ACMOC
Login | Register
ACMOC
8T with mag problems MJK MAG

8T with mag problems MJK MAG

Showing 1 to 10 of 16 results
1
oldbeek
Topic Author
Offline
Member
Send a private message to oldbeek
Posts: 781
Thank you received: 0
Cant get any spark out of my mag. Just finished a job and drove it home. Got there and found my fuel tower bleeder had come open. Fuel everywhere on my machine. Next day I move it into an area to clean it up. Washed. it down all over (hadn't been cleaned in a while). Just used high pressure water hose. Went to start it and guess what. Pony spins (12 Volt elect ) great. Wont start. Has been starting fine. Check for spark. NONE. Hmm?   water in mag? open mag and sure enough moisture. Stick paper towel in it leave it open all night. Should start. This morning put cap back on still no spark. Go to basics. Put a screw driver on coil output tang and look for spark at coil output. None. That bypasses rotor. See sparking at points. ???  Pulled it and was going to tear it down to dry it. Can't get the rotor off. Cant see a retainer. Any help there? Any suggestions at all?
Please log in or create an account to join the conversation.
Fri, Nov 5, 2021 6:54 AM
edb
Offline
Member
Send a private message to edb
Posts: 4,027
Thank you received: 0
Hi OB,
if the points and innards appear dry then maybe disconnect the magneto kill switch and see what you get--if the switch has water in it it will likely be shorted to ground resulting in zero spark.
High Pressure washers and water in general should be kept away from electrical devices.
Cheers,
Eddie B.
Please log in or create an account to join the conversation.
Fri, Nov 5, 2021 10:42 AM
oldbeek
Topic Author
Offline
Member
Send a private message to oldbeek
Posts: 781
Thank you received: 0
Reply to edb:
Hi OB,
if the points and innards appear dry then maybe disconnect the magneto kill switch and see what you get--if the switch has water in it it will likely be shorted to ground resulting in zero spark.
High Pressure washers and water in general should be kept away from electrical devices.
Cheers,
Eddie B.
Dont even have a kill switch or wire on the mag. Use the fuel shut off. It does put out enough spark to shock me but not enough to jump a .010 gap. Coil?
Please log in or create an account to join the conversation.
Fri, Nov 5, 2021 11:27 AM
Old Magnet
Offline
Send a private message to Old Magnet
Posts: 16,666
Thank you received: 0
Reply to oldbeek:
Dont even have a kill switch or wire on the mag. Use the fuel shut off. It does put out enough spark to shock me but not enough to jump a .010 gap. Coil?
Check resistance of the secondary coil winding. Should be approximately 6200 ohms.
Also try cleaning/filing the points.
Please log in or create an account to join the conversation.
Fri, Nov 5, 2021 12:00 PM
oldbeek
Topic Author
Offline
Member
Send a private message to oldbeek
Posts: 781
Thank you received: 0
Reply to Old Magnet:
Check resistance of the secondary coil winding. Should be approximately 6200 ohms.
Also try cleaning/filing the points.
OK 6300 ohms resistance for an instant then a open circuit. Ordering new coil.  BUT< Still need help. Is my rotor just stuck tight Or is there some kind of a keeper on the shaft? Dont want to pry to hard on it. Already tried screw driver from each side prying up, but don't want to break anything. Parts book illustration does not show a keeper. Going to hit it with liquid wrench and let it soak. 
Please log in or create an account to join the conversation.
Sat, Nov 6, 2021 2:08 AM
Old Magnet
Offline
Send a private message to Old Magnet
Posts: 16,666
Thank you received: 0
Reply to oldbeek:
OK 6300 ohms resistance for an instant then a open circuit. Ordering new coil.  BUT< Still need help. Is my rotor just stuck tight Or is there some kind of a keeper on the shaft? Dont want to pry to hard on it. Already tried screw driver from each side prying up, but don't want to break anything. Parts book illustration does not show a keeper. Going to hit it with liquid wrench and let it soak. 
There is no retainer or keeper used. Just a snug male/female fit of the mounting shaft that is about 1/2" long. Has to come straight out as it is keyed so that it does not rotate in the gear coupling. Good candidate for rust if some lube or antiseize is not used.
Please log in or create an account to join the conversation.
Sat, Nov 6, 2021 6:41 AM
rax200
Offline
Member
Send a private message to rax200
Posts: 823
Thank you received: 0
Reply to Old Magnet:
There is no retainer or keeper used. Just a snug male/female fit of the mounting shaft that is about 1/2" long. Has to come straight out as it is keyed so that it does not rotate in the gear coupling. Good candidate for rust if some lube or antiseize is not used.
Hi oldbeek,
To change the coil you do not have to remove the rotor, just remove the gear the housing (opposite end to the cap) and undo the 2 screwsthat hold it in , these may be hard to undo, for mine I heated the housing around the screws (had to do several times) with a low heat and eventually they came loose. On installation I put antiseze on the screws before installation, now it works great.

