Need help understanding starter problem

[Sam_Slaby]

The other day I drove for about an hour, parked and turned off the van for about 3 minutes, then went to restart the engine and it wouldn't start. Just a click. I banged on the starter 4 or 5 times with a metal water bottle and the thing started right up. Woo! Bought a reman the next day, installed without a hitch. Now when I try to start the engine the starter just spins and doesn't engage the flywheel. I pulled the starter back off, bench tested it off the battery and it seemed fully functional. The starter gear both spun and extended to engage the flywheel (with lots force I might add). I made sure the wire from solenoid to motor was tightly fastened, reinstalled the starter, and the same thing happens - the starter just whirrs but doesn't engage the flywheel at all.

What's going on here? Is this a mechanical issue (starter gear not engaging flywheel because of angle, shims, something i'm unaware of, etc) or is it an electrical issue?

[Burntboot]

The very first thing to do would be to verify that the starter you bought and installed is correct to the van.

Did you compare it to the old one to verify that the nose cone/gear travel is the same length?
And is the number of teeth on the drive gear the same as the old one?
Have you inspected the teeth on the starter (old and new) and ring gear?

[Sam_Slaby]

I compared the two starters visually and they appeared to be well and truly identical but I will check those finer details this afternoon and report back. The teeth on the flywheel looked good (none missing in the area visible and not even chewed up really)

[Jdelgado]

I would recommend replacing the starter contacts on the original one!

https://www.ebay.com/itm/141695813725

[Sam_Slaby]

Compared both starters and made some measurements. Both drive gears have 9 teeth and extend the same distance tho the new starter’s drive gear is about maybe 3/16” “shorter” if that makes sense. I put the old one back on the van and the engine started right up. I think I’ll take Jdelgado’s advice and just rebuild the original Denso.