Folks, if it's okay, I'm going to try to keep this head replacement project contained in one thread rather than post fifteen different "Now what" threads.

My 1986 300SDL with a #14 head is showing enough symptoms that we think replacing the head is justified. Pressure in cooling system overnight (and for weeks after), very short time from engine cold start to full running temperature, and overheating every time it comes near a steep hill.

The parts engine was a pull-a-part find out of a 300SDL. We're PRETTY SURE (but not positive) that what we've got is a junkyard bottom end from a 3.0liter just like our block, BUT the junkyard parts engine already has an inclined injection head on it. Can't remember the casting number and it's currently at home with my dad instead of at school with me. But definitely higher than 14. What we suspect is that our junkyard engine ($150.00 or so for everything from the fan to the flywheel) cracked its own #14 and a previous owner had an inclined injection (3.5l?) crack resistant head put on.

The head was put on by a gorilla with a tool bag. Some of the head bolt heads were almost stripped (one came out with an air wrench and one came out with a hammer and chisel; the rest could be taken out by wrench like you're supposed to) and the injector lines were the old straight-injection lines that had been poorly bent to fit. They didn't put the plastic spacers in and the lines had rubbed themselves almost through to leaking in a few spots.

I've got a few questions that I haven't gotten a clear answer to from all the threads I've read about this (about fifteen total) and I'm going to post them here and then when I've got a progress update or a new question, I'll come back. My dad is doing most of this this week (hopefully) while I'm at school, 100 miles away from the car. However, I'll be down there this weekend to check it out, and this is still the best way to get our answers. So please bear with me for not looking at this thing in person while I ask some of our questions.



1. Do we use the cam shaft from our existing block that we're transplanting the replacement head onto, or does the camshaft stay with the head instead, requiring us to use the cam from the donor engine?

2. I've read some people who say that you can mix and match injectors, and others who say that *injectors from a 3.0 liter engine will NOT screw directly into an inclined injection head without modifying the prechambers*. If the latter statement is true, WHAT is the nature of the prechamber modifications, and specifically WHY is it necessary? We do not currently have a prechamber puller and were not planning to take them out, but we will if we have to.

We want to, if at all possible, use the injectors from my old 3.0 engine with the straight cracked head. They're a matched set and all original or at least all M-B. The ones that came in the parts engine were a mishmash of all sorts of different things.

3. What's the deal with the bolt lengths that changed either with time or head design or both? We're planning to measure the stretch of the bolts that we remove from my 3.0 engine and use *as many as safely possible* of these. We'll only use the head bolts from the donor engine if we absolutely have to since they showed more evidence of abuse. We believe my 3.0 cracked head is original. The replacement is itself a replacement and so those bolts have already probably been used twice.

Which bolts have to be longer than "the book says to use"? That's what I'm remembering; when you do this swap, according to some threads; the factory specified longer bolts for about 4 of the holes (IIRC) than the book will state. I've got a paper printed FSM for the 603 series engines so those are the diagrams we'll be using.



I will post more of our questions here as we come to them. Generally a "one thread for all related questions" approach as long as they are on the same subject gets a friendlier response around here than fifteen questions all about the same procedure, so I'll confine it here unless a mod. suggests otherwise.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Either cam will work fine,
The inclined-injection head has different pre-chambers, need to modify yours to fit in the inclined-injection head and use your injectors,
the two bolts in the chain cavity are longer on the inclined-injection head.

__________________

Gone to the dark side

- Jeff

1) What Jeff said.

2) Injectors and prechambers are matched between early and late heads. No two ways or modifications between injectors and prechambers. Early prechambers can be modified to fit a late head. It's hardly worth the effort to force early prechambers onto a late head if you have late prechambers and injectors. Spend the money instead getting the late injectors in good shape.

3) There are three lengths of head bolts, each with an elongation tolerance. All these bolts are the same for early and late heads. The two bolts that go into the engine front cover are longer on the late head and are separate from the three lengths of head bolts. The two smaller bolts, and a couple others by the fuel filter aren't part of the head bolt torquing sequence. I think the FSM describes them as a and b.

Don't be too hard on the folks who installed the head. If the original head cracked, it's likely coolant, mostly water, got into the head bolt holes and corrosion ensued. Be a little hard on them. They should have cleaned the threads and oiled the bolts before fitting a new head.

Sixto
87 300D

Thanks very much. If I understand correctly, what I need to do is remove the prechambers from the 3.5 head and put them aside since they are not useful. Remove the prechambers from my existing 3.0 cracked head, lathe them down a tiny amount so that they will seat evenly at the top and the bottom, and mount them in the 3.5 head, and then screw my old 3.0 injectors back into them (the same ones they've always had).

