Saturday 26 July 2014

E60: Engine Rebuild 4 - Replacing Pistons, the easiest way.

EDITED August 2015:

** I never completed this job as I ended up replacing the entire engine, but did get pretty involved in it and thought I'd somewhat finish the guide anyway. **

If you're only replacing one or two pistons then the engine does not need to come out and the crank can stay on, but this is still a hardcore task. Still, I was determined to replace two of mine this way until a crack in the timing-case and other issues made me swap the engine, which was a lot more work and cost. Pistons are about £250 each new, but with 2nd-hand ones and new rings you could probably replace two for about £300, including gaskets and fluids. 

The biggest problem with accessing the bottom-end of the E60 engine is that the sump is an all-cast-alloy design that sits very snugly into the power-steering rack and front subframe. It also bolts completely to the gearbox bell-housing at one end. You will need an engine-crane to lift and support the engine an inch, then a bit of guts to unbolt and lower the subframe with the engine hanging precariously above you, so if this is beyond what you think you can do then it's time to bung the car over to someone with ramps, as you cannot get the sump off without doing it.

This thread on Bimmer-Forums [] puts the process of trying to get the sump off without all the effort, then realising it is essential, quite succinctly and was a huge help for me.

You will need:
  • Ramps
  • Engine crane
  • 1 or 2 Trolley jacks
  • 1 or 2 spare Axle stands

You will need to remove:
  • Cylinder head etc. [See this post].
  • Engine under-trays and metal reinforcer-plate.
  • Prop-shaft at gearbox end.
  • Exhaust from back of turbo.
  • Turbo hosing.
  • Engine-mount top nuts.
  • Front anti roll-bar centre-mounts.

Basic Process:
  • Suspend the engine so the front is raised about one inch.
  • Remove all the screws holding the sump to the block and the gearbox-housing.
  • Unbolt the front subframe, the one the engine mounts sit on. The rear two bolts may not need fully removing.
  • Have someone pry down the subframe and work the sump out from the rear of the engine.
  • Bolt the sub-frame back up.
  • Lower the engine back onto the mounts.
  • Remove the bottom-end guard.
  • Remove the big-end from the affected piston.
  • Use a wooden drift to knock the piston(s) out of the top of the block.
  • Fit the new piston(s) and repeat the process to refit the sump.
** As I say, I did not complete this job. I lifted the engine and lowered the subframe a bit, but could not get the sump out first try. A second try never came before I decided to engine swap, though I'm sure it would have come out. Refer to the thread linked above for far better instruction. **

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