Magneto timing

During my annual I found that the left magneto was timed to 29 degrees BTC. Right side is lightspeed electronic ignition. Hadn't noticed any performance issues. I reset the magneto to 25 BTC. (Per Superior manual) Should I have seen any obvious issues with the timing being that far off?

Thanks.

If the magneto timing has changed due to points wear, then the magnet timing is no longer matched to the points timing. This will cause a weak spark condition.
This condition occurred on my impulse coupled mag, so the engine was very hard to start, although it ran OK once I got it running.
I sent my mag in for service, it was very old. I think the points condenser was bad, causing the points to run hot, which overheated the rubbing block allowing the points gap to decrease. When I looked back thru the engine log, this mag had a history of points resetting, and indeed, the points adjustment was maxed out.
when I upgraded the mag to a Pmag, I also lost some radio problems. So my mag might have been broadcasting a lot of electromagnetic interference?
My point is that you get about one timing correction without problem, but if you need to do more than 6 degrees (?), then your mag's E gap timing might be too far off and you will get a weak spark. This indicates an internal mag problem, which should be looked into.
Check your engine log, see how many hours are on the mag since it's last servicing, and look for any entries that indicate the mag timing has been reset and or the points reset. A history of mag adjustments that do not resolve on going timing drift would be a sign that the mag needs some work.

Opening a can of worms

I myself have not seen this yet personally, although I suspect recently O/H Slicks on a friends G36 had a couple of degrees of error after only 30 hours, but????

??there is a story from a credible source (magneto O/H shop) who has been communicating with Champion about the Slick points recently supplied that have been showing these symptoms and they seem to not care less about it.

Wait till this happens on a Chieftan and toasts and engine or worse!

You will see a drop in stress on your engine and lower CHT's unless you have too much advance already from your EI.

A tiny bit of advance helps with LOP ops, but other than that a conventional magneto is doing everything it should and nothing it shouldn't. Except when poor quality parts are involved. Which is a worry?

I would investigate this problem with some priority. That is a lot of drift. Especially in one year and I assume not many hours. How many hours since new or new points were fitted and since the mag was set last?

I seem to remember reading a 4 degree drift being the lifetime limit for mag bumping before a point or cam replacement was required (or specified anyway).

RV10inOz said:

...
You will see a drop in stress on your engine and lower CHT's unless you have too much advance already from your EI.
...

Click to expand...

That would be true if his timing went from 25* BTDC to 21* but going from 25 to 29* will cause his CHT's to go up (Assuming the mag fires before his EI.) and his EGT's to go down. This is because more of the fuel-air mixture burns Before Top Dead Center, creating more pressure, before the exhaust valve opens.

Resetting his mag to 25* should lower his CHT's and raise his EGT's, again, depending on what his EI is doing.

Is there proof that it was previously correct? May have been mis-timed from the beginning.

New engine with less than 100 hours on it. This was the first time I've checked the timing so it is certainly possible that it's been incorrectly set all along. I will keep an eye on it and check it a few times between now and it's next condition inspection to make sure it's not drifting.

Don't forget

New engines from Lycoming do not have their magnetos timed,
You have to time them yourself.
Not sure where you got your engine but more than likely it was not timed
properly before it first ran.

N941WR said:

That would be true if his timing went from 25* BTDC to 21* but going from 25 to 29* will cause his CHT's to go up (Assuming the mag fires before his EI.) and his EGT's to go down. This is because more of the fuel-air mixture burns Before Top Dead Center, creating more pressure, before the exhaust valve opens.

Resetting his mag to 25* should lower his CHT's and raise his EGT's, again, depending on what his EI is doing.

Click to expand...

Bill, read my post again please

That is exactly what I said. Going from his excessively advanced 29 to normal 25 will reduce the peak pressure and lower CHT.

Remember I teach this stuff from real data. I reckon you misread my post, and that could be my fault.

Cheers.

Sorry David, I misread your post to be you would have lower stress, etc. at 29 degrees vs 25, which, as you know, is not correct.

no wuckers


Another bit if South pacific lingo for ya!

Have you checked to see if this mag is subject to the Slick service bulletin SB2-08 that requires an annual (and/or 100-hr) timing check to determine whether the timing has drifted 4* or more?

I will look into that, thanks.