Replace magnetos on over tbo engine?

[ryoder]

My engine is at 2400 hours and has excellent compression, doesn't burn oil, didn't have metal in the screens etc but the mags seem to be weak. We get a large mag drop when going to the right mag on initial startup. Once we fly it for a while (my cfii is an a&p/ia) the motor smoothed out and a post flight runup shows great mag drops of about 90rpm or so. He says that I should consider replacing the mags or the entire motor and mags. Is it a waste of money to do the mags now if I plan to rebuild the motor in six months? Also should I consider the electronic mag? I like the concept of reduced maintenance and better economy that it provides through advanced timing during low load operation. It kind of reminds me of the electronic ignition I had on my carbureted 1982 Z28.

[ryoder]

Also, this engine had a prop strike at 1000 hours or so and had a tear down and top overhaul then. Some new cylinders were put in back in the 80s and it has had a history of sitting in storage for two five year stretches with preservative steps taken and full annuals after five years of doing nothing.

[romair]

What kind of engine? Dual magneto? Do you have an engine monitor? Consider doing an in flight mag check lean of peak before you blame the mags. Read about the procedure on mike busch's webinars, so that if the engine quits during the procedure you don't go back to both mags immediately.

Stefan

[1964-M20E]

Why would you consider overhauling the engine if compression are good, little to no oil consumption, good oil analysis and overall it is running good?

 

How many hours on the mags?

 

If you are really concerned about your mags giving up replace the left mag, since that is the one you start on, do a good bore scope of the cylinders if all is well continue flying that engine.

[BigTex]

Why replace the mags? If the engine is strong, I'd have the Mags IRAN'd for around $1200 and keep flying. Do virtually everything on condition.

[ArtVandelay]

Regarding Slick mags, they used to say it was best (cost effective) to just replace with new mags...is this still the case, there seems to be different opinions on this? I'm inclined to IRAN mine, they have 1000+ hours on them?

[orionflt]

it use to be that slick mags were cheap enough to just replace but since Champion bought out Unison they prices have gone thru the roof. 5 yrs ago i would have recommended putting slick mags on today i would say stick with the bendix mag. i definitely would overhaul a slick before replacing it with a new slick mag, I may consider putting bendix mags back on.  right now i'm waiting for E-mag to get thru the certification process, I think they or some one with a similar product will be the way to go in the future. 

 

brian

[KSMooniac]

Why replace the mags? If the engine is strong, I'd have the Mags IRAN'd for around $1200 and keep flying. Do virtually everything on condition.

 

Do this.  Mags should come off every 500 hours for inspection... in your case if you suspect they're weak do this and keep flying.  If you end up overhauling the engine 100 hours later, just put those mags back on.  There is nothing in the regs that requires you to overhaul mags when you overhaul an engine.

[N601RX]

If your planning to use an A&P for the overhaul this will not matter, but if your planning on sending it out to an engine shop then you need to discuss it with them first. Many of them will not reuse mags even if they are almost new are have just been overhauled.

[Mooneymite]

I'm a big believer in "on condition" and have no compunction about running an engine beyond TBO assuming the vital signs are good.

 

However.  

 

Nothing lasts forever.  At some point, the engine, not you, may make the decision "it's time" forcing an off-airport landing and all the associated "relocation costs".  When my first engine went over 2400 hours, I went the factory reman route.  I have no idea if that engine would have gone 6000+ hours, but the manufacturer obviously suggests otherwise.

 

It isn't just the engine that's beyond TBO, but a lot of the pieces and parts necessary for reliability are also getting old (the engine driven fuel pump comes to mind).  At some point, the cost of maintaining reliability will approach the cost of an overhaul.

 

Your mags may just be giving you a gentle nudge.

[DS1980]

Congrats on getting one of the good engines. Don't tear it apart to find out why it was working so well. We did that in the military and it drove me nuts.

[ryoder]

Why would you consider overhauling the engine if compression are good, little to no oil consumption, good oil analysis and overall it is running good?

 

How many hours on the mags?

 

If you are really concerned about your mags giving up replace the left mag, since that is the one you start on, do a good bore scope of the cylinders if all is well continue flying that engine.

My thoughts exactly. The right mag is the one with the drop and I actually don't know oil history yet since I just bought it but during the annual the screens were clear. It isn't burning oil or leaking it. I'll send out for analysis when I get to 25 hours. I only have five hours on it right now.

[ryoder]

If your planning to use an A&P for the overhaul this will not matter, but if your planning on sending it out to an engine shop then you need to discuss it with them first. Many of them will not reuse mags even if they are almost new are have just been overhauled.

It will be the a&p doing it as the costs are lower and I have more control over what I replace.

[ryoder]

Do this.  Mags should come off every 500 hours for inspection... in your case if you suspect they're weak do this and keep flying.  If you end up overhauling the engine 100 hours later, just put those mags back on.  There is nothing in the regs that requires you to overhaul mags when you overhaul an engine.

This is what my a&p is suggesting but I wonder how much labor costs I am sinking into it if the thing still runs rough and has high mag drops on startup and I decide to go full overhaul.

[ryoder]

What kind of engine? Dual magneto? Do you have an engine monitor? Consider doing an in flight mag check lean of peak before you blame the mags. Read about the procedure on mike busch's webinars, so that if the engine quits during the procedure you don't go back to both mags immediately.

Stefan

I don't know if it's true dual bit it is a O360A1D if memory serves. I'll check the webinar. I don't have a monitor.

[WardHolbrook]

I'm a big believer in "on condition" and have no compunction about running an engine beyond TBO assuming the vital signs are good.

