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AuthorMessage
mholyoake
mholyoake

Posted: Mon Dec 01, 2014 6:25pm

Post Subject: Engine losing revs

Hi Tony, I have a Barrus Shire 50HP engine with 200Hrs clocked. The strangest phenomenon started to occur quite recently. Whilst cruising the tickover dropped from 900rpm to 500rpm and obviously the engine vibrated viciously and cut out. This happened a number of times, so I decided to increase the tickover to 1250rpm. Now when I start the cold engine it revs to 1250 until it heats up then drops back to 800rpm. This is a 'sticking plaster' cure but I have lost 450rpm? I've checked that the fuel is clean, air filter is clean and replaced the fuel filters to no avail! Answers to this problem would be much appreciated. Mike

Tony-B
Tony-B

Posted: Mon Dec 01, 2014 8:10pm

Post Subject: Engine losing revs

I do not know how an experienced canal boater you are but when the words "recently", "number of times, and reduction of revs are mentioned in the same post I think "new boater and leaves around the prop. The only thing I am not clear about is if "until it heats up" equates to "when its is hot" or "after cruising for a while". If it means "after cruising for a while" the when it does it next time drop it into neutral, give a short, sharp burst of astern, pause and then resume ahead. If you look at the back of the boat I suspect you will see a great of fallen leaves in the prop wash. You may have to do this every few minutes with lot of leaves in the canal. You also get this if there's a lot of weed about. It is a perfectly normal situation and is no cause for concern. Just use the burst of astern procedure at the first sign of the engine working harder or slowing down. If you are experienced and already employ this technique then please come back. Please also make sure that you have more then 6 inches of fuel in your tank, the more the better. The fuel pick-up pipe should be several inches clear of the bottom of the tank to avoid picking up water. If the level is low the engine might be running out of fuel as the boat moves. Tony Brooks

mholyoake
mholyoake

Posted: Tue Dec 02, 2014 8:33pm

Post Subject: Engine losing revs

Hi Tony, Thanks for your reply. I am an experienced boater with a sound knowledge of diesel engines, well at least I think so!! This problem has baffled not only Barrus Shire but other engine experts. The boat is motionless in neutral , I start the engine which always starts first time and runs at 1250 revs. After about 15 minutes when the engine heats up the revs drop to around 800rpm. The engine will stay at this tickover for the remainder of the day whilst cruising. The RPM will only revert back to 1250 when the engine is cold once again. I have done all the obvious ie checked for clean fuel, replaced the fuel filters, removed the fuel lines to ensure there was no blockage, I have even replaced the 12V fuel pump but this annoying problem still persists. It seems that it may be heat related but I'm afraid that I am out of my depth! Any help would be much appreciated.

Tony-B
Tony-B

Posted: Tue Dec 02, 2014 9:19pm

Post Subject: Engine losing revs

I agree that from what you say it does sound heat related but I think it would be a good idea to check the fuel pump delivery. The pick up pipe in the tank may have a strainer on it and there is a faint chance that it may be clogging as the engine draws fuel and when the engine is stopped some of the muck floats away until it is next started. However I do to see how that squares with clean fuel filters. If the electric fuel pump is like a long cylinder with a bayonet cap on one end take that cap off and make sure the small filter in there is clean (unless you have already done this. It woudl also be worth taking the return to the tank pipe off near the engine, running the engine while directing the return flow into a canister. In that way you will get an idea about the fuel flow and how much air is being returned to the tank. This woudl give some idea if you have an air leak on the system. Make sure all the valve clearnesses are correct. Sometimes a tight valve clearance will hold a valve open when hot and that could explain the loss of revs and the rough running. Too loose is far better than too tight. Apart from that I fear that you may be suffering a partial engine seizure, but why I have no idea. I suspect it may be time to talk to and possibly pay Barrus to sort it out. They should know all the little foibles of their engines and it may well be cheaper in the long run. I have known injectors jamb when hot but if that was it I would expect you to have mentioned excess or more smoke. Its the fact it does it in neutral that bothers me. When some drive plates break up they can cause misalignment between gearbox and engine giving rise to similar problems, likewise an over-tight stern gland or a broken engine foot but again they should not do it