I have a io520 that sometimes stops turning over on the compression stroke on the first start of the day cold. The starter doesn't sound like it is slipping or makes a loud noise just sounds like it stops turning as hard and doesn't have enough momentum to keep pulling through like a car with a dead battery. If I retry it has enough power to crank through with no issues.

I was going to replace the battery but my a&p wants me to replace the starter adaptor when I told him, however I don't have the lightweight starter and it seems like its just a weak starter since I don't hear it spinning without the prop moving. Batter is a concorde 35axc replaced in 2016. My 0470 would do this sometimes also and I didn't give it a second thought

What propeller?
What starter?

These are important considerations.

The battery is getting pretty old. That would be the first step for me.

Could be crappy cables?

Both of my 185's have struggle a little with the first start, you have to bump em to get them to come through the first compression stroke.
If your adapter is not slipping it is very doubtful that is the issue

Clean all terminals and nuts on the Battery, solenoids and starter itself;

I did have a master solenoid Not to be confused with the starter solenoid that would not let enough juice through once.
It clicked and acted fine everything powered up in the cockpit but wouldn't carry the amp load.
Thats probably a pretty rare problem though.

Good luck

I wouldn't replace the starter adapter "just because"-- they're about a thousand bucks & a PITA to change out.
You can't expect too much more than 5 years from a battery, I'd replace it.
Clean up all the power & ground connections on the starter circuit.
Be sure you have a good ground between the engine & the airframe / battery.
Seems like turning the prop through by hand a few blades first helps the starter turn it past that first compression stroke.

Squash wrote:What propeller?
What starter?

These are important considerations.

3 blade hartzell, and the starter is the stock tcm that shipped with it, not the lightweight skytec. Will replace the battery first and see how it goes. Don't know what a starter slipping sounds like but imagined it as the starter spinning up without the prop turning.

After you check to make sure you have a good power source (battery stuff), you may want to check your starter. If the stock starter turns out to be an Iskra starter, you can go ahead and junk that. Depending on whether you are running an old or new style adapter, you could potentially get yourself a new starter appropriate for the adapter.

Had that problem on a470u with cont starter slow turning,they are old Ford type starter easy to oh.mine needed cleanup bushing brushes good need to cut down commutators the mica between them polish lube bushings .the commutators wear down and copper dust shorts across and magnetic field gets messed up