OM617 Head Gasket Replacement w/o Rebuild? - PeachParts Mercedes-Benz Forum

gottarollwithit · #1 07-23-2020, 04:12 AM

So far, i've tilted back the intake/exh mani/turbo. It's at a point where i could easily put in a new intake/exh gasket and fix the exh leak.

However, i'm contemplating replacing the HG just for thoroughness of the repair. (It's externally leaking oil and i already bought a HG kit). Motor has never been overheated, so the block and head will be straight. Problem is, i'm not very well versed in diesel motors w/ prechamber.

I don't want to dump $$ into this motor (even though it's a Tauschaggregat) because it has a low oil pressure on startup issue, not a caused by the oil filter housing. I'd assume main bearing or oil pump related - IE i'll be putting in the spare motor when that dies.

What are the consequences if i just replace the head gasket and head bolts? Realistically, straight is straight, resurfaced or not. Won't be guaranteed crack free, but it runs well, so assuming crack free is pretty safe.

Can I resurface the head w/o resetting or doing anything with the prechambers? Looking at the head, i think i'd need to reset the prechamber nipple height?

Thoughts on a mega low budget HG swap?

hercules · #2 07-23-2020, 05:35 AM

Only need to surface head if it is not straight or pitted in some way.

gottarollwithit · #3 07-23-2020, 06:29 AM

That’s what I’d say if this was a traditional gas motor.

Need I worry about the prechamber nipple that protrudes into the cylinder? Would be mighty bad for it to collide with the pistons...

hercules · #4 07-23-2020, 01:05 PM

If swapping heads from different engine,measure head thickness,if stock there should
be no problem. If head has been surfaced you may need thicker per chamber shim.

gottarollwithit · #5 07-23-2020, 07:55 PM

Just talked to my machine shop. While I might be able to resurface the head and run it, this would require removal of the prechambers, then likely shimming them up. Mechanistically, the shop would probably run a big fly cutter across the heads deck. No way to cut around the prechambers.

Also, supposedly these heads tend to develop a wavy surface after a lot of miles, so a simple gasket swap without resurfacing might not work.

Anybody confirm this?

hercules · #6 07-23-2020, 09:32 PM

Sounds like a lot of hear say going on. The only way to know is ck.
My 300sd blew a head gasket at 640,000 mi.Just plain old age,checked for straightness,
was good,cleaned up reinstalled,Using old head bolts,they did ck with-in specs.
Have repaired thousands of these Mercedes,stay with-in the specs,use common sense,
things well be good.

Sugar Bear · #7 07-23-2020, 09:49 PM

Going to have to pull it to know. It's a coin toss on whether or not it will need to be resurfaced. There is a minimum head thickness, find that spec before resurfacing and measure the head.

IMO I'd do a compression test before pulling the head to ID a leaky valve or ring/piston problem. Lot of work to find a leaky valve later. At a minimum have the machine shop vacuum/leak test the valves.

As far along as you are, yes I'd replace the head gasket as the oil leak will only get worse.

Good luck and keep us posted.

gottarollwithit · #8 07-23-2020, 11:00 PM

On one hand, I share the same opinion as Suga. Leak is only gonna get worse and the bulk of the fight to replace the HG was with the intake/turbo.

On the other, I’m thinking that this motor has a funky low oil pressure on startup issue not resolved by swapping oil filter housings. Takes about 4 sec to develop oil pressure if I haven’t driven it for a day or so.

Prior to disassembly, it ran fine. I’m just hesitant to mess with it, risking needing to rebuild the head, which is a waste of $$

ROLLGUY · #9 07-24-2020, 03:41 PM

Quote:

Originally Posted by gottarollwithit

Just talked to my machine shop. While I might be able to resurface the head and run it, this would require removal of the prechambers, then likely shimming them up. Mechanistically, the shop would probably run a big fly cutter across the heads deck. No way to cut around the prechambers.

Also, supposedly these heads tend to develop a wavy surface after a lot of miles, so a simple gasket swap without resurfacing might not work.

Anybody confirm this?

Having done MANY of these, I would NEVER put a head back on without giving it a rebuild. The cost for parts and the labor (even if doing it yourself) is not worth it without putting a rebuilt head back on. The valve guides wear, as well as the seals, so they should be replaced whenever the head is off. If the head has never been off, you can go with the standard thickness prechamber seals (done it many times), as long as no more than ten thousandths is removed from the head. If more, thicker seals are available. Yes the prechambers have to be removed. It is best to remove them with the head bolted to the block. Even though some say it is okay to reuse the old head bolts, again, it is not worth the $ to use the old head bolts, and find that they have stretched beyond their limit AFTER you get into torquing them down......Rich

gottarollwithit · #10 07-24-2020, 05:46 PM

Yes, this is the kinda info I’m looking for.

I’m not too concerned about the valve guides, valves or stem seals. I can inspect that stuff at home, and they’re not currently causing a prob.

However, I’m mostly worried about the head not being straight. While it’s never been overheated, it is possible that 170k mi of running distorted it a bit. True??

I want to toss a hg in with all of the old valves, guides, etc because I don’t think this engine has another 100k mi left in it

ROLLGUY · #11 07-24-2020, 06:12 PM

Quote:

Originally Posted by gottarollwithit

Yes, this is the kinda info I’m looking for.

I’m not too concerned about the valve guides, valves or stem seals. I can inspect that stuff at home, and they’re not currently causing a prob.

However, I’m mostly worried about the head not being straight. While it’s never been overheated, it is possible that 170k mi of running distorted it a bit. True??

I want to toss a hg in with all of the old valves, guides, etc because I don’t think this engine has another 100k mi left in it

Well, it is your car, and you can do as you please with it. I guess I should say that you "gottarollwithit".

gottarollwithit · #12 07-24-2020, 09:33 PM

Now the big question is, do I pull it and Risk needing a few hundred bucks in repairs or do I seal it back up the way it is and run her til she blows?

ROLLGUY · #13 07-24-2020, 10:15 PM

Quote:

Originally Posted by gottarollwithit

Now the big question is, do I pull it and Risk needing a few hundred bucks in repairs or do I seal it back up the way it is and run her til she blows?

It's you $, so do what you feel best about. However, I would spend the $ if it was mine, because "ALL OM617's MATTER"............Rich

Maximan1 · #14 07-28-2020, 11:45 AM

When I rebuilt my OM617 (that had a melted piston from the previous owner), we checked the head for flatness at the machine shop. I had to do no machining on the head, it was perfectly flat despite the abuse. In fact, I only had to machine the block because I put in new cylinder liners.

I would have the head checked, but definitely set the $$ aside to do it right if the head isn't flat.

gottarollwithit · #15 07-28-2020, 03:28 PM

After much debate, I’ve decided to pull the head and rebuild it. Such a waste of $$, but I like being smog exempt.

I figure, I’ll run this motor til it blows then transfer the head to the spare motor when the time comes