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Chris Mundy
New member
Username: chris_mundy
Post Number: 1
Registered: 09-2007
| | Posted on Sunday, September 02, 2007 - 09:55 pm: | 
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I have an old P55 in a small Huon Pine boat (have had it for some time, I rebuilt it about 10 years ago) It is saltwater cooled. Although it goes well, corrosion always worries me. Does anyone know whether there should be any sacrificial anodes fitted to screwplugs in the engine, as there are in more modern saltwater cooled engines? Also, should I remove the cover on the side of the cylinder block and scrape out corrosion around cylinders or is it better off left untouched. The engine, although I rebuilt it because a crank journal broke, is not restored, it has been in active service all its life and has always been kept full of salt water (for about the past forty years) There does not appear to be any corrosion problems with the motor, however it is always a worry. |
Peter Ogborne
Senior Member
Username: peterogborne
Post Number: 213
Registered: 09-2002
| | Posted on Monday, September 03, 2007 - 06:52 am: |
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Chris I would say that if you removed the cover on the side of the block you may get a shock .After all those years in salt water there is sure to be quite a lot of corrosion. You have been lucky .But for the sake of reliability I would lay the boat up and do a overhaul of the engine ,clean out the pump and the valves etc also the water jacket.
I made a fresh water cooling system for another engine and I intend doing the same for my boat when it is finished.Just a header tank and a seperate chain driven pump .
Interested to hear you repaced a big end jounal. |
Rob Ripley
Visitor
| | Posted on Monday, September 03, 2007 - 07:44 am: |
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... I made a fresh water cooling system for another engine and I intend doing the same for my boat when it is finished.Just a header tank and a seperate chain driven pump .
I plan to do the same when I finish my the boat for a P5 .. why not use the water pump on the engine? Did you have a radiator or underwater cooling pipes? |
Richard A. Day Jr.
Senior Member
Username: richardday
Post Number: 515
Registered: 11-2003
| | Posted on Monday, September 03, 2007 - 07:47 am: |
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Peter, My experience has taught me never let a saltwater cooled cast iron engine water jacket dry out. If you do it will crack and once that starts you cannot stop it. All my engines that were salt water cooled have their water jackets filled with auto antifreeze to keep the air away from the salt. Since I started that practice back in about 1960 I have had no more trouble. Before that I used the old timers solution which was used auto engine oil. Cheap but messy if it were to leak. I fill the jackets from the bottom up using a plastic tube and funnel. When the jacket is full to the very top I tape the plastic tube to the engine so I it were to leak I can see the level dropping in the tube. Regards, Dick |
Chris Mundy
New member
Username: chris_mundy
Post Number: 2
Registered: 09-2007
| | Posted on Monday, September 03, 2007 - 07:26 pm: |
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I know the best long term solution would be keel cooling pipes... I take it that type of system would run fine off the existing water pump, and just use copper or steel pipe?? Steel would be safer as far as corrosion protection for the engine goes, however it would require more pipe as it does not conduct heat as well. Does anyone run this type of system and if so what length and size of pipe do they use?? Anyway, short term that is not going to happen, I just dont have time at the moment. The boat is used constantly and i think this works in my favour. Surely as a preventative measure, to pull a screwplug out of the cooling system and relace it with a screwplug with a zinc anode on it could do no harm? My main worry is, while I still saltwater cool the engine, is it better to leave alone deposits in the waterjacketing?? |
Peter Ogborne
Senior Member
Username: peterogborne
Post Number: 214
Registered: 09-2002
| | Posted on Tuesday, September 04, 2007 - 07:02 am: |
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Dick ...yes I do the same ,real messy with diesel.
Chris use copper if you are doing that,keel cooling pipes,easy to work .An anode ...I dont know how it would go .The problem with salt water cooling in my experience is not so much the corrosion but the scale build up coupled with corrosion.
Rob ,I retained the original Stuart Turner pump for the fresh water . The system comprises of a heat exchanger made from 3 inch brass tube .It has a tube bundle made from half inch copper tubes. I made the water space at the ends of the H x as the raw water entry and exit .My thought were that any marine growth could be accessed for cleaning.The fresh water was on the inside of the Hx .
To circulate the raw water from the outside of the hull then over the side I used a small chain driven gear pump from the fly wheel, it runs at about crankshaft speed . The fresh water circuit needs an expansion tank |
Chris Mundy
New member
Username: chris_mundy
Post Number: 3
Registered: 09-2007
| | Posted on Tuesday, September 04, 2007 - 08:56 pm: |
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Peter, thanks for the advice. I think the general consensus is that I should try to scrape the scale out of the engine. It just worries me that this could acellerate corrosion! I think long term I will look at fresh water cooling.I am unsure yet whether to go shell and tube h-ex or keel cooler. In your h-ex, how long was the brass tube and how many copper pipes?? I may have access to shell and tube heat exchangers (copper nickel) that are used for marine refrigeration that may be ideal.Copper-nickel components have good heat transfer,and as far as I know should be compatible with the cast Iron block and not present any corrosion worries. They are the metal of choice for condensers on steel fishing boats... I just need an idea of the size of yours to get an idea of the heat rejection required ( I trust yours cools more than adequately when the engine is working hard?? with a seawater temp of about 18 degrees??) Does anyone have any idea how high the return temp to the engine can be whilst maintaining adequate cooling?? I am sure to overheat the engine would be worse than to saltwater cool it!! Also, another question. Do you have any idea how many litres per minute your chain driven pump delivers?? Peter, you said you were interested that I had replaced a big end journal... you might be interested the engine did about 3 hrs running to ge me home with the broken journal! It broke on an angle and the engine ran fine still because the big end bearing held it together! ( albeit a bit noisier than usual!) A hint found from experience for anyone pulling apart a stuart crank if there is any wear whatsoever in the journal holes in the crankwebs because it has been dismantled once or twice, it is a good idea to put a small spot of weld on the nuts to fix them to the journal and the crankweb after you align it. If you dont, I found it didn't matter how tight I did up the nuts ( and the journals were still a press fit into the webs) the crank would slip out of alignment if the engine backfired due to lean mixture! The small spot of weld might sound a bit dodgy but it is good insurance against a lot of grief! |
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