M112 Engine Review

My MB Tech friend called the other day to tell me that he had one of these new high tech engines apart if I would like to come by and see it. I made the time.

The engine was actually the v8 version, but everything is virtually the same except for the extra two holes. The car had been in a wreck which busted the oil filter housning and it lost just enough oil to cause some lower end problems.

This engine is an absolute engineering masterpiece.

Starting at the top, the rocker arm/cam followers look like something from a high buck race car. Roller followers and solid alloy construction. They're offset which makes them look even more exotic. The offset is necessary because of the three valve arrangement, there would be no other way to fit them all under the valve cover.

The liners are some sort of exotic alloy. They have a tan look to them, and after 50,000 miles, you couldn't tell that a ring had touched them. They are fit into the block such that there is plenty of cooling liquid all the way around them, something that would not be exposed with the head off of most engines.

The rods are very interesting. They forge and machine the rods, then break them at the parting line. I'm not sure of the reason. I can see where it could eliminate some machining steps, but I can also see that this would make for a more precise fit.

The main bearing caps and webs are really great. There are four vertical bolts and THEY'RE CROSS BOLTED. This is a racing engine feature. The only other engine that I've ever seen apart that used this technique for incredible bottom end strength was the 427 Ford of the mid sixties. I was told that MB actually started doing this with racing engines in 1948.

I missed the pistons. They have almost no skirt at all. The story on this is that the dual spark plugs which are fired about 40 degrees of crank rotation apart, if I remember this correctly, have minimal rocking allowing for the no skirt design.

The ring package is very low tension, this evidently works together with the alloy liners, the piston configuration and the dual spark plug usage.

As I said before this engine is an absolute masterpiece. It wasn't very long ago, when this technology would have been the makings of a very nice Formula One engine.

Well for those who may be interested, there it is. It was well worth the trip and the time out of my day to see it. Now, I just hope that's the last time I see inside of one for many years. Since mine will be given a steady diet of Mobil One frequently, I hope to keep it off the engine stand for many years.

Thanks,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

Thanks for taking the time to post this. These are some things that can certainly be appreciated by those who have been inside engines.
Did you notice anything about the crank ? Steel unit ?
Are these engines reverse cooled (coolant flowing to the heads first) ?

With all of the other things that have gone wrong with my new Benz, it good to know at least the engine won't fall out of it (I hope)

[73MB280SEL]

Howdy,

Sounds like something I'd definately make time for too.

As far as the connecting rods, the other engine I'm familiar with that does this is the Chevrolet LS1. There, the technology is called "cracked PM" for cracked powdered metalurgy. Chevrolet makes their rods by press forming metal alloy powder in a mold at high temp. This blank is then heated again and forged as a normal con rod is done. The advantage to this is that the exact quantity of metal is known due to the accuracy of measuring the amount of powder originally put in the mold. They then scribe a stress riser on the big end and crack it (after machining the bearing surfaces).

The advantage to the cracked big end is that the surface roughness helps locate the cap onto the rod accurately.

Due to the accurate limits on finish weight, LS1 rods do not have balance pads on them as other Chevrolet V8 rods have always had. Is the same true of the MB rods? I'd suspect MB engine balance requirements are tighter than Chevy requirements thus still requiring balance pads.

The LS1 also uses cross bolted mains. It in fact has 6 bolts to locate the main bearing caps. Four are bolted from below (much like a M117 engine) and two are bolted at 90 degrees from the side. Two advantages to this are (1) location of the main more rigidly leads to less engine vibration and (2) with an aluminum block, you're going to need more location than the usual American V8 2 bolt main.

Historically, the Chrysler Hemi engines were cross bolted which made them very desireable for drag racing duty. Most Chevy V8's that were 2 bolt motors were converted to 4 bolt by redrilling the webs at an angle. The main caps would then be located more rigidly because the 2nd set of bolts have some triangulation relative to the OEM bolt holes.

One other change with the LS1 that older Chevy V8's didn't have is that the LS1 main webs extend below the level of the crank (as required by the cross bolts). This in itself makes for a much stronger engine.

Sounds like a neat demo. I'm really interested in the 2 spark plug combo. Having the 2nd plug not only allows you to get the combustion over in a shorter period of time, but changing the timing of each spark plug individually with RPM would allow you (as you indicated) to lower the rocking moment. It could also create low RPM turbulence, which adds to output torque and efficiency: very good things.

Sholin

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Lt. Blue 1973 MB 280 SEL (108) with sunroof and console shift.
1996 Chevy Camaro Z-28 LT1.

I was looking to see the parting line in the crankshaft when I was distracted and never got back to it.

I don't remember if there were balance pads on the rods. I think if they were not there it would have caught my attention.

As you say the idea of a block extending below the centerline of the crankshaft in itself makes the lower end stronger. I never had a hemi apart, I did not realize that they were crossbolted. It's not surprising. In the sixties the Fords and Chryslers proved their long term engine durability over Chevy and most other GM cars. The GM's were typically faster(with the exception of the hemi, of course) but did not have the bottom end strength. Also there were more valve train problems with the GM stud mounted rocker arms. Chrysler and Ford both had shaft mounted rocker arms.

Thanks for the response,

------------------
Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

[Jim H]

I thought BMW also used the same technology on the rods. It makes for a much stronger fit, as there is no slipping like you would find in machined surfaces under the same bolt pressure.

Saw on TV that the ME109, which used a Daimler engine, had a crankshaft that "could not be duplicated today" according to a Rolls Royce engine specialist.

BCingU, Jim

I could easily be wrong, but I would not have thought that the texture preventing movement would be the reason for doing this. Given the way a properly produced rod is indexed by the bolt. This is why you can't just stick a new bolt in a rod without remachining considerations.

This could certainly part of the reason.

Have a great day,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

[Oliverp]

Not meaning to sound too ignorant, but which model does this engine relate to?

I'm not too up on the engine codes. I know all the chasis codes (W126 etc) but i'm really not too sure about the 'M' codes.

Sorry for being stupid!
Oliver

[Jim H]

http://media.gm.com/gmc/lb7ben.html

"FRACTURED CONNECTING RODS"

"Each connecting rod is hot-forged as one piece, then broken across the crank bearing journal prior to assembly with a sharp, fracturing blow. This metallurgical technique gives each rod and cap its own unique, uneven mating surface. When bolted together, the two pieces mate precisely. The fractured surface keeps the rod and cap from sliding in any direction, greatly reducing the potential for adverse bearing wear."

I found the above excerpt about GM's new diesel engines while searching on "fractured connecting rods."

You learn the neatest stuff on the Internet.

BCingU, Jim


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'96 E300D 60k mi (wife's daily ride)
'95 Audi 90 120k mi
'92 GMC Suburban 139k mi
'85 300SD 234k mi (my daily ride)

Jim,

Thanks for the research. You learn something new everyday, especially at MShop.

Oliver,

The M112 is the current V6 engine. Mine is the 2.6 in my '01 C240. This is the same engine, except different bore/stroke, as the 3.2 as in the new C320 and the E320. The engine I saw apart was a V8 which is basically the same engine, except with two extra cylinders.

This is an absolutely state of the art engineering masterpiece.

The M is just the prefix for the MB engine codes, just as the W is the prefix for the chassis codes.

Have a great day,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles