Any reason swapping an engine from an '87 300td into an '84 300td is a bad idea?

[forjanice]

This may seem like a foolish reaction, but I seem to be having some gasket issues -- white smoke from engine, coolant and oil rather quickly, etc. This is happening in the '84. I also have an '87 engine with half the miles available to me for $500 bucks. It seemed smart enough, possibly easier, and maybe cheaper to just go ahead and do the swap, rather than doing necessary repairs on the existing engine. Am I right about this? Is there any reason an engine swap from an '87 to an '84 may be more complicated than I'm imagining?

[mike-81-240d]

Om603 into w123 is a very popular swap in europe.

Although the 603 is known for it's cylinder head fiasco.

I'd say as long as you know it has a newer head casting, and you know it's not a direct bolt in swap go for it.

Part of me is considering a OM602 and 5 speed in my 300TD.

[forjanice]

How do I ensure it's a newer head casting? And how do these engines size up to one another in quality?

[mike-81-240d]

By the injectors between cylinder 2-3 is a full part number.

For example "R 603 016 14 01"

The 14 means it is a #14 head which is prone to problems.

Once the head is sorted they are fantastic motors.

[Shortsguy1]

I was under the impression that the transmission bolts differently to a om603 than a om617. In other words, I thought you would need to swap the tranny as well, or purchase some sort of expensive adapter. Just something to investigate before you commit to purchasing the engine.

[mike-81-240d]

Originally Posted by Shortsguy1

I was under the impression that the transmission bolts differently to a om603 than a om617. In other words, I thought you would need to swap the tranny as well, or purchase some sort of expensive adapter. Just something to investigate before you commit to purchasing the engine.

It will not bolt up to the OM61X trans. That's part of the reason I said it's not a bolt in swap. To some that is a advantage though, as you can easily source a 5 speed manual for it.

[Skippy]

603/five speed in a W123 sounds like a lot of fun. It will be considerably more work than just swapping a head gasket though.

[Zacharias]

A few more things to keep in mind, aside from the engine:

1. What transmission will you use?
2. How will you hook up the speedometer and the tach?
3. Custom driveshaft fabrication
4. Wiring issues if you want to keep the factory preglow system
5. Custom exhaust work will be needed

Motor swaps are fun but you need to go in with a plan. Otherwise you may get nickel and dimed to death.

The price of motor isn't really the primary concern.

[jay_bob]

Systems integration is going to be fun on that one.

A few that come to mind
- Climate control system sensors are different. One thing you will need to consider is the Klima controller for the a/c compressor. This is necessary to save the serpentine belt from a compressor failure. This was not an issue on the OM61x due to the dedicated belts.
- Tach is different - 123 sensor is on the balancer, 124 is on the ring gear. I believe the 123 tach is 1 pulse/rev and the 124 tach is 144 pulses/rev. The elements do not swap directly in the cluster. The application of some old school TTL electronics (or an Arudino) might help this.
- Oil pressure is mechanical on the 123 and electrical on the 124. Although you should be able to put the pressure line into the port where the oil sensor is on the OM603 (looks like a silver can).
- Not sure if the resistance curve of the engine temp sensor is compatible between a OM61x and a OM603.
- I would plan on bringing over the EDS controller at least to manage the idle smoothing function.
- glow plugs- the control is basically the same, so that should swap over pretty easy. You'll need to use the relay from the 124.

I would head over to 124-zone.com and download the wiring diagram for the 124 engine and climate systems.

I don't know if you have access to the donor car for the ancillary bits but if not any 1st gen 124 Diesel (not gas) will have the control system parts you will need.