Regards
Please log in or create an account to join the conversation.
Sat, Nov 6, 2021 7:42 AM
edb
Offline
Member
Send a private message to edb
Posts: 4,027
Thank you received: 0
Reply to rax200:
Hi oldbeek,
To change the coil you do not have to remove the rotor, just remove the gear the housing (opposite end to the cap) and undo the 2 screwsthat hold it in , these may be hard to undo, for mine I heated the housing around the screws (had to do several times) with a low heat and eventually they came loose. On installation I put antiseze on the screws before installation, now it works great.

Regards
Hi Team,
courtesy of Old Croak Magneto is a link to a Bosch MJK Service Manual.

https://oldcroak.com/mjk-ed-a-b-c-service-manual/

Hope this helps.
Cheers,
Eddie B.
Please log in or create an account to join the conversation.
Sat, Nov 6, 2021 9:48 AM
oldbeek
Topic Author
Offline
Member
Send a private message to oldbeek
Posts: 781
Thank you received: 0
Reply to rax200:
Hi oldbeek,
To change the coil you do not have to remove the rotor, just remove the gear the housing (opposite end to the cap) and undo the 2 screwsthat hold it in , these may be hard to undo, for mine I heated the housing around the screws (had to do several times) with a low heat and eventually they came loose. On installation I put antiseze on the screws before installation, now it works great.

Regards
I figured that out. not worrying  about the rotor any more. I am starting to realize I have been through this all before. This same mag gave me fits about 3 years ago. I remember having it on a magneto test bench and it magically started sparking perfectly, so I put it back on. Ordered a new coil this time. Thanks for all your help.
Please log in or create an account to join the conversation.
Sat, Nov 6, 2021 2:09 PM
oldbeek
Topic Author
Offline
Member
Send a private message to oldbeek
Posts: 781
Thank you received: 0
Reply to oldbeek:
I figured that out. not worrying  about the rotor any more. I am starting to realize I have been through this all before. This same mag gave me fits about 3 years ago. I remember having it on a magneto test bench and it magically started sparking perfectly, so I put it back on. Ordered a new coil this time. Thanks for all your help.
While working on the mag problem, I spun the engine over and the mag drive gear got moved. Now I have a timing problem. Got the mag back on close. The pony runs ok till I engage the engine. Pony just slows down and sometimes quits even after I remove the load. Think I have it off time and retarded one tooth. Any thoughts? Advance one tooth and it would back fire through carb I think. Only been doing this stuff for 65 years but my brain is failing me.
Please log in or create an account to join the conversation.
Wed, Nov 17, 2021 1:47 PM
kittyman1
Offline
Send a private message to kittyman1
Posts: 577
Thank you received: 0
Reply to oldbeek:
While working on the mag problem, I spun the engine over and the mag drive gear got moved. Now I have a timing problem. Got the mag back on close. The pony runs ok till I engage the engine. Pony just slows down and sometimes quits even after I remove the load. Think I have it off time and retarded one tooth. Any thoughts? Advance one tooth and it would back fire through carb I think. Only been doing this stuff for 65 years but my brain is failing me.
Oldbeek: my experience with gasoline engines, backfiring back thru the carb is too lean of fuel mixture 90+% of the time....double check you have proper flow supply to carb...and carb passages are clean etc...

-if timing is overly advanced, starting will be difficult, engine unresponsive and generally not happy, of course, the spark is igniting the fuel mixture too soon...
-if timing is too late, engine will be sluggish as well, and the exhaust system tends to be very hot, as the fire is lit too late and is still burning in the manifold, muffler etc....
-have a close look at the plugs, they tell a story if you read them..
Please log in or create an account to join the conversation.
Thu, Nov 18, 2021 4:04 AM
  • Add an image

  • Showing 1 to 10 of 16 results
    1
    YouTube Video Placeholder

    Follow Us on Social Media

    Our channel highlights machines from the earliest Holt and Best track-type tractors, equipment from the start of Caterpillar in 1925, up to units built in the mid-1960s.

    Upcoming Events

    KORUMBURRA WORKING HORSE & TRACTOR & 100 YEARS OF CAT RALLY

    Chapter Nineteen

    | 5875 STH GIPPSLAND HWY, NYORA

    Booleroo 2025

    Chapter Thirty

    | Booleroo Centre, 54 Arthur St, Booleroo Centre SA 5482, Australia

    CAFES 2025 TULARE, CALIFORNIA

    Chapter Fifteen

    | Tulare, California

    Wheatlands Warracknabeal Easter Rally

    Chapter Nineteen

    | 34 Henty Hwy, Warracknabeal
    View Calendar
    ACMOC

    Antique Caterpillar
    Machinery Owners Club

    1115 Madison St NE # 1117
    Salem, OR 97301

    [email protected]

    Terms & Privacy
    Website developed by AdCo

    Testimonials

    "I also joined a year ago. had been on here a couple of times as a non-member and found the info very helpful so I got a one year subscription (not very expensive at all) to try it out. I really like all the resources on here so I just got a three year. I think its a very small price for what you can get out of this site."
    -Jason N

    Join Today!