 

However.  

 

Nothing lasts forever.  At some point, the engine, not you, may make the decision "it's time" forcing an off-airport landing and all the associated "relocation costs".  When my first engine went over 2400 hours, I went the factory reman route.  I have no idea if that engine would have gone 6000+ hours, but the manufacturer obviously suggests otherwise.

 

It isn't just the engine that's beyond TBO, but a lot of the pieces and parts necessary for reliability are also getting old (the engine driven fuel pump comes to mind).  At some point, the cost of maintaining reliability will approach the cost of an overhaul.

 

Your mags may just be giving you a gentle nudge.

One question that I would have is is this engine a first run or has it been overhauled previously? At 2400 hours, that engine doesn't owe anybody anything. My only concern would be the possibility of running some very expensive parts beyond limits and not being able to use them for the core credit. Sometimes a few hundred extra hours can be disproportionality expensive when you finally get around to overhaul. 

[cliffy]

I think you're jumping the gun here. You have several things to check before you determine it is the mag.

 

How old are your plugs? Have you religieusly cleaned and gapped them every 100 hrs? Have you checked the plugs internal  resistance? Have you tested them under pressure in a test unit after you cleaned them? What shape is the center electrode ? Are they fine wire or massives?  Have you rotated them top to bottom every 100 hrs? Are they in fact the correct plug for that engine? Has the well below the center electrode been clean to the very bottom after servicing or is there still lead deposits in the bottom?

 

Now lets go to the leads. Have you done a high tension leakage check on them? What shape are they in? How old are they? I had a low speed misfire that cleaning plugs and repairing mags didn't cure. Changed out the plug leads and it solved the issue.

 

Now lets go to the mags- How long have they been run without a good 500 inspection and repair? Any good A&P can do a good 500 hr on either a Bendix or Slick without too much trouble. They need a 500 hr insp even though it's only recommended, you need to do it. 

 

By your own comments that it runs good after a flight I'd be inclined to think plugs long before I did an overhaul on the mags. I'd for sure do a 500 hr if you haven't done so and replace the plugs if they continue to cause the problem. You can get "hotter" plugs to help eliminate fouling if that is what is causing your issues. Check the spark plug effectivity chart for your make and model engine

[Tom]

To the OP:

 

I'd swap one mag for the EI.  The EI theoretically will last longer than you and it will pay for itself in 400-500 hours.  It might even give you a little speed/climb nudge. 

[ryoder]

I think you're jumping the gun here. You have several things to check before you determine it is the mag.

 

How old are your plugs? Have you religieusly cleaned and gapped them every 100 hrs? Have you checked the plugs internal  resistance? Have you tested them under pressure in a test unit after you cleaned them? What shape is the center electrode ? Are they fine wire or massives?  Have you rotated them top to bottom every 100 hrs? Are they in fact the correct plug for that engine? Has the well below the center electrode been clean to the very bottom after servicing or is there still lead deposits in the bottom?

 

Now lets go to the leads. Have you done a high tension leakage check on them? What shape are they in? How old are they? I had a low speed misfire that cleaning plugs and repairing mags didn't cure. Changed out the plug leads and it solved the issue.

 

Now lets go to the mags- How long have they been run without a good 500 inspection and repair? Any good A&P can do a good 500 hr on either a Bendix or Slick without too much trouble. They need a 500 hr insp even though it's only recommended, you need to do it. 

 

By your own comments that it runs good after a flight I'd be inclined to think plugs long before I did an overhaul on the mags. I'd for sure do a 500 hr if you haven't done so and replace the plugs if they continue to cause the problem. You can get "hotter" plugs to help eliminate fouling if that is what is causing your issues. Check the spark plug effectivity chart for your make and model engine

I don't know how old the plugs are but I could find out. My mechanic cleaned them and checked the gaps and said they are ok but showing signs of wear. Good point about the leads and I don't know if they were checked. How much do mags go for anyway? What are typical labor rates? It would be nice to have fresh mags leads and plugs if it didn't cost an arm and a leg.

[philiplane]

You should have the plugs and mags checked to see what needs repair or replacing. If you have Champion plugs, test them for internal resistance and replace them if above 5000 ohms. If you have Slick mags with more than 500 hours on them, they will need a 500 hour inspection and you should expect to replace some internal parts.

[ryoder]

Thanks for the info. I'll share this thread with my mechanic.

[jetdriven]

A friend of mine recently replaced his Slick mags and after, #4 began to run very hot. After a few rounds of troubleshooting the mechanic declared the #4 cylinder and the cam bad, and it needed an overhaul. He dutifully ponied up the 20k or so, but the engine shop called and all the internal parts were good. Worse yet, the overhauled engine ran very hot on #4. Turns out the new slick mags were bad.

[ryoder]

A friend of mine recently replaced his Slick mags and after, #4 began to run very hot. After a few rounds of troubleshooting the mechanic declared the #4 cylinder and the cam bad, and it needed an overhaul. He dutifully ponied up the 20k or so, but the engine shop called and all the internal parts were good. Worse yet, the overhauled engine ran very hot on #4. Turns out the new slick mags were bad.

That sucks.

[N201MKTurbo]

If your mags haven't been opened in a long time and they are giving you trouble, readjusting the point gap and possibly replacing the points will probably fix your problem. Points are $40.

[cliffy]

Had a local 206 (government plane and shop) get a new engine (factory overhaul) and had starting problems for 100 hrs. Tried everything including new engine fuel system to no avail. Turned out the "new" Slick mags were bad from day one. Internal timing was way off. Who would have thought.