What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Slick magneto question

J

JimWoo50

Well Known Member
I have a line on a used mag kit with one 4370 and one 4371 mag. for a good price. The problem is that the Slick kit as offered by aircraft spruce has a 4373 mag instead of the 4371. The difference is the 4371 has 20 degrees of delay(?) while the 4373 has 25 degrees. What is meant by delay or lag and does it make any difference for my 0-320b3b?
 
The purpose of the delay in the impulse mag is to reduce timing to "0" degrees during start. If your engine uses a timing of 25 degrees before top dead center, which I'm pretty sure it does, then you will need an impulse mag with 25 degrees of delay.
 
I, too, have run into this and checked with a few mechanics and in the end ran my 20 degree mag at 25 degrees BTDC with no apparent problems. However, this is in no way an endorsement for doing this.
 
Slick magneto model numbers

All,
Thanks for starting this thread because it hits my target. My O320-D1A also says 25 degrees on the data plate and my mags are Slick 4370 and 4371. I called AERO and the recommended Slick mags are 4370 and 4371. I was told the OEM mags that came on my engine back in the late 1980's were Bendix and that is where the 25 degrees comes from on the data plate. I am wondering which information is correct. What you say about the 4373 Slick mag makes sense. Where did you get your information? I tried to go on-line at Lycoming.com but couldn't find anything. The ACS website doesn't show the 4373 mag as an option; only the 4371. Is the 4371 mag the wrong part? Where to go for definitive answers?

Thanks very much

Sincerely,

Brian Vickers, RV4

(Just painted the interior yesterday!!! Yippee!!! My back is stiff from bending over all day masking and spray painting; but it?s done and looks great!!! Done = good)
 
I had bendix mags too

bought the engine disassembled and it came with Bendix mags. They look really tired and the harness is shot so I was looking to upgrade.
 
Do a search on magneto lag angle here on this site and all will be answered. :) It has been talked about several times thus far.
 
Mags

Jim,
I just called Aircraft Spruce and you are correct. Our engines use the 4373, not the more common and less expensive 4371. I specifically asked for him to check the B3B for you. Thanks very much for bringing this to my attention. This is probably something I would not have check had it not been for your thread post. I now need to sell my new in the box 4371.

Thanks again,

Sincerely, Brian Vickers, RV4 finishing
 
20 lag for 25 timing is OK

My Superior XP IO-360 Plus is specified for 25 degrees BTDC and has 20 degree lag magnetos. This is how they are delivered; it is not a mistake. The Vantage (certified) engine has the same specifications.

The built-in lag is only approximately what the actual impulse retard will be; the variation comes from the variation from "perfect" in the e-gap of the points. In real-life, one of my mags retards to just after TDC and the other to a couple of degrees before when both are set at exactly 25 BTDC for normal firing. While the lag is not adjustable, the actual retard is, a little.

This information is not intended to persuade anyone to use either 20 or 25 degrees lag, merely to inform.
 
The 20 degree lag time is probably ok in most cases, but with the new faster turning starters, you will be taking a little more of a chance of "kick back".
 
Starters, etc

I just called the local mag overhaul shop where I had my new - old stock mags inspected. My units are new but were manufactured in 1998. I took them in for inspection last year. He essentially repeated what Mel and H. Evens posted; the 4371 can be used in place of the 4373. I was planning to use the reman Prestolite starter (looks like new) that came with my engine because it's paid for and I am anticipating my minimal panel, wood prop RV4 to be tail heavy. The heavier starter will assist in the CG problem I expect to have. From what you all say, the older Prestolite starter cranks the engine slower. Sounds like my setup with 20 degree mag and old starter are a suitable match.

Thanks,
Brian Vickers, RV4 finishing
 
My engine came with a 4373, I replaced it with a 4371 6 years ago and it's been just fine. 180 HP 9-1 pistons and happy, 1500 0n the tack. Larry
 
My 2004 aero sport o360 A1A came with the 4371 mag and was replaced 500 hrs later with the same 4371. I just replaced it again with the 4371 and had it Kick back on initial start. Now I see this engine calls for a 4373 mag which has a 25’ lag. Something has changed in the original 4371 as it no longer works on my engine. I’m waiting on my 4373 to arrive and hope it works.
 
You must log in or register to reply here.
Back
Top