Ignition Switch

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mfullmer
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Joined: Mon May 21, 2018 10:32 pm

Ignition Switch

Post by mfullmer » Wed Mar 06, 2019 2:53 am

Anyone know the correct replacement for the ignition switch on a 108-1? Univair sells the Bendix brand switch for about $500. When I called to ask if there are any alternatives, the guy told me the ACS A-510-2 would work (~$200). Naturally, I bought the cheaper alternative. It does NOT work.

When doing a mag check, it seems to run fine on Both. 200-250 rpm drop when running on Left. When running on Right, it coughs and sputters like crazy.

My mechanic pulled the right mag and opened it up. Like new inside. We also replaced the P-leads. Same problem.

Finally, we disconnected the P-leads from the switch, and did a mag check by manually grounding the P-leads one at a time. Runs great.

Any suggestions?


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Mark and Julie Fullmer
'47 108-1 N8368K

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Will.Ware
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Re: Ignition Switch

Post by Will.Ware » Wed Mar 06, 2019 3:48 am

Sure it’s the switch?

Running fine BEFORE the switch install?


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Will Ware
Rockwall Texas 1F7
N97954 108-1
Follow my restoration blog at https://www.N97954.org

mfullmer
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Joined: Mon May 21, 2018 10:32 pm

Re: Ignition Switch

Post by mfullmer » Wed Mar 06, 2019 4:19 am

The original switch seemed a bit loose, and a frequently had to wiggle the "key" to get a good connection. Since it was a 70+ year old part, I decided to replace it. The new one flat out doesn't work right. When I bypass the switch, the engine runs fine.


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Mark and Julie Fullmer
'47 108-1 N8368K

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Ignition Switch

Post by admin 1 » Wed Mar 06, 2019 4:42 am

What I meant was this. Did the engine run smooth during the mag check with the old switch?

A mag switch is either going to open or close the P-Lead ground to a mag, I don’t think “Rough” running is going to come from a Mag switch.

Do you have an per cylinder engine monitor? Can you tell which cylinder is running rough?


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lawheelock
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Re: Ignition Switch

Post by lawheelock » Thu Mar 07, 2019 9:55 am

Mark,
Somehow you have it wired wrong. Did you get an instruction copy with the "cheaper" switch?
Does it have a drawing of the back side of the switch?
The ACS unit it a copy of the bendix as far as I know and will work the same way. The only way I can think of that the engine coughs and sputters is if the 12 V line that the starter portion of the switch is connected to a wrong terminal and it is applying 12 V to the P lead instead of it being open for that mag to operate.
Recheck the wiring. It is wired wrong. It does include a twist to start function? On most all planes except Franklin powered, the switch is designed or has a jumper wire or link to ground the right mag for starting because most engines only have the impulse on one mag. Franklin has impulse on both makes so you want them to have their P leads open while the starter is activated.
Larry Wheelock, A&P/IA
Stinson 108 N584LW 180 Lyc
Texas in Winter; Indiana in Summer

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lawheelock
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Re: Ignition Switch

Post by lawheelock » Mon Mar 18, 2019 6:19 am

Mark, have you resolved your ignition switch issue?

Please let us know, or if you need further help.
Larry Wheelock, A&P/IA
Stinson 108 N584LW 180 Lyc
Texas in Winter; Indiana in Summer

mfullmer
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Joined: Mon May 21, 2018 10:32 pm

Re: Ignition Switch

Post by mfullmer » Mon Mar 18, 2019 12:41 pm

Hi, Larry;

Yes, I believe the issue is resolved. It appears to be related more to the frigid temps up here than a wiring problem. Doug Still mentioned Franklin Service Bulletin 46. After reading that bulletin, I realized my recent testing was done when the OAT was 20°F or below. I've since made two flights at 25° or above (with a little carb heat) and had no issues.

As always, thanks for your help.
Mark and Julie Fullmer
'47 108-1 N8368K

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