Mag Timing Problem

[melctl]

Happy New Year!!
Confused... Am I doing something wrong? Bad mag?
In the middle of my condition inspection, checked mag timing and found that right mag is perfect at 25 deg BDC, but left mag points only open after impulse coupler drops at TDC.

I am not the builder but do my maintenance under supervision of A&P. He just left town for two weeks so wondering if I can figure this out sooner than later.

Background:
We (A&P and I) timed the mags a couple of months ago, both perfectly 25 BDC and in sync. No problems since then (until now), both mags checked OK at run-up. Using induction type buzz-box for timing. Tried rotating the mag by hand in case it had loosened, but it seems tight.

Did notice couple of drops of oil at lower case mounting bolt, can't tell origin, assumed it was from recent timing when mounts were loosed and re-tightened during recent timing.

Have tried all switch positions (L,R, both) to no avail. 0-360-A1A, Slick mags.

Thanks in advance for any help.

[Brantel]

You have to let the impulse coupler snap then back the engine up to about 30deg BTDC then move back fwd and check the time.

Don't backup too far or the impulse coupler will reset.

Thats the purpose of the impulse coupler....to retard the timing to TDC at low RPM.

Make sure you have the plug wires disconnected and pull the plugs for safety!

[Geico266]

Originally Posted by Brantel

You have to let the impulse coupler snap then back the engine up to about 30deg BTDC then move back fwd and check the time.

Don't backup too far or the impulse coupler will reset.

Thats the purpose of the impulse coupler....to retard the timing to TDC at low RPM.

Make sure you have the plug wires disconnected and pull the plugs for safety!

And a set of plugs removed.

[melctl]

Yes, I remember that now- duh. Do have a set of plugs removed. Thanks for the quick replies.

Mike Leger
RV6A

[GLPalinkas]

Don't you just love VAF. A post was made for help in timing the mags. 3 minutes later a very complete and correct answer appeared. By a very trusted source. (Your welcome Brian )

Sort of like your very own mechanic hotline. Well worth whatever I donate a year.

[melctl]

This year I will become a donation plus member. I can't say how much I appreciate the site and all of the input advice from those who are willing to share their knowledge.

Giving some extra $ is how I fell I can make some sort of contribution.

[jrs14855]

I am passing along information that I got from other very knowledgeable sources:
It is fine to verify mag timing but if the timing is off more than one or two degrees this is an indication of internal timing problems with the mag. When new breaker points are installed it will take a while for the plastic cam follower to wear in. This may require a small correction in the mag to engine timing. Except for this there should be no significant change in timing for the 500 hour overhaul period for the mags.
If you verified the mag to engine timing at 25 degrees and 100 hours later it is at 20 degrees, it is time to remove the mag and have a mag shop overhaul or repair as necessary.

[GLPalinkas]

Originally Posted by jrs14855

I am passing along information that I got from other very knowledgeable sources:
It is fine to verify mag timing but if the timing is off more than one or two degrees this is an indication of internal timing problems with the mag. When new breaker points are installed it will take a while for the plastic cam follower to wear in. This may require a small correction in the mag to engine timing. Except for this there should be no significant change in timing for the 500 hour overhaul period for the mags.
If you verified the mag to engine timing at 25 degrees and 100 hours later it is at 20 degrees, it is time to remove the mag and have a mag shop overhaul or repair as necessary.

Again, GREAT info. I didn't know that but now I do thanks to this forum. The information also matches my experience. I timed my new engine/mags and when I did my condition inspection last year the timing had changed a few degrees (approx 135 hrs). I reset them to 25*per the engine data plate. This year and another 100+ hours I find that the mag timing is spot on. Now I know why.