I have top mount starters and 1 out of 5 times it doesn`t like to engage.. just spins but doesn`t grab the flywheel.
It did this last year with a stock starter, now its doing it with a brand new IMI hi tq starter. I cleaned up the flywheel teeth.. took off some material of the flange of the starter to bring it closer to the flywheel for better engagement .. that helped a bit but it still troublesome... any ideas?

Voltage issues? Sounds like bendix is not fully engaging and that can be caused by voltage or ground

I would like to help with your issues but I can only see both your Avatars!

dan,did you change anything other than the starters?

Ive had the same issue with my tractor it was a bad ground, not sure but worth a look

I think that could be it, I was having issues getting the fuel pump to build pressure (everything was dry) so I kept cranking the motor over and possibly the battery voltage was getting low...s

thanx guys I`ll see what a full charge will do..

I had a problem just like this that was very hard to find problem! I did new starters,custom starter brackets,pulled motor,shims,flywheel,new batterys,new wiring ect ect.... The problem for me was the starter was engaging but the clutch in the starters where not strong enough to keep the starter engaged it would kick back off flywheel. And to the ear it happens so fast it sounds just like its missing the flywheel from the start. And mine would be fine like yours for 8-10 times. But the time the motor was just right on compression stoke the starter would kick out.... ZZZINGGGGGG So most all high tq starters use the same clutch. (This i did not know) I found a place that puts a HD clutch on starters for like high compression Harley guys have the same problem. After he put HD clutch in my so called high tq starter. It has been two years PREFECT!!!!! I finally have confidence when i turn key i will not sound like a fool!! It took two years to get that back.

TY Skydog

I played with this issue for a few hours today , it seems the throw on the IMI starters isn`t long enough. The contact of the starter gears on the flywheel is only at most .18

The original GM starter has a contact pattern of .40.. and that starter works every time.

So back to IMI for them to modify the throw of the starters, not real impressed with these IMI starters.
This is the second time going back.. one of the would not retract.