MTFCA Forum

My touring car came with a repop. It's been acting up, and I'm tired of rebuilding mufflers every time it cuts out and backfires. I'm looking for a usable switch and key

Contact Ben Martin in Georgia - get on his list - it's worth the wait !

Is he a rebuilder of switches, Steve?

Yeah. Hes the best. (770) 938-3376

It sounds like you've made up your mind, but if you decide to work on your existing switch, they're pretty simple. First, disconnect the ground wire from the battery. Then remove the four screws attaching the switch assembly to the dash and pull the switch assembly out a ways (you don't need to disconnect any wires).

The backs of the repro switches I've seen are the three pin type, just press (hard) and twist to release the back of the switch from the housing. Then, wire brush or sand any corrosion off of the switch contacts and bend the movable contacts up a bit so that they press harder against the contacts on the housing. Then index the back to the housing, press (hard) and twist to re-engage the pins into their slots.

It's the key cylinder on the repros that isn't worth a Big Sh-- !!! I've not had any problems with the internals BUT you buy one of the "best" on the market back panel & be done with it !

Think its best to begin with the circumstances surrounding the backfiring event. It is a know problem that switching from bat to mag should be smooth and quick. If too slow unburnt gas fills the tail pipe and muffler and kaboom! Or your switch contacts may need cleaning and takes a bit for them to make full contact.
Check this discussion to see if anything applies to your driving habits
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As far as the switch being the problem.... A picture of the backing plat (no need to disassemble) would help diagnose the issue
I have rebuilt many switches too. There isn't much to them and in some cases the parts used in the repro switches are what are used to rebuild them.
The only parts available for a rebuild are the backing plates (pin or clip type). The repro locks are not a good fit but with some modification will work.
Mark as shown in his attachments a pin type backing plate and the internal parts. The inner ring is turned by the key to select the voltage choice for starting and driving while the outer ring is used to power the lights. So if you have an issue is with the inner ring and wiring to it. First how does the key feel when switching from Mag to Bat (does it seem to need a bit more effort to index it onto the brass contact?) Next you need to confirm that there are no loose or frayed wires. If all Okay then you need to do a continuity test on the inner screws when switching from MAG to BAT
The backing plate usually has wear marks/tracks or initial groves from the contact movement.
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The original backing plates were compressed paper & subject to warping --
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Reproductions have been made with different materials. This is a picture of the latest --
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Note that the switch parts are different thicknesses for Pin & Clip types --

I bought box of miscellaneous parts and I think there might be one in the mix. I will know in a few days when the box arrives here.

Scott C. wrote: ↑

Fri Aug 11, 2023 1:14 am

I bought box of miscellaneous parts and I think there might be one in the mix. I will know in a few days when the box arrives here.

Thanks Scott, appreciate it

With the screws removed from the back and the switch contacts polished, you can look in th screw hole to determine if the contact is centered on the terminal.

You do have to be sure the screws that hold the wires in place are not long enough to go through the contact area on the switch side.

Finding a good key cylinder is the hard part.

All the repros are .015 to .020 too large and cannot be turned down to the proper size.

I am still waiting on those parts to arrive. I will let you know when ever that happens.

As Scott pointed out the repro key cylinders have issues, but not only in diameter but with the end that is to be inserted into the small inner disk. The end's hump isn't symmetrical and overall requires fitting into the small inner disk. Now replacing the cylinder has its challenges and depends on how the key handle is fitted. The easy one is those handles that have tabs that are bent over the small inner disk ves the slotted type that have a flange the fits behind the switch plate face. These require removing the rivets holding the steel cup. - --
There were also different manufacturers of the rectangular ignition switch (Briggs & Stratton & Clum, etc) . Some Clum have their own style key cylinder. Original common style on the left, Clum on the right --
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Since you haven't provided pictures of your switch, front or back, its difficult to determine what you may need. Some "repro's" were just refurbished originals

RajoRacer wrote: ↑

Wed Aug 09, 2023 4:18 pm

Contact Ben Martin in Georgia - get on his list - it's worth the wait !

See the post on the forum before trying to contact Ben, he is not going to be doing anything for a few months nor from the sound of the post, taking calls.
https://www.mtfca.com/phpBB3/viewtopic.php?f=2&t=38152

I finally received that box of parts. Here are some pictures of that switch.

Scott C. wrote: ↑

Sat Sep 02, 2023 10:57 pm

I finally received that box of parts. Here are some pictures of that switch.
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Scott , that appears to be one of the less popular designs. Thy come apart quite easily. I need to check to see if the backing plate is standard, but the internal parts are not. Having said that,its likely that they don't need to be replaced. See if you can tell who made the backing plate. If its the CLUM (one on the right) they have a very nice internal design but all unique parts. I believe that the backing plate is unique (notice the thickess0 and don't match the repro backing plate contact positions. The tumbler is also different (bottom one). BUT its a really nice design & less likely to fail. It may just need to be taken apart, cleaned up and painted. It may require a CLUM branded key as well
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It probably is a Clum, it has that same triangle marking on the back. The tumbler looks good, I can get a key in it but, it does not turn. I sprayed some PB Blaster in it for now. The headlight switch does turn.

I got the tumbler turning with a 57 key. It locks the key in when turned to battery and mag. I got all the screws out and tested it with an ohm meter and all the contacts are making. It should be a good restorable switch.