Tue Sep 06, 2005 9:54 pm
Can I add my two penn'orth?
Because the studs are steel and the head is alloy, you get corrosion on the thread interface. The heat of the engine accelerates this process, so most old engines are going to have studs which stick. I think e30s also have thread locking compound on the studs?
You stand most chance of getting it out with the engine hot, as it'll be relatively loose, (ally expands at twice the rate of steel when it's heated, so when its hot the hole is bigger than the stud) but doing it with the head still on is so high risk. Most ordinary garage mechanics are not good enough to do this job, you need an apprenticeship trained Fitter.
Drilling out will work, but you really need a bench milling machine, so that the hole stays more or less concentric. Using a hand drill is likely to cause a lot of damage if it slips, especially as you get to the larger sizes.
I would take the head off, you can't afford not to. Then get a drift and whack the end of the stud a few times to loosen it. Apply some releasing oil which is high in phosphoric acid. WD40 will do, but there are better products. Or use diesel, which uses phosporic acid for combustion. This converts the rust from iron oxide to iron phosphate, which takes up less volume than rust. Leave for a few days.
Then the choice is yours. Drill it or use a stud extractor. You MUST centre-punch the stud. I personally would use the stud extractor, as the better quality sets take a lot to make them snap, i.e Goliath. Avoid the Halfords set as, although they seem to making great efforts to produce good tools, the quality may not be what is needed.
You can get a 'feel' when using extractors as to how much torque they'll take before they snap. Drill the biggest hole you can get into the core of the stud , only about 5-6 mm deep. There is about 15 mm of stud in that hole.
If it won't turn then you'll have to use gentle heat. You could try playing a blowtorch on the area, but you could easily warp the head if you let it get too hot. You could put the head into your domestic bath with the hottest water you can stand, but then you might have to change the bath! The family might not be happy. That'd mean stripping the head of course, asthe carbon steel parts must not be wetted with water.
The tip about the washer is brilliant, (one for the notebook), but it may not work if you need more than one weld layer, as the flux needs to be chipped off the weld after each run. If your stud is deep below the head surface the weld may not catch on the top of the stud. Bear in mind that steel melts at 1200 degrees C, wheras aluminium is much lower, so using welding equipment when you're not used to it could melt the head!
Hope this helps
)
but brilliant article in PPC mag about the MX-5 
