Magneto Timing Question

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.

In article IMJpk.70$482.47@trnddc06, "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.

Since you are probably using 100LL in an 80 octane engine, you are
probably just going to get a little more than 85 HP, with no damage.

--
Remove _'s from email address to talk to me.

On Sat, 16 Aug 2008 23:54:16 GMT, "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.


not sure of the C-85 but on the O-200 there are cylinders out there
made before a subtle design change was implemented that have a history
of departing the engine on engines with advanced timing.
my own engine has four of those early cylinders and so runs with
timing a little retarded from what it could be. (as per the AD)
if it need be done that may be why.

Stealth Pilot

On Aug 16, 5:54 pm, "Dick" wrote:

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.

There should be timing marks on the prop flange. They'll be
on the bottom when the #1 cylinder is at TDC, and you line them up
with the crankcase seam. Shouldn't need the other timing doodad, which
isn't all that accurate.

Dan

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
wrote in message
...
On Aug 16, 5:54 pm, "Dick" wrote:

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.

There should be timing marks on the prop flange. They'll be
on the bottom when the #1 cylinder is at TDC, and you line them up
with the crankcase seam. Shouldn't need the other timing doodad, which
isn't all that accurate.

Dan

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.

"Orval Fairbairn" wrote in message
news
In article IMJpk.70$482.47@trnddc06, "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.

Since you are probably using 100LL in an 80 octane engine, you are
probably just going to get a little more than 85 HP, with no damage.

--
Remove _'s from email address to talk to me.

Please reconsider your response. Detonation is not the only concern. These
old Continentals can built up of parts of unknown age, condition, and
history. Even when new, these engines didn't handle high cylinder pressures
very well. So even if the cylinder pressures are not high enough to cause
detonation with 100LL, they can still be high enough to pull cylinder base
studs out of the case, crack cylinder heads, hammer main bearings, and flex
or distort crankcases over time.

I'm not sure the OP's method for checking timing is accurate, but if his mag
timing is in fact 2 degrees advanced, it should be reset to the values on
the data plate.

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.

Dale,
If OP means original poster, that is me. For the record, my timing is 2 deg
more advanced but still BTDC by 32 deg. After an A&P rebuilt and installed
my mags about 100 hours ago, I'm not sure if they were installed per the
manual spec 30 deg or the 32 deg I found by test recently. A different A&P
doesn't have a problem with it either way.

I any case, I am just curious about any range established per "rule of
thumb", experience or paracticality..

Thanks for taking the time to give your opinion.


"Dale Scroggins" wrote in message
...

"Orval Fairbairn" wrote in message
news
In article IMJpk.70$482.47@trnddc06, "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.

Since you are probably using 100LL in an 80 octane engine, you are
probably just going to get a little more than 85 HP, with no damage.

--
Remove _'s from email address to talk to me.

Please reconsider your response. Detonation is not the only concern.
These old Continentals can built up of parts of unknown age, condition,
and history. Even when new, these engines didn't handle high cylinder
pressures very well. So even if the cylinder pressures are not high
enough to cause detonation with 100LL, they can still be high enough to
pull cylinder base studs out of the case, crack cylinder heads, hammer
main bearings, and flex or distort crankcases over time.

I'm not sure the OP's method for checking timing is accurate, but if his
mag timing is in fact 2 degrees advanced, it should be reset to the values
on the data plate.

"Dick" wrote in message
news:2c2qk.130$p72.75@trnddc05...
Dale,
If OP means original poster, that is me. For the record, my timing is 2
deg more advanced but still BTDC by 32 deg. After an A&P rebuilt and
installed my mags about 100 hours ago, I'm not sure if they were installed
per the manual spec 30 deg or the 32 deg I found by test recently. A
different A&P
doesn't have a problem with it either way.

I any case, I am just curious about any range established per "rule of
thumb", experience or paracticality..

Thanks for taking the time to give your opinion.


snip

I can't give you a rule of thumb. I can pass along an informed opinion
developed over the last thirty years as aircraft mechanic, with several
thousand hours of that spent working on small Continentals.

1. You shouldn't run your timing more advanced than specified. Two degrees
is too much excess advance for your engine; 30 degrees advance is a lot of
advance for an engine that turns about 2,000 rpm most of the time.
Continental specified 30 degrees to get good performance at a cost in
durability. When I set mag timing, I'm happy only when it's within 1/2 a
degree. But I would worry if it were 1/2 a degree too much advance on a
small Continental.

If the mechanic who put the mag on set it right to begin with, then your
points are wearing faster than the cam rubbing block, and the timing will
continue to advance as you fly. And the e-gap, or internal mag timing, is
drifting too. If the timing shifted 2 degrees in 100 hours, you have
something wearing too fast.

How, if you could not see the prop flange markings, did you establish TDC?
Are you fully confident that the advance is 30 and 32 degrees? By the way,
if you can see the flange markings from the top, but not the bottom, you
could time the mags using a cylinder other than #1. The second A&P may have
doubts about your methods. How did the first A&P set the timing; could he
see the prop flange markings, or did he use a timing wheel? The wheels can
be inaccurate if improperly set up or if the pointer friction is excessive.

2. How old are your cylinder heads? Not since overhaul, not since cylinder
barrel replacement, but since the heads were new? Have they ever been
welded? How old is your case? How many hours total time? Who did the
overhaul, and what was the condition of the mating surfaces and bearing
journals? Continental hasn't made a C85 in quite a number of years, and
advancing the timing a couple of degrees, especially from a fairly advanced
setting to begin with, will result in significantly higher cylinder
pressures. Are all your engine parts up to that?

The questions I asked above would be questions I would have in making the
decision to reset the timing. But, in the end, I would probably use the
time-rite or timing wheel and recheck the mag timing. If it had any excess
advance I would reset the timing. If it had two degrees excess advance, I
would pull off the point covers and look at the points.