I remember my overhauler having this problem back in the early 90’s – he said that he used a frightful amount of heat to loosen the,…!!! Here’s some old newsletter gen:
This was Chris Ward in May 1998:
With the engine out, the first order of business was to remove the cylinder head (this is where the trouble started). All but two of the nuts came undone with out problems, these two were soaked in WD40 for two days, but still would not budge. More force was used which sheared the studs off about 2 inches from the base of the barrels. This would not have been a problem had the barrels not seized on to the two sheared . studs. We had to set the engine up on a pillar drill. Using a flat bottom drill to cut away the top of the studs until the barrels came away.
Andre in November 2000:
Don’t fear the stuck barrels! No need for another set. There are plenty of options.
It is obviously caused by the studs sticking to the barrels – so remove all the studs!
Penetration oils like WD40 don’t penetrate deep and fast enough (I’m talking about penetration OILS) to overcome that problem.
If you’re not in a rush spray WD40 on all studs you couldn’t remove (usually the ones between cylinders 1 and 2 or 3 and 4) regularly until the barrels or studs can be removed. This can take a few months!
However there are cruder techniques!!
On my RC engine the inlet side stud between 3 and 4 was the culprit. I also tried penetrating oil and heat but to no avail. I gave up and handed the barrels/engine case over to someone who had some experience with VW Beetle engines and who also had access to a huge collection of tools.
One of the options I was thinking about was welding a huge nut onto the stud and remove it with a huge wrench. He took a similar but different route. He clamped the stud into a vice and rotated the engine (actually the upper case and barrels) so that the stud then came loose.
I guess that if you have an un-mounted engineering vice then you could leave the motor on the bench and rotate the vice.
Needless to say the stud was ready for the bin but after that stud came loose separation of barrels and case was very easy.
Apparently the WD40 (and application of heat) only worked itself through the upper few cm’s of the stud whereas the alu-oxide that caused the sticking was at the bottom of the barrels.
I’ve heard of even more crude options: drilling out the stud, removing some barrel materials and cut through the stud but both are more aggressive to the engine parts.