Can I install an inboard diesel engine myself?
I need to repower my 1980s 32-foot sailing yacht. The old Volvo Penta MD11C is dead, and I'm looking at a new Beta 25. Can I actually install this myself to save on boatyard labour, or is it too complex for a competent DIYer?
Answer
Yes, you can install an inboard diesel engine yourself if you have mechanical skills, a methodical approach and the right lifting gear. The hardest phases are modifying the engine beds to fit the new footprint and achieving perfect alignment between the gearbox flange and the propeller shaft.
Modifying Engine Beds
When you rip out an old lump like a Volvo Penta MD11C or a Bukh DV20, the new engine (such as a Beta 25 or Yanmar 3YM20) will have a different footprint. You must measure the distance between the existing glass-fibre stringers and compare it to the new installation drawings. Modern engines are often narrower. You will likely need to bolt or glass in steel angle irons or GRP brackets to bridge the gap.
Check the vertical clearance carefully. The new sump must not foul the hull. The gearbox output flange must drop perfectly into line with the prop shaft. Use a wooden mock-up or a cardboard template of the engine to test clearances before the real thing arrives.
Lifting and Positioning
Getting a 150kg block of iron down a sailing yacht companionway requires patience and rigging. Strip the engine of its alternator, starter motor and exhaust manifold. This saves weight and reduces the risk of smashing fragile parts.
Rig a chain block from a stout timber beam across the companionway hatch, or use the main halyard if your mast and boom are rated for the load. Never stand directly beneath the suspended engine. Lower it slowly onto temporary wooden blocks across the engine beds. Leave enough room to slip the new flexible rubber mounts into place.
Aligning the Propeller Shaft
Alignment is where DIY installations succeed or fail. If the gearbox flange and the shaft coupling are not perfectly aligned, you will destroy the cutlass bearing and chew through the stern gland packing. This causes severe vibration.
Adjust the nuts on the engine mounts to raise, lower or tilt the engine until the two metal faces meet flush.
- Bring the flanges together without bolting them.
- Insert a feeler gauge around the circumference of the gap.
- Adjust the mounts until the gap difference is no more than 0.1mm (0.004 inches) at any point.
- Tighten the mount locknuts to the specified torque (usually 40 to 50 Nm for a 25hp engine).
Always fit a flexible coupling, like an R&D Marine or Vetus Bullflex insert, to absorb minor misalignments. A boat hull flexes. You must re-check the alignment after the yacht has been back in the water for 48 hours.