Two different starters, one cheapo one from Flea Bay and then my old Bosch core rebuilt by a local pro. Usually ONLY on the first try, the helix doesnt engage the flywheel, it sort of crunches and then spins free. On 2nd or sometimes 3rd try , it engages properly and fires. ???

Before I put the car on ramps and take a gander, what the heck ought I be looking for?> tia...... I hate R&R starters without effect! This ol 606 fires instantly as well. Great compression, and glow system.