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  #1  
Old 03-03-2021, 10:32 AM
lndwarrior lndwarrior is offline
 
Join Date: Mar 2015
Location: Cloverdale CA
Posts: 297
Default Tips on installing new Bendix magnetos?

I will be installing new Bendix S4LSC-21/204 magnetos in my O-235. They are replacing my old S4LN-21/29 mags.

When the original mags were installed 4 years ago I had an A&P help me. I can't remember if there was anything special about the install itself.

Other than making sure the impulse mag is on the right side is there anything else about the physical install I need to know?

Or is it simply a matter of:
- putting new gaskets
- slipping mags in place
- loosely set the bolts
- hook up the wires
- timing
- torque bolts

Appreciate any comments!
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  #2  
Old 03-03-2021, 10:35 AM
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rocketbob rocketbob is offline
 
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Location: 8I3
Posts: 3,669
Default

No offense but it really sounds like you still need an A&P to help you.
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N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
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  #3  
Old 03-03-2021, 10:51 AM
lndwarrior lndwarrior is offline
 
Join Date: Mar 2015
Location: Cloverdale CA
Posts: 297
Default Which is

Quote:
Originally Posted by rocketbob View Post
No offense but it really sounds like you still need an A&P to help you.
Which is partly why I'm asking the question.

Are you suggesting that someone who has built an entire aircraft, installed the engine, carburetor, fuel system, electrical system and everything else to complete - would necessarily need an A&P to install a set of magnetos? Not arguing, asking a serious question.

Last edited by lndwarrior : 03-03-2021 at 10:58 AM.
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  #4  
Old 03-03-2021, 12:13 PM
Jrskygod Jrskygod is offline
 
Join Date: Dec 2011
Location: Edinburg, TX
Posts: 637
Default

What Bob is trying to say is based on the information you provided there are several very important steps you need to do to install magnetos correctly and time them properly. I'm not saying that you might be able to get self taught through research, utube etc. but its a heck of a lot easier to find someone to show you how to do it properly and make sure the installation is correct. That person does not have to be an A&P to work on an experimental aircraft. There are also special tools you will need to do the job as well.
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Last edited by Jrskygod : 03-03-2021 at 12:15 PM.
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  #5  
Old 03-03-2021, 01:38 PM
lndwarrior lndwarrior is offline
 
Join Date: Mar 2015
Location: Cloverdale CA
Posts: 297
Default Well

I would very much appreciate if someone would at least provide an outline of what I am missing in the process and what tools would be needed.

FYI - I have researched youtube videos and read the limited install info available on the net. Nothing I have seen has suggested there is some hidden issues. Assuming you know how to find TDC.

If there really are some install details that only an A&P knows can you at least tell me what they are???

It just seems absurd that on a homebuilt aircraft forum that I have been a member for years, that the only response I get is "call an A&P" without any elaboration on why.
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  #6  
Old 03-03-2021, 01:50 PM
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rocketbob rocketbob is offline
 
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Quote:
Originally Posted by lndwarrior View Post
Which is partly why I'm asking the question.

Are you suggesting that someone who has built an entire aircraft, installed the engine, carburetor, fuel system, electrical system and everything else to complete - would necessarily need an A&P to install a set of magnetos? Not arguing, asking a serious question.
Yes I am suggesting exactly that. Its easily done wrong and not something I would teach over an internet forum. Its best to learn from experience with this directly working with an A&P.
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N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.

Last edited by rocketbob : 03-03-2021 at 01:52 PM.
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  #7  
Old 03-03-2021, 02:23 PM
WA85 WA85 is offline
 
Join Date: Apr 2010
Location: Royse City, TX
Posts: 151
Default Installing a Bendix Magneto

Timing Bendix magnetos can be a bit of a pain and getting an experience mechanic to help is a plus, however here is a very high level look at how Bendix magnetos are typically timed. Your results may vary

Assuming you are starting with both Bendix mags removed, one with direct drive and one with an impulse coupling on a Lycoming 4 cylinder engine.

