connecting rod: 2 holes or 1 enough ??

[Danaero03]

Hello dear all,
I am rebuilding my engine 280 SL.
I face the same questions than many I could read thé postes through the forum.
--> The connecting rod of my engine presents 2 holes for spraying oil at the rear of the pistion, as the current bearing.

--> The bearings I have bought present only 1 hole, at the right position to spray opposite to the oil filtre side.

I have red many posts affirming the engine will run with only 1 hole, and will reduce the oil consomption.
At the opposite the supplier of the bearings indicates I must drill the 2nd hole , to be in the original conformity.

Has anyone the lived expérience of having mounted a 1 hole bearings instead of a 2 holes ??

[Benz Dr.]

No oil spray is needed so don't drill any new holes.

[Danaero03]

Hi Dan, thanks for your answer. I ve read many posts along 15 years from you and others, about this issue. So no doubt you know it very well.
I understand, the answer of the seller of these bearing. He doesn't want to risk any responsibility in case the engine collapses.
But what do you mean ' no oil spray is needed '?
I have read that the later versions of 280 SE/SL were keeping 1 hole in the con-rod to oil a preferential part of the piston. 
And so I must be sure that the one hole remaining in the bearing I have got are feeding the right hole of the con-rod oiling the right part of the piston !  What do you think??

Another particularity is that all the crankpin are machined to +0.25 mm , but N°4 which is machined to +0.5 mm. I will not change the bearing of N°4 con-rod which is in good state, and will remain with 2 holes for lubrication ...
Do you see any problem to have 5 con-rod bearings with one hole , and 1 con-rod N°4  bearing with 2 lubricating holes ??

[stickandrudderman]

Another particularity is that all the crankpin are machined to +0.25 mm , but N°4 which is machined to +0.5 mm. I will not change the bearing of N°4 con-rod which is in good state, and will remain with 2 holes for lubrication ...
Do you see any problem to have 5 con-rod bearings with one hole , and 1 con-rod N°4  bearing with 2 lubricating holes ??

I see a problem with an out of balance engine. You should consider ensuring that all con rod bearings are of the same. I would never dream of assembling an engine with unequal crank pin sizes.

[Benz Dr.]

280SL engines seem to come with different types of connecting rods. Some have two holes for oil spray, some have one hole and some have none at all. MB had a number of engine failures early on where they had to replace complete short blocks due to heavy oil consumption. The extra oil sprayed on the cylinder walls from those oil spray holes was found to be the cause.

 Now, normally I take things I find on the internet with a grain of salt, and in this case, I would have, but I happened to ask Mike at Metric Motors about it and he told me NOT to drill any extra holes. And, since he would know this, I definitely believed him.

 So now you know the rest of the story. 

[Shvegel]

The "supplier" of the bearings said to drill the holes but not the manufacturer.  I doubt any manufacturer would condone doing that.  They spend a fortune on equipment to make the bearings flat and smooth and round.  I doubt they would take kindly to anyone attacking them with a hand drill.  Engine bearings run in tiny clearances to the crankshaft.  If you create a raised spot from drilling a bearing you run the risk of wiping the bearing and in effect the entire engine.  I am 59 years old and have spun wrenches since I could barely talk and I would never do that.

[ja17]

It would be nice to see this in documented factory literature one way or another. Any official documentation out there?

[Benz Dr.]

It would be nice to see this in documented factory literature one way or another. Any official documentation out there?

This has been discussed before and I don't remember that any service bulletins were ever found. However, it is well understood that MB had to replace a number of short blocks due to high oil consumption which stopped once they dropped the oil spray design.
  I have to go with the advice from a place that rebuilds at least 200 MB engines per year  ( Metrics ). I do 4 or 5 in an average year so you can imagine that you and I, and others, ask questions or compare notes looking to perfect our build quality. I asked the same question once and received a very quick answer - NO!

[ja17]

Most likely good advice if Metrics says "no" on the second hole.

[Danaero03]

Thanks to all of you for your answers and concerns.
The base data : This engine I bought is n° 30601. It's not an early production. It's been commissioned perhaps during year 70. At this time -we can suppose- MB had overcome the pb of oil consumption.
It's a uncommon prod. The Cylinder head is identified SEL/SL , comp rate 9: , camshatf 09 ....
This engine has been repaired or rebuilt -as I Found the con-rod n°4 bearing at the 2nd cote -0,5 mm with 2 holes, as the other bearings which are at the first remachning -0,25 mm .

My ascertainments : The oil spray ( 1 or 2 holes?)  are absolutaly anavoidable to lubricate the bearing of the the con-rod small end, and I think less for the walls.
The hole on the procured bearing is diam 3 mm. It is the same on the current bearing, situated on the side of the feeding for the small end bearing of the -con-rod.
The hole missing on the delivered bearing is diam 2,5 mm on the current bearing.

The  question I had to face : do I prefer add some oil once on a while, and be sure the bearings and the walls are gona be well oiled, or do I prefer to have a -supposed somehow- lowed oil comsumption and take the risk of an untimely wear (cylinder  piston and small end bearing ) due to an insuffisant lubrication ??
I didn’t find any lived experience and certitude about this. So may be I am too cautious, but I decided to low the risk and I did drill the second hole ….
I will let you know the consumption of oil when the engine rotates.

[Benz Dr.]

OK. I should have pointed out that if you have a gun-drilled connecting rod designed to oil the pin bushing, then yes you would need to use a bearing shell with a hole in it.  Since 280 rods are not gun-drilled, I didn't see the need to bring that up.

As a rule, there's generally more than enough oil flying around to lube everything that needs it. In this case, they drilled holes on the small end of the rod and oil will drip off of the bottom of the piston. It seems to work OK because I've never seen that much unusual wear on the pin bushings of any I've looked at. I always change them anyways on a full rebuild.

[ja17]

I agree with Dan and I have never seen engine failure on one of these engines due to a worn wrist pin. It would still be nice to see factory documentation on the subject.