. Here it is.

Propeller Installation on ShortWingPipers

Remove #1 spark plug. Rotate crankshaft till pressure begins to build
(place thumb in spark plug hole to feel/hear pressure building).
You are coming up on TDC for #1 cylinder. Continue rotating crankshaft
until #1 piston is TDC (use timing mark on back of ring gear aligned
with crankcase split or use markings on front of ring gear aligned
with punched hole in starter housing).

With #1 cylinder on TDC, the prop should be installed such that it is
Horizontal, ie level to the ground.

There should be a small "no 1" stamped near the hub on one prop blade.
That blade goes "over"/"toward" the No. 1 cylinder. It is permissible
to install the prop "180° out", but only as a "fix" for a SLIGHT vibration
at cruise. Nine times out of ten, it will NOT be an issue. Torque prop
correctly (visit Sensenich's website for detailed instructions or see pdf
file on this site) and safetie prop bolts, reinstall spinner and spark plug.
Button up airplane. Your prop will now be in the PROPER position not only
for handpropping, but more importantly will also be "timed" to best act as
a "flywheel" with the crankshaft.

Don't forget that this is not Preventative Maintenance, and requires
a Logbook entry by an appropriately rated Mechanic.

[Bultaco Jim]

After reading this info again, I realized that one of my planes didn't have a "number 1" stamped on it. However, I read, (just tonight), that it is the same side as the stamped serial number on the prop. Hope this helps. Jim