Hello everyone! I have this posted in the vintage section too, but this place seems to be a bit more popular. I'm hoping someone on here can help me out. Here's my story:

I bought a '78 240D about three years ago. It ran great for about a year, and then it had a small electrical fire under the dash somewhere. We had to have the instrument cluster replaced, and the mechanic said the cause was related to a faulty fuel cutoff switch or something, which also got replaced. Sometime shortly thereafter, the car decided it wouldn't start. I replaced the starter myself, and it ran great again for about seven months, at which point it wouldn't start again.

Well, the symptoms were exactly the same as before, so I got a replacement starter for free since the other was under its one year warranty, and replaced it again. This time it only ran for about three days before the engine completely seized up and the battery exploded. I did do a search on this forum for starter and/or ring gear issues with 240D's, and saw a thread discussing the two variants of Bosch starters. It sounds like I may have received the newer model of starter without knowing any better and doing this to myself. I will have to go back to the auto parts store and see if they can elaborate on that.

Anyway, I got it towed to a shop, where they removed the starter, and instead of simply having worn down teeth, like the other times, this time the teeth were all mangled and twisted. Not good. The mechanic also said that the ring gear was damaged and needed to be replaced.

I want to fix this thing, but would like to know what the root cause of all of this is. Is it electrical and somehow related to the fire way back when? I think it might be since the battery literally exploded. Is the ring gear the problem? Personally, I don't see anything wrong with it (other than some metal shavings I figured came from the starter, and I realize these could be a major issue) but I have included a link to a photo of it so that maybe somebody here can tell me what they think of it.

Also, if I have to replace the ring gear, is there some kind of engine balancing issue that I have to keep in mind? And are there any good instructions you know of to replace a ring gear? I do have the Chilton's for it, and it gives instructions for removing the engine, and for taking apart the clutch, but anything else that may help would be appreciated. I've never attempted removing an engine, so I'm sure this will be a "fun" project.

Anyhow, I'll go into it further if you all have questions, which I assume there will be many.

Thanks!

Ring gear

__________________
'78 240D

No, Replacing the ring gear does not cause you to have to rebalance anything....
THe MB factory shop manual has instructions on this...

You seem to indicate you think that putting the later more powerful starter for the turbo 300 on your tiny underpowered 240 may have done some damage... to the contrary... all 240 owners pray that their original starters will give out so they can upgrade to that one.... they fit exactly the same ( except some california models)...

Hello N8Scafe
No; the dash fire is not related to current issues.
Why pull the engine?
The ring gear is damaged and needs to be replaced.
Removing the transmission would be my choice.
The damage to the flywheel ring gear teeth; is caused by incomplete gear engagement, (the starter gear did not go deep enough to make full contact).
Please; you are confusing the issue by using the wording "the engine completely seized up", if it is seized up, that implies that the pistons will not move in the block, is this the case?????

From your description; the starter motor jammed the flywheel ring gear teeth, which locked the engine momentarily????
If the starter motor jammed the flywheel ring gear teeth, you have a dead short across the battery, each time you attempt to start, the battery overloads, warping the plates and generates hydrogen gas = Boom, one spark from overheated warped battery plates and you have a mini sulphuric acid bomb, very dangerous.

Replacement of the flywheel does not require engine balancing.
There are good instructions to replace a flywheel, look in your Chilton’s under Flywheel or transmission removal.
Have a great day.

__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

Switching out the ring gear would not require rebalancing, but this thread does contain the claim that the flywheel is balanced with the engine as a unit:

123 chassis 4-speed conversion parts available

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

whunter,

Thanks for the response. I obviously don't know a whole lot about engines, although I'm learning more all the time. I thought that I had to pull the engine. The Chilton's lead me that way, but if removing the transmission is easier, I will go that route.

I'm glad you seem sure about the battery issue. That is the one part of all this that caused me the most worry. If it all ties back to the starter/ring gear thing then I can handle that.

I'm still inclined to believe that I was using the more powerful starter, and that is what caused these problems to begin with. If you're curious, here's the thread I was talking about:

240D Early/Late Starter interchangeability

Thanks again for the responses so far. It looks like I'll be able to get this thing running again for under $300, and I'll take that.

Do not use a later starter on your early 616 engine. Along about 1980 or so, there was a very slight difference in the starter and/or mounting position. The starter will fit in place, but will be in a bind.

In fact, it's possible that you don't have the correct starter on your car and that this is part of your problem.

Hope this helps,

Thanks Larry, I knew that would be your response as you were the originator of the thread that I found on this topic. I am definitely going to get the older model this time around. And if that is the root of all of this I'll be ticked, because essentially the parts store screwed me over. Unintentionally, but still.

Well, the Chilton's says that the engine/transmission should always be removed as a unit, and that the transmission-to-bell housing bolts can only be reached from the inside. So now I'm back to thinking that I have to pull the engine.

If anyone has any input on this, please let me know.

I work off a hoist with a transmission jack.

That's true, but it doesn't stop you from removing the transmission and bellhousing in one piece.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Well, I verified that I was actually using the SR 61x model of Bosch starter, which is the correct model, so it wasn't the problem I thought it might have been.

So then I figured that maybe there was something wrong with the ignition and the signal wire on the starter wasn't getting switched back off. To test this, I've put in a new battery, and hooked up a voltmeter to the starter's signal wire and ground, and turned the ignition on about 50 times. Each time, the voltage went right back down to zero as soon as I let off the ignition. So again, it seems like that's not the problem.

That leaves me with the ring gear being the problem. So I guess I will replace that, get a new starter, and hope for the best.

If there's anything wrong with my logic and/or troubleshooting so far, please let me know.

__________________
'78 240D

That's another good example of what a Chiltons manual is worth. I think they are the worst manuals on the market. I don't know how they stay in business.

Pulling an engine while leaving the transmission in place is doable on both the 616 and 617. It is MUCH easier on the 616, however. In fact, the last time I put a clutch in my 240D I pulled the engine and was done in less time than the times before working from underneath.

The 617 is a PITA to work on compared to the 616, but you can still get the engine out. You will need plenty of different extensions and universal joints to get the starter and bellhousing bolts out though.

Have a great day,

Bumping to see if anyone else has any thoughts on this whole deal.

__________________
'78 240D

Regardless of whether something else is wrong, you're going to have to replace that ring gear.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Chilton, Motor, Haynes and other vehicle service information have weak points; and strong points.
If you only work on Chevy and Ford; Chilton and Motor are just fine, (most of the time).
If you work on Jaguar, Mercedes Benz or Rolls-Royce; do not go near Chilton and Motor IMHO.

Larry, I object to the blanket statement, not the content.
I LOVE Chilton, it sends me so many interesting first time attempted DIY cars to work on!