Alternator Handedness - Left hand or right hand?

[Pete Morrison]

I have a Beta 38 engine that needs a new alternator, the previous one was a left-hand Lucas A127 75A type. 

That would probably suggest I need a left-handed replacement, but since they apparently do work (just less efficiently) with the wrong handedness, I wanted to ask if there is a "standard". 

If all beta 38 engines turn the same way, then perhaps you know the answer to this question!!!

[Tony Brooks]

Left and right handedness usually refers to how the end brackets are configured to fit to the engine, basically on the left or right-hand side, that is down to the engine manufacturer/mariniser. I suspect that you are talking about clockwise or anticlockwise in respect of rotation.

 

You are correct that alternators work equally well whichever way they turn, but the cooling fan may be a different matter. Some are handed and if you use the wrong hand, then the alternator might overheat. If the fins on the fan radiate on the radii than it is not handed, if they run at a tangent to the radii then it is handed.

 

The standard is whatever the mariniser, Beta in your case, says you need, as far as left or right-handed goes, but most, if not all three through bolt alternator brackets can be easily reconfigured for the other hand, even if it means drilling out one threaded hole and using a nut and bolt.

 

Most engines revolve clockwise, looking at the front, but a few do not, so there are no universal standards across all engines. E.G. The smaller air cooled Listers drive their alternators anti-clockwise and some, usually older, twin engine boats have engines running in opposite directions.

[BEngo]

Left or Right  handedness has nothing to do with the rotation of the alternator.  Handedness describes where the mounting lugs are.

An A127 can easily be swapped from LH to RH or vv by undoing the three long screws  that hold the alternator together and rotating the front half one screw clockwise or anticlockwise as suits to get what was the single lug lined up with the back one of the double lugs

  After that you may need to drill out the thread  in what was the single lug, so the mounting bolt will fit through.  The 'new' single lug will not have a thread so the adjuster will need to be secured with a  nut and bolt/machine screw.

Direction of rotation does affect the fan.  Reversing the rotation requires only  a new fan.  Running the fan the wrong way gives poor cooling and a short life if any  serious output is to be delivered.  Reverse fans are available, bug not common.

[Pete Morrison]

I see, so I probably want to buy the left-hand one (which would be mounted on the left when facing the pulleys side, although this is on the starboard side of the boat). But good to know that I can swap over the handedness if I get the wrong one. But, it still doesn't really help me understand about the rotation. Or can I just trust that the alternator will likely rotate the correct way regardless of handedness? The fan does seem like it has a correct rotation direction .

 

The alternator and fan looks like this. Is this fan supposed to rotate clockwise or counterclockwise when looked at from the pulley?

 

[BEngo]

That is a clockwise from the pulley fan.

[Tony Brooks]

2 hours ago, Pete Morrison said:

can I just trust that the alternator will likely rotate the correct way regardless of handedness?

 

In all probability, yes you can trust that the fan will be correct for the engine rotation because Beta engines rotate the same way as maybe 98% of all similar engines, but it is not a 100% certainty for any engine. In ant case, as long as you get another A127 the fan from the old alternator should fit, and that one would be for the correct rotation or a universal one. The time things may get difficult is if you bought a different make, then the shaft size might be different.

[IanD]

2 hours ago, Pete Morrison said:

I see, so I probably want to buy the left-hand one (which would be mounted on the left when facing the pulleys side, although this is on the starboard side of the boat). But good to know that I can swap over the handedness if I get the wrong one. But, it still doesn't really help me understand about the rotation. Or can I just trust that the alternator will likely rotate the correct way regardless of handedness? The fan does seem like it has a correct rotation direction .

 

The alternator and fan looks like this. Is this fan supposed to rotate clockwise or counterclockwise when looked at from the pulley?

 

Clockwise like most alternators, the cooling fan pulls air out of the casing.

 

(the alternator itself will work either way)

Edited January 12 by IanD