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Driving over a mountain pass I noticed a sudden lack of power accompanied by some shuddering of the engine (almost like very frequent and evenly spaced misfiring). The engine was running 100% before, performing well and not a puff of smoke.

I then changed the spark plugs and checked the plug leads...all fine.

I noticed that when the engine runs you can remove the center two plug leads from their plugs without much noticable difference in the idling speed/sound. When you remove either the nr 1 or nr 4 plug lead, the engine dies.

There doesn't seem to be coolant in the oil and the old plugs looked reasonably healthy when I took them out (like I said, the car was running fine shortly beforehand).

The oil pressure is still as before (quite high at about 75, not sure if the gauge is right) and there is no smoke.

I'm not an experienced mechanic, so I'm asking for advice. From what I've manage to read it sounds like a blown head gasket, perhaps between the center two cylinders.

Diagnosis?

head gasket 100%

Thanks guru. Any idea what could cause it?

Is that oil pressure I mentioned not too high?

Hi, long shot but could be manifold gasket on the inlets, but would be strange as they don't generally go out of the blue like you said good luck

The verdict is a small blow out in the gasket between the two middle cylinders. This is my first time performing this kind of open heart surgery on a car. I need to clean the carbon off the piston crowns and valves before refitting. Using the Haynes manual. If anyone has tips over and above what's available in the Haynes, please let me know. I'd particularly like to hear what people do to clean the piston crowns while preventing carbon entering the small gaps next to the crown. Is it safe to use a drill and wire brush to clean the head and block mating surfaces?, without applying much pressure of course!

Id use a stanley blade very carefully just to gently scape it clean.

Do not use emery cloth wrapped around a spatular (or the like) to clean it off...as mentioned in well known mini magazine article!!!

Umm, discarded grain off the cloth..in the bores...um...smells like lapping paste to me.

Make sure your head is flat before putting all back together..it's not got over heated recently and are your head bolts in good order??

Is your torque wrench working properly and accurate?

Thanks mk1rally. I've put a bit of grease around the edges of teh piston crowns to keep rubbish out. This is what Haynes suggests. Not sure if its a good suggestiong. I've got blades, that sounds like a useful idea.

A couple of the head waterways at the surface where it meets the block were almost completely blocked with sh!t, so I wouldn't put overheating related warping out of the question. I'll have a look. Another thing is however that I was surprised that none of the head nuts seemed to be of equal tightness when I removed the head. Perhaps this points to the head nuts not being re-torqued after the engine was rebuilt by the previous owner and driven for a while At least I'm hoping that's what it is.

My torque wrench is brand new, so I hope it is working and accurate.

If anyone else has any other suggestions/advice, I'd be happy to hear it. Like I said, this is my first time doing this. Hopefully I can get most of the way to being done after work today.

i personally wouldn't use grease.
i just get out the vacuum, and get that sucking as i scrape off the old gasket.

i would probably flush the cooling system, as well. mainly to get as much of the "crap" that has been collecting in there out.

emery cloth wrapped around a spatular (or the like) to clean it off..

Is that REALLY the case, some "expert" really suggested that . . . . . . . .

If your torque wrench is new it should be fairly accurate, but remember to slacken it off FULLY when youy have finished with it, because if you don't you will stretch the spring & it will read progressively higher & higher meaning your nuts will be slacker & slacker. Its staggering how many people forget to do this & rely on a totally knackered torque wrench.