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Old 03-27-2020, 01:37 AM
Roy25101 Roy25101 is offline
Join Date: Mar 2014
Location: Jekyll Island, GA
Posts: 56
Default Bendix Magneto Install, Lock washers?

We are in the process of reinstalling overhauled Bendix S20 mags on an 0-320. The previous mechanic used the traditional internal teeth lock washers while mounting. My mechanic wanted to switch to split lock washers because he preferred them but unfortunately the studs are not long enough to accommodate the thicker washer.

My question is has anyone ever used something different than the traditional lock washer and nut when installing magnetos. As important as they are I am surprised there is no mechanism to lock these nuts down. Perhaps a drilled nut with safety wire or an all steel lock nut would work well.

I am just curious if anyone has any input into this thought..Thanks in advance.....
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Old 03-27-2020, 06:37 AM
Walt's Avatar
Walt Walt is online now
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,518

Why re-invent the wheel, use new internal lock washers as specified in the engine manual and move on.
Walt Aronow, DFW, TX (52F)

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Last edited by Walt : 03-27-2020 at 06:40 AM.
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Old 03-27-2020, 07:59 AM
RV7 To Go RV7 To Go is offline
Join Date: May 2011
Location: Ontario, Canada
Posts: 229

Originally Posted by Walt View Post
Why re-invent the wheel, use new internal lock washers as specified in the engine manual and move on.
+1. I always use new lock washers when reinstalling or after adjusting. Never had one come loose yet. Our engine/maintenance shops do many mag changes and timing adjustments on our 28 ship fleet every year. Never had an issue. Why change what works...especially when it follows the KISS theory.
RV4 - Bought 2013 Sold 2017 after 450 hrs
RV7 - Built in 6.5 yrs & Flying 2017
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Old 03-27-2020, 08:35 AM
bnt83 bnt83 is offline
Join Date: Sep 2014
Location: Lincoln NE
Posts: 74

Even when the D2000 series magneto clamp issues came up they still used the internal tool lock washer on the new clamp...
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Old 03-27-2020, 03:18 PM
chaskuss chaskuss is offline
Join Date: Mar 2005
Location: SE Florida
Posts: 1,497

The manual specifies that new internal star washers are to be used each time. The only other thing that would work here would be wave washers. See

Probably best to stick with the stock washers.

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Old 03-27-2020, 03:45 PM
krwalsh krwalsh is offline
Join Date: Nov 2009
Location: San Francisco, CA
Posts: 334
Default Nord-Lock Washers

Take a look at this video of various lock washers and the relative ineffectiveness of them:

You can purchase Nord-Lock washers from McMaster-Carr here:

I've got a whole bunch of these and when I do maintenance on my engine I replace the star washers and split ring washers.
Kevin R. Walsh
Cozy Mk-IV
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Old 03-27-2020, 08:13 PM
jrs14855 jrs14855 is offline
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,365
Default Mags

It important to use the special flat washers that are used on many Bendix mags. They are larger and thicker than standard AN washers. I have never had a problem with the star lock washers. If I have torqued the mag nuts and have a need to loosen them, even if the engine has not been run I replace the star washers.
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