Have had a few people ask me about the shim I used to save my head so thought I'd put some info down to let people know now that its been 9 months, 4500 miles and I know it works.
At this point, 6 months after changing the head gasket for an MLS one I knew I had some problems..
Took the head off the car, cleaned it up and had a look. Over heating had caused faint rings to become quite deep, the fire rings being the circles you can see where the cylinders sit against the head.
Knew I would need quite an aggressive skim to get down to a flat surface but knowing the K series head and the fact that I have fire ring indentations already confirmed to me that the head had dropped below the magical 95 brinell hardness rating needed to prevent them from occurring in the first place.
So I had a few options, gamble on a scrap yard head, or pay for a tested VVC head at £600...
Gave it a little thought and decided I just needed to make the head face harder, stainless steel is about 395 brinell so it seemed such a simple idea, a stainless steel shim, thick enough to transfer the concentrated load of the cylinder.
So I got onto Gosnays and got a shim that they produce for use in k series turbo applications where they need to lower compression and ordered this. The 1.9mm stainless steel shim.
Now there is a shim that comes part of the MLS gasket set, bit it is too thin for what I needed. Not only do I need to to protect the soft ally of the head but I also needed it to be thick enough to spread the concentrated pressure of the cylinder pressing into the head.
This is the shim from the MLS gasket set.
This it the 1.9mm stainless steel shim.
Realized why I'd not put this up sooner, because my camera packed in and so have no more pictures!
Anyway, I did some work on the head and then took it for a skim. Now I could probably have just fitted the shim over the rings but its going to lower compression as it is designed to do in turbo applications.
So the more I could skim off the less of a difference I was going to make when the shim went on.
Cleaned the skimmed head and the shim with ethanol and then bonded the shim to the head face using Loctite 5920.
http://www.loctite.co.uk/cps/rde/xchg/henkel_uke/hs.xsl/fullproduct-list-loctite-4995.htm?countryCode=uke&BU=industrial&parentredDotUID=productfinder&redDotUID=1000000IYQW
Have worked will all types of Loctite but it was the one that stood out for what I needed and as I said, its working...
Clamped the shim onto the head just so I could clean up any excess that squeezed out, you could do the same with just pressing it down by hand.
10 mins later I bolted the head to the vehicle and torqued it up, I then covered the engine and left it for 24 hours to fully cure before fitting all the other bits.
As pointed out its been 9 months now and the engine is fine, I don't know exactly how much the Gosnay's shim was as I just put it on my card but I don't think it would be much more than £30-£40. A lot better than the £600 quoted for a tested VVC head!
I should really do a compression test to see what the effect has been, will try get that sorted next time I change the plugs.