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Ignition Switch

Mark Fullmer
Active Member

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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Topic starter Posted : 06/03/2019 1:53 am
Will Ware (Webmaster ISC)
(@stinsono)
Member Admin

Sure it’s the switch?

Running fine BEFORE the switch install?

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Posted : 06/03/2019 2:48 am
Mark Fullmer
Active Member

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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Topic starter Posted : 06/03/2019 3:19 am
admin 1
Eminent Member

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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Posted : 06/03/2019 3:42 am
lawheelock
Prominent Member

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/IAStinson 108 N584LW 180 LycTexas in Winter; Indiana in Summer

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Posted : 07/03/2019 8:55 am
lawheelock
Prominent Member

Mark, have you resolved your ignition switch issue?

Please let us know, or if you need further help.

Larry Wheelock, A&P/IAStinson 108 N584LW 180 LycTexas in Winter; Indiana in Summer

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Posted : 18/03/2019 5:19 am
Mark Fullmer
Active Member

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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Topic starter Posted : 18/03/2019 11:41 am
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