48 Cub Magneto Timing Help?!

Thu Oct 03, 2013 11:32 am

Hey all,

I am trying to get my 48 Cub going for the first time that I recently acquired, anyways, after having a rebuilt magneto sent to me and trying to time it to the enginr I accidentally broke the plastic rotor piece, (the rookie mechanic that I am...) I replaced it with my old magneto rotor and I don't know how to make sure its properly aligned with the distributor coupling on the back.... I am having trouble time it to the engine now and I imagine that is causing the error, anyone got ideas?

Thanks for the help

Re: 48 Cub Magneto Timing Help?!

Thu Oct 03, 2013 11:46 am

G'day to you and congrats :applause: on acquiring that '48 Cub and your 1st new to you Cub. Be careful they are addictive and they kinda multiply.

These articles should help you with your timing issue:

  1. How To TIme A Magneto - Method #1
  2. How To Time A Magneto - Method #2
  3. How To Understand Firing Order
  4. How to time a Magneto-Equipped Cub...film at 11:00


Also, in the GSS-1007 - Engine Blue Ribbon Service Manual:

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and the GSS-1012 Electrical Equipment Blue Ribbon Service Manual - pages 4-7.,,,

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I strongly recommend that all new members should follow the links below to access the immense amount of information that we have available for our members.

Image to Farmallcub.com :big smile: Forum Family. And you have come to the right place for all things Cub related. If you click on the Site Rules, Regulations, & Important Information, it will point you to :arrow: the Welcome Wagon wherein you will find links to many useful sites and topics. One of the most important resources are Owner's Manuals, Parts Catalogs and Service Manuals. The Cub Manual Server is the home of the jpg versions and the PDF Manuals -- well the pdf's of course :wink: Enjoy!.

Re: 48 Cub Magneto Timing Help?!

Thu Oct 03, 2013 3:33 pm

Also, the plastic rotor times to the (plastic or metal) pinion. The rotor has a cast scribe line down one side, and the pinion has a cast dot or triangle. Those two marks MUST line up; the pinion only goes on the shaft one way. That gets all INTERNAL timing correct in the magneto; after that, time it to the engine using one of the methods Rudi pointed you to.

Re: 48 Cub Magneto Timing Help?!

Thu Oct 03, 2013 8:58 pm

I imagine that your governor is assembled correctly. I found Hengy's youtube video very easy to follow.
Dave

Re: 48 Cub Magneto Timing Help?!

Fri Oct 04, 2013 12:05 am

I watched the video by Hengy, that is a pretty good one. I know understand how to get the magneto to trip over before tightening down all the way, I was trying to pull it out the wrong way but the bracket that attaches it to the engine block now makes much more sense for how to do that trick! Tomorrow I will check on the pinion to the rotor, that is probably not aligned as I didn't know how to before.

Re: 48 Cub Magneto Timing Help?!

Fri Oct 04, 2013 1:41 pm

Ok, I am almost positive the magneto is timed to the engine now! I got her to fire up, by hand cranking, the engine ran by itself for about 20 seconds then died. There is electronic starter on there however I need to replace some wires I think before I try to use it. Should I be able to start it up fine with just the crank? I tried hand cranking again after the first time she ran with no luck, just 3 or 4 quick puffs but it won't take off. (This is the first time I think the tractor has been fired up in at least 5 years, maybe more...) I got a new carb installed and the fuel is making it to the engine as far as I understand, I closed the carb and then opened it a bit after a couple cranks, throttle is at 1/3, gear should be in neutral, now I am not sure what to try next any ideas?

Re: 48 Cub Magneto Timing Help?!

Fri Oct 04, 2013 2:36 pm

Starting with the crank is just fine. Did you choke it when you tried to restart it?

Re: 48 Cub Magneto Timing Help?!

Fri Oct 04, 2013 2:53 pm

I am not exactly sure which direction is open or closed. (carb is a new zenith) I imagine it is open when it is just sitting without the choke rod pulled out?

Re: 48 Cub Magneto Timing Help?!

Fri Oct 04, 2013 3:02 pm

Since engine ran. Check for spark from coil wire to ground. Check that the impulse coupling snaps when the mark on the pulley matches the pointer.

Roll engine over until pulley mark lines up with pointer. Remove distributor cap and see if rotor still points to either #1 or #4 spark plug wire location on distributor cap. Check condition of rotor and distributor cap.

Magneto kill switch get shut off? Disconnect kill switch wire from side of magneto.

Did you prime the oil pump? Conduct compression tests?

More thoughts and suggestions to follow.

Choke position. Remove the air cleaner hose to carburetor. Pull choke lever and look into carburetor throat. Choke plate should be closed. Then push in the choke lever and check again. Choke plate should be open.

Re: 48 Cub Magneto Timing Help?!

Fri Oct 04, 2013 7:16 pm

I followed through your entire list Eugene except for the oil pump priming and coil wire spark to ground. How do you do both of those? The original manual mentions nothing about an oil pump that I can see...

Re: 48 Cub Magneto Timing Help?!

Fri Oct 04, 2013 7:27 pm

farmergiffIV wrote:I followed through your entire list Eugene except for the oil pump priming and coil wire spark to ground. How do you do both of those?
Priming the oil pump - needs to be done on engines that have sat a long time, before engine start up. Remove oil filter cap. Inside oil filter housing, about an inch down towards the front is an opening. Install about 1/2 to 1 cup of engine oil in the opening. Then cranking over engine with out starting, observer oil being pumped out of the opening.

Coil wire. Simple remove the spark plug wire from the center of the distributor cap. Locate the end of this plug wire about 1/4 inch from engine block. When you crank over the engine, with kill switch in on position, you will see a nice blue spark as you rotate the engine.

Compression test results were?

Re: 48 Cub Magneto Timing Help?!

Fri Oct 04, 2013 9:35 pm

Primed with oil, put a couple drops of sea foam down each spark plug hole, and double checked magneto, she fired up no problem I ran it for 5 minutes or so. I probably primed too much oil as some spewed out through the exhaust all over...

Re: 48 Cub Magneto Timing Help?!

Fri Oct 04, 2013 9:42 pm

farmergiffIV wrote:she fired up no problem I ran it for 5 minutes or so. I probably primed too much oil as some spewed out through the exhaust all over...
Sound normal. Engine will expel the oil.

First time I fired up my Cub's engine, been sitting for many years, I got showered with hazle nuts then oily soot.

Re: 48 Cub Magneto Timing Help?!

Fri Oct 04, 2013 9:59 pm

Eugene wrote:
farmergiffIV wrote:she fired up no problem I ran it for 5 minutes or so. I probably primed too much oil as some spewed out through the exhaust all over...
Sound normal. Engine will expel the oil.

First time I fired up my Cub's engine, been sitting for many years, I got showered with hazle nuts then oily soot.


Ok, phew! I thought I messed something up but I was pretty stoked to see the engine running well! Thanks for the help :{_}: