How far should the pinion gear engage the clutch shell/primary? Mine only engages about half way & its slipping off sometimes when I try to start it.

Now this seems strange because I cant make it go any farther, you'd think it would go more. The same pinion shaft worked fine a few years ago.

I have a el cheapo starter solenoid so maybe its not holding hard enough? BTW I'm now a firm believer in accel parts now.

 

There can be an issue with engagement.
However, you may actually have a worn starter drive clutch.

The engagement issue can be several things, including.......

Incorrect shimming behind the starter shaft main driver gear.
Poorly mounted solenoid.
Incorrect thrust washer.
Wrong collar.
Worn clutch basket bearing.
Worn ring gear.
Worn starter drive gear.

The flange on the "starter collar" should line up as best as possible with the outer face of the ring gear, with a thrust washer to suit, so that the starter clutch can engage as fully as possible.
This may the require re-shimming of the drive gear on the other end of the shaft.

If engagement has been poor, wear may be causing the issue now, whereas before the wear it was able to function despite the less than perfect fitment.

The starter clutch itself may have failed, giving the impression of "slipping".

If the clutch can be turned both ways, it is worn out.

Try turning it with varying pressure, and a jiggling motion. It should only go one way.

Good news. If it is the starter clutch, accel make one.

 

Pull the starter gear shaft, the last two sportsters I've worked on 76, 80 both showed your same problem. On inspection I found the starter gear shaft was snapped in two.As soon as pressure was applied it would chatter an spin never turning the engine over.

 

As a matter of fact I put a new starter drive clutch in it so that isnt slipping. With the primary cover off (& negitive bat disconnected) I pulled the pin holding the engagment arm off & pull the pinion gear all the way out & the gear will only engage half way. I can pull it farther out of course but it then pulls away from the starter gear.

This is strange.....one may think that the shaft was made wrong but it worked before. If the setup is right maybe the solenoid isnt holding it hard enough but that dosnt seem right either.

 

I already explained why it worked before.

 

The solenoid is not ruled out. Some things are likely, many things are possible.

 

True words there DynaMan, truth is you can guess all day but until its apart you'll never know for sure