Cub Magneto Timing

Farmall Cub Forum -- Questions and answers to all of your Cub related issues.

Moderator: Team Cub

Forum rules
Notice: For sale and wanted posts are not allowed in this forum. Please use our free classifieds or one of our site sponsors for your tractor and parts needs.

Cub Magneto Timing

Postby John Wilkinson » Wed Feb 19, 2014 9:40 pm

Oh, boy. I'll try to be brief, as maybe what I'm fighting is well known out here amongst the Cub cognoscenti. When I first looked at timing my new-to-me Cub, I noticed that the magneto was advanced as far as it could be (turned clockwise all the way, from the distributor cap end view). The impulse couple snaps at about 8 degrees after TDC. I can, of course further retard the impulse, up to maybe 30 degrees after TDC, but the manual wants TDC. After carefully going through the procedure in the manual several times I was unable to get any better than the 8 degrees after TDC. I usually expect a rotational adjustment of this sort to be about in the middle of its range of motion when it's "on" the spec... not pegged. Since I can't even get to the spec, I'm wondering if the magneto-governor drive gear is off by a tooth. I suppose that it might be possible to get to this condition due to excessive wear, but that would be one heck of a lot of wear to my thinking. But you see where my best thinking has gotten me... BTW, I'm trying to deal with a no-start situation. Carb/fueling seems to be right on specs, and I do get good spark. The magneto was a bit dirty and I cleaned it with kerosene per instructions. I have seen this tractor run, and I drove it before I bought it. It seemed to have plenty of power then... Any ideas, anyone? Thanks a bunch!
John Wilkinson
 
Posts: 7
Joined: Sun Feb 10, 2013 2:40 pm
Zip Code: 49445

Re: Cub Magneto Timing

Postby Rick Spivey » Wed Feb 19, 2014 9:49 pm

Something is wrong in the way your magneto is aligned. Either the governor was installed a tooth or three off, or the rotor and pinion are off. Since the issue is noticeable in the impulse coupling, it points to the governor being off. When mag is removed, the two drive slots in the governor gear should be at approximately 2:00 and 8:00 positions as viewed from the driver seat. If not, you need to remove and reinstall governor. There are timing dots on the teeth, but hard to see with mag seal installed. Also uses helical gears, so you have to guess where to start in order to end up in the right place. You should be closer to the middle of your range of movement when the impulse snaps.

Also, make sure that your pulley has only one notch that lines up with the pointer at TDC; if two slots, you should be using the second one as TDC.
Rick Spivey
'52 Cub ("Great Personality") 148xxx
'48 Cub with FH ("Gunny Cub") 38xxx
'57 Lambretta (a slow work in progress)
'74 Triumph TR6 (Mama's toy)
User avatar
Rick Spivey
Cub Pro
Cub Pro
 
Posts: 1738
Joined: Sun Jul 01, 2007 10:07 pm
Location: SC, Simpsonville 29681
Zip Code: 29681
Circle of Safety Award
Circle of Safety: Y

Re: Cub Magneto Timing

Postby Eugene » Wed Feb 19, 2014 10:03 pm

John Wilkinson wrote:I'm wondering if the magneto-governor drive gear is off by a tooth.
Quite possible since one idler tooth represents 10 crankshaft degrees.

Rotate engine to TDC #1 cylinder and remove the magneto. The magneto drive slot should be around 2 and 8 o'clock.
I have an excuse. CRS.
Eugene
Team Cub Mentor
Team Cub Mentor
 
Posts: 12512
Joined: Fri Jul 02, 2004 9:52 pm
Location: Mo. Linn
Zip Code: 65051
Circle of Safety Award
Circle of Safety: Y

Re: Cub Magneto Timing

Postby John *.?-!.* cub owner » Thu Feb 20, 2014 9:40 am

John, several years ago i bought a cub from a long time owner that had supposedly been overhauled. The shop told him his magneto was bad, among other things, and sold him a distributor. since it was all original other than that and the carb. I decided to put a magneto back on it and ran into the same problem. I fought it over an hour before I realized what the problem had to be. There is an idler gear that runs on the crankshaft and turns the governor which drives the magneto. Both the idler gear and governor gear have to be timed to the crankshaft to get the magneto to trip at the right point, and they had mine a tooth off. You can verify if this is your problem by comparing your engine with this picture. The drive slot should be at this angle anytime the TDC pointer is lined up. If not the gears are not timed right.
Image

If it is not at this angle, you will have to retime the gears. You can with a little work remove only the governor and turn it one tooth and reinstall, but that may take a little trial and error. To time it by the marks the front end assembly has to be removed, the crankshaft pulley removed (requires a special puller), and the cover removed. Due to the differences in the way they are designed, you can replace the magneto with a distributor and not have to retime the gears if you prefer going that route.
"The Constitution is not an instrument for the government
to restrain the people, it is an instrument for the people to restrain the
government lest it come to dominate our lives and interests." Patrick Henry
User avatar
John *.?-!.* cub owner
Team Cub Guide
Team Cub Guide
 
Posts: 19457
Joined: Sun Feb 02, 2003 2:09 pm
Location: Mo, Potosi
Zip Code: 63664
Tractors Owned: 47, 48, 49 cub plus Wagner loader & other attachments. 41 Farmall H.

