I'm considering replacing the #14 cylinder head on my 300sdl with a #17 head from a 350SDL I found. My car has been displaying signs of a cracked head: smoke, disappearing coolant, high cold pressure in the coolant system, though no mixing oil/coolant. I'm also seeing oil seeping from the head gasket area. It could just be a head gasket, but since I plan on getting some more horsepower out of this car in the future, I figure I may as well replace the head while I'm in there. Is there anything I will need to do with the 17 head beyond simply swapping it out? I've read how some of the om603 heads have angled injectors, different injector threads, or different prechambers that require compensating for.

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1987 300SDL

Does it have prechambers and injectors in it? If so its probably angled meaning you'll have to bend the injector lines a bit. Not sure if straight prechambers will fit. The angled prechamber takes a different injector holder.

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CENSORED due to not family friendly words

Vertical prechambers from a #14 head can be trimmed to fit. You'll need injectors for vertical prechambers which you already have. Ideally, use a set of injector lines from a 603.97x or 3.5 liter 603. Or bend the lines you have as suggested. You'll have to check with tuners whether there's a performance advantage to .96 or .97 injectors and prechambers. IIRC they use the same nozzles. The inclination is in the head casting so there's no avoiding that.

The 2 bolts that go into the front cover are ~20mm longer in the #17 and later head castings. They're not special bolts. Get what fits.

I'll mention it since some folks ask - use a head gasket for the block the head's going on. 603.961 or simply 3-liter in your case.

Sixto
87 300D

Thank you! That's exactly the information I was looking for. Since it's coming off a complete engine, I'll have the option to pull the injector lines, the longer bolts, and even the injectors and prechambers, though at an added cost.

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1987 300SDL

How's you #14 to #17 project going? I have an 86 300SDL that's awaiting a cylinder head to replace the once just pulled, as it has some cracks. Will you be able to use the original injectors with the #17 pre-chambers?

Thanks for the help.

The glow plugs are also different lengths depending on inclined injection or not.

Recommend you keep the new lifters with the new head, and you should mark each lifter to ensure it goes back onto the same valve. If you can't do that, then you should bleed down each lifter prior to installing. There is a small hole on the side of each lifter in the oil groove: point that down, then pump the inside assembly with your thumbs to force the oil out of the hole. If you don't do this, and the new lifter has too much oil (because the valve stems are at different heights because the valves wear into the valve seats), then the lifter will hold that valve open and that cylinder will never develop compression until the oil pressure in the lifter bleeds down. I'm sure you can guess how I know this...

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

so... what's different on the .971 head gasket?

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