Scania Starting issue

[whistler2]

I have a 2008 Scania R420 with a starting issue.

July 2021 had a new starter motor fitted.
January 2022 the issue started with starter grinding against the rig gear did this a few times and had a new starter motor fitted. Within a day the issue happened again. The batteries were changed and all the earths checked and cleaned. The problem still persisted but was intermitte ignitionnt. We found that the ring gear had a chunk out it. In April the ring was changed along with a new clutch. Within two weeks the problem was back. The contact switch was changed on bottom of the ignition barrel still no joy.

Any ideas of where to look now.

TIA

[Franglais]

Not Scania specific, but i would be thinking along theses lines.

Run a direct power cable to the starter*. This will eliminate all elec circuits, so if all is good look at wiring.

If direct power doesn`t cure the issue, then it is either the starter-motor or ring gear, isn`t it?
Inspection hatch in bell-housing? Any chucks of metal from ring?
Starter motor off for inspection and bench test.

*Ed,
I don`t mean just spark a jump cable on the contacts. Do it properly.

[whistler2]

Have run a direct cable to the starter still no joy. Starters 1 and 2 are chewing the new ring gear. The new ring gear is a genuine Scania. its getting to the stage where its going to be another ring gear but need to find the problem as don't want to be in the same situation in a couple months. Both starters are Hella going to try another make.

[cav551]

Check the number of teeth on the starter motor pinion (and its rotation) and the ring gear and then ask Scania a few questions about how many each should have. Remote possibilty that the crank has too much end float but that would be in desperation since you ought to have other symptoms; easy enough to check though.

[Old John]

Why did you have to change the starter in the first place?
If it was just an electrical issue, and not the same symptoms as you describe with the second starter, then it sounds as though the second one is not compatible with the ring gear. I've once had to fit a starter on which the pinion was slightly different to the proper one to keep me going for a couple of days till I could get a new one. It would start the engine no bother, but you could hear that it wasn't right, and sometimes I'd have to start and stop the engine a few times before the starter would disengage with the flywheel.