Guide To Buying Boat Engines – FAQS

There are many questions new and even experienced boat buyers like to know so we have tried to give a brief outline of the most important questions and observations you will need to know when buying an engine for your boat.

How do i check the engine?

There are two different types of engine, the outboard which is bolted or clamped to the back of the boat, or the inboard which is located inside the boat. There are three different types of outboards. Direct injection two stroke engines, two stroke engines and four stroke engines.

What is a two stroke outboard?

These are the thirstiest of all the outboards and require you to mix the fuel and oil separately unless the outboard has oil injection. On buying second hand, ask if there is any history and warrantee left on the engine.

Ask to see it running (this must be done in a tank of water) check to see if there is water pumping out of the engine. If not walk away, this could mean the impellor needs replacing (not expensive) or the outboard could have been run without the water cooling it causing other damage. Ask if they know if the compression is O.K all cylinders should be within 10% of each other or it means one or more of the cylinders could be losing compression (very very expensive).

What is PTT?

PTT means power trim and tilt, this is when the outboard has a ram which will lift the leg of the outboard out of the water (great to have) check it works and does not sound rough. (can be expensive).

What is direct injection outboards?

These boast in most cases to be 35% more fuel efficient than normal two strokes, these outboard have only been around for approx 5 years. These outboards are lighter than four strokes so in a lot of cases seem a better buy. These outboards do require computers some of the service works, so check the history. As well as that check as above.

What are four stroke outboards?

They are the most economical of all outboards; all the same checks are needed. These outboard are far heavier that the other two types.

What is an inboard engine?

They are always located inside the boat and are more difficult to do check we advise to get a trained marine engineer to look at the engine on your behalf. BE WARNED inboard motors are far more expensive to run and maintain. Great for wakeboard boats as they are very heavy and provide great torque and balas.

How do i maintain my outboard or inboard motor?

We recommend to anyone who owns an inboard or outboard motor to get is regally serviced, not only will this prolong the life of the engine it will ensure smother running. A must of all seawater run engines is to flush the through with fresh water.

There are different ways of doing this

Using flush muffs
Using a flushing attachment
Running in a test tank or bin full of fresh water

This enables the engine to flush all the salt water deposits out of the cooling system therefore reducing internal corrosion.

There products on the market which will also help protect your engine.
Quicksilver Corrosion guard
Spray this over the working parts of the engine and it will coat it in a film to protect the engine from corrosion.
Quicksilver Power Tune
Spray this into the carbs and it will help with performance
Quicksilver Fogging oil
Spray this into the cylinder when the outboard is running and it will coat the inside of the engines to stop rust though winter. This can only be done if you are not using your engine for a few months. Change the spark plugs regularly.

How to determine the correct outboard shaft length

First, lets get a better understanding of outboard shaft lengths and what they mean. Shaft length is simply a “what your boat requires” matter. In other words, you don’t really have a choice. A long shaft doesn’t go any faster or slower than a short shaft. However, selecting the right shaft length is crucial and improper selection could result in severe engine damage.

Measure from the top of your transom to the bottom of your keel. If it is 15″ to 17″ you’ll need a “short shaft” outboard. If it is from 20″ to 22″ you’ll need a “long shaft” outboard. Tohatsu/Nissan outboard shafts are measured from the bottom of the engine mounting clamp bracket to the cavitation plate (large fin above propeller) on the lower unit – see diagram below. Generally most boats need either a short or long shaft although some boats require a 25″ “ultra-long shaft” outboard. Below is a diagram on how to measure your transom for proper shaft length. NOTE: ANY OTHER MEASUREMENT OTHER THAN THE ONE DISPLAYED BELOW WILL BE USELESS INFORMATION

Correct Boat Shaft Length

For normal operation your engine’s cavitation plate should be even with the bottom of the hull. A gap of 1-2″ in either direction is acceptable and considered normal. If you are still unsure as to which shaft length your boat needs contact your hull’s manufacturer. Your outboard owner’s manual will also contain more information on shaft length and proper installation.

Shaft engine length - FAQ'S

Q: Can I use a long shaft engine on a short shaft boat?
A: We don’t advise it but many folks do. Having a long shaft engine on a short shaft hull can create extra drag and could have an effect on manoeuvrability.

Q: Can I use a short shaft engine on a long shaft boat?
A: No. This will not allow the engine to intake adequate cooling water resulting in overheating and severe engine damage

Q: I have an adjustable outboard motor bracket can I use a short shaft
A: Yes, if the bracket is correctly installed and allows for proper travel so that the engine is in the proper operating position in the bracket’s down position

Q: Can you convert a short shaft to long shaft?
A: Possibly. Some manufacturers have kits available to complete this shaft length conversion. Not all makes and models have these kits available. Tohatsu/Nissan has several kits available for certain hp’s and models

Q: My motor cavitates and comes out of the water. Do I have the wrong shaft length?
A: Likely so. This can occur if you are in very high seas, especially if the engine is mounted at the stern. However, if this is occurring more often you may need to adjust the tilt pin, motor/transom bracket (if possible), or you likely have the wrong size shaft length. Engines that cavitate frequently can wear out water pumps prematurely as well as not allow for adequate engine cooling both which could lead to severe engine damage. You should take corrective action immediately.

Part Names of an Outboard Motor