re0installing Slick 43** mags

[kenora]

Lycoming O-320 E2D on a Thorp T-18. I hope I can post here in the engine forum since I am a T-18 guy (although I did start an RV-3 back in the early 80"s ).
I removed them to change out gaskets, I "thought" I understood the process but am having an issue timing the left mag. Here is the process...
a-I removed the mag without using the timing pin thinking I could time it before reintallatiion.
b-I removed the mag, cleaned the mating surface and replaced the gasket.
c-I then used the Lycoming timing pin as directed turing the shaft till the pin seated.
d-I then located TDC on #1 cylinder (right front as viewed from the cockpit).
e-I then backed up to 25 degrees BTDC (mark on starter bracket and ring gear aligned).
f-I then re-installed the left mag with the pin in place, wiggling it about to get the teeth to mesh.
The marks I put on the mag and case before disassembly are pretty close indicating I should be "in the neighborhood".
g-I then hooked up the buzz box and note the right mag is timed properly but the left mag is waaaaay off!

Where did I go wrong?

Thanks

Tim

[osxuser]

Did you make sure the pin was in the correct hole for direction of rotation when you timed it? Also, when you say "way" off, that doesn't give an accurate idea of how bad... is 5? way off or 30??

[kenora]

sorry....Its about 90 degrees off

[Jim P]

If you don't have the timing pin installed on removal, and the mag turns, I'd think the only way to get this timing back is to do the internal timing, pin it, then install the mag with #1 at TDC.

[DennisRhodes]

Just as OXS says: be sure the pin is in the correct hole for the hand rotation of the MAG ( not the position of the mag) . That rotation is marked on the mag. Also don't believe that the internal timing can get off unless you have dissassembled the mag . The fact that the pin was not inserted on removal shouldn't make any difference if you use the pin and position the prop correctly at #1 cylinder TDC less the 25deg on reassembly.

[kenora]

This is starting to make sense...

I didn't have the pin in when I took out the right mag either. I was able to get the pin to seat in the L hole kinda like a buck knife locking open, (a good click and it sat in the hole right to the built in shoulder) when I went to reinstall it.

On the left mag I once again used the L hole (its a left rotation as well) but the pin never seated as smartly. I tried all sorts of different positions and thought I had the pin in properly, it never went in to the shoulder . I now speculate that I did not seat properly.

It will come off again and I will have another go at it.

Thanks and keep the ideas coming, I belong to the Thorplist and get great ideas for Thorp specific issues but this is the "true source" of engine related info.

thanks all.