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BMC 1,800 alternator

BMC 1,800 alternator

Just taking the old one out and putting the new one in.

Couldn’t be more straightforward really.

Old one looked plenty dirty. I think the water pump leaked when that broke, meaning the engine compartment was very humid. This is reflected by the black gunk coating the mounting, blades and inner workings of the old alternator.

BMC marine alternator - old and new
BMC marine alternator – old and new

Plenty dirty, and a bit smelly.

I’m sure the pump leaked a fair bit of water onto the belt as well, this has sprayed off in streaks around the various fitting and furniture of the engine compartment.

TBH, it was only a matter of time before it stopped working.

Started it up this morning. It appears to have made no difference whatsoever to the charging.

More charge

25th Sept – As an update – Did a 2 hour cruise, with reasonable engine speeds and it seems to have had a longer lasting charging effect on the batteries.

The voltmeter was showing this for around 3 hours. A two hour or so improvement on before the new alternator was fitted.

It indicates the battery bank is at between 12.5-13V.

BMC 1800 waterpump

BMC 1800 waterpump


Just resting in bed one morning, engine running. Suddenly it started making a crunching noise. Sounded ominous.

Ran out and immediately turned the engine off.

This happened twice or three times. A loud metallic crunching sound.

Next day when I started it up, it began overheating quite badly.


Most of the coolant ended up squirted all over the engine compartment floor.

When I started the engine, after about an hour, it started ‘boiling out’. The coolant was just boiling off the top of the cylinder heads and being forced out.

This can point to a badly bled system, or a more serious problem with your cooling system.


BMC 1,800 marine waterpump

After talking to a couple of people, I was fairly convinced that the problem was with the waterpump.

BMC 1800 marine waterpump
BMC 1800 marine waterpump

Symptoms including:-

  1. Metalic crunching sound; the pump scraping on it’s housing.
  2. Overheating.
  3. No oil in water or water in oil: Not being a problem with the head gasket.

Procedure for removing waterpump

The waterpump resides behind the engine. The fan belt rotates around it, along with the alternator and the drive-shaft.

  1. Loosen screws on waterpump wheel: There are four nuts that need to be loosened.
  2. Loosen alternator: Slacken the belt off.
  3. Remove waterpump wheel: Fully take nuts out and gently lever the wheel from the waterpump. Keep this, you will need it later!
  4. Remove water from your system: Pick the place where the cooling system piping is at it’s lowest. Remove the pipe here and bleed the coolant out.
  5. Remove pipes: There’s a pipe which connects the waterpump to the cooling jacket. Carefully remove this.
  6. Remove waterpump: There are 4 nuts and washers holding it on. Slacken these off and remove the pump.

You should be left holding your old and broken waterpump in your hand.

You may want to dispose of this in the best way you see fit.

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