Broken Sump bolts

[Clarkie]

OK - today I was under the car starting work on replacing the water pump. Whilst I was there I noticed that two of my sump bolts are errrrrr - stuck on - or they have been previously overtightened / broken and are now being held loosely on by gasket compound . Either way I now have two broken bolts to get drilled out and replaced - fortunately no oil leaks - in fact remarkably clean. All the other bolts seem good.

How difficult is it to get this sorted? Any ideas on cost?

[rally-chris]

Depends how easy access is to drill and helicoil through the sump flange without taking it off. The original bolts are probably aluminium which is how they came to be broken so easily. BMW state that Ali bolts have to be used on the N52 engine to prevent electrolytic corrosion against the magnesium outer block. Which raises questions over what might happen when you put a steel helicoil in...

A safer plan might be to drill and re tap the holes to a larger size than original and then fit oversized aluminium bolts.

Chris

[Silverzedtom]

That won’t be a problem for a decent mechanic. You could even diy it. Not a very nice job though.

Bang a center punch in the middle of the remains, drill a pilot hole into the mark you just made and insert a left hand thread extractor tool. Unwind as usual

[Clarkie]

Depends how easy access is to drill and helicoil through the sump flange without taking it off. The original bolts are probably aluminium which is how they came to be broken so easily. BMW state that Ali bolts have to be used on the N52 engine to prevent electrolytic corrosion against the magnesium outer block. Which raises questions over what might happen when you put a steel helicoil in...

A safer plan might be to drill and re tap the holes to a larger size than original and then fit oversized aluminium bolts.

Chris

I guess the alternative is to whip the sump off to get easier access to the broken bolts and then replace the whole bolt set and a new gasket - seems like a fairly heavyweight solution though. I am guessing these bolts have been like this for a while - so l am thinking I probably don't need to rush into a solution - car is only used fairly infrequently.