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Inspecting BMT pt 7


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First and foremost engines can be complicated,expensive bits of engineering and are really best left to someone with experience to check out for you.Saying that there's a couple of things that the novice potential boat buyer can look for before calling in the experts.

Even though boats can be powered by different types of engines including diesel stern drives I'll keep the discussion based on outboards as this is the most commonly  fitted engine to a boat a first time boat buyer would buy.

As before I like to start at the bottom and work up.

First up is the prop.

Props can and do take abuse when either running aground or hiting some underwater obstacle etc.Missing paint on an alloy painted prop is no big deal which is caused by running in the shallows stiring up sand/mud. it's bent,broken or cracked blades that's when it becomes a concern.image.jpgThis prop has seen better days and should be replaced.If you drive the boat like this you will experience severe engine/steering vibration.

  If you already have a boat and hit something and immediately get this vibration always check the prop and that you haven't cracked the gear case housing or bent the prop shaft.More on that later.image.jpgStainless props can suffer the same fate.Being stainless there's more chance of the next thing I'm going to show you happening as they are much more solid than an alloy prop when you hit something which can/will transfer the shock to other engine components such as the gear case housing,bearings and prop shaft.

image.jpgThis engine has a stainless prop fitted with a matching cracked gear case housing to go with it.Im betting the owner has struck something solid.

Another thing that can happen when hitting anything with the outboard is cracked/broken skeg.image.jpgPrime example here of a destroyed prop and broken skeg.If you still have the broken piece they can be welded back on depending on where the break is relative to the gear case.image.jpgHere's one that's been repaired.

Testing for a bent prop shaft(Engine Stopped).

Ensure the engine is switched off and in neutral giving the prop a good spin by hand.It should spin true with no oscillations.

Grab the prop in the 12 and 6 o,clock position and the 9 and 3 o,clock position wiggling side to side and up and down pushing in/out.

There should only be the slightest play.

Testing for bent prop(Engine running)

Start the outboard in neutral on the muffs and put it in fwd gear with a little throttle.

Stand back behind the outboard and watch the outside edges of the prop blades or prop hub spin.A perfect circle should form.Anything that looks like a oval while it's spinning and you may have a bent shaft or distorted prop.

If the owner will allow take the prop off and check for fishing line behind the prop that can eat into the seal for the gear housing.Its just a matter of undoing a nut and removing a few spacers/washers and sliding the prop off.image.jpgThis is what you don't want to be greeted by.Theres an oil seal behind that line which if compromised will allow water in to the gear case which you don't want.

Theres other things that can go wrong with props like bad bushes etc but these are the main things to look out for.

I'll continue In pt 8.

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