flickroll

flickroll

Well Known Member
What is an acceptable mag drop for Slicks on a Lyc O-360? I'm seeing 100 RPM, +/- 10-20. Seems excessive - used to get about 75 or so on Slicks on a Cont. IO-520. If excessive, what is a likely culprit? The engine has 300 hours TTSN. Thanks
 
Lyc. Mag Drop

Jim,

Lycs seem to always have a bigger mag drop than Contis, regardless of mag maker. A smooth 150 RPM drop (max) with no more than 75 RPM diff. is the common acceptable standards for Lycs. Your 100 drop sounds fine, as long as it's relatively smooth. Your little red Lyc. Operators Manual should verify that.
 
Thanks All. The engine runs smoothly on one mag. The engine and mags have 300 TTSN. Probably OK, just a little larger drop than I am used to seeing.
 
Different numbers in my....

BlndRvtr said:
Jim,

Lycs seem to always have a bigger mag drop than Contis, regardless of mag maker. A smooth 150 RPM drop (max) with no more than 75 RPM diff. is the common acceptable standards for Lycs. Your 100 drop sounds fine, as long as it's relatively smooth. Your little red Lyc. Operators Manual should verify that.
Click to expand...

...Lycoming O-360 Operators manual.

It says a 200 rpm max. drop with a max. 50 rpm difference - starting at 1800 rpm (2000 max)

Just to confuse things, my Tiger certified O-360 aircraft manual calls for 175 max drop and a max. difference of 50 rpm.

Mechanics have told me that the difference is the important number, as both magnetos really should be operating/wearing evenly.

I would stick with a 50 rpm max. difference, rather than the 75 rpm you quoted.
 
Mag Drops

Lycoming says mag drop is supposed to be 50 and 75 RPM. In 300 hours I would expect the timing has drifted off slightly, the plugs have eroded slightly with some lead build up. All this will cause a larger mag. drop but this is all normal. I would pull the plugs, check for lead, clean & regap. Then check my mag timing with a buzz box and retime if needed. I have 300 hours on my 0-320 and I do this every year during condition inspection as routine maintenance. It appears to me that mag drops get a bit greater as I put time on the engine between annuals

Oh, I also rotate the bottom plugs to the top as the lower ones usually get leaded up faster than the upper ones. I use a cheap automotive spark plug sand blaster to clean them.

Dick DeCramer
RV6 N500DD flying
RV8 fuselage
Northfield, MN
 
Mag. Drop Corrected

I stand corrected and Gil is correct...the 0-320 Lycoming Operators Manual says " Drop off should not exceed 175 RPM and should not exceed 50 RPM between Magnetos". The 0-360 may differ a bit and no reference is made towards any difference between Slick or Bendix Mags.

Dick DeCramer
RV6 N500DD
Northfield, MN
 
DickDe said:
In 300 hours I would expect the timing has drifted off slightly, the plugs have eroded slightly with some lead build up. I would pull the plugs, check for lead, clean & regap.

Oh, I also rotate the bottom plugs to the top as the lower ones usually get leaded up faster than the upper ones. I use a cheap automotive spark plug sand blaster to clean them.
Click to expand...


Dick - this was all done two weeks ago. Timing was reset, plugs cleaned and gapped.
 
az_gila said:
...Lycoming O-360 Operators manual.

It says a 200 rpm max. drop with a max. 50 rpm difference - starting at 1800 rpm (2000 max)

Just to confuse things, my Tiger certified O-360 aircraft manual calls for 175 max drop and a max. difference of 50 rpm.

Mechanics have told me that the difference is the important number, as both magnetos really should be operating/wearing evenly.

I would stick with a 50 rpm max. difference, rather than the 75 rpm you quoted.
Click to expand...

Hey Gil,

What's date of your 0360 manual?

My book is dated December 2007 with a change bar along side the mag check numbers. Max drop is 175 rpm with a difference of 50.
 
Rich mixture effect on magneto drop

Hello Jim,
The fuel mixture setting can have a direct effect also on checking magneto cycle drop. An excessively rich mixture on run-up will cause a larger rpm drop when cycling than then a properly correct set mixture. Try a little leaner on your next run-up and see what effect it has on the rpm drop.

Thomas S.
www.g3ignition.com
 
sc_acro2 said:
Hello Jim,
The fuel mixture setting can have a direct effect also on checking magneto cycle drop. An excessively rich mixture on run-up will cause a larger rpm drop when cycling than then a properly correct set mixture. Try a little leaner on your next run-up and see what effect it has on the rpm drop.
www.g3ignition.com
Click to expand...

Thomas - funny you should mention that - I'm still tweaking the settings on a new carb and I think it is still a little rich.
 
I believe the numbers are different for C/S vs. fixed pitch applications. Make sure we're comparing apples to apples here, folks.

Also, mag drops depends upon what RPM you are running up to. I know that in my old Cessna 172 days, you would run up to 1700RPM and look for no more than 125RPM on either mag.

On my -7A I have dual slicks, C/S prop, run up to 1900RPM and see ~100 RPM drop on each mag.
 
I stand corrected...

David-aviator said:
Hey Gil,

What's date of your 0360 manual?

My book is dated December 2007 with a change bar along side the mag check numbers. Max drop is 175 rpm with a difference of 50.
Click to expand...

...mine is a 1989 Lycoming Manual with updates to 1996.

But, in re-reading it, I think I got the helicopter number for the 200 rpm drop - Sorry, an old age brain fart....:rolleyes:

Your 175 max drop, 50 max diff numbers are correct.

The Tiger manual I referenced is a 1977 version.

Unlike a previous post, I can see no difference in my version of the Lycoming documentation between FP and CS engines for mag drops.

As I mentioned ealier, mechanics have told me that the difference is the big thing to watch, each magneto should act in a similar manner.
 
You must log in or register to reply here.