BMC 1.5 / Thornycroft 90 Raw water cooling pump

[Andy Allen]

I have an old BMC 1.5 / Thornycroft 90 fitted to my boat that is raw water cooled, unfortunately it is not pulling enough water through and has caused the engine to overheat leaving a trail of white steam behind me.

 

I have been on the Jabscoshop website looking for a service kit but the only pump they show for this enging is a pedestal mount and the one fitted to my engine is engine mounted and crank driven.

 

Ive tried to contact Jabscoshop for advice but to no avail

 

can anyone point me in the direction of someone who can supply advice and a service kit for my water pump

 

Cheers A

Edited December 6, 2013 by Andy Allen

[Tony Brooks]

Never seen a crank driven raw water pump but one marinisation I know used different timing chain cover and drove the pump form the camshaft. The pump I saw was a fairly standard three bolt fixing pump.

 

If you look on the disk shaped end plate you should find part numbers. However if the cover has been reversed to combat wear these will be on the inside and may be worn away..

 

The pump I am thinking of does not have a wear plate under the impeller and the shaft runs in the pump body with a grease cap for lubrication. If the pump body wear then the pump will suck air via the shaft. If the body wears in the pumping chamber there is not much you can do about it (Unless Richard has some brazing & machining ideas!) The Impellers are fairly standard so if you get the old one out and there is still at least one "wing" on it any decent chandler should be able to match it.

 

I assume that you have checked the mudbox/seainlet & strainer for blockages, including on the outside of the hull, also all the joints on the suction side of the system including any strainer cover. On older engines it is worth checking the exhaust mixing elbow has not furred up and the exhaust hose is not delaminating. Both can cause back pressure in the exhaust and thus the cooling system so the pump can not deliver sufficient water.

 

Make sure the end cover is not badly grooved where the impeller wings run over the cam. If it is try reversing it after taking note of the part numbers. Also make sure no one has used an old cornflakes packet to make a gasket. Too thick gaskets will reduce pumping.

 

 

 

I am sure there will be a new pump to fit but it may well look different and I dread to think about the price.

[Mick_B]

On my BMC1.5 setup I have a second heat exchanger for the gearbox oil. This is before the raw water pump so water is sucked through it. I had a similar problem this year and discovered that over time small bits of weed had gotten around the weed filter and built up on the inlet side of the heat exchanger. This led to water being seen to exit the exhaust but still overheating. Due to the slow build up it was hard to notice the difference but I certainly did after removing the small amount of weed. (less than an egg cup full) Worth checking.

[p6rob]

Asap supplies list a crankshaft driven Jabsco water pump. It's a special order item and there isn't a picture of it. If it's any help, the part number is JAB-29440-1051.

 

http://www.asap-supplies.com/marine/crankshaft-mounted-engine-cooling-pumps

[Andy Allen]

On my BMC1.5 setup I have a second heat exchanger for the gearbox oil. This is before the raw water pump so water is sucked through it. I had a similar problem this year and discovered that over time small bits of weed had gotten around the weed filter and built up on the inlet side of the heat exchanger. This led to water being seen to exit the exhaust but still overheating. Due to the slow build up it was hard to notice the difference but I certainly did after removing the small amount of weed. (less than an egg cup full) Worth checking.

Mick_B

 

Thank you exactly the same problem and solution.

Back to a proper spout of water exiting the exhaust and no steam.

 

also a big thank you to Tony Brooks, I will follow your recommendations as well, as the poor old girl has been mechanically neglected for many years and I am now tasked to bring her back to some form of former glory