OM606 head machining info - PeachParts Mercedes-Benz Forum

diesellover 92 · #1 09-18-2017, 10:26 AM

So i have my head removed and at work. I just so happen to have access to an r&d department with several journeyman tool and die makers. Unfortunately none of them have done engine work. I would like to skim the head .002 thou. But im not sure if i would remove material around the valve area or only around the chambers. Head is currently sitting on my bench with layout dye. Going to stone the surface and remeasure to get a better idea.

Maxbumpo · #2 09-18-2017, 10:32 AM

Don't do it, unless it is REALLY not flat. Aluminum heads will flex a little when you torque them down. Read the factory service manual. A certain amount of out-of-flat is allowed. If you take off any material, you have to take off the amount specified in the manual and use the thicker "repair" head gasket. If you remove material but don't use the thicker gasket, you will have at least two problems. The pre-chamber nozzles may contact the pistons. The timing chain will be effectively longer, and cause problems with valve timing and injection pump timing. You can correct the valve timing with an offset key IF they are available. IP timing is adjustable.

ROLLGUY · #3 09-18-2017, 10:35 AM

You should check the head to see if it is flat across the entire surface. Most machine shops have a precision ground straightedge that is used with feeler gauges. .002 may not be enough to make the head flat. The head surface laying on a stone table (not exactly sure of the exact name) will work too, using feeler gauges around the edges. The straightedge is better for measuring the center between combustion chambers.

Diesel911 · #4 09-18-2017, 12:04 PM

Sounds like a close reading of the factory service manual is what is needed.

diesellover 92 · #5 09-18-2017, 01:33 PM

I don't have the manual, only what is on w124 performance site. I tried buying some tek star time but keep getting an error with a known good card. So we setup the head using some GDT. Geometric dimensional tolerance. The head has a .010 thou bow in the middle. I will check after work what the parallelism is between top and bottom. Perhaps the head is flat but slight curved, which will be remedied by being bolted down.

Diseasel300 · #6 09-18-2017, 01:56 PM

There's a reason why so many folks suggested getting a copy of the FSM before touching that first bolt.

ROLLGUY · #7 09-18-2017, 02:40 PM

Quote:

Originally Posted by diesellover 92

........... Perhaps the head is flat but slight curved, which will be remedied by being bolted down.

It needs to be flat and not "curved" BEFORE it is bolted down. If the head is sitting on a precision flat surface, and there is a gap on opposite corners, or a gap in the middle with both ends tight on the surface, (I assume that is what you mean by "curved"), it will need to be machined flat BEFORE it is bolted to a block.

spock505 · #8 09-18-2017, 03:30 PM

The metal MB sandwich gaskets are pretty chunky, wouldn't have thought that sort of distortion would matter.

diesellover 92 · #9 09-18-2017, 05:34 PM

Quote:

Originally Posted by Diseasel300

There's a reason why so many folks suggested getting a copy of the FSM before touching that first bolt.

Yeah and I tried to get one. It's not a big deal, I picked up this car for cheap. Worst case scenario I wait until I get a used motor. Feel free to send me a pdf if you have one. Haven't decided, might skim it and put the stock gasket on and see how it runs or I'll put a new gasket and see how it runs. Based on the vmi, first head gasket was done at 95k. Had the timing chain done at 150k along with the second gasket, rebuilt injectors, trans service and a.c. compressor replaced. Guy I bought it from paid 4100 a few months ago at 190k. Now at 195k head gasket went.

spock505 · #10 09-18-2017, 05:38 PM

Could be the garage re-used the stretch bolts, this can be done but need to be in spec, wouldn't use them a third time however.

ROLLGUY · #11 09-18-2017, 05:41 PM

Quote:

Originally Posted by diesellover 92

Yeah and I tried to get one. It's not a big deal, I picked up this car for cheap. Worst case scenario I wait until I get a used motor. Feel free to send me a pdf if you have one. Haven't decided, might skim it and put the stock gasket on and see how it runs or I'll put a new gasket and see how it runs. Based on the vmi, first head gasket was done at 95k. Had the timing chain done at 150k along with the second gasket, rebuilt injectors, trans service and a.c. compressor replaced. Guy I bought it from paid 4100 a few months ago at 190k. Now at 195k head gasket went.

Sounds like a substandard head job last time (they might not have surfaced the head, and/or used the head bolts over). You can also get thicker prechamber seals. Measure the seals that came out, and compare to the thickness of stock and oversize. Yes they will compress a little, so your measurement may not be exactly the same as a new one.

diesellover 92 · #12 09-18-2017, 06:00 PM

I am also not to keen at spending much on this engine due to the amount of sludge i found when i pulled the valve cover. It did start up instantly and idled smooth with nice cloud of smoke, but i would not consider the substance lubricating the engine "oil". Cam journals did not look bad, not heat damage or scoring so maybe its find but who knows.

97 SL320 · #13 09-18-2017, 06:34 PM

Specifically where and how did the head gasket fail?

With a cam in head engine, the cam bore will be warped also. Some automotive machine shops will measure the amount of bow, place shims on each end of the deck then bolt the head to a flat surface. The whole mess is then baked in an oven to pull the head back flat, at this point it only needs a slight cut to clean the surface.

diesellover 92 · #14 09-18-2017, 06:47 PM

Quote:

Originally Posted by 97 SL320

Specifically where and how did the head gasket fail?

With a cam in head engine, the cam bore will be warped also. Some automotive machine shops will measure the amount of bow, place shims on each end of the deck then bolt the head to a flat surface. The whole mess is then baked in an oven to pull the head back flat, at this point it only needs a slight cut to clean the surface.

Couldn't tell you, bought it blown. Guy was early 20s. He said that he added coolant a few times when the light came before he realized where it was going. Then parked it at the random shopping center he was at 15 mins from his house. I will never know how hard he beat on it,

97 SL320 · #15 09-18-2017, 07:48 PM

What I'm asking is did you look at the actual gasket to determine point of failure?

Many people call any loss of coolant a blown head gasket / cracked block.

When making any repair, it is critical to determine the exact point of failure in order to make a lasting repair.