Mercedes-Benz Forum banner

Cracked Cylinder Head Repair/Replace

37K views 63 replies 10 participants last post by  winmutt 
#1 ·
Today I found out I have two cracks in my 602 aluminum cylinder head, from my '91 300D 2.5TD. The car is in good shape, ran great until the cracks, and I want to continue with the repair.

I'm looking for experience and suggestions on either repairing the cracks or replacing the head. I would prefer to weld the cracks, at a recommended shop. I am in central Illinois.

Thanks! Wade.
 
#2 ·
I took the aluminum head to Ram's Cylinder Head Repair, downtown, St. Louis, MO, they are specialists in aluminum head repair and were very confident they will bring it back to standards. When I receive the head, am re-assembled and running, I will report back.
 
#4 · (Edited)
The OM602 does not have a history of cracked cylinder heads, unlike its older 6 cylinder cousin the OM603.

I'd suspect the cracks were caused by something utterly stupid, such as ignored overheating issues or running on non-MB approved coolant such as the generic green stuff or worse yet GM DEX-COOL.

I seriously doubt that a shop can fix this and restore the head to 100% condition, regardless of what the shop may say. After all, we're not dealing with a Chevy small block.
 
#6 ·
snip.....I seriously doubt that a shop can fix this and restore the head to 100% condition, regardless of what the shop may say. After all, we're not dealing with a Chevy small block.
Don't be so sure. There is a well documented procedure for 'stitching' cracks in valuable engine blocks that renders them 100%. While I don't know of something similar for aluminum heads, I'm at least open to the possibility that some old machine shop in St.Louis has success with this.

Kevin
 
#5 ·
Were you able to identify the cracks via a visual inspection? Pics? I'd love to get a report about the viability of this procedure. The earlier OM603 heads were prone to experiencing "micro-fissures" that allowed combustion gases into the coolant, rather than coolant leaks into the combustion chambers. What were the symptoms that led to the conclusion that you have head cracks?
 
#7 ·
Hi Kevin, I did not ask them to document with photos, though I can call and ask if they will. I found this Brodix video online, which I found informative. I wish Brodix worked on other products. Welding Aluminum Cylinder Heads.

Sbaert, I have put 100K miles on the car in the five years I have owned it; the engine has run at 82C since I have owned her. Variation from winter to summer is 3-5C. During the first two years of ownership, I broke a fan belt, and she ran hot for about 15 minutes. Three years later the cracks in the head occurred. I can tell you the exact second the crack occurred, as I blew a radiator hose and overheated to 120C at the snap of your fingers. I thought the t-stat had failed, which I replaced, with no luck. A coolant test revealed hydrocarbons, which pointed to the head gasket. I thought that had failed since I had a slow coolant leak from right side #5 cylinder which I have been tracking for two years. I used a $45 cooling system sealant from Advance, which most likely I should not have. It sealed the coolant leak for almost two years until I brought the car to a Chicago winter, which seemed to damage that temp seal.

After dis-assembly, I see many coolant passages are partially or completely blocked with what looks like an opaque salt, which I suspect came from a combination of the sealant and electrolysis through poor bonding. I will add several additional electrical bonding straps during re-assembly.

Sbaert, I have not run MB coolant in the system, I have run medium quality domestic coolant. I will switch to MB coolant after this repair. She never has run low on coolant, in my five years of ownership, up until the time I thought I had a t-stat problem. GM Dex-Cool has not been in the engine. There is a measurable quality difference in domestic and MB coolant?

Hi Zeitgeist, I have taken a hundred or so photos for documentation for re-assembly, and did get photos of the head, but only before a local machine shop pointed out the cracks. After I found Rams, I hand couriered the head and cam, wrapped in blankets, in my suitcase, on the train, as train fare was $28 round trip, far cheaper than packing and shipping. I will call the shop in the AM to see if they can get a detailed photo of the cracks before repair. My photo shows discoloration to cylinder head #'s 3&4, where the cracks are. They are hairline, about 1/4" long, emanating from center outward to the pre-combustion chamber nozzle protrusion. I am in classes for the weekend, on Sunday or Monday I can post a photo or two. I used your posts and photos on your injector pump leak/fuel pre-heater corrosion coolant leak thread to help with the job, thanks so much for posting that valuable information!

