MB 10v Cylinder head cracks

oliverjl · 28-10-17, 09:44 AM

As this is this is my first post, Hello, thanks for having me on the forum!

Can someone with experience of these engines tell me if hairline cracking between the valves on a 10v MB head is a problem? One chamber is quite pitted, but also every cylinder has a small crack between the valves. My old-fashioned regular engine re-builder seems to think this is fine and was common on Audis of the period, car has been stood for about 15 years and I'm working through everything, as the engine is out/stripped at the minute I'm trying to avoid re-assembling it and finding a problem then!

Head 1.jpg

Head 2.jpg

Many thanks.

Hanuman · 28-10-17, 10:21 AM

It's not uncommon in the WR engine, which is fundamentally very similar. Cracks between the seats can be quite pronounced. Personally, I'd say that's not a concern.
What about the pitting?

I also have a damaged WR head where the pitting has been quite excessive, especially inside a port, and has gone porous.

quattrodave · 28-10-17, 10:36 AM

Had that problem on my WR back in 1991 when I rebuilt the engine, the valve seats were fine so just left it as it was and the engine ran fine following the rebuild, if you are really concerned about the pitting then there are options to have a skull cap made like the one on this old triumph bonneville engine see link -

http://www.lpmcc.net/motor/bike_tss7...=Mark%20Turner

Scroll down to see the picture, some of these bikes had problems with porous castings when new and this is an engineers solution, no idea where it was done, the post is about 6 years old I remember seeing the finished bike at the classic motorcycle show in stafford a few years ago must have spent a fortune.

oliverjl · 28-10-17, 11:04 AM

Thanks a lot for the quick replies, I'm not particularly concerned about the pitting in terms of how it looks, it's not something I will have to look at very much.. Was just hoping to find out if others had had similar scenario and if that caused problems sooner rather than later.

Hanuman · 28-10-17, 11:26 AM

The cracks are not significant (imho). The reason I'm curious about the pitting isn't about looks, but whether it is localised and limited just to the chamber area, or if it also appears further into the port.
Porosity appears to be a favourite failure on the earlier heads, especially (or specifically, maybe) where coolant quality has not been maintained. Add in pitting, it might make it easier for there to be a breakthrough between the water jacket and the port, as the walls are relatively thin in places.

Alburglar · 28-10-17, 11:28 AM

The pitting is not a question of cosmetics, the concern is wether the block is porous, as said.
A simple check is to block the holes up (valves shut and water tight etc), and fill the chamber up with a liquid, like you would if you cc head. Then sit and watch for any micro bubbles coming up from pitted parts. With a cracked head, the crack would need sealing too, for this test to work.

mikes2 · 28-10-17, 12:16 PM

From the workshop manual

28-10-17, 10:21 AM	#2
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,006	It's not uncommon in the WR engine, which is fundamentally very similar. Cracks between the seats can be quite pronounced. Personally, I'd say that's not a concern. What about the pitting? I also have a damaged WR head where the pitting has been quite excessive, especially inside a port, and has gone porous. __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

28-10-17, 10:36 AM	#3
quattrodave Grown up member Classic Audi Club Member Join Date: Dec 2010 Location: Bingley Posts: 634	Had that problem on my WR back in 1991 when I rebuilt the engine, the valve seats were fine so just left it as it was and the engine ran fine following the rebuild, if you are really concerned about the pitting then there are options to have a skull cap made like the one on this old triumph bonneville engine see link - http://www.lpmcc.net/motor/bike_tss7...=Mark%20Turner Scroll down to see the picture, some of these bikes had problems with porous castings when new and this is an engineers solution, no idea where it was done, the post is about 6 years old I remember seeing the finished bike at the classic motorcycle show in stafford a few years ago must have spent a fortune. Last edited by quattrodave; 28-10-17 at 10:47 AM.

28-10-17, 11:26 AM	#5
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,006	The cracks are not significant (imho). The reason I'm curious about the pitting isn't about looks, but whether it is localised and limited just to the chamber area, or if it also appears further into the port. Porosity appears to be a favourite failure on the earlier heads, especially (or specifically, maybe) where coolant quality has not been maintained. Add in pitting, it might make it easier for there to be a breakthrough between the water jacket and the port, as the walls are relatively thin in places. __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

28-10-17, 12:16 PM	#7
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	From the workshop manual __________________ 1991 90 quattro 20v sport 1991 90 quattro

28-10-17, 11:04 AM	#4
oliverjl Grown up member Join Date: Oct 2017 Posts: 59	Thanks a lot for the quick replies, I'm not particularly concerned about the pitting in terms of how it looks, it's not something I will have to look at very much.. Was just hoping to find out if others had had similar scenario and if that caused problems sooner rather than later.

28-10-17, 11:28 AM	#6
Alburglar Grown up member Join Date: Sep 2017 Location: Dover, Kent Posts: 270	The pitting is not a question of cosmetics, the concern is wether the block is porous, as said. A simple check is to block the holes up (valves shut and water tight etc), and fill the chamber up with a liquid, like you would if you cc head. Then sit and watch for any micro bubbles coming up from pitted parts. With a cracked head, the crack would need sealing too, for this test to work.