Bump Switch

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Super-Cuda

MOPAR .. Move Over, Plymouth Approaching Rapidly!
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Hi guys,

I was wondering if any of the Electrical Guru's on here have a schematic for a bump switch I can build to help in turning over the engine when I want to set timing. I would prefer this over using a bar on the crank bolt to turn the engine over and I'd like to know how it works.
I'm assuming it connects across the ignition side of the starter solenoid , replacing the key circuit but not 100% sure. Dell? AJ/FormS ??
 
Between B and S

solenoid.jpg
 
Hi guys,

I was wondering if any of the Electrical Guru's on here have a schematic for a bump switch I can build to help in turning over the engine when I want to set timing. I would prefer this over using a bar on the crank bolt to turn the engine over and I'd like to know how it works.
I'm assuming it connects across the ignition side of the starter solenoid , replacing the key circuit but not 100% sure. Dell? AJ/FormS ??
I used to sell these. Not cheap though but nice and heavy duty.

SS55HDA.jpg
 
Then what TMM posted.
10 ga or 12 ga (same size or larger than the solenoid wire)
2 aligator clips with boots.
Any type of spring loaded switch.
 
This explains how start up works.
For bumping we really don't want the power to go to the ignition.
So leaving the key in off and using an external switch across the Bat and Sol terminals works well.


When the key is turned to start, here what happens:
Initially current flows through the key switch and wire S2 to the starter relay and back to ground (through NSS for automatics).
Whenever the distributor points are closed current flows through J3 to the coil, and back to ground.
upload_2021-2-19_14-12-54-png.png


Next, the energized relay closes the connection between Bat & Sol on the relay.
Current flows from the battery to the starter's solenoid..
upload_2021-2-19_14-17-39-png.png


Then starter will connect and draw power.
upload_2021-2-19_14-49-11-png.png


Current returns through the grounds.
 
Last edited:
Gee whiz, I thought ever'body knew about bump switches by now. Things get a little more inconvenient with the newer ones (pickups)---that use a plug in relay in the relay box, and "you can't get" to the starter itself
 
I built one out of an old door bell switch back yrs ago , worked ok .
the first car i had had a busted ignition switch

at first i just jammed a screwdriver in there and used that to start the car
but back then, i would get pulled over for speeding alot and the cops never took too kindly to my screwdriver key
so i ended up rewiring it and using a door bell switch as a push button starter
 
Gee whiz, I thought ever'body knew about bump switches by now. Things get a little more inconvenient with the newer ones (pickups)---that use a plug in relay in the relay box, and "you can't get" to the starter itself


Not all of us ! LOL !!

I just don't want to use one the wrong way and start burning out solenoids and starting motors. Better to ask the knowledgeable folks on here and be sure.
 
This explains how start up works.
For bumping we really don't want the power to go to the ignition.
So leaving the key in off and using an external switch across the Bat and Sol terminals works well.


When the key is turned to start, here what happens:
Initially current flows through the key switch and wire S2 to the starter relay and back to ground (through NSS for automatics).
Whenever the distributor points are closed current flows through J3 to the coil, and back to ground.
View attachment 1715700007

Next, the energized relay closes the connection between Bat & Sol on the relay.
Current flows from the battery to the starter's solenoid..
View attachment 1715700008

Then starter will connect and draw power.
View attachment 1715700009

Current returns through the grounds.


This is exactly what I wanted. Thanks Mattax !!
 
Not all of us ! LOL !!

I just don't want to use one the wrong way and start burning out solenoids and starting motors. Better to ask the knowledgeable folks on here and be sure.
A lot of racers mount one permanent to the firewall. They are always adjusting valves.
 
I’ve had the same Snap-On MT302 starter switch for the last 40 years. Still looks and works good. You could definitely build one cheaper than the new ones. Just make sure the switch you use is rated for enough current to run the starter motor. The new Snap-On switches are rated at 40A@12V, and that would be a good standard to work to. I sold dozens of these things of my truck when I was a dealer, and they were rock-solid. You could also get parts if someone tore one up. I’ve used a screwdriver too, just not a Snap-On. Sparks in the engine bay aren’t a good thing, however.
 
The best trick I saw lately was on a duster where the builder put a stationary bump switch on each side of the firewall near the hood hinges. Like what Mike said for lashing the valves. A bump button always within easy reach.
 
I’ve had the same Snap-On MT302 starter switch for the last 40 years. Still looks and works good. You could definitely build one cheaper than the new ones. Just make sure the switch you use is rated for enough current to run the starter motor. The new Snap-On switches are rated at 40A@12V, and that would be a good standard to work to. I sold dozens of these things of my truck when I was a dealer, and they were rock-solid. You could also get parts if someone tore one up. I’ve used a screwdriver too, just not a Snap-On. Sparks in the engine bay aren’t a good thing, however.
"Just not a Snap on one" :rofl: That's why you keep an old Craftsman around. For a chisel, scraper, and pry bar also. LOL
 
I had a "friend" once use one of my snap on combination wrenches to tighten the positive lead on a GM starter without disconnecting the battery first. :mad: That snap on steel sprays like nothing else I've ever seen when it becomes the hot link in a short circuit... No wonder Strap-On gives away stickers that advise against loaning them. :BangHead:
 
Not all of us ! LOL !!

I just don't want to use one the wrong way and start burning out solenoids and starting motors. Better to ask the knowledgeable folks on here and be sure.

i remember being a young buck and putting new points in my dirtbike (which at the time was my only means of transportation)
im not sure how i managed to do this, but when i pulled of the flywheel and dropped the key
of course im working outside and that key was gone forever

of course, its a friday night and i lived out in a small town so i was out of luck
but, this is a dirtbike were working on, not a spacerocket so i figured, i can eyeball it

so after i replaced the points and gapped them properly, i put the flywheel on and trying to hold the crank on the right spot i put the nut back on hoping i was close enough

button it all back up, i jump on the kickstarter and boy did she fire right up
it sounded awesome, crisp, like a brand new dirtbike
so needless to say, im feeling pretty good about myself, and with it being friday nite and me getting thirsty, i pointed the bike towards the local watering hole, kicked her in first, popped the clutch and went over the handlebars flat on my face as my bike shot out from underneath me...backwards

i guess i was off just a little on the flywheel and got the timing so far advanced that it sparked too early in the compression stroke, it ignited and kicked it backwards
once it was running backwards it ran fine

you should have seen the looks on the guys faces as i showed up driving backwards on my dirtbike
 
Momentary right?
Yea if you're looking to buy one that would be the easiest.
OP said something about making with what he had so I wrote spring loaded.

of course that's not a crucial, just be quick and skilled enough to open it fast
raw.gif
 
I've got a nice old school Bump start that was my Dad's that he used in the Fiftys. I have to get a pic of it. Has about a 5' cord so you can get to the far valve cover for Valve adjustment.
 
I've got a nice old school Bump start that was my Dad's that he used in the Fiftys. I have to get a pic of it. Has about a 5' cord so you can get to the far valve cover for Valve adjustment.

all being said , i still prefer to roll it by hand , 1 1/14'' socket and an 18'' ratchet .
AINT HARD ON UR STARTER AND RING GEAR EITHER !
 
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