retard breaker lag time??

[Browncbr1]

This past Fall, I had done my 500 hour slick mag overhaul.  The left mag that was on it previously was the 4347 which had a 25 lag on the retard breaker, but champion and Lycoming both insisted that I needed the 4345, which has a lag of 15.

The data plate on my IO-360-A1A says 20 degree timing, but I want to go back to the original 25 degree timing.  I don't fly in extreme cold and I have found that my CHTs are just never high enough anyway.  (cruise in low 200s)

I'm also confused why they insisted that I use that mag, which would mean starting fire would be 5 degrees before TDC?  I thought it should be 0 degrees??  They said that the 4347 with 25 retard lag could cause kick back and that their recommendation would be safer... Have I incorrectly understood how breaker lag is measured?

 

My question is, if I move the timing back to 25 BTDC, do I need to replace this relatively new mag with the 4347 with the 25 breaker lag?

Edited February 8, 2016 by Browncbr1

[N601RX]

I believe if you look in the slick overhaul manual you will see all the internal parts are the same between the 45 and 47.  Other than the data plate difference in the 45 and 47 is during assembly the contacts are rotated a little more in one than the other.  The Slick T-100 toolkit vise has a degree wheel on the back and the overhaul manual instructs you to set the retard to the amount stamped on the data plate of the mag.  It is set in reference to the main points.

[Browncbr1]

Just now, N601RX said:

I believe if you look in the slick overhaul manual you will see all the internal parts are the same.  Other than the data plate difference in the 45 and 47 is during assembly the contacts are rotated a little more in one than the other.  The Slick T-100 toolkit vise has a degree wheel on the back and the overhaul manual instructs you to set the retard to the amount stamped on the data plate.  It is set in reference to the main points.

So 4345 and 4347 are the identical mags, but the retard breaker is adjusted differently from the shop?    An A&P can change the retard breaker timing?

 

[N601RX]

Its easily adjusted with the slick toolkit, but the problem then becomes a paperwork issue.

[Browncbr1]

ok, thanks!

[cliffy]

http://generalaviationnews.com/2012/05/08/ask-paul-what-is-the-correct-timing-for-my-engine/

 

The above link may be of great help to you and your A&P.

The correct magnetos for your engine are listed in Lycoming publications and the engine Type Certificate. Don't just take someone's word for it..

Be positive you have the correct magnetos..  There is no need for guesswork here. it's all in publications.  Find them and read them.

Any good shop will have them available on computer to research. 

[jetdriven]

The timing is also in the 1E10 type certificate.....25 degrees.  

Edited February 18, 2016 by jetdriven

[cliffy]

There is a SB that allows the timing to be set to 20 degrees by engine s/n as noted in the link I provided above. 

[Andy95W]

He references Service Instruction 1325A, which is no longer listed on the Lycoming website.

But which takes priority- the Tpe Certificate as Byron mentioned, or the Service Instruction?

[jetdriven]

The type certificate.  The SI1325A is optional.  I chose not to have it

[Andy95W]

Also how I read that.

But what if the engine data plate says 20°?

[jetdriven]

Make a log entry denoting the removal of SI1325 and restamp the data plate to 25 degrees.  Install the correct magneto lag angle for the 25 degrees timing and roll on. If 201ER and  can do it on factory engines under warranty you can too 

[Browncbr1]

Yea, there is an optional SI that set it to 20 degrees... and as I understand it, data plates were automatically changed to this on overhauled engines some time ago... In spite of the data plate, I found evidence in the logs that the previous owner had set timing to 25 but didn't stamp the data plate.  this explains the performance difference I had experienced when the new mags were installed according to the data plate.

I was referred to a mag shop in TX and I talked with them... they will open up on my 4345, inspect, and reset retard timing and put a new data plate on it for $75...  So, I'll be doing that in a couple months at annual.