Why is it that I can't use the 3.5 prechambers and 3.5 injectors and simply mount the whole assembly onto my 3.0 block? Are the injectors themselves interchangeable?

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Thank you. You answered most of what I just posted for me while I was typing it. never mind that new question I just asked

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

You can.

Have you confirmed that the new head has inclined injectors? You can't easily tell when they're installed, thought I think the inner surface of later prechambers is splined while early prechambers aren't. To be absolutely sure, remove the injectors and check the thread configuration. [edit] Error noted by Billybob corrected - Late in the top row, early in the bottom row -



Prechamber inclination is cast into the head so early and late prechambers will look inclined when installed. There's an obliqueness to the injection pattern to the late prechamber and injector that you can't discern by looking at the head.

Sixto
87 300D

Check the engine number on the horizontal surface of the block ahead of the IP. 603960 or 603961 is a 3.0 block. 603970 or 603.971 is a 3.5 block. If there's no engine number at that location, check the passenger side of the bellhousing for a riveted tag identifying the engine.

Sixto
87 300D

The head is a #22 so I didn't think to check if somebody had already replaced the prechambers with old-style. Will report back.

EDIT spoke too soon. Dad reports that we DO have a screwdriver-slot looking spline on the top of our prechambers in the replacement head. So I'd say yes, fairly certainly, we do have inclined injectors with the new head.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Might want to double check and correct the commentary or change the picture!

The picture shows the late inclined injectors in the top row, they have finer threads at the bottom ot the nozzle holder, this allows then to be installed directly into the threading of the prechamber itself (the same threading that the precamber puller tool actually threads into), this is necessary because the inclined injection scheme uses the splined prechamber rings to secure them into the cylinder head.

The early style stanmdard injectors are in the bottom row, they have larger threads higher up on the nozzle body. This is because like 615/6/7 injectors they actually thread not into the prechamber itself but into the internal threads of the pin style prechamber securing ring.

I have an SDL with a 14 head and the second row "later" style injectors? Is this normal or has someone changed my prechambers? My understanding was that with the 14 head I should have the early injectors?

__________________
Serenity-86' 300SDL 482,000 miles (on a "14" head!)

I'd be happy to be corrected, but I was under the impression that the inclination was in regard to the way the nozzle holder (injector) interfaces with the prechamber, it does so at an inclination of 5 degrees. That is why the injector threads into the prechamber rather than the securing ring, the prechamber is keyed into position in the cylinder head with the small semi-circular protrusion. The securing ring can't be the recipient of the injector because it's rotational position is indeterminate, the injectors could end up arrayed in any haphazard positions in relation to the prechamber ball and openings as well as to the other injectors in the row, the hard lines would be impossible to re-attach if every injector didn't end up in exactly the same position.

I've got both a #14 OM 603 cylinder head and a OM 602 inclined injection cylinder head sitting in my parts washer and will get a read on any difference tomorrow if no one points to verification of some difference in the position of the prechambers between them.

Slotted or Pin type prechamber securing rings are usually associated with early style standard injection. I don't know if the pin type rings can be used with inclined injection prechambers and injectors. It may be that the change to the splined rings was necessary to prevent interference with the inclined injector body because the 5 degree inclination leans the injector off the center bore and the Pin type rings are too small an ID to accomodate that design change.

If your head shows the early pin style rings I'd be more inclined to believe it uses the early style injection system and the prior owner has already modified the early style precahambers to be used in the later style cylinder head.

The only way to know for certain is to pull one of the injectors though!

All six are pulled out and sitting on the bench but they are two hours away and my first opportunity to post a picture of them or describe them will be this Friday. My fault for starting a thread from somewhere besides 10 feet away from the car

The debate can continue until then regardless of what my personal head has; I'll just stick a picture up here when I have one and we'll sort it out then. Sounds like we're still not sure which bits go with which heads no matter what I've got in the basement.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Cam profile is the same. What you really should do is plastiguage every combination of cam/head journal and use the one that is nearest optimal factory specs. Loose cam journals mean low oil pressure.

__________________
1998 E300 +310,000K
1996 E300 +460,000K

Check the lobe height also, and look for scoring. I have mic'ed four of my cams and found ~.010" difference between highest and lowest, I'd use the highest (least worn).

I believe that the actual injector (nozzle) is the same, it would probably be as or more cost effective to remove your injectors from your nozzle holders, and have them inserted/balanced in the inclined-injection holders (about $20/ea here and probably less than any machining work on the pre-chambers).

__________________

Gone to the dark side

- Jeff