Magneto synchronizing question

pa38112 · #1 02-01-2015, 05:22 AM

Yesterday I reinstalled my magnetos after their 500hr inspection. After I synchronized them I pulled the prop through to check the syncrnazation on cylinders 2 - 4. I was surprised to find that it was off on 2 - 4, but back in sync when I got back to #1. Does this make any sense? If so, shouldn't I set them for the best average? I would guess it varied by about 1 or 2 degrees.

az_gila · #2 02-01-2015, 09:25 AM

One local shop that balanced my prop checked for this. The Slick mags have two cam lobes and they can be made/installed/wear slightly differently.

He had some spare lobes that he had adjusted to make the "opposite" spark time correctly.

My mags checked out OK, but differences can happen.

IIRC the cam lobe is in the top middle of the 14-15 breakout on this pic -

pa38112 · #3 02-02-2015, 06:53 AM

Interesting! Thank you for the drawing too. I am going to verify it again tonight. If it is still off I think I'll send them back. After a $870 service I think I should expect the lobes to be correct.

SteveL · #4 02-02-2015, 02:08 PM

Good afternoon,
I'm assuming you have some type of Lycoming engine with Slicks Mags? If that's the case your number 1 cylinder is the forward cylinder on the right side. Depending on what type of TDC locator you are using find 25 degrees or what ever is on your engine data plate or engine TCDS. Slick mags install with a timing pin located in the housing with the ignition wire cap removed. install that locator pin in either the "L"/"R" (mag rotation) . Install the mags, remove the locator pin and then fine tune them to the number 1 cylinder with whatever type of "buzz box" you have. If they'll time in that position the rest will be fine. If they won't time in that position you probably have some type of E gap setting problem which is highly unlikely since you just had them inspected. Contact me if you'd like.
SteveL
AP/IA

az_gila · #5 02-02-2015, 02:30 PM

Quote:

Originally Posted by SteveL

Good afternoon,
I'm assuming you have some type of Lycoming engine with Slicks Mags? If that's the case your number 1 cylinder is the forward cylinder on the right side. Depending on what type of TDC locator you are using find 25 degrees or what ever is on your engine data plate or engine TCDS. Slick mags install with a timing pin located in the housing with the ignition wire cap removed. install that locator pin in either the "L"/"R" (mag rotation) . Install the mags, remove the locator pin and then fine tune them to the number 1 cylinder with whatever type of "buzz box" you have. If they'll time in that position the rest will be fine. If they won't time in that position you probably have some type of E gap setting problem which is highly unlikely since you just had them inspected. Contact me if you'd like.
SteveL
AP/IA

Not always... the two cam lobes may have slightly different heights which will make the "non-timed" cylinders fire a little off from the original setting...

Slick calls it "cam spread" in their OH manual.