1/2 Bad--1/2 Good ????
 

After reading many questions on S/G, they all seem to be on the generator/charging side of things. I have a problem with the starter side on a early 100. When I get it started, it will charge and the battery shows 13.3 volts. I can put a jump box on it, and it will not turn the engine over. When I jump it off a tractor with a full size 12 battery, it only hums. When I hook the starter/charger from the shop up, it spins the starter fairly fast and starts. The belt is new, tight,and running straight. I have a new pulley on also. Should i have the thing checked at the electric shop? What else am i missing? Is it possible, the generator part is good and the starter is bad? Thank you for any help,I 'm about ready to push the thing over a cliff.

Sounds like a bad connection with your jumper cables, or possibly very worn brushes. Check all your connections, especially your grounds on the frame.

Check your ground-it could be a ground issue.
I ran a 6 or 8 gauge ground wire from the negative direct to the back bolt of the starter-generator. It helps.

Does it try to turn the engine over (half revolution)?

I have an early numbered 100. The cam shaft does not have a compression release from the factory. It would turn the engine over a half revolution if you were lucky. I replace the cam with a cam that has a compression release built on it.

Loosen the spark plug a 1/4 turn and try starting it. If it spins over easier you have a non compression release cam.

What is the serial number of your 100?

Thanks for the help.I will try the plug idea next week when i get home.I can get the ser#-the man i bought it from said they bought it in October of 1963.I will report back what i find.Thanks for the quick reply.

If that's true, it is a very early one indeed! :bigeyes:

Do the 100's have a compression "release"?

The engines without the compression release have a smaller pulley on the S/G to help overcome the compression. Maybe yours has the larger pulley the later Cubs used and the starter just doesn't have enough torque.

My 100 (serial number 89462-June 1964) did not have a compression release. It also had a big pulley on the starter. I'm not sure it has the original starter because the back cover does not have a bearing in the housing. The cam was replace with a cam that has a compression release on it.

My 100 (serial number 110216-February 1965) has a compression release. It also had a big pulley on the starter.

My 70 (serial number-113360-March 1965) has a small pulley.

Do any of the 7 hp engines have a compression release?

I don't remember.......I rebuilt the engine in my 70. Been too long ago.