Magneto Timing Question

Dick wrote:
yes there are timing marks. Unfortunately I can't access the case seam due
to nosebowl and air plenum sheetmetal that I'd prefer not removing.

So I guess my question still remains on difference between 30/32 and
28/30...

Thanks anyway, Dick

The correct answer as to why we like to maintain correct magneto timing in aviation is to prevent catastrophic engine failure such as
loss of cylinders, holes burned through pistons, thrown rods and other negative consequences of detonation. Is this answer clear
enough for you? Does it help that I'm an A&P? Why would you even bother to check the timing if you weren't going to do anything about
it except wring your hands and beg other people to tell you it's OK? Do you go through the same agony when your oil's low, or your
tire pressure's low? I can't believe that in the two days you've spent waffling over this, you couldn't find the time to loosen 4
nuts, rotate 2 mags, torque 4 nuts and make a logbook entry.

--
John Kimmel


I think it will be quiet around here now. So long.

Thanks John but I was aware of the potential problems before you took the
time out to chew on me. Since you're wrong about "wringing my hands and
begging for an okay", I don't consider your being an A&P any help at this
time...

However since most specs have a range of values, I am looking for that
range.

"John Kimmel" wrote in message
...
Dick wrote:
yes there are timing marks. Unfortunately I can't access the case seam
due to nosebowl and air plenum sheetmetal that I'd prefer not removing.

So I guess my question still remains on difference between 30/32 and
28/30...

Thanks anyway, Dick

The correct answer as to why we like to maintain correct magneto timing in
aviation is to prevent catastrophic engine failure such as loss of
cylinders, holes burned through pistons, thrown rods and other negative
consequences of detonation. Is this answer clear enough for you? Does it
help that I'm an A&P? Why would you even bother to check the timing if
you weren't going to do anything about it except wring your hands and beg
other people to tell you it's OK? Do you go through the same agony when
your oil's low, or your tire pressure's low? I can't believe that in the
two days you've spent waffling over this, you couldn't find the time to
loosen 4 nuts, rotate 2 mags, torque 4 nuts and make a logbook entry.

--
John Kimmel


I think it will be quiet around here now. So long.

Dick wrote:
The specs for my C-85 are upper plugs mag @ 28* BTDC and lower @ 30*BTDC.

My results are upper @ 30* BTDC and lower @ 32* BTDC.

I couldn't find a "flower pot" with attached degree wheel to borrow and
attach to the prop hub so used a little "mickey mouse" circular protractor
with a free swinging needle/pointer.

Two separate readings confirmed my 30-32. TDC was identified and impulses
unloaded before taking the readings.

My question is whether my results are acceptable for a low speed ,
experimental or need to be readjusted??

If need to be redone, I'd appreciate a little on why, please.

Thanks, Dick

PS: If listening G, I think "highflyer"(?) gave me some mag advice
during an "annual" a few years back which was appreciated.


Teledyne Continental has issued MSB94-8C-1. With rare exceptions (mostly
for turbo'd engines), the magneto to engine timing tolerance is +/- 1
degree.

Your results, per the manufacturer, are one degree out of specification.

Rip
A&P/IA

Actually found my original technique was poor and was able to use Dales
advice of timing a different piston to the upper case split. Right on @ 30
and 28deg per spec. Thanks to all who advised.
"Rip" wrote in message
...
Dick wrote:
The specs for my C-85 are upper plugs mag @ 28* BTDC and lower @ 30*BTDC.

My results are upper @ 30* BTDC and lower @ 32* BTDC.

I couldn't find a "flower pot" with attached degree wheel to borrow and
attach to the prop hub so used a little "mickey mouse" circular
protractor with a free swinging needle/pointer.

Two separate readings confirmed my 30-32. TDC was identified and impulses
unloaded before taking the readings.

My question is whether my results are acceptable for a low speed ,
experimental or need to be readjusted??

If need to be redone, I'd appreciate a little on why, please.

Thanks, Dick

PS: If listening G, I think "highflyer"(?) gave me some mag advice
during an "annual" a few years back which was appreciated.
Teledyne Continental has issued MSB94-8C-1. With rare exceptions (mostly
for turbo'd engines), the magneto to engine timing tolerance is +/- 1
degree.

Your results, per the manufacturer, are one degree out of specification.

Rip
A&P/IA

The TCM shop manual for my IO-550 engine says to set the magneto timing plus
or minus 1° from spec.

Dennis