OM603 3.0L to 3.5L cylinder head interchangeable?
 

I recently found out that the #14 head on my om603 3.0 has cracked (no surprise).

So, ive been trying to find, either a new 3.0 #16 or better head, but ive also found 1 or 2 3.5L heads kicking around on the interwebs.

Can i just use a 3.5 head instead of the 3.0? I hear they are better than the 3.0's.

And if i do pick up a 3.5l head, is it as easy as putting on the new head? or are there going to be different parts that i have to pick up?

yeah it will work.

It's virtually a direct replacement. You will need to either bend your injection hard lines, or replace them, as the injectors are positioned differently. Also, the injectors are not interchangeable. Other than that, no difference.

The small bolts that secure the head to the timing chain case may be a different size.

Make sure the replacement head comes with its original cam towers.

Preferable to bending the lines is getting the head with a set of proper lines for oblique injectors. Or get them separately.

Vertical injector prechambers can be machined to fit #17 and later head castings. That way you can keep your injectors and injector lines.

Later heads use different length glow plugs than the original head. Short plugs should work in a long plug application but not vice versa. More relevantly, later glow plugs are afterglow rated and should last longer; though in my experience, non-afterglow rated plugs have lasted years of afterglow duty. The point is, be ready to get glow plugs for the later head, which you'd probably do anyway while they're accessible.

Make sure you get a head gasket matched to the block, not the head.

Sixto
87 300^2

so i'm in just about the same situation. having #14 head issues on my 1987 300td but have found a w140 with the 3.5l om603 and #22 head. if i get the head, i will need to get the injectors and lines? will the 3.5l injectors work on the 3.0? if so i won't even remove them from the #22 head. is there anything else i will need from the donor engine? only new items besides little stuff like fuel return lines are a good head gasket for the 3.0 block, head bolts, valve cover gasket and i'll do the timing chain so that too. I don't want to do this job again but i'm just 18 and don't have a ton of money now so will i need to pay a machine shop lots of money to resurface this new head before i install it? ill get back with the mileage on the car so you have an idea of regular wear. thank you!

I think the prechambers can be swapped into the newer head, eliminating a few issues.

what are the issues with the newer pre chambers with the 3.0 engine?

Benz Turbo I thought you might be interested in a #17 head I just got it back from the machine shop they did a pressure test and it pass it use to be in a 3.0 engine with pre chambers and injectors from the 3.0 engine it comes with cam, injectors for a 3.0 engine let me know if you are interested

I'd want to keep the angled injectors since they run so much cleaner.

-J

#14 (OE US 3.0) head castings take a specific prechamber that takes a specific injector and slotted lockring. Likewise, #17 (OE US 3.5) -22 head castings take a specific prechamber that takes a specific injector and splined lockring. A 3.0 prechamber can be machined to slip into a #17-22 head. The only reason to do this is to avoid the cost of obtaining 3.5 prechambers and injectors.

Ideally, get the cam and cam towers with the head if only because of 1-2-300K miles of wear on the bearing surfaces. On a budget, who cares? The main head bolts are the same so there's no need to replace yours if they're in spec. You'll need the pair of longer bolts that go into the front cover. Nice to have OE bolts but anything you find at the hardware store that fits will work.

Make sure you get a 3.0 head gasket like you mentioned. About the only part that you can't/shouldn't use in the swap is a 3.5 head gasket. Oh, and the glow plugs. Use glow plugs for a 3.5.

There's no reason to replace the chain unless it's elongated beyond spec. If you need a new chain, replace it before or after messing with the head, not during the head swap. You don't need more variables if you're doing this for the first time, and the only step in common to the jobs is pulling the valve cover. To be clear, replace the chain, get the car running properly, then swap the head; or swap the head, get the car running properly, then replace the chain.

At least have the replacement head checked for flatness. Even a seller with the best intentions might not know if the head is warped.

If you fit new valve stem seals, use only genuine MB seals. Some aftermarket seals are known to leak and the price difference isn't worth the risk of that PITA of a job. Heck, it isn't even an easy job on a bench!

Despite what the FSM says, don't use a magnet to remove the lifters. Magnetized lifters will trap ferrous particles circulating in the oil. Use a suction cup like a valve lapping tool.

The 3.5 temp sender has an additional pin for an afterglow relay. I *think* it'll work with an early gauge if you change connector shell and you'll be ready for an afterglow relay upgrade.

Sixto
MB-less

thank you so much for the detailed reply! am getting this head at a local junk yard that is owned by one of my dad's friends so i want to get everything i could need the first time. i won't be paying any more if i leave the injectors in it, glow plugs, cam or anything like that. and thank you for clearing that up on the timing chain. i won't mess with that yet. very cool about the afterglow setup! i'll grab the relay to mess with later if it's there. are there any threads on 603 head removal and or installation? i'm on my own removing the head and haven't done it before so things like "remove the lifters" are good to know haha! and to clarify, leaving all the 3.5 #22 injectors, pre chambers, glow plugs, and injector lines will all be good upgrades? will the angled injectors have any power improvement or allow for better mpg? and the cam and towers should be gotten with this new 3.5 head as well?

When removing the head, CLEAN OUT AND DRY EACH HEADBOLT FIRST! Also, go to snap on, and buy the XZN tool set. It's about $140 it's worth it. The bolt heads are shallow, and if you are even slightly off center, you need to drill out and or grind off your mistake...
Find a diagram of the HEADBOLT tightening sequence, and remove in the opposite order.

You should take a hinge handle and a speed wrench with you for bolt removal, also bring a magnetic pan for bolts, and a magnet-on-a-stick and good flashlights... Dropping things is annoying!

ok, cool! i do have access to my friends quality triple square set and i will be very sure to clean the bolts so the tool bit can seat. on another note, this #14 head i have now confuses me. sometimes i can drive it and the hoses will not build up any pressure on a good drive. and other times the hoses will be stiff and leaving it over night there will still be a little pressure left when i pop the cap off. no loss of oil or coolant. wierd

Im also looking at a replacement, a #17 head off a 92 300SD 232K miles. Curious to know how many miles are on the #22 donor head you're looking at? Here is a tightening sequence pic courtesy of sixto from a previous thread that maybe helpful, 603 diagram at bottom.