Starter just free spins

[DaKing]

1987 Jeep MJ with complete 1991 XJ running gear

Jeep drove great, with exception of starting. It would have to crank for about 5 to 8 sec before starting. There was a clacking sound too as cranking, but not as running (I was thinking low fuel pressure, reads 39psi)

Starter finally failed, just fee spins, does not engage. (bad solenoid?)

Buy new starter, same results. Just spins, never engages the flex-plate gears.

New starter bad too?

Also, it has a new flex plate, less then month old, less then 30 starts. So I doubt broken teeth.

Jeep is not near me, I have no visual on it at this time.

Any ideas on what too look for?

 

[Hypoid]

Check the bell housing to block bolts.

 

[8Mud]

Check the bell housing to block bolts.

That would be my first guess also.

Other possibilities, the starter relay is full of rust and it isn't passing enough amps to properly work the solenoid. The starter relay to solenoid wire is fried, heat damaged or frayed. The ring on the end of the solenoid wire is frayed. It takes some relatively high amps to work the solenoid, voltage isn't everything. You can jump the solenoid wire at the starter relay for a test. Do you have the Renix electrical or the post 90 electrical?

Just a remote possibility your starter sits a little wrong, bolt holes drilled a little off or the diameter of your ring gear is a little off. You can test this quick by loosening the bolts off a *little* and pulling the starter away from the block. Be careful not to put your hand between the started and the block as it may try to pinch it when you crank it over. You can actually shim the starter so the drive gear engages deeper into the ring gear (pretty common with Chev starters, not so much with Jeep starters).

Unlikely on two starters, but if the rubber cover for the solenoid piston gets torn, the piston can rust and get sticky.

If your overrunning clutch fails it will also cause it to turn without driving the drive gear. A possibility with a rebuilt starter. The overrunning clutch rarely fails and a re-builder may not have tested it. Unlikely for both starters to have a failed overrunning clutch.

Best guess is starter bolts or something with the solenoid wire.

Trying to jump the battery to add a little more juice for the whole starting process may also tell you something. Low voltage may also be an issue? Clean your battery posts shiny clean, make sure your cables are good.

 

[DaKing]

Thanks for both of your ideas! I never thought about the bolts, I'll check em.

I'm driving there tomorrow to inspect.

 

[DaKing]

Well, turns out the teeth on the flexplate have been chewed up. This is a new flex-plate, less then 30 starts, installed just weeks earlier. Not sure how the teeth on the plate got damaged. I'll post a picture shortly.

Engine and trans are tight and aligned. Starter was tight an correctly installed. The original starter teeth look good.

This is frustrating because weeks earlier I had a rebuilt transmission installed. They failed to notice the cracked flex-plate. So, a week later, we dropped the Transmission to replace the flex plate. And, YET AGAIN, the transmission will need to be pulled to replace this flex plate. So 3 times in just as many months I've had to pull the Trans! Its a real F'n pain to pull. Long arm mount supports the transmission...

 

[DaKing]

 

[Kingkong0192]

OP, put a 3/4" socket on the crank bolt in the front of the engine, and try to manually turn the motor over. See if it's locked up or hard to move.

Looking at that picture you just posted that bolt head i see in the picture is alarming. I have no idea what it's for or why it's there. Unless it's different on an MJ those outer bolts should be facing the other way, holding the torque converter in place.