350 SDL "Rod Bender" - PeachParts Mercedes-Benz Forum

Dee8go · #1 04-23-2007, 09:37 AM

I have heard these cars referred to as "Rod Benders," which I figured must have something to do with tolerances being too close with the valves. Is this a correct assumption on my part? Also, if this is the case, I wondered if there is a "fix" for this that is financially reasonable.

I did a brief search of this topic and didn't see anything. If this is redundant, I apologize.

rkohut · #2 04-23-2007, 09:50 AM

This may not exactly be the reason, but from my understanding;

The connecting rods were not stiff enough and they flexed. This resulted in irregular forces against the cylinder liners which caused egg shaped wearing patterns, quickly rendering the motor inoperative.

Hit Man X · #3 04-23-2007, 09:54 AM

Ah, I don't think it was the rod itself being the only issue... I believe it was a combination of issues.

babymog · #4 04-23-2007, 11:25 AM

I believe that Mercedes has changed the rod to a stronger design to prevent this. Unfortunately, the updated rods present a substantial investment in rebuilding the engine.

DslBnz · #5 04-23-2007, 01:43 PM

Quote:

Originally Posted by babymog

I believe that Mercedes has changed the rod to a stronger design to prevent this. Unfortunately, the updated rods present a substantial investment in rebuilding the engine.

And there have been posters on this board with those type of "updated" engines that have failed, more or less, the same. With the security blanket feeling that they were safe upon initial purchase of the car.

You gain no benefit by going to a 350 engine from a 300. Except for the fact that the engine may self-destruct. Its a long, drawn out process of denial the whole way down.

rkohut · #6 04-23-2007, 01:53 PM

With MB engineering being what it is (or was) this whole scenario is amazing. It seems that there might be something else concerning the motor design that plays into this.

Then again, I hear stories of originals that never had this problem.

Or is this

Dee8go · #7 04-23-2007, 02:00 PM

Quote:

Originally Posted by rkohut

This may not exactly be the reason, but from my understanding;

The connecting rods were not stiff enough and they flexed. This resulted in irregular forces against the cylinder liners which caused egg shaped wearing patterns, quickly rendering the motor inoperative.

So, the costs of owning a 350 probably far outweigh the benefits? Is there any reason that you could not easily transplant the 3 liter engine into a 350SD or SDL? Assuming one found a good engine from a 300 and a good 350SDL whose engine had already metamorphisized into scrap?

pj67coll · #8 04-23-2007, 02:05 PM

I don't know about the technical aspect's of retrofitting a 300 into a 350 body but there might be legal problems. In states with strict emissions standards you might not be able to "back rev" the motor. California I think. Maricopa county in Az too perhaps?

- Peter.

Dee8go · #9 04-23-2007, 02:11 PM

I wasn't even thinking about that aspect of it. So, are you saying the car would be required to meet the emissions requirements for the model of the car, not of the engine that is in it?

I have read of a lot of people here transplanting engines from one car (one 126 model into another 126). Don't recall hearing anyone talk about the legalities of it.

bgkast · #10 04-23-2007, 02:48 PM

Quote:

Originally Posted by Dee8go

So, the costs of owning a 350 probably far outweigh the benefits? Is there any reason that you could not easily transplant the 3 liter engine into a 350SD or SDL? Assuming one found a good engine from a 300 and a good 350SDL whose engine had already metamorphisized into scrap?

There is a member of this forum doing just that.

Dee8go · #11 04-23-2007, 03:07 PM

Who is that, BG. I looked (not searched), but didn't see anything that sounded like what you're talking about. Is there a thread about thier conversion?

Hit Man X · #12 04-23-2007, 03:18 PM

Sixto tossed in a 3.0L into his W140. Runs nice now.

I've heard EGR issues, too thin of cylinder bore (about .080" more than the 3.0), weak headgasket, etc.

DeliveryValve · #13 04-23-2007, 03:26 PM

Quote:

Originally Posted by DslBnz

And there have been posters on this board with those type of "updated" engines that have failed, more or less, the same. With the security blanket feeling that they were safe upon initial purchase of the car..

Quote:

Originally Posted by Hit Man X

.....too thin of cylinder bore (about .080" more than the 3.0), weak headgasket, etc.

I've read that the problem is actually coolant seeping into the combustion chamber. Since the coolant can't be compressed, it then bends the rods. As DslBnz stated, I too have read that new rods can bend also because of this. I wonder if it is a simple matter of getting the proper head gasket?

Hit Man X · #14 04-23-2007, 03:30 PM

Quote:

Originally Posted by rmarzan

I've read that the problem is actually coolant seeping into the combustion chamber. Since the coolant can't be compressed, it then bends the rods. As DslBnz stated, I too have read that new rods can bend also because of this. I wonder if it is a simple matter of getting the proper head gasket?

See my Post No 3.

I've read even the 3.0L had a crap headgasket before the later was released.

Hell, maybe it was a bad run of headbolts...