I made up a spacer for the contact and this seems to work well. I dismantled another motor that was a bit eractic also. I don'tknow what it does,but seems to run smoother now. It is above the credit wheel, the most left beside the other relays.

to make it work now, I put in 20 cents and it automatically starts. there is no need to push the start button.

Whilst playing, credits are given and show by accumulating on the credit wheel.
When the current game finishes, a new game can be started by pushing the start button. This reduces the credit wheel by one. 

it all seems to work fine now.

The only unusual thing is if I have credits and I add a coin, the credit wheel decreases. Is this normal?