Been thru 5 starters (different brands from 2 different stores - all rebuilds) in 14 months. Car runs flawlessy with 180,000 miles but on every 3th or 4th start it starts to turn then WHAM WHAM - it's like the starter gear is hitting something. If I keep the key in start positon it will "drive" through it and come back up to speed and start after a second or so. Happens mostly when cold although occasionally it will happen even when hot.

The latest mechanic examined it and pronounced the ringgear and fly wheel flat, not out of round, solid and the gear has all the teeth with no signs of wear. He says his gut feeling is that it is an ignition thing like a backfire that is pushing back against the starter, although he says the timing is dead on. He said he's seen cars so out of time that the starter breaks. He thinks the only possible explanation is the module that advances the timing for start is malfunctioning and he didn't know how to test it.

So the question: Does any body think this is a reasonable possibility and know how to test this module - what ever it's called. Or is there something else I should be looking at? I've got about a month left on the current starter and the current store is starting to look at me funny...

Thanks in advance.

could it be a shim problem?
The mounting pad for starters is machined on the block as is the mounting surface on the starter itself...if it was machined a little thin on either the starter or the block the pinion gear (starter gear) would engage the ring gear on the flywheel at the tooth root and cause a jam.

I've not noticed starters on volvos installed with shims, but many other cars have them to adjust the starter teeth correctly. I think they're available at most auto parts stores. You can test for tight starter teeth/ring gear by grounding out the ignition wire and spin the engine over with the starter and listen for proper engagement.

I'd put one thin shim (.010 or so to start) in between the starter and the block....

Yeah, it could be that the crankshaft sensor is doing something wrong. They're only $30 or so, worth the replacement. And an easy replacement, if you're into contortion. Held in by one 10mm bolt, and be very careful extracting it (gently) so you don't break that fragile bracket. Other than that, easy. See how that works out. It's kind of a sucky way to diagnose a problem (replacing things) but it can NEVER hurt to replace the crank sensor.

Other than that, control unit malfunction could cause that, but it's not that likely. Not much else retards or advances spark enough to cause that specific fault when you're cranking the engine.
--
Chris Herbst
1992 745, 68k

And others:
93 944, 150k
90 245, 110k
88 744, 160k
87 245, 185k

Chris sez: "it could be that the crankshaft sensor is doing something wrong"

Interesting. My crankshaft position sensor (aka RPM sensor, RPS, and several other names) is flakey. Flakey means sometimes it works, and sometimes it don't. The starter began going "wham!" (sometimes) when the sensor started to go flakey. Maybe it wasn't a coincidence.

I'll check for starter damage when I change the sensor this weekend.

-Ron

Ron,
Was wondering if your "WHAM" problem with the starter went away after you replaced the crankshaft position sensor. I've still got the problem. I can't image how this could cause a sound that sounds like gears jamming but I'm game to replace it if it worked for you. I just put in starter number 6 (over 14 months). This one is a big heavy Bosch original from the late eighties. It's holding up well but is making the noise every 3rd or 4th start and it will be toast in a month or so.
Thanks,
Robb

The car has never been disassembled in any way so it couldn't be a reversed ring gear. And it runs flawlessly. If the knock sensor had failed wouldn't it run poorly? Also, I forgot to mention how the starters fail. The bushing on the outer end of the shaft that the little gear slides on get all beat up eventually causing so much play in the shaft that the gear won't engage the ring gear anymore. The last one failed rather spectacularly - the whole casting holding the bushing cracked in half!

How does it perform in general? I am thinking that perhaps the knock sensor has failed so that the timing is way off.

The flywheel could be reversed (inside out). In this case, the flyweel teeth look O.K. but eat the starter gear. Was the transmission out before this problem started?

Vin