cylinder head corrosion - can it be fixed properly?

[Randell]

as a followup to the fairly tragic end of this thread: http://www.bimmer.info/forum/showthread.php?t=22262

the head has just come off, there is corrosion around cylinder 6 which has caused hydrolock. there seems to be no other damage (phew). must have been the starter motor making that dreadful noise

not sure what caused this, the head gasket was done 80000km ago so it must have been between then and now, maybe an poor HG job.. being run on green coolant by the PO probably didn't help either

the head has been sent to a shop to get pressure tested and get a quote on skimming and welding, but that sounds like a recipe for future problems.. my mechanic insists that this is a solid solution because they have 'new methods' for welding heads.. JBweld ?

am i better off sourcing a good second hand head? i won't get the quote for a couple of days, i'm assuming it won't be cheap.. what's the cost generally for a head repair of this nature?

the news was better than i was expecting but it's still gonna run out of my budget and i don't get paid for another 15 days... ahhh, i feel like a smoker going through withdrawals!

[genphreak]

They can weld the surface of alloy heads fine, but a lot of cracks are too hard to fix without risk of a split at a later date. I'd insist on seeing it when it comes back from the machine shop. It's good news the block is ok, but how can they be sure? What broke when it made that horrible noise??? Cylinder 6 is the one that goes wrong- as the rear one is the hardest to get to when the engine is in the car. If the headjob was not done well last time this could might be a where problems occur if there was any foreign material in the gasket. The gasket should be carefuly inspected on removal, and the (renewed) surfaces, when brought back together, should be perfect to the touch and eye.

Check the parts listing on the valvegear section in www.realoem.com so you can go over the head and make sure it is all there and the right way round (are they good w BMW heads?) particularly the little bolts at the rear are installed the right way round and with the right o-ring. These are damn near impossible to check once the engine is in. Important are the coolant orifices so the coolant can circulate into the head okay- with bad coolant and problems these tend to block with scale and oxidised iron from the block. If your shop or mechanic isn't very familiar with M30s you should do all this unless they are really methodical people and highly competent that will check the right book on all the little things and check their suppliers work over well; a lot of mechanics expect the head to come back ready to go on and will only notice something that leaks or is missing, not a nut screwed in incorrectly... or an oilsprayer bar installed around the wrong way. The big problem in Aus (you may know), apart from saying after the fact that 'it's not my fault but theirs', is that any of us used to working on local cars have trouble changing our approach, the BMW way is very specific and can seem silly and weird to people that do not 'know better', if u comprenendt vhat vee mean, ya?

Also, make sure the mechanic is guaranteeing their work so you don't have to npay if it needs to be done again. Best thing is to be paying a fixed fee (from someone who knows how to compelte this exact job of course)...

[Paul in NZ]

my take Randell is this....How do youknow that a second hand head is any better?When you say corrosion what do you mean?

[rob101]

I am thinking perhaps a build up of scale,
because SOMEBODY didn't change his coolant often enough
I read into this one day after reading all the blue coolant arguments, basically when the coolant goes too acidic you get scale and too basic you get corrosion (could be the other way around). they are not the same thing.
but if you have too much scale it clogs the coolant passages in the head.

[genphreak]

I am thinking perhaps a build up of scale,
because SOMEBODY didn't change his coolant often enough
I read into this one day after reading all the blue coolant arguments, basically when the coolant goes too acidic you get scale and too basic you get corrosion (could be the other way around). they are not the same thing.
but if you have too much scale it clogs the coolant passages in the head.

Yep, and on M30 that means Cylinder 6 first once you check it out; the rear passages around 6 are always the first to clog up- the lack of cooling there causing a hotspot that can make life very hard for the gasket... I think that's hit it on the head Rob- yet another L6 awfully polluted by the wrong coolant.

[rob101]

Yep, and on M30 that means Cylinder 6 first once you check it out; the rear passages around 6 are always the first to clog up- the lack of cooling there causing a hotspot that can make life very hard for the gasket... I think that's hit it on the head Rob- yet another L6 awfully polluted by the wrong coolant.

well, i wouldn't say the wrong coolant, you can use decent green coolant (castrol) IF YOU CHANGE IT EVERY YEAR. blue just has more "residual alkalinity" so it will last longer before going acidic. all coolants unfortunately go acidic after a while its just a matter of how quickly.
that was what my research led me to believe.

[genphreak]

well, i wouldn't say the wrong coolant, you can use decent green coolant (castrol) IF YOU CHANGE IT EVERY YEAR. blue just has more "residual alkalinity" so it will last longer before going acidic. all coolants unfortunately go acidic after a while its just a matter of how quickly.
that was what my research led me to believe.

Yes perhaps, but with the stories we see all the time, it is not worth being 99.9999% right is it?

I reckon one should only use the factory stuff, period: I learned this (again) another way just recently; I bought some red Nulon stuff in a my gf's mum's Toyota Camry, the books all said ok, but Toyota said only add this Part# (can of red concentrate) we sell. I wish I did, cos I later found the fill procedure pretty much makes a proper flush with premix damned hard.

So there we go. Next year its going to get the right Toyota stuff and that's that. I'm not ever messing with different coolants again!

[joshua43214]

Jaguar had a terrible problem with the heads pitting on the inline 6 engines. They issued a service bulitin telling you to pull the head and use JB Weld to fill the pits. I have done this on serveral cars and had good results. You just can't fill any pits that are on the sealing portion of the head gasket.

If they can weld it and stand behind the work, I see no reason not to let them do it. Did they offer any suggestions as to the cause of the sound? or are they just saying that they have to fix this before they can go any farther? If they have the head off, they can check for a bent rod by comparing piston hights to each other.

[Jon K]

Seriously - with the availability of M30 heads, I would honestly buy a used one, have it checked for cracks, make sure it's straight, mayeb swap your valves and train swapped over and going that route. Welding the aluminum head is fine if you have a surface crack x-rayed and proven to not be that bad, but trying to repair corrosion with a weld - sounds like a lot of mystery work to me.

How does an aluminum head corrode by the way?!


Btw - hopefully the snap noise you heard wasn't teeth stripping off of the starter and or flywheel.

[rob101]

Yes perhaps, but with the stories we see all the time, it is not worth being 99.9999% right is it?

I reckon one should only use the factory stuff, period: I learned this (again) another way just recently; I bought some red Nulon stuff in a my gf's mum's Toyota Camry, the books all said ok, but Toyota said only add this Part# (can of red concentrate) we sell. I wish I did, cos I later found the fill procedure pretty much makes a proper flush with premix damned hard.

So there we go. Next year its going to get the right Toyota stuff and that's that. I'm not ever messing with different coolants again!

yeah the red stuff you have to be careful
some of that has organic additives and some is just your normal green coolant with red dye in it.
anyhow i was surprised to find that the premix castrol stuff has a BMW UK approval
explain that one!
and as i said before its not corrosion its scale!