Question for the Diesel Experts, 1967 200D head crack - PeachParts Mercedes-Benz Forum

tram · #1 01-12-2012, 10:52 PM

1967 200D.

Engine suddenly overheated and *appeared* to pump compression into the coolant. I got it over here and ripped into it. I was able to drive it around the lot and into the shop. It ran super strong, but got hot within about ten minutes.

No apparent faults with the head gasket. In fact, what happened was that the new German thermostat failed- it won't even open in boiling water.

So, I'm examining things, checking flatness with a straightedge, checking valve seats/ valves using the brake fluid test, and getting ready to put things back together. The customer also had been noticing sudden excess smoke and poor MPG just prior to this. From what I can see, the #3 piston is carboned all to heck, indicating an injector issue.

But wait... on #2, I notice what appears to be a tiny crack. I clean things up really well for closer examination, and it's about a 10mm long tiny fissure that runs from the prechamber that sticks down into the combustion chamber AWAY from the valves, pointing towards the manifold.

My gut instincts tell me that this probably isn't a problem, but this is a daily driver car, and I don't want to put the customer back on the road this way unless I'm reasonably sure I'm correct. The problem is that 200D heads don't grow on trees anymore. If they did, there wouldn't be any question that I'd replace it as a matter of course.

What says the jury?

mercmad6.3 · #2 01-13-2012, 01:34 AM

you dont know how hot the customer has had it, and that crack will get worse not better.Do you have a head shop that can pressurize it for you ?

tram · #3 01-13-2012, 01:45 AM

Quote:

Originally Posted by mercmad6.3

you dont know how hot the customer has had it, and that crack will get worse not better.Do you have a head shop that can pressurize it for you ?

No, I don't. Wish I did. It *seems* like it's in an area that shouldn't be subject to any stresses (like valves) or anything like that (which also begs the question- why is it there?) and it could be shallow. I just don't feel confident enough to make a decision on this.

As to how hot the customer got it- I'm not seeing any signs of heat damage, or even paint burned off, and except for carboned- up #3 with the clattering injector, the combustion chambers and "burn trails" look perfect. Other than that stupid little crack- which doesn't seem heat related at all- I'd have had it back together and running already. I almost didn't even see the damn crack till I cleaned it up and examined the head under a bright light with a magnifier. Now that I know it's there, I see it of course, but it's still a sort of "is that really a crack? Yes, it is" kind of thing.

mercmad6.3 · #4 01-13-2012, 03:02 AM

I was doing a 617 head last year and my engine machinist tells me new heads are available very cheaply for those. I don't know if you can get them in US though ( chinese i would say) .
Any crack is a worry in diesel though,there is too much compression to allow them.
Is it the actual head casting or the prechamber?

tram · #5 01-13-2012, 04:19 AM

It's the head itself. This is an OM621, cast iron head.

mercmad6.3 · #6 01-13-2012, 04:51 AM

Mercedes benz engine OM612 cylinder head - Detailed info for Mercedes benz engine OM612 cylinder head,Cylinder Head for Mercedes benz engine OM612,Mercedes benz engine OM612 cylinder head,Mercedes benz OM612 on Alibaba.com

These people can supply you with 50,000 per month ...ha ha ha

daw_two · #7 01-13-2012, 07:48 AM

I have a complete 200D engine with manual transmission. PM sent.

engatwork · #8 01-13-2012, 08:40 AM

Wonder what the unit cost is when you purchase 50K?

t walgamuth · #9 01-13-2012, 09:20 AM

If you would like to ship it to Lafayette In my machinist has a head pressure tester. I imagine the crack has a good chance of being a problem. PUshing pressure into the coolant is a pretty strong sign of head sealing or cracking issues.

It may be weldable too.

1960mog · #10 01-13-2012, 11:44 AM

Never reuse a 621, 615, 616, 617 head with a crack.
Even if it passes a pressure test.
This cracks are heat related and can occur just because of normal expansion / contraction of the cast iron, or are triggered by overheating.
They always originate in a valve seat.
If the crack isn't deep enough to reach the water jacket jet, it will do so in a short time if you reuse the head.

tram · #11 01-13-2012, 04:45 PM

Quote:

Originally Posted by 1960mog

Never reuse a 621, 615, 616, 617 head with a crack.
Even if it passes a pressure test.
This cracks are heat related and can occur just because of normal expansion / contraction of the cast iron, or are triggered by overheating.
They always originate in a valve seat.
If the crack isn't deep enough to reach the water jacket jet, it will do so in a short time if you reuse the head.

This one originates from the prechamber hole and radiates about 8mm DIRECTLY AWAY from the valves. The valves aren't involved. If they were, I wouldn't be asking this question. The head, cam, and valves are like new.

whunter · #12 01-13-2012, 05:30 PM

Quote:

Originally Posted by tram

This one originates from the prechamber hole and radiates about 8mm DIRECTLY AWAY from the valves. The valves aren't involved. If they were, I wouldn't be asking this question. The head, cam, and valves are like new.

What country and/or state are you in?

.

tram · #13 01-13-2012, 07:12 PM

Quote:

Originally Posted by whunter

What country and/or state are you in?

.

I'm in Eugene/ Springfield, Oregon USA.

I'm going to attempt to get a clear picture of what I'm talking about posted here shortly.

whunter · #14 01-13-2012, 08:27 PM

Have you checked with these places for pressure testing the head?

Drummond Automotive Machine
83660 Hawks Way
Creswell 97426
(541) 895-3010

Southworth Inc
754 Fillmore Street
Eugene
(541) 431-0556

Carrothers Machine Shop
1555 North Pacific Highway
Cottage Grove
(541) 942-7373

Caldwell Automotive & Machine Shop
2310 Main Street
Springfield
(541) 746-9661

Engine Research & Development
4440 Main Street
Springfield
(541) 744-6206

.

tram · #15 01-13-2012, 11:50 PM

whunter, thanks for that info. I've had unsatisfactory dealings in the past with a couple on that list. I guess I'm also victim to that Teutonic dim view that people who appear to be incompetent rednecks usually are. LOL. In this part of Oregon, getting anything done correctly has been, at least for me, a crapshoot, so the longer I'm here, the more I do things 'in house'. This way I know it's done the way I want it done and I'm not going to be upset later.

But there's one place on there that I've never seen or heard of before- and they're supposedly about 20 blocks away from my home on Main st. in Springfield, so I'm going to check it out.

Now- I wound up answering my own question about the crack. I wanted to resolve this before going any further. If it were my own car, there wouldn't be any question that I would have adopted a 'try it and see' attitude, but not on a customer's.

I spent some time perusing my old 3 volume 1959- on dealer repair manual, and found that they did indeed address the issue of cylinder head cracks specifically on the OM621 engines. They show a drawing with four cracks, A,B,C, and D. Mine is an "A" type (how fitting to my personality!) and it says, specifically, "Cracks 'a' which run from the bore of the prechamber and are no longer than 15 mm do not affect the proper functioning of the cylinder head, since they do not extend towards the water jacket. Cylinder heads with this type of crack should on no account be discarded, they are absolutely safe."

So, the godz have spoken. NOW I'll likely see if this place down the street exists, have the head pressure checked if they can do that, and reassemble this heap.

Thanks for the help, and hopefully this info will be of use to someone else down the line!