Diesel Flywheel Issue - Do I Need to Replace?

[JHZR2]

My MB 1991 350SD has occasionally had a grind and lack of engagement when starting.

It used to be maybe once every fifty starts or more. Recently it happened more, and I’ve encounter times where it happens more than once.

Here is an example:



So I got a Bosch remanufactured starter, and pulled it. Very easy on this car. It’s the same starter on my 4, 5, and 6 cylinder engines of this OM60x series so I figured it was not a risk to buy it.

The old starter looked like a recent Bosch remanufactured unit. Very clean.

I didn’t have jumper cables handy to test the benefit end or whatnot.

When I had the starter off, I turned the engine over and looked at all of the flywheel.

Some spots are pretty bad.

The new starter gear looked identical to the one coming out. I guess it is a good deal harder than the flywheel.

I can’t easily turn this engine over by hand in the case that the flywheel was ever completely shredded in a spot. At least without removing the fan and clutch.

Is there any chance to remediate this flywheel? Maybe, say, carefully wire weld to the bad teeth then file it smooth?

Seems like flywheel replacement is the right approach but that’s a transmission replacement-level labor task, I’d think, so it’s best to wait on that if I can.

How did this happen? Is it a sign that the current starter in there is bad and not getting the gear far enough out? It does spin the engine as evidenced by the video I posted above.

Thanks!

 

[meep]

It looks like the wear pattern on the old starter only engages half the length of its teeth. If thats by design, then you probably have a problem on approach at some point. If the gear can be pushed farther to mesh the rest of the teeth, it will probably be fine for a long time. I’d start fiddling there…

 

[Chris142]

You heed a ring gear or flip yours around. Either way the transmission and clutch has to come out.

 

[JHZR2]

It looks like the wear pattern on the old starter only engages half the length of its teeth. If thats by design, then you probably have a problem on approach at some point. If the gear can be pushed farther to mesh the rest of the teeth, it will probably be fine for a long time. I’d start fiddling there…

This isn’t like an old GM starter that gets shims (the research I did indicated that some older ones use that approach…), it mounts hard against the transmission housing and is held in with two long bolts that thread right to the starter (they are threaded in the started body). No sign that the old starter was loose or anything. So I guess the gear could not extend properly, far enough for whatever reason, but otherwise I don’t see how approach would be an issue here…?

 

[JHZR2]

You heed a ring gear or flip yours around. Either way the transmission and clutch has to come out.

It’s an automatic transmission car.

That’s my concern, removing the transmission opens up a ton of other work for one labor. Then I might as well throw a rebuilt transmission in, which makes the job a lot more. But it seems silly to drop the transmission otherwise. No idea how many hours labor to do so but I assume it’s quite a few, especially if I DIY…

 

[drtyler]

Does the starter gear move to the same place on both starters? That might be a place to look for why it is damaging the flywheel.

 

[JHZR2]

Does the starter gear move to the same place on both starters? That might be a place to look for why it is damaging the flywheel.

I don’t know. I’ll try to test the old one tomorrow first thing before work or else after.

 

[Chris142]

It’s an automatic transmission car.

You said flywheel. If it's an automatic it's called a flex plate. At least on Japanese and American cars. If the transmission is working ok I would not replace it.

 

[Chris142]

Btw you Asked why this happened. All engines stop in just 2 places regardless of where they were turned off. Nobody can explain why,

 

[Oro_O]

I don’t know. I’ll try to test the old one tomorrow first thing before work or else after.

If it proved to be that a different starter engaged further, I’d be tempted to try dressing the flywheel teeth and trying the new starter. It’s a worth a shot vs. the labor of pulling the trans.

 

[supton]

Btw you Asked why this happened. All engines stop in just 2 places regardless of where they were turned off. Nobody can explain why,

Wouldn’t it be on a compression stroke? As the rotating mass runs out of energy, it likely is going to stop on the compression—if it gets past TDC, the compressed air will finish pushing down, until likely another compression stroke id imagine.

 

[JHZR2]

Btw you Asked why this happened. All engines stop in just 2 places regardless of where they were turned off. Nobody can explain why,

Strangely, I have three spots where there is wear.

I’d suspect it has something to do with the compression stroke of the strongest cylinders?

