What causes pits in the cylinder head? - PeachParts Mercedes-Benz Forum

Benzcrusher · #1 07-19-2010, 12:02 PM

Here's the head I just took off my 617.912 I've driven this car daily at times up to 200 miles in a day. Since this past winter it got harder and harder to start, lately it would crank for about 30 seconds while hot to start; ran fine otherwise. Note the heavy pitting. Injectors good, piston crowns are fine, just the head is pitted beyond reopair plus a crack or two...

mach0415 · #2 07-19-2010, 03:12 PM

Perhaps this is from ether use/detonation. I had a 1981 VW diesel with the same issue.

whunter · #3 07-19-2010, 03:19 PM

Quote:

Originally Posted by Benzcrusher

Here's the head I just took off my 617.912 I've driven this car daily at times up to 200 miles in a day. Since this past winter it got harder and harder to start, lately it would crank for about 30 seconds while hot to start; ran fine otherwise. Note the heavy pitting. Injectors good, piston crowns are fine, just the head is pitted beyond reopair plus a crack or two...

Cavitation
http://www.peachparts.com/shopforum/showthread.php?t=272132

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Brad123D · #4 07-19-2010, 03:38 PM

I've seen this before. Cracked head = coolant in cylinder . I think the high heat in the cylinder makes the coolant corrosive. Get the head pressure tested and it will probably leak at the crack.

vstech · #5 07-19-2010, 06:34 PM

in addition to the cavitation issue, I'd bet before you pulled the head it was losing coolant alarmingly fast, and plain water was poured in. water in the cylinder = RUST and pitting.

mach0415 · #6 07-19-2010, 08:25 PM

I thought cavitation occurred from the inside of the cooling jacket out, forming pin holes from the inside out. These pics (albeit not totally revealing, like a good ole fashioned eye ball look) do not necessarily indicate holes all the way through from the combustion chamber into the coolant passage. It appears that the pits are crater-shaped from the head surface and indented into the cylinder head. However, I do see the cracks, which may indicate overheat concerns. It appears that #1 has the least damage. Are all four others showing cracks? If no cracks, coolant could not have entered and caused damage to the un-cracked respective cylinders/combustion chambers. I would be interested in seeing what the water pump and impeller looks like, as this is one of the first places cavitation rears its ugly head as a result of aeration, when added to the vibration of the engine. Also, I would be interested to find out the condition of the turbo's compressor fan blades - sharp and straight vs. round and knurled, just to eliminate debris entering the engine from unfiltered air (cylinder wall damage will show this, as they will be scratched). Could abnormally high boost cause damage to the head and not the piston surface? (just a "ruling out" thought)
With that being said, all my years working on the Ford Power Strokes had us performing regular maintenance on cooling systems by adding 2 bottles of Motorcraft FW 15 or FW 16 anti-cavitation additive (thin blue liquid). Does MB recommend such an additive to coolant/antifreeze?

whunter · #7 07-19-2010, 11:29 PM

Quote:

Originally Posted by mach0415

I thought cavitation occurred from the inside of the cooling jacket out, forming pin holes from the inside out. These pics (albeit not totally revealing, like a good ole fashioned eye ball look) do not necessarily indicate holes all the way through from the combustion chamber into the coolant passage. It appears that the pits are crater-shaped from the head surface and indented into the cylinder head. However, I do see the cracks, which may indicate overheat concerns. It appears that #1 has the least damage. Are all four others showing cracks? If no cracks, coolant could not have entered and caused damage to the un-cracked respective cylinders/combustion chambers. I would be interested in seeing what the water pump and impeller looks like, as this is one of the first places cavitation rears its ugly head as a result of aeration, when added to the vibration of the engine. Also, I would be interested to find out the condition of the turbo's compressor fan blades - sharp and straight vs. round and knurled, just to eliminate debris entering the engine from unfiltered air (cylinder wall damage will show this, as they will be scratched). Could abnormally high boost cause damage to the head and not the piston surface? (just a "ruling out" thought)
With that being said, all my years working on the Ford Power Strokes had us performing regular maintenance on cooling systems by adding 2 bottles of Motorcraft FW 15 or FW 16 anti-cavitation additive (thin blue liquid). Does MB recommend such an additive to coolant/antifreeze?

Read through the links on the topic, they will surprise and educate you.

t walgamuth · #8 07-20-2010, 06:39 AM

I would have thought coolant in the combustion chamber did that but I am not a machinist.

funola · #9 07-20-2010, 10:44 AM

Quote:

Originally Posted by whunter

Cavitation
http://www.peachparts.com/shopforum/showthread.php?t=272132

.

Hey Roy! Thanks for the link! Just looked at the kobe-u one and it's amazing! Just took a quick look at the other links. I have read the Dieselstop one before but not the others, which look like good one too. I'll have to read them with more thoroughness when I get a chance.

I am impressed with how organized your are at archiving and finding info and posting links. Mind telling us the system you use?

whunter · #10 07-20-2010, 02:50 PM

Quote:

Originally Posted by funola

Hey Roy! Thanks for the link! Just looked at the kobe-u one and it's amazing! Just took a quick look at the other links. I have read the Dieselstop one before but not the others, which look like good one too. I'll have to read them with more thoroughness when I get a chance.

I am impressed with how organized your are at archiving and finding info and posting links. Mind telling us the system you use?

A good memory.
Extreme reading speed.
35+ years experience.

Benzcrusher · #11 07-21-2010, 11:22 AM

Replaced the junk head with this one and now it starts right up like a gasser..

vstech · #12 07-21-2010, 11:26 AM

what are you using the glow wires for? testing? or is it wired to a solenoid?

Benzcrusher · #13 07-21-2010, 12:52 PM

I got this head from James Harris. Asked for a "loop" glow plug 617.912 head and got this pencil version instead. The red wires supply power to the gp's from the single lead from the 80amp fuse block. As it's wired each plug gets 2.4v. if one burns out then 4 plugs will get 3v and so on. They are now parrarell and not series like the pesky loop plugs.

vstech · #14 01-06-2011, 06:57 AM

Quote:

Originally Posted by Benzcrusher

I got this head from James Harris. Asked for a "loop" glow plug 617.912 head and got this pencil version instead. The red wires supply power to the gp's from the single lead from the 80amp fuse block. As it's wired each plug gets 2.4v. if one burns out then 4 plugs will get 3v and so on. They are now parallel and not series like the pesky loop plugs.

actually, as it's wired in the photo, all plugs get full 12v (if the battery could put out that much current...)

The way a loop system is wired, all the plugs, and links form a resistor that drops the voltage to each plug around 2.5v if one burns out. NONE of the plugs get any power.

http://onlinephys.com/circuit3.html

http://www.physicsclassroom.com/class/circuits/u9l4e.cfm

charmalu · #15 01-06-2011, 11:36 AM

Quote:

Originally Posted by whunter

Cavitation
http://www.peachparts.com/shopforum/showthread.php?t=272132

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The link is dead.

Charlie