Dual Mag Timing Issue?

[Scott Ashton]

I just had my dual mag exchanged with a Kelly dual mag after 750 hours time in service with the old dual mag on my 201 .  The First flight or two after the exchange were great and the Savvy flight test profile that I ran showed everything well matched regarding the in-flight mag check.

went to go flying this morning and on the run up, the left mag showed little drop and the right mag dropped over 400 rpm, though it continued to run.  On the second run up the engine was backfiring during the run up.  

is it plausible that the timing on the right mag “walked”.  The mechanic who did the install will look at it on Monday but I’m curious as to what’s going on….

 

thanks

Scott

[KSMooniac]

There is a non-trivial chance your Kelly mag is junk out of the box. If your mechanic confirms it, I'd return it for a full refund and get a good one from a better vendor that specializes in the dual mag.

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[toto]

As I understand it, Kelly is essentially the only company that makes replacement parts for the Bendix dual mag. They have a PMA for every component including the housing. 

[N201MKTurbo]

Yes, My experience with a dual mag for 20 years is they eat points. The cams have two lobes on them and they rarely line up. If you get the two points open perfectly on one lobe, they are all over the place on the other lobe. You should have somebody check out the points. I just readjusted mine this morning, so I'm a little bit grumpy about them right now.

[kortopates]

It could be a mag or a plug issue.


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[Bartman]

Maybe I’m just lucky, but in 1,500 hours I have had exactly one problem with my dual mag. That was 10 years ago and one side died in flight.  Keep your own magneto maintained by a shop known for that, not named Kelly.  Do not exchange. 
YMMV

[N201MKTurbo]

So, the timing can be different, but no more than 2-3 degrees. 
 

As @kortopates said, it is more likely to be a plug issue.

[EricJ]

Also recheck the timing.   Sometimes they move a little as the new points wear in.    Between checking the timing, plugs, wires, etc., you'll likely find the problem.

[OR75]

easy to check if it is the plugs / harness 

I would not be surprised if it one of the contact assembly is messed up

 

[larrynimmo]

My AI told me when setting the timing of a double mag, the only time he is concerned is when the contacts open at exactly the same time

[skykrawler]

It sounds more like a plug with the misfire/backfiring. 

The points on these mags can loose the gap if the cam and felts are not lubed correctly.  The cam is supposed to be infused in an oil bath under heat.   Without the lube the heat from friction will melt the points rubbing block.  The lube is crazy expensive (there must be an alternative, but not 'legal')

In a drop from a change in timing the engine still runs pretty smooth.  From a bad, lead fouled or oiled plug there will be a dead miss on a cylinder and rough running.  A dead miss is indicated by a loss of EGT on the cylinder.

You need to supply more info for your  free online diagnosis.

 

[Scott Ashton]

3 hours ago, skykrawler said:

It sounds more like a plug with the misfire/backfiring. 

The points on these mags can loose the gap if they cam and felts are not lubed correctly.  The cam is supposed to be infused in an oil bath under heat.   Without the lube the heat from friction will melt the points rubbing block.  The lube is crazy expensive (there must be an alternative, but not 'legal')

In a drop from a change in timing the engine still runs pretty smooth.  From a bad, lead fouled or oiled plug there will be a dead miss on a cylinder and rough running.  A dead miss is indicated by a loss of EGT on the cylinder.

You need to supply more info for your  free online diagnosis.

 

On one mag, one and two dropped off and three and four acted normal.  Engine backfired a bit too.  With that I’m leaning toward two bad plugs. They are getting pulled tomorrow so I guess I just have to wait and see.  It actually gives me hope that they don’t have to pull the mag again.  
 

 

[OR75]

5 hours ago, larrynimmo said:

My AI told me when setting the timing of a double mag, the only time he is concerned is when the contacts open at exactly the same time

ChatGPT ? 

[N201MKTurbo]

It just takes a minute to put a mag timer on it. That will tell you if there is a timing problem. Especially if you are pulling the plugs, which makes the timing test easier and safer.

[N201MKTurbo]

If you really want to be disappointed with your dual mag. Adjust the points so they open at exactly the same time, then precisely set the timing to the engine on cylinder 1. Then check it on cylinder 3.

[Scott Ashton]

Not to belabor this, but we did pull the mag and returned it to Kelly - they found that the points on one side were bad and needed to be replaced after only 3 hours TIS.  Ugh.  Anyway, she's back flying now and running great and only 497 hours until I go full dual electronic!   

 

 

 

 

 

[KSMooniac]

Did Kelly offer any reimbursement for your mechanic labor?  

Unfortunately this is just another log on the bonfire of poor quality tales from them.

[OR75]

3 hours ago, Scott Ashton said:

Not to belabor this, but we did pull the mag and returned it to Kelly - they found that the points on one side were bad and needed to be replaced after only 3 hours TIS.  Ugh.  Anyway, she's back flying now and running great and only 497 hours until I go full dual electronic!   

 

 

 

 

 

what did they mean by "bad" ?

[philiplane]

There is normally some initial wear on the nylon part of the points that rides on the steel cam. This few thousandths of wear will result in the timing becoming retarded by 2-3 degrees in the first 100 hours.

Knowledgeable shops will set the gap slightly wider to account for this initial wear.

[jetdriven]

18 hours ago, Scott Ashton said:

Not to belabor this, but we did pull the mag and returned it to Kelly - they found that the points on one side were bad and needed to be replaced after only 3 hours TIS.  Ugh.  Anyway, she's back flying now and running great and only 497 hours until I go full dual electronic!   

 

 

 

 

 

I wouldnt fly an airplane with a Kelly overhauled dual mag.   Dual electronic is just as complicated, and only a slight improvement.  Its expensive, and not sure if its more reliable.

[N201MKTurbo]

Did Kelly charge you for the repair? A set of points is only $40 and it takes about 15 minutes to set them.

[Scott Ashton]

5 hours ago, N201MKTurbo said:

Did Kelly charge you for the repair? A set of points is only $40 and it takes about 15 minutes to set them.

No it was under warranty....flew it today and yesterday - fired right up and ran great.  Did the Savvy in flight mag checks and they looked good too.  I pulled the data from the last flight and you could see where two cylidners went awry mid flight..   I'm hoping this is the last I have to think about this for a while now....

[redbaron1982]

8 hours ago, jetdriven said:

I wouldnt fly an airplane with a Kelly overhauled dual mag.   Dual electronic is just as complicated, and only a slight improvement.  Its expensive, and not sure if its more reliable.

Are them that bad? Mine was overhauled by Kelly. They have roughly 30 hours in, so far so good. Engine run great LOP. And I did a mag check in flight running LOP and it was very smooth.

[EricJ]

27 minutes ago, redbaron1982 said:

Are them that bad? Mine was overhauled by Kelly. They have roughly 30 hours in, so far so good. Engine run great LOP. And I did a mag check in flight running LOP and it was very smooth.

Kelly did a 500-hour/IRAN on mine (which was nearly an overhaul) two years ago.   I've put nearly three hundred hours on it since and it's been trouble-free so far.   I had to make minor retiming adjustments a couple times as it has worn-in, but that's it.

 

[toto]

28 minutes ago, redbaron1982 said:

Are them that bad? Mine was overhauled by Kelly. They have roughly 30 hours in, so far so good. Engine run great LOP. And I did a mag check in flight running LOP and it was very smooth.

I’ve got roughly 80 hours on a dual mag that was IRANed by Kelly, and everything seems to be running well.