Other symptoms included audible popping noises as the coolant reservoir cap released pressure, small white puffs of smoke during starting (did not happen often) where I suspect a drop or two of coolant leaked into the cylinder, and just very odd temperature variations after that hose blew/suspected t-stat failure. I mentioned before, she ran rock solid at 82C for five years with the one exception of breaking the serpentine belt over three years ago, and the recent problems.

Replacing the head option exceeded the value of the car. Repairing the head is worth my time and, paying for the repair and gasket kit, and taking the risk on the repair. I will update this post as I make progress.

Wade.
 
#9 · (Edited)
The vacuum pumps on these models are not rebuildable unlike the older MB diesels. Think of it as a cheap insurance part considering a dying vacuum pump can grenade the engine without warning. I recommend replacing the pump at every 100,000 mile interval.

If you hear chain clatter upon startup in the morning, then it is time to check the tensioner and/or measure timing chain stretch. Usually not an issue to worry about until you've hit at least 150,000 miles or 250,000km. Replacing the tensioner is easy, but the chain and related guides are a major bear of a job you only wish to do once.
 
#10 ·
Thanks for the reply sbaert. I did see I have exposed bearings on my vacuum pump, I would like to get newer version sealed bearings. I'll replace it.

The vehicle has 325K, I've put on 100K, last timing chain replacement unknown. No noise or slap, timing is spot on w/ mark on dampener and camshaft marks, and good visual inspection, guides are not worn, no marks or indications of slap. I am going to replace the chain, would like to test the tensioner, if I can, before just replacing it.
 
#11 · (Edited)
Given the mileage, and unknown chain replacement history and you're going to replace the chain anyway I can only recommend to just go all the way.

Replace the chain, tensioner, guides, everything at once. These parts all have to work together. Doing a chain replacement and leaving the guides alone with higher mileage like yours is not recommended. Don't use the "cheater method" by cutting the old chain and feeding the new chain through. Take the front of the engine apart and do it right as the factory recommends.

The tensioner is the easiest of the bunch to replace. For critical components like these, I would use genuine MB parts only.

If it were my car, and there is no chain stretch, no chain clatter, I'd just leave everything alone except for the tensioner (perhaps).
 
#13 ·
My intake system- from air filter housing all the way to the intake manifold outlet into the head, was slathered in engine oil. Is that normal for an old Diesel?

Two years ago I had the intake system apart to access and replace glow plugs; I cleaned it to a shiny interior, and two years later it's oiled an coked up again. Abnormal?

I run several thousand miles before needing to add oil, my engine doesn't burn much oil at all. The engine and compartment, however, are caked in oil/diesel, I'm spending much time cleaning as much as I can access. Starting to look nice. I LOVE a clean engine and compartment. Makes working on it a pleasure.

Are there one or two culprits/weak points on these 602 engines to allow so much oil to cake on the engine and compartment, such as the timing chain cover?
 
#15 · (Edited)
Thanks Zeitgeist; I found this post on Rotor Rooter job for the EGR valve, will see if I can achieve success with this procedure. Or does that level of tar/coke indicate failure and simply needs replacing?

http://www.benzworld.org/forums/w12...-video-egr-valve-tar-removal.html#post3571613

OBTW, the machine shop had completed welding the head cracks before I called them, no detailed photos. I will post the ones that I have though, showing discoloration.
 
#16 · (Edited)
Photos of the cracks. Machine shop is shipping head back today, job complete, can't wait to get it back.

Found out the culprit, and it was me. I added a sealant to the coolant to stop a leak at the head/block/gasket, passenger side #5 cylinder- which was successful, and according to my local radiator shop, also plugged up my radiator, eventually almost completely blocking the flow. So the overheat, blown hose, low coolant which led to a cracked head was me caused by me taking a shortcut- how many times have I learned that lesson in life? Too many.

Well the head gasket was about to fail regardless, one ring was almost blown through. So timely, and a little more expensive.

