Can starter motor have "flat spots"?

[JC220]

Hi all,

I have an issue on my 1995 S500 which I never got to the bottom of. Background summary:

Car came to me with a seized engine. It also had a new starter motor installed. New as in aftermarket/ aftermarket rebuild not sure which.

I then got another good used m119 and gave it a full refresh. Timing chain etc is all new and correctly set.

The problem can be heard in this older video of mine. Go to starter motor sound at 53 seconds mark for an example:

On almost every startup there is a momentary pause/ hesitation in the startup of the car. I have tried so many different things before and all is good on this car. Ignition system is new etc. Crank sensor and EZL replaced and no difference either. It still does it.

What I want to ask is if anyone has experienced issues like this with the Starter motor itself. Remember this car had a seized engine and I swapped all ancillaries. I bet the PO burned out the original starter then fitted a reman unit and even though it works I wonder could it have been damaged in such a way that it can behave like this? Irregular torque / performance from burnt areas giving this hesitation on cranking. Thoughts?

 

[gsxr]

Joe, that is really odd. I would swap in a different starter (ANY other starter) and see if the hesitation remains.

 

[Alphasud40]

I second what Dave said. Replace the starter motor. It’s not hard to damage a starter motor if the engine is seized. Both the solenoid contacts and the commutator on the motor might be pitted from the flash arc.

 

[JC220]

Thanks for the replies, yes I was thinking along the same lines.

I have a couple of spare original m119 starter motors so I'll leave one of them with my rebuilder to refurbish / test before I go ahead and install it in my coupe. That way starter or not it only needs swapped out once.

I will report back when I get to that will be a few weeks. If swapping the starter doesn't make a difference then I'll investigate further in due course.

 

[Rouven036]

Would also guess the comutator or what it's called the collector thing going to the coils or one of the coils itself is shorted/burned

 

[JC220]

Would also guess the comutator or what its called the collector thing going to the coils or one of the coils itself is shorted/burned

Yes fingers crossed it is something to do with the starter. It seems to stop almost and try to go backwards for a split second. The engine had a leak down test carried out before it was resealed and it was very good condition so I do not think it is a mechanical issue with the engine.

With the POs efforts requiring a new starter motor and that coming fitted on the seized engine it does strongly suggest they gave it a hard time and something may be burnt internally. If it does turn out to be the starter I'll take it apart and take a look see

 

[500AMM]

It sounds like the starter solenoid works as intended, but the power doesn't pass through to the el.motor - but the el.motor spins fine when it starts running. Not much left in there to fail than the brushes and brush holder plate. I vote for a overheated brush holder plate which may have weakened the springs pushing the brushes towards the commutor. Or in worst case a partial melt down.