Mag Timing

[TCONROY]

I am performing the first condition inspection on our RV-7 with an IO-360-M1B and did a timing test using a "buzz box". I read the directions and believe I performed the test correctly which shows both mags set to approx 28-ish degrees. Could this be correct? Both mags off by exactly the same amount? Should I loosen the hold down nuts and adjust to 25 degrees accordingly?

[BobTurner]

Make sure you have taken any backlash out by moving the prop past 0 deg to snap the impulse couplings, if any; turn back about 35 deg; then move in usual prop rotation direction. If they are still at 28 then yes, move forward to 25, loosen the mag hold down nuts and adjust.

[WA85]

Based upon the picture, yes it looks like the R and L magnetos are timed at about 28 deg BTDC. New magnetos, with new points and cam actuators tend have a bit of timing drift over the first 25 to 50 hrs due the contact areas wearing in. Pretty normal. Some magneto overhaul facilities put a tag on the magneto that states to check the timing after the first 25 hrs. Adjustment is easy, loosen the two hold down nuts for the magneto and adjust as needed. I always do the RH non impulse first, then the LH with impulse, but that is my opinion. Loosen the nuts just enough to turn the magneto, but not so loose that the drive gears get sloppy meshing, which affects the timing adjustment. Re-torqueing the nuts can change the gear mesh / timing slightly, always double check. Remember to take the gear lash out my turning the prop about 30 degs beyond the timing marks, then in direction of rotation to the timing marks.

[Low Pass]

Originally Posted by BobTurner

Make sure you have taken any backlash out by moving the prop past 0 deg to snap the impulse couplings, if any; turn back about 35 deg; then move in usual prop rotation direction. If they are still at 28 then yes, move forward to 25, loosen the mag hold down nuts and adjust.

Shouldn't you back into the proper setting to take out gear lash? I.e., pull the prop well past set point, release the impulse coupling if applicable, then rotate the shaft backward to the proper position?

[BobTurner]

Originally Posted by Low Pass

Shouldn't you back into the proper setting to take out gear lash? I.e., pull the prop well past set point, release the impulse coupling if applicable, then rotate the shaft backward to the proper position?

No. Approach 25 deg in the usual direction of prop rotation. If set going backwards, it may be off going forwards.

[Low Pass]

Originally Posted by BobTurner

No. Approach 25 deg in the usual direction of prop rotation. If set going backwards, it may be off going forwards.

Got it. Mag drive gear loads the same whether the pistons are driving the crank or the propeller.

[TCONROY]

Great, thank you for the feedback!

[RV10inOz]

Also be aware, recently supplied (say manufactured in 2014-15) points from Slick have been known to drift by a few degrees.

CASA, Champion and even the FAA seem to have their heads in the sand over SDR's issued by engine shops.

You may want to check this too as the internal timing may have changed.

[vic syracuse]

David is right. Make sure you get a set of points manufactured late 2015 and you should be ok. The date code is stamped on the box.

Vic