Re: Cub Magneto Timing

Postby John Wilkinson » Thu Feb 20, 2014 11:22 am

Yeah, my magneto drive is not where it should be, much as I suspected--and feared! The notion of going in through the governor has a lot more appeal than pulling the crank pulley, timing cover, &ct. This option was not apparent from looking through my manual. So... I'll start there at the governor and see how it goes. I'll post the results, bloody knuckles or no, and hopefully without have to (delete explicatives). Thanks to all.
John Wilkinson
 
Posts: 7
Joined: Sun Feb 10, 2013 2:40 pm
Zip Code: 49445

Re: Cub Magneto Timing

Postby John Wilkinson » Thu Feb 20, 2014 11:24 am

Oh, and special thanks for the photo and Patrick Henry!
John Wilkinson
 
Posts: 7
Joined: Sun Feb 10, 2013 2:40 pm
Zip Code: 49445

Re: Cub Magneto Timing

Postby Hengy » Thu Feb 20, 2014 1:48 pm

Changing the governor timing is not that difficult, but can be time-consuming. If you remove the pin that holds the carburetor reach rod, two bolts that hold the rockshaft on the tractors left side, then remove the two bolts that hold the actual governor. This should allow you enough play to be able to pull the governor out from the engine block enough to adjust the position of the drive slot. Your block should have a punch mark on it just like the one in John's picture above (it is at about 2:00 on the round housing). This will allow you to be able to do it without seeing the punch marks on the gears inside. Just make sure that your engine is on TDC #1 cylinder first!! Once you get it all lined up, install all the bolts you removed, then make sure that the carburetor rod is adjusted properly and you should be good to go on the mag timing.
Mike (Happy as a Lark in Allison Park, PA)
Image Image

Check out my Restoration Thread (1955 Cub, Lewis)
User avatar
Hengy
5+ Years
5+ Years
 
Posts: 7073
Joined: Sat Feb 18, 2006 8:12 pm
Location: PA, Allison Park (Am Hengelsberg)
Zip Code: 15101
eBay ID: lacrosseorgans
Skype Name: Mike.Hengelsberg
Tractors Owned: 1949 Cub "Merlin"
1955 Cub "Lewis"
Cub Trailer
A-60 Blade
Cub-22 Mower
193 Plow
Circle of Safety Award
Circle of Safety: Y

Re: Cub Magneto Timing

Postby John Wilkinson » Thu Feb 20, 2014 3:10 pm

Okay! Fifteen minutes, and I got to position on my fourth try--had to figure out the helical gear "offset" as the governor housing slid in. No bleeding, and no explicatives need be deleted. You guys are great! Thanks.
John Wilkinson
 
Posts: 7
Joined: Sun Feb 10, 2013 2:40 pm
Zip Code: 49445

Re: Cub Magneto Timing

Postby Hengy » Thu Feb 20, 2014 3:45 pm

That is STRONG WORK, John W! Congrats! Does the mag now trip as it should??
Mike (Happy as a Lark in Allison Park, PA)
Image Image

Check out my Restoration Thread (1955 Cub, Lewis)
User avatar
Hengy
5+ Years
5+ Years
 
Posts: 7073
Joined: Sat Feb 18, 2006 8:12 pm
Location: PA, Allison Park (Am Hengelsberg)
Zip Code: 15101
eBay ID: lacrosseorgans
Skype Name: Mike.Hengelsberg
Tractors Owned: 1949 Cub "Merlin"
1955 Cub "Lewis"
Cub Trailer
A-60 Blade
Cub-22 Mower
193 Plow
Circle of Safety Award
Circle of Safety: Y

Re: Cub Magneto Timing

Postby Bill Hudson » Thu Feb 20, 2014 4:51 pm

John Wilkinson wrote:Okay! Fifteen minutes, and I got to position on my fourth try--had to figure out the helical gear "offset" as the governor housing slid in. No bleeding, and no explicatives need be deleted. You guys are great! Thanks.


John,

You lead a charmed life!

Bill
"The probability of life originating from accident is comparable to the probability of the unabridged dictionary resulting from an explosion in a printing shop." Edwin Conklin, biologist
Bill Hudson
Team Cub
Team Cub
 
Posts: 6387
Joined: Wed Jul 26, 2006 10:50 am
Location: OH, Madison
Zip Code: 44057
Tractors Owned: :
57 F-Cub
64 Lo-Boy
68 Lo-Boy
52 F-Cub
Circle of Safety Award
Circle of Safety: Y


Return to Farmall Cub

Who is online

Users browsing this forum: Baidu Spider [2.0] and 7 guests