having problem removing 3 headbolts on left side head -- center bolt & rear 2 bolts at firewall side -- using 16mm 6 point 1/2" drive socket -- socket has slipped on bolt head & head is now slightly deformed; socket will not grip securely on bolt head to allow removal; tightening 18" breaker bar allows socket to slip off bolt head before turning; all other 17 headbolts came loose without any problems;
I would think someone else may have had this problem before -- can anyone offer suggestions on how I can get these 3 remaining headbolts to loosen? I retightened bolts adjacent to the stuck bolts but this action didn't seem to help;
any ideas for some different tool or method would be very much appreciated; I am pulling heads mainly to replace headgasket on right side that was blown to outside edge;

 

The bolt heads are 5/8". You can try a 5/8" 6 pt socket, it will fit a little tighter than a 16mm socket. 5/8=0.625 and 16mm= .630"

When I pulled my heads I had an issue with the rear bolt next to the exhaust manifold on the drivers side head due to access.

 

If they bolt heads get bad, try these:

http://m.harborfreight.com/38-in-drive-sae-bolt-extractor-sockets-9-pc-67897.html

 

you should un-torque the head in the opposite direction that you would torque the head.
you now have all the pressure locked down by just those last two bolts, a common mistake.
i would reinsert the other head bolts to release the tension, then you should be able to remove the rear head bolts using a 6-point 5/8 shallow impact socket and a short extension.

 

use a 5/8 socket not a 16mm. If you have a helper around have them hold the socket straight down on the bolt while you turn the breaker bar.

 

This is a good idea, but just to be clear don't try to 'torque' the bolts back to spec. Just put some tension on them to equalize the pressure across the head.

 

that is correct; you just want to release a little tension

 

Use the 5/8" 6 point BLACK impact socket.
Only impact will hold up.

On top of that put an impact svivel joint.
Then a short stub extension.
Then a breaker bar.
Put a pipe over the breaker bar for leverage.
That will get it off.

From March 2012 in Boulder CO

https://www.flickr.com/photos/76579732@N07/

There are some examples in the pictures of what you are attempting to do.

 

many thanks for all the help & advice! I was able to remove the last 3 bolts today;
using the 5/8" impact socket plus having a helper to steady the socket while using breaker bar did the trick! I thought the Rovers were all metric fasteners -- but I was wrong; not much size difference between 5/8" & 16mm -- but enough to make a big difference! busy this weekend, but plan to start reinstalling the new gaskets & cyl heads next week! will keep posted when my 2003 D2 is up & running again!
Thanks again - very much appreciate all the help!