"Ali-Mac" Repower  to a VM Motori MR704LH engine

Here is a great step by step review of a marine engine repower project of "Ali-Mac" to a VM Motori MR704LH engine.

After lengthy consideration and much pondering the plunge was taken to repower “Ali-Mac” a 1995 Salthouse Coastal 32 built by the renowned Bob Salthouse.

The repower consisted of removing the original engine Volvo TAMD31B 130HP @ 3800rpm, which should be mentioned was running like a swiss clock at 3900 hrs, and installing a VM Motori MR704LH 210HP @ 3800rpm.

 On 02 April 2016 Ali-Mac started the transformation, being hauled out of the water at Pine Harbour Marina

To remove the engine additional supports were required to strengthen the floor for manoeuvring the engine through the saloon, without seeing it take a sudden exit through the floor and out of the hull bottom !

Then the removal of the trusty old Volvo began. A beam, made up from old logistics pallet racking, was placed through the side windows onto blocks positioned on the deck. With tongue in cheek the weight was taken up, closely watching the beam deflection.

Clear of the engine room, finally the engine was out on the saloon floor and wheeled back to the rear ready for removal from the boat using a truck mounted crane. It all went surprisingly well without too many missed heart beats!

The installation of the new VM Motori MR704LH only required minor modifications to the existing engine bearers as both engines had very similar foot prints.

Finally the new engine could be craned through the saloon doors and placed on the floor to make the reverse journey of the old Volvo.

The engine was then lowered down onto the revised engine bearer which was a perfect fit. Exhaust alignment was nearly the same, only requiring a special fibreglass 90° elbow to join the engine exhaust mixer to the water lock muffler. Electrical harnesses and cable connections were then all completed.

The propeller shaft was removed and shortened to accommodate the different engine length and shaft coupling design. All shaft bearings were extracted and replaced and the original Chatfield inner shaft seal housing was reconditioned to save major modifications to the shaft log.

The engine transmission output flange coupling type was changed from a direct shaft coupling to include a short Carden Shaft with triple universal joints for minimal UJ angle and smooth operation.

On the 26 April 2016 Ali-Mac was put back in the water for seatrials.

The process of achieving the correct propeller selection was frustrating to say the least, with 8 propeller variations in total!

However the final result was a real success as detailed in the speed run results.

Engine Specifications:

New  Old 
Make:   VM Motori Make:    Volvo    
Model: MR704LH Model:  TAMD31B 
Power: 210 HP @ 3800 rpm Power:  130 HP @ 3800 rpm  
Trans:   MG5012SC @ 2.4:1    Trans:    Volvo @ 2.6:1   


The MR704LH is a 4-stroke, turbocharged and aftercooled diesel engine with electronically controlled common rail injection, offering excellent performance with low fuel consumption.

RPM MR704LH LPH MR704LH LPNM MR704LH Knts Volvo Knts
1000 1.48 0.33 4.5 3.5
1600 4.78 0.67 7.1 5.5
2000 8.17 1.00 8.2 6.6
2600 15.95 1.58 10.1 7.8
3000 22.45 1.89 11.9 8.7
3200 27.16 2.07 13.1 9.0
3400 33.00 2.36 14.0 9.5
3600 38.65 2.58 15.0 10.7
3800 45.30 2.83 16.0 11.0

By Scott McAlpine: Marine Product Sales & Engine Technical Support, TDX Ltd

View our VM Motori repower range of engines here