Found an inexpensive used radiator, original, good price, in great shape, and at the shop for testing. European Auto Group on south Georgia, I've bought many fair priced parts from them, always in good shape, and they take returns no problem. Great outfit.

I've got photos in small JPEG's, as soon as I figure out how to post, I will.
 

Attachments

#18 ·
Fianally opened up repaired cylinder head

Here are some repair photos; Repair is on the left, original is on the right. The shop said they pressure tested the repair, I'm looking forward to re-assmebly.

All timing chain components, sprockets, oils pump chain and sprocket, IP timing gear, are new and Benz manufacture, as well as new bearing design on vacuum pump.

I have replaced every gasket and seal I can find on the way, including oil pan, front and rear (replace when can get on a lift to drop trans) crank seals, timing cover, turbo oil in/return, the list goes on. I am dreaming of a leak-free engine.
 

Attachments

#19 · (Edited)
Washer for fuel/coolant port

The machine shop removed two nuts for me as I could not, the front head coolant passage, and the rear coolant passage for fuel heat exchange. The front nut had a metal washer, the rear did not.

Does the rear nut require a washer? I am unable to find an exploded diagram in my manual.

Photos below.

- (Zeitgeist brought to my attention these washer are in the head gasket kit. Thanks!)
 

Attachments

#20 · (Edited)
Fuel injector dust cover?

When I removed my injectors, I found remnants of what looked like plastic dust covers to keep dirt, oil from collecting in the cavity between the injector and the cylinder head. My parts supplier said Mercedes no longer makes them.

Does anyone know of these covers/caps, and where to find them? The broken pieces I found fit in the serrated edges in the photo below.

The area around the injectors were packed with dirt, grease, when I removed them, would like to prevent that from happening again.
 

Attachments

#22 · (Edited)
Black "Plastico" Injector Dust Shields

I haven't been able to find them, anywhere.
Mercedes stopped using/offering them Years ago.

Those Two Coolant outlet pipes on your "New" Head use a rubber O-Ring each to Seal between the Coolant pipes (on the front lower Passenger Side) (And on the Fuel Pre-heater Exchanger)
'same part number for both applications. #012 997 51 48

Please let us know how the "New" Head performs (Updates on it.)
 
#23 ·
Good to know they are the same part number, the seals, I will install two new ones.

Black Plastico Injector Dust Shields- nice to know the name, that may help in the hunt. Took me forever to clean that area before removing injectors, they serve a good purpose.

Will do on the cylinder head performance reports.
 
#24 · (Edited)
The O-rings fit into the Unshown Sides of the two fittings

You still need the metal seals the "Z" told you about for the "fittings to head" interface.

And Black "Plastico" is just my terminology (I've no idea what Mercedes calls them.)
[Save your self some time,unless you can get the "Factory" in Stuttgart to tell you who
made the plastic dust shields (AND they,whomever they are, have some left-over in a dark corner) you're out of luck.]
 

Attachments

#25 ·
remnants of "Black Plasticos"

Compress Ignite,

Here's a photo of the best remaining dust cover I had, not well designed with heat in mind. I wish they were upgraded and still around, that open area was packed with grime.

I'm thinking of trying a hardening commercial furnace firebrick caulking, something that will withstand the heat, and form a seal, like an O-ring, which I can pry loose with a pick.
 

Attachments

#26 ·
I'd not try anything like that

The OM617.XXX series 5 cyl Diesels (Predecessor to the OM 602 + 603) had no such Plastic
dust cover and worked just fine for many.many Millions of miles.

I'd just blow out the Injector Recesses gently with C.A. (Compressed Air) if I couldn't stand
the dust buildup.
 
#27 · (Edited)
Shes' coming along nicely

Repaired cylinder head in place, new timing system components. With re-assembly, I feel like I'm over the hump toward running again.

This is my first time with timing a Diesel, and replacing all timing components. Getting the timing right was quite involved, next time will be much easier I'm sure. I've been triple+ checking my work.

Getting the timing case cover on and off without damaging the pan and cylinder head seals is far more difficult than I imagined. Dropped the pan back down to help.
 

Attachments

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top