Raw (wa­ter) deal

Canal Boat - - Back Cabin: -

My BMC 2.2 en­gine has an over­heat­ing prob­lem. I sus­pect it may be re­lated to the wa­ter pump prim­ing. I checked the weed traps and both were sealed with rub­ber sealant but I sus­pect there should be some sort of gas­ket. Could it be that the pump is not able to prime as air is com­ing into the sys­tem. How do I prime the pump?

IAN BUSTIN, via email

TONY REPLIES... You are cor­rect, the caps on the sea in­lets should be fit­ted with rub­ber seals, and as the pipework be­tween the sea in­let and the brass raw wa­ter pump is nor­mally all un­der suc­tion, it is vi­tal to en­sure that there is no pos­si­bil­ity of air leaks. Raw wa­ter pumps are nor­mally self-prim­ing, so if one will not self-prime, you have a prob­lem. Look at the top of the thin­ner part of the body on your raw wa­ter pump (Jab­sco). If it has a sort of ‘mini tin can’ stuck out of the top, this is a grease cap. Un­screw it and fill it with any easy to get grease. Give it a twist ev­ery day. If it still won’t prime, you might have a worn pump body.

Undo the ring of screws that hold the plate on the front of the pump. Then re­move the im­peller and in­spect it. The ‘wings’ should have no splits at their base and the tips should be ‘rod’ shaped – not oval. It should not be cov­ered in grease. Also in­spect the pin that may be screwed through the im­peller to al­low the shaft to drive it. The in­side of the front plate and the back of the pump should be flat with min­i­mal groov­ing (my guess is that there are deep grooves in both).

Get hold of the shaft and try to ‘wag­gle’ it in the body. It should have only a tiny amount of move­ment.

Re­assem­ble the pump us­ing a new im­peller and gas­ket if re­quired. See if it will prime, if not, screw down the greaser while the en­gine is revving. If it then primes, the body is worn and a new pump is re­quired.

If the face plate is grooved, it can be turned over, but I fear some­one may have al­ready done this.

For spares, try Cleghorne & Wear­ing or ASAP Sup­plies, but be aware that many older pumps are no longer ob­tain­able. If so, think about us­ing an elec­tric pump fed from the ig­ni­tion switch.

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