Chose which OM617 head to rebuild - PeachParts Mercedes-Benz Forum

gottarollwithit · #1 07-13-2020, 04:02 PM

I'm contemplating doing a head gasket replacement on my 83' 300DT.

-I have a spare motor 84' w/ 170k mi on it, crashed, shattered the oil cooler, ran for a couple min afterward. Looks like an honest original motor that's seeping some oil externally out the HG. Obviously, that ran dry for a minute or two.

-My current motor is one of the famed Tauschaggregat factory replacement motors. Dunno when it was installed, but i'd assume it has about 150-200k mi on it.

Reason i bring this all up --- Tauschaggregat factory replacement motors are not actually brand new engines. From what i gather, they are nicely done factory rebuilds (new sleeves, IP, turbo, etc).

Do these motors feature brand new cylinder heads? Or, are they refurbs?

The core head might have many more miles than 170k, hence possible additional cracking. Which do you guys rec rebuilding?

ROLLGUY · #2 07-15-2020, 03:19 PM

The only real way to know for sure is to remove it and inspect. If no cracks, it should be a good candidate for a rebuild. Every (Good) head rebuild should have the following: Pressure checked, Prechambers removed, Hot Tank, Valves and Seats ground, Head surfaced, New Valve Guides and Seals installed, Thicker Prechamber Seals if needed. New head bolts should always be used. Some say they can be measured and re-used if in spec, but not worth the effort in my opinion. Peace of mind is worth the cost of a set of new bolts.

t walgamuth · #3 07-15-2020, 03:22 PM

My machinist always measured the head bolts before any re-using of them,,.I've never a problem re using them. It is in the FSM how to do it. The heads on a 617 seldom crack, but it is always good to check them as Roll guy says.

5cylinder · #4 07-15-2020, 08:29 PM

Quote:

Originally Posted by t walgamuth

Take solace in the fact that the heads on a 617 seldom crack.

It is not often my nature to throw dung and I won't start now...the fact that you've made 35,000+ posts also factors into my calculus, LOL.

Having said the above...
If you say so...but that does seems a bit out on the margins to me for being true. But hey, maybe you got this thing down pat.

On a related subject, I'm a little foggy on this but I seem to recall from many years ago that head refurbishment, the big leagues kind, had a refurbisher actually x-raying heads to ensure that any cracks were found.

ROLLGUY · #5 07-15-2020, 09:27 PM

Quote:

Originally Posted by 5cylinder

It is not often my nature to throw dung and I won't start now...the fact that you've made 35,000+ posts also factors into my calculus, LOL.

Having said the above...
If you say so...but that does seems a bit out on the margins to me for being true. But hey, maybe you got this thing down pat.

On a related subject, I'm a little foggy on this but I seem to recall from many years ago that head refurbishment, the big leagues kind, had a refurbisher actually x-raying heads to ensure that any cracks were found.

Common practice nowadays is to pressure test, or magna-flux. The smallest of cracks that a x-ray would detect, are probably of no consequence on these engines. Out of the many OM61X heads that have come across my path (there have been many), I only remember one that was cracked bad enough to be considered scrap.

5cylinder · #6 07-15-2020, 09:42 PM

Quote:

Originally Posted by ROLLGUY

Common practice nowadays is to pressure test, or magna-flux. The smallest of cracks that a x-ray would detect, are probably of no consequence on these engines. Out of the many OM61X heads that have come across my path (there have been many), I only remember one that was cracked bad enough to be considered scrap.

This is helpful information. Thank you for explaining.

gottarollwithit · #7 07-16-2020, 01:35 AM

There’s a local machine shop that’s pretty well versed in OM617 heads, so I’m not too concerned with the thoroughness of the rebuild.

However, do the Tauschaggregat factory rebuild motors feature new or rebuilt heads???

It is better to rebuild a head that’s never been rebuilt before.... wouldn’t it be smarter to chose whichever has the least miles on the core head casting?? If the Tauschaggregat head has been rebuilt, that means it had miles and maybe warpage on it before it became Tauschaggregat, thus it has already been resurfaced. There’s not much to shave off in these heads.

Also, as everybody knows, once a cast iron head is cracked, it can’t realistically be welded back. It can be drilled and pinned to stop propagation, but it will never really be as good as uncracked. Yea, you can put it in a furnace, weld it, slow cool, etc but I’m sure what that costs exceeds the cost of another core.

Granted, the best way to determine the best rebuild candidate would be to pull both heads and assess them side by side. As that’s a mighty hassle, I’d like to only pull one..

barry12345 · #8 07-16-2020, 08:18 AM

The rebuilt head has probably been shaved a little already. So it will have to be flat basically to rebuild again. I was actually wondering if a properly rebuilt head at 170K was really needing another rebuild to start with.

Most my engines at around 200-225k do not seem to have any head issues. Head rebuilds were cheap at one time in comparison to today.

How many true miles does a 617 head go on average before needing serious attention? I would factor in the condition of the car to make a decision about to rebuild the rebuilt head or not.

Plus how the car is used. A daily driver or one relegated to only occasional use. If the current engine runs really well and the head is still flat I might just change the head gasket. The head gasket may have just rotted with age. That way you still also have a complete lower milage engine on hand. They will become scarce at some point.

What you are asking involves a lot of personal unknown factors in my opinion. That change what a person might do.

t walgamuth · #9 07-16-2020, 09:44 AM

Quote:

Originally Posted by gottarollwithit

There’s a local machine shop that’s pretty well versed in OM617 heads, so I’m not too concerned with the thoroughness of the rebuild.

However, do the Tauschaggregat factory rebuild motors feature new or rebuilt heads???

It is better to rebuild a head that’s never been rebuilt before.... wouldn’t it be smarter to chose whichever has the least miles on the core head casting?? If the Tauschaggregat head has been rebuilt, that means it had miles and maybe warpage on it before it became Tauschaggregat, thus it has already been resurfaced. There’s not much to shave off in these heads.

Also, as everybody knows, once a cast iron head is cracked, it can’t realistically be welded back. It can be drilled and pinned to stop propagation, but it will never really be as good as uncracked. Yea, you can put it in a furnace, weld it, slow cool, etc but I’m sure what that costs exceeds the cost of another core.

Granted, the best way to determine the best rebuild candidate would be to pull both heads and assess them side by side. As that’s a mighty hassle, I’d like to only pull one..

Is your head gasket leaking? I don't believe you have said.

barry12345 · #10 07-16-2020, 12:07 PM

He was contemplating a head gasket change. So I assumed right or wrong it was the issue. The rebuild only as the head was removed to do it. Needless to say assumptions are dangerous.

gottarollwithit · #11 07-16-2020, 09:11 PM

My current Tauschaggregat motor is leaking oil externally from the HG in the passenger corner behind #5. Runs fine, just leaking oil... and exhaust from the intake/exh gasket.

So, just for confirmation, do Tauschaggregat engines feature rebuilt or new cylinder heads???

If it’s been rebuilt once already with MB, it’s not worth playing with. There’s no way to know what the owner of the “core” did with it.

The machine shop said that after 170k mi, it is worthwhile to recut the valve seats to assure good sealing. Makes sense - if I had the head is off and at the shop I’d do it anyways.

t walgamuth · #12 07-16-2020, 10:13 PM

I don't know if they use new heads or not. I would assume if using a used block they would use a used head too unless for some reason a new head was called for. I would not worry about going through a head more than once. The fsm gives all critical dimensions including thickness of head and how much to deck the block. Following them should yield good results. If the head is off and has significant miles on it yes. do a valve job.