If it proved to be that a different starter engaged further, I’d be tempted to try dressing the flywheel teeth and trying the new starter. It’s a worth a shot vs. the labor of pulling the trans.

What do you mean by dressing the flywheel teeth?

I was thinking to maybe take a small file, smooth any asperities, and then either use a wire flux welder or JB weld (what’s the worst that can happen?) to fill in the flywheel teeth and then refile.

I suspect that rough imperfect “fixed” flywheel teeth may be worse news for meshing in the starter, but it beats the alternative. It’s also why something like jb weld would seem like a better bet if it would actually “grip”, since it could be shaped easier upfront and after. Maybe even with some sort of mold.

 

[IndyIan]

I wonder if you can engage the start in two stages? 1st to move the starter gear in, then "start" the starter once the teeth have full contact? I assume the starter teeth are beveled so the gear can rotate to fit in between the flywheel gear teeth?

 

[JHZR2]

I wonder if you can engage the start in two stages? 1st to move the starter gear in, then "start" the starter once the teeth have full contact? I assume the starter teeth are beveled so the gear can rotate to fit in between the flywheel gear teeth?

Well I think that is what happens…. When I get that horrible noise in the video, the engine is turning. The tachometer is signaled by a Hall effect sensor right near the starter, which is affected by the movement of the teeth on the flywheel.

So I assume though it’s a horrid sound, that it’s moving the engine a bit, moving the engine to another spot where maybe it gets better bite/meshing.

I didn’t see any spots that would outright reject the entry of the starter gear, but maybe I should check and file any asperities down…

 

[IndyIan]

Well I think that is what happens…. When I get that horrible noise in the video, the engine is turning. The tachometer is signaled by a Hall effect sensor right near the starter, which is affected by the movement of the teeth on the flywheel.

So I assume though it’s a horrid sound, that it’s moving the engine a bit, moving the engine to another spot where maybe it gets better bite/meshing.

I didn’t see any spots that would outright reject the entry of the starter gear, but maybe I should check and file any asperities down…

That is odd that motor turns without good gear engagement? Usually I've heard just a straight "zing", and the motor never turning over and the starter spinning before gear engagement.
Probably a starter rebuilder could tweak it a bit to only turn the starter motor when the starter gear is further out? I guess now you have two good ones now so maybe moving the point when the starter solenoid closes the contacts for the motor?

 

[c502cid]

I know you don't want to hear this, but no jb weld or any kind of welding on the teeth is going to work long term, probably not even short term. The flexplate has to come out, and you might have one that a new ring can be put on. If you are keeping the car long term, just know it has to be done at some point.

 

[JHZR2]

I know you don't want to hear this, but no jb weld or any kind of welding on the teeth is going to work long term, probably not even short term. The flexplate has to come out, and you might have one that a new ring can be put on. If you are keeping the car long term, just know it has to be done at some point.

I recognize that for sure. I’d just rather defer until the transmission needs a real service…

 

[JHZR2]

That is odd that motor turns without good gear engagement? Usually I've heard just a straight "zing", and the motor never turning over and the starter spinning before gear engagement.
Probably a starter rebuilder could tweak it a bit to only turn the starter motor when the starter gear is further out? I guess now you have two good ones now so maybe moving the point when the starter solenoid closes the contacts for the motor?

I guess I need to understand better how these “bendix type” starter gears work. If the sequence is to start spinning which forces the gear forward, or to force the gear forward then spin.

I just don’t really get how such a slight engagement coukd be a thing unless it was the starter… or enough deformation of some teeth on the flywheel that they csnt mesh, and if the starter hits those it just grinds them off?

 

[MSCH]

Wouldn’t it be on a compression stroke? As the rotating mass runs out of energy, it likely is going to stop on the compression—if it gets past TDC, the compressed air will finish pushing down, until likely another compression stroke id imagine.

when factoring in multiple cylinders, the theory that engines always stop in the same place is wrong.

 

[JHZR2]

when factoring in multiple cylinders, the theory that engines always stop in the same place is wrong.

Well for my six cylinder engine I think I can see four specific spots where wear and engagement occurs. Each one is different than the next. I assume this means one is more frequent than the others.