Step 1. Remove one spark plug each cylinder
Step 2. The RH front cylinder is the #1, place your thumb / finger over the open spark plug hole and rotate the prop carefully until compression is felt.
Step 3. locate the timing marks on the front of the ring gear, typically its 20 / 25 deg BTDC. Aline the proper timing mark with the "dot" on the starter. Do not us TDC (Top Dead Center)
Step 4. Remove the round inspection cover from the "tall side" of the magneto
Step 5. Rotate the magneto drive gear until the RED mark on the distributor drive gear is located approximately the center of the hole. IMPORTANT - by gently rotating the drive gear to place the red mark in the hole, you will feel the "null point" of the magneto and can be confirmed by using a timing light to confirm when the points just open, provided the internal E-gap is properly set.
Step 6. Without rotating either the prop or magneto, place the magneto into the accessory housing and ensure the drive gear teeth properly mesh. There are special tools that will hold the magneto in a locked position to prevent rotation. Most are plugs that screw into the inspection hole and lock into the distributor drive gear.
Step 7. Secure the magneto tot he accessory housing using the proper hardware and tighten it to remove any looseness, but still able to be rotated with the slotted ears of the magneto.
Step 8. Using a timing light or buzz box, verify that the prop has not moved and the timing marks still aligned. Rotate the magneto on the engine to find the point where the points just begin to open, tighten the magneto hardware.
Step 9. With the magneto secured and the timing light / buzz box still connected, rotate the prop backwards about 20 degrees. Bump the prop in the direction of rotation. When timing light / buzz box show the points just beginning to open, stop. Look at the timing marks on the ring gear, if the proper timing mark is aligned with the dot, you are set.
If not, Keep adjusting until you set the proper timing.
If you cannot time the magneto to the engine without hitting the ends of the slotted ears, it is possible that magneto needs to removed and re-inserted if the magneto moved from the null position, or the internal magneto timing E-gap is out of time internally (points to cam lobe).

NOTE - when installing the magneto with the impulse coupling, you must verify that the impulse coupling has been "snapped" / the fly weight arm has disengaged and released from its wound up position or the timing will not be correct.
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  #8  
Old 03-03-2021, 02:37 PM
Taltruda Taltruda is offline
 
Join Date: Oct 2017
Location: Las Vegas, NV
Posts: 633
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I donít like the tools that hold the internal mag gear from turning.. it could put strain on the little gear tooth and cause a crack that may come apart down the road. Just line it up, and put it in. Verify that it didnít move by looking in the vent hole or using a bore scope if you canít get your eyeballs on it. I agree with the above guys.. donít be hurt that they recommend you to get an A&P to help. I would agree. Now let me sign off of here while I go ask the steps how to perform brain surgery on myself from a medical forum.
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  #9  
Old 03-03-2021, 03:28 PM
lndwarrior lndwarrior is offline
 
Join Date: Mar 2015
Location: Cloverdale CA
Posts: 297
Default

Quote:
Originally Posted by WA85 View Post
Timing Bendix magnetos can be a bit of a pain and getting an experience mechanic to help is a plus, however here is a very high level look at how Bendix magnetos are typically timed. Your results may vary

Assuming you are starting with both Bendix mags removed, one with direct drive and one with an impulse coupling on a Lycoming 4 cylinder engine.

Step 1. Remove one spark plug each cylinder
Step 2. The RH front cylinder is the #1, place your thumb / finger over the open spark plug hole and rotate the prop carefully until compression is felt.
Step 3. locate the timing marks on the front of the ring gear, typically its 20 / 25 deg BTDC. Aline the proper timing mark with the "dot" on the starter. Do not us TDC (Top Dead Center)
Step 4. Remove the round inspection cover from the "tall side" of the magneto
Step 5. Rotate the magneto drive gear until the RED mark on the distributor drive gear is located approximately the center of the hole. IMPORTANT - by gently rotating the drive gear to place the red mark in the hole, you will feel the "null point" of the magneto and can be confirmed by using a timing light to confirm when the points just open, provided the internal E-gap is properly set.
Step 6. Without rotating either the prop or magneto, place the magneto into the accessory housing and ensure the drive gear teeth properly mesh. There are special tools that will hold the magneto in a locked position to prevent rotation. Most are plugs that screw into the inspection hole and lock into the distributor drive gear.
Step 7. Secure the magneto tot he accessory housing using the proper hardware and tighten it to remove any looseness, but still able to be rotated with the slotted ears of the magneto.
Step 8. Using a timing light or buzz box, verify that the prop has not moved and the timing marks still aligned. Rotate the magneto on the engine to find the point where the points just begin to open, tighten the magneto hardware.
Step 9. With the magneto secured and the timing light / buzz box still connected, rotate the prop backwards about 20 degrees. Bump the prop in the direction of rotation. When timing light / buzz box show the points just beginning to open, stop. Look at the timing marks on the ring gear, if the proper timing mark is aligned with the dot, you are set.
If not, Keep adjusting until you set the proper timing.
If you cannot time the magneto to the engine without hitting the ends of the slotted ears, it is possible that magneto needs to removed and re-inserted if the magneto moved from the null position, or the internal magneto timing E-gap is out of time internally (points to cam lobe).

NOTE - when installing the magneto with the impulse coupling, you must verify that the impulse coupling has been "snapped" / the fly weight arm has disengaged and released from its wound up position or the timing will not be correct.
Thank you very much for taking the time to explain. I appreciate it.

I intend to get an a&p to help now that I understand the challenges.

Last edited by lndwarrior : 03-03-2021 at 03:30 PM.
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