8 Steps to Install A Boat’s Diesel Engine

March 21, 2017 - 9:00 AM by Samantha Pudney


Ever wondered how a professional installs your boat’s diesel engine system? For insight into this highly technical process, we’ve outlined the steps below. Please note, we do not recommend attempting to install an engine yourself and would always advise that you enlist the service of a qualified professional.

A boat’s engine and drive system must be precisely aligned to minimise wear and vibration. However, the most carefully installed drive system can go out of alignment when the boat is out of the water. Periodic checking and careful investigation of any untoward vibration or hull noise will pay dividends.

1. Choose Flexible Mounts

These comprise of steel shells with rubber bonded between them. Primarily, they insulate the hull from engine vibration. When choosing the correct size the torque and thrust from the propeller must be taken into account.

Once fitted, a professional should avoid at all costs spilling fuel or lubricating oil into the rubber as it will in time soften and swell.

2. Align the Propeller Shaft

Whether the engine is mated to its drive shaft by a flexible coupling or connected to the propeller shaft flange, it must be carefully aligned. A professional will ensure that the engine output will run both square and concentric with the mating propeller shaft flange.

Perfect alignment can be difficult to achieve. In the case of significant misalignment, excessive wearing of the bearings will occur. If the drive flange is not square, the propeller shaft will vibrate, causing rapid wear of the bearings.

Alignment of the diesel engine is carried out by a professional who will adjust the engine mounting bolts for position and height to achieve close contact on all parts of the connecting flanges. They must test for close contact by trying to insert a feeler gauge between the flanges.

3. Align Flexible Drive Couplings

Unless it is specifically designed to allow an angular misalignment, the same care must be taken to line up a flexible coupling and its engine. This will extend the life of the coupling, shaft bearings and gearbox bearings.

4. Tighten the Flange

Conventional seals consist of a stuffing box into which are laid several layers of grease-impregnated packing. The box is closed by tightening the bolts in the outer flange, which compresses the packing and causes it to seal against the shaft.

The flange needs to be tightened just enough to stop leaks. If you overtighten the bolts, the result will be heat and wear on the shaft seal. This could possibly cause twisting and failure of the rubber sleeve that connects the stern tube.

If a leak is seen, retighten the flange immediately. If leaks are persistent, change the packaging.

5. Select a Seal

Rubber seals may also be used, similar to those in the engine. They seal in oil around the shaft but are made from a material that is compatible with water.

In recent times, face seals are becoming increasingly popular. They work by mating a precisely ground stainless steel face against a carbon face. Rubber gaiters hose-clipped to their shaft and stern tube provide flexibility.

Face seals may need special lubrication procedures during launch and initial start up. In this case, a professional will refer to the manufacturer for instructions.

6. Balance the Propellers

Propellers need to be balanced to run smoothly. Any imbalance caused by chipped blades or other damage will produce vibration and reduce bearing and gearbox life. A feather or folding propeller may be fit for long passage making – the benefits in terms of extra boat speed can outweigh the cost.

7. Install the Propeller Shaft Support Bearings

To keep the shaft aligned and provide support, it is held by two sets of bearings – one supporting the gearbox, fixed inside the boat, and the other either in the sternpost or in a P or A bracket extending from the hull.

The bearings in the gearbox or the boat provide both thrust and radial support. The outer bearing provides only radial support. Usually, it is of the cutless type where the shaft turns into a rubber sleeve, grooved to assist water lubrication.

8. Insulate the Engine Compartment

An engine compartment must not only let in sufficient air to feed the engine, but also keep out any seawater that threatens to disable the engine. A single cup of water in the inlet manifold will disable and ruin an engine. This could put lives and your boat at risk.

The diesel engine is protected against water filling the cockpit in bad weather, with engine covers and access doors secured against water entry. The compartment of your diesel engine needs to also be insulated against noise and for your own safety.

Notably, engine compartments should be kept free of all wiring save for what is needed for the engine.

Power News – Sign Up Here