1976 W115 300D motor into 1979 W123 300D
 

I have the opportunity to buy a 1979 W123 300D with a bad motor (low compression). Would the motor from a 1976 115 body 300D be able to be put into the 123 body car?

Also, the 115 car has a bad injector pump (3 injectors aren't getting fuel). Would the injector pump from the motor in the 123 fit on the motor from the 115?

Thanks!

Yep, you can swap the engine from the 115 into the 123 body. The blocks are the same with some minor differences. You may have to swap some of the exhaust/intake manifold studs, engine mount studs, engine and trans mounting brackets may have to be swapped but should fit the block and trans, AC bracket mount, and so on. Belt pulley may be different diameter, so use the one off the 123 to drive the accessories. The thermostat housing may have to be swapped, but the mounting studs are in the same position.

Injection pumps should be interchangeable. The linkage will have to be looked at.

While the engine is out I would suggest replacing leaking gaskets and oil seals while they are easy to get at.

A while back I rebuit a Euro 300D and replaced my US 300D engine and the above are some of the things I had to deal with. Otherwise, everything fit and the swap was easy in that regard.

Good Luck!
Tom

I have to do the exact same swap: a 76 300D engine into a 79 300D. I was wondering if you did do this project. If so, what kind of snags did you run into? Any recommendations?

Denis Larsen

115 300 into 123 body
 

you will find that the ac mounts changed along about 80 or 81. the earlier cars used the york compressor, which does not convert well to the new freon, with a fiendishly complex and inconvenient bracket that holds it that bolts to one or two engine mount bolts, one or two water pump bolts, and a couple of other places. it is a royal pain to change a water pump after installing one of these brackets so if you do it be sure to put in a new water pump before installing the ac compressor. from my experience i would not do the swap you are contemplating unless ac was not needed where i lived. (not in indiana where the summers get hot and humid). there are other differences too such as the automatic transmission. i am not sure the time that they change.
the best thing is to get a second car of the same year with the engine that you want and swap everything. otherwise you will be killed buying small bits and pieces and the project will be more likely to stall out. i have done this twice. once with a 76 300d into a 74 240d. another time a 83 300d euro stick into a 83 240d automatic, us. both times a good success. both donor cars were bought for around $700 with major cosmetic issues. the euro engine also had to be rebuilt. when swapping a 300 into a 240 123 body one engine shock bracket has to be fabricated. i believe this had to be done on the 115 body too. the euro car motor has a different throttle linkage which has prevented hooking up the cruise control. i didn't do the work myself but i know all the details because i ran down all the odd parts that were needed. when swapping the 300 into a 240 the rear ends should be changed, drive shafts, radiators, glow plug relays, and the speedos as well. i believe i paid around $1,000 labor, maybe a little more. the 300 non turbo motor with a stick is very nice. the heavy flywheel about eleminates the bouncy idle of the five cylinder.
i advise selling the good 115 motor and buying a second car with the same year and the (good running) motor that you want. good luck. it is an adventure and not a one weekend project.

115 300 into 123 body
 

sorry,
i just re read your post and see that your 123 car is a '79. i believe most of my objections probably do not apply. the brackets for the ac should be the same. i don't know about the transmission. be sure to look at all the details to be sure you know what you're getting into. it might be pretty good.

Walgamuth,

That's an old thread you dug up... Swap was done 2 years ago without major issues. I had the complete parts car so everything was available. The only snag was that I had to fabricate one custom engine mount and one bracket to hold the power steering fluid reservoir. Other than thatit was fairly straightforward. Also had to swap injection pumps. AC was pulled out as it is not essential in Quebec. I put about 20 hours into pulling both engines and installing the good one back in.