headgasket weakness exposed

Euro '83 635 CSi manual production date 11/82.
It had been running at 1/3 normal operating temperature. Water pump had been spewing for some time as evidenced by dried splatter marks on hood and coolant under the weep hole. Installed new waterpump, thermostat, new hoses, and cool blue...
Some steam from exhaust at startup. Ran at idle for 20 minutes bleeding system. Temp needle went 1/8" past halfway but never more. Never actually drove the car at that time. Checked under oil cap: very light swirling milkiness evident... Car sat for one week.
Drove the car yesterday... Some steam from exhaust at startup; went away after a few seconds. Drove for maybe 4-5 miles. Left idling for a few minutes; steam not billowing but still there. I noticed a gentle misfire accompanied with a puff of steam. This symptom was also evident at idle. Temp guage at normal. Shut off engine. Checked under oil cap: even milkier than previous. There was no evidence of oil in the coolant. Dipstick did not have any foam or milky color to the oil drips. Have not pulled plugs yet. Car is sitting waiting for the head to be pulled... I plan to replace the head gasket and replace whatever may be necessary on the head itself; if it is still useable. Will examine block/bores as well.

Man, am I glad I have not sold the 540...

Question: If I undersand correctly; the euro motors are a 10:1 Compression Ratio. The US models were somewhere in the 9:1 range. Was this accomplished with different pistons? Real OEM gives the same part number for the head gaskets and cylinder heads themselves between US and Euro M30B34s. What differences between Euro and US motors should I be aware of during the process of repairing the head and replacing the gasket?

o_O

If you saw steam at startup, that should have immediately told you not to drive it. There's a chance that you have a crack between a cooling passage and an exhaust port and maybe even into an oil passage but not major there since you're getting milky, but not milkshake. I'm really suprised you drove on it seeing some of the tell-tale signs >.<

It was cold (~42°) outside so I figured some steam at start would be normal. Exhaust did not smell sweet like coolant or abnormal in any way. The first time I saw very faint swirliness on the cap; I thought it might be condensation; as the car had been sitting for a few weeks. Oil looked clear. Coolant looked clear (including the stuff I drained out prior to pump change). The plugs I pulled previously (three weeks prior) had no signs of steam cleaning/just worn out. Was not overheating. Did not have my compression/leakdown tester handy. ;-) Signs pointed to me being paranoid. So I took it for a short drive around the block with one eye on the road and one eye on the temp gauge. So here she sits with busted gasket, and the only two symptoms displayed are the light but puffy steam and the oil cap milk swirlies. So just let it be a warning to anyone else here... Indeed this is why I posted the lead-up information in the first post. The new waterpump/thermostat combination pushed a weak headgasket over the edge in just a few short revs.

Anyone with Euro M30 motor experience have advice/cautions/warnings?

Will you be having the head checked and resurfaced during the HG operation?

Yes. I plan to turn the head over to someone with the experience and proper tools to disassemble the head, clean, pressure test, and resurface if necessary. Since this will be my first foray into any head past a valve adjustment; I think it would be more cost effective this way. I (with a couple of friends) will do the grunt work of removing the head and then replacing it when it has been gone through. I have seen and read multiple write-ups (thanks esp. to shogun for: http://www.bmw7resource.co.uk/TechDo...acement%20.pdf) and feel confident about getting it off and on properly.