I traded a beat up Cummins first gen pickup with strong mechanicals for a beautiful 300sd that has given me trouble ever since. I have adjusted valves and messed with hard cold starts for years and now the second tranny is acting up so I am considering my options.

The option that makes sense is to put in an om606 motor with a 603 injection pump. I am a modest mechanic but I have put a Cummins in a Suburban, a 4bt in a Scout, and I am finishing a 617 swap into another Scout. For whatever reason Mercedes motors intimidate me and I would really like to find one set up like I want ready to roll rather than doing the pump swap myself. Also junkyards around here have no Mercedes so I would rely on eBay and this forum for parts and info.

Here are a few questions;
1) Has someone done this swap and where is a good thread?
2) will this fit?
3) what transmissions will fit?

Thank in advance.

Car will be daily driven and hot rodded on occasion.

Have you checked your timing chain stretch? That could retard timing, making for hard starts.

Have you had your injectors rebuilt/balanced? that also causes hard starts.

Have you drip timed your pump (after correcting chain stretch and injector balance)? That can also cause hard starts.

Are all 5 glow plugs glowing properly...you guessed it, hard starts.

For the transmission, have you checked your vacuum modulator, bowden cable, and modulator pressure? All 3 are relatively easy. That should help with shift points and slipping.


For the 606 swap-a 606 with an upgraded 603 pump will make lots of power. It will fit, but you might have to rearrange some stuff under the hood. custom motor mounts will be necessary. There are 5 speed transmissions readily available for the 606, I don't know the numbers offhand

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment