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Dieselstressed 10-30-2009 04:12 PM

91 350 SDL Engine Swap
I have a 1991 350 SDL with engine problems, probably the notoriuos bent rods. I have read numerous posts on this site that provide a lot of information on the issues of bent rods. It not my intention to start that discussion over again. I have already replaced the head and glow plugs.
My intention is to just pull the factory motor and put in a different one. The proverbial "straight forward swap." Is there such a thing?
From researching my vehicle info I have discovered that I have a 603.970 block that produces 134 HP. This year and model also came with a 603.971 block that produced 140 HP. If this information is correct, is the rod probelm inherent in both? What is
the easiest,
best scenario
for an engine swap that will get me the reliability and performance I was expecting with a 350 Benz?

babymog 10-30-2009 04:44 PM

The .971 engine is the same "rod-bender" and might be okay, but might not. The difference in hp is a higher RPM limit on the .971 (which is the W140 engine, never went in the W126).

First, what is the engine problem? Verify that it is a bad block/bent rod before you get in too deep, it can be a gasket on your new head replacement. However, if it is bent rod(s):

You already have the new head, put it on the new engine. The best swap and fairly trouble-free is to find an '86/'87 SDL engine: OM603.961 (3.0L). It was stock 148hp with the trap-ox which you'll not use so you will likely get a hp or two more. You can pretty much stick it in as-is, but here are the changes I'd suggest:

Use your new head, the OE head on the .961 engine is prone to failure and you have the better one (search #14 head here). Also the injectors, injector lines, glow-plugs, and valve train from your .970 engine as assembled on/in the head.

Use your .970 Injection Pump (IP). It has a better injection profile, but have it turned up to .961/.962 RPM limits to get the full power from the engine (the ~150hp) to make up for the decreased displacement of the 3.0, you'll actually have more power than the original engine. If you find a .971 IP you're pretty much there on RPM and power and don't need to mess with it.

Use your .970 turbo and plumbing, it doesn't have the ARV valve and has a 55-trim which should mean more boost from less exhaust to help bring back the bottom end which is where the 3.5 really shined.

If you can't find a .961 (SDL) engine, and you instead find a nice OM603.960 ('87 300D) engine, you will want to do the above, but also swap your throttle hardware and oil-filter housing, also the engine mounts.

I might have missed something, others here will (GXSR and Sixto) have any info I missed.

sixto 10-30-2009 05:13 PM

I wouldn't put a preference on a .961 over a .960 simply because everything you need to make it work is already in your car.

If you find a .97 block with an ID tag riveted to the bellhousing flange ahead of the block heater, there's a good chance it's a factory replacement block with beefed up rods. There's no guaranty the rods won't bend but you're that much further ahead.

From my experience with a W140 3.0 swap, you'll notice the loss of low end torque of the 3.5. The turbo in a 3.5 is just gravy around town. gsxr will tell you to do a 606 turbo swap :)

87 300D

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