cylinder head repair, jb weld? - PeachParts Mercedes-Benz Forum

Gerard · #1 10-25-2008, 06:26 PM

After water locked the no6 cylinder last week, I removed the head to replace the gasket (replaced 4 years ago too!) but discovered that the no6 chamber was corroded and venting to the coolant passages!
I have several options,

1 strip the head, get it welded, machined and re-install (most work)
2 buy another head (most expensive)
3 drill out the corrosion pocket, tap and thread in an aluminium bolt, file flush. seal with j-b weld (close to valve seat!!)
4 prepare, clean and fill with j-b weld. (cheap and fast)

I'm interested if any of you guys have used jb weld for such repairs?
M103 engine. 1991 300ce. A picture of the chamber is now on my gallery

compress ignite · #2 10-25-2008, 07:05 PM

#1 (will require an Expert machine tool operator,who is also an Artisan Welder)
OR
#2

The other mentioned options probably will not last through one "Warm Up".

deanyel · #3 10-25-2008, 07:13 PM

#3 and #4 sound like more fun. Can you attach a picture?

wbain5280 · #4 10-25-2008, 08:03 PM

Please take a pic of the head so I can see what it looks like. I have some experience in this area.

220S M180 Engine Work

Gerard · #5 10-25-2008, 08:31 PM

I already posted a pic in my gallery, maybe you guys cant see the link though. will try to post it in the thread.
G

OK heres the same pic below,
Might upload some more tomorrow. Better go to bed, its later here!

wbain5280 · #6 10-25-2008, 08:51 PM

It looks like pretty extensive damage. A few pics of the damaged area from other angles would also help. From the one pic, the damage looks extensive and would require a replacement head.

Gerard · #7 10-25-2008, 09:07 PM

more pics

Pete Geither · #8 10-26-2008, 08:08 AM

Get another head.

t walgamuth · #9 10-26-2008, 08:24 AM

yep.

SLacker · #10 10-26-2008, 10:27 AM

That type of damage can be welded up, but the heat put into the head during welding will likely warp it a small amount, requiring the head to be surfaced (plane the gasket surface) by a machine shop. It may take .010 or .015" to clean up.
You also will have locally "drawn back" the heat treatment of the aluminum material in the area of the repair. A purist will say that you have to re-quench and temper, but a softer spot on the head may or may not be a problem. It is reasonable to take a chance on that considering the savings.

Gerard · #11 10-26-2008, 10:50 AM

Guys, thanks for all your advice.
Despite a friend telling me to "go for it" and that he used it on a Porsche (not his own), I see no-one here recommending a jb repair.
Why should I be surprised. I guess its what I wanted to hear!! heh heh!!
My first reaction was a weld repair, but now i think a replacement head may be the safest option. The welding may be a bit close to the valve seat, and requires a skilled guy too.
What does a new bare head cost from Mercedes anyone?
I will check breakers for a 2nd hand one tomorrow.
Thanks again
G

t walgamuth · #12 10-26-2008, 10:57 AM

I would let the head repair shop decide if its repairable or not.

whipplem104 · #13 10-26-2008, 10:59 AM

I do not know what you have to pay where you live but here I could pick up and whole engine for less than 500 dollars. 900 for one out of a salvage yard with a warrenty. I have seen them on craigslist for 300 and less. A new head at the dealer is going to be a whole lot more.

Kestas · #14 10-26-2008, 12:20 PM

Quote:

Originally Posted by SLacker

... You also will have locally "drawn back" the heat treatment of the aluminum material in the area of the repair. A purist will say that you have to re-quench and temper, but a softer spot on the head may or may not be a problem. It is reasonable to take a chance on that considering the savings.

Not so with aluminum. Aluminum is solution treated and aged, not quench and tempered. Welding would render the localized area overtempered (soft). This area cannot be "drawn back". The only way to reharden the area is to re-solution treat and age the whole head.

The damage looks familiar to me. I've seen it on heads I've studied in the lab where nucleant boiling of the coolant takes place. This occurs on heads where the coolant doesn't have a high enough boiling point. Nucleant boiling produces an corrosive/erosive effect on the area that sees boiling. Coolant that is at the suction side of the water pump enhances this effect.

Gerard · #15 11-16-2008, 12:08 PM

I got a 2nd hand head from ebay germany. It seems OK, came with valves, which were all OK in their guides. I transferred the cam and rockers last weekend, and the head is waiting to go on, prob in 2 weeks time (I'm studying away from home, so this is awkward for me).
Hopefully will be back on the road by Dec 1st.
The head was not as expensive as I thought, I got it for 181 EURO incl delivery from Germany to Ireland.

I was thinking on its failure, I put it down to using crap coolant, and gradual weakening of the crap coolant by topping up with water. Didn't seem serious at the time, but this all took place over 4 years, i guess the strength was well diluted. This time. I'm going for a pre-mixed Daimler Benz approved coolant.

Will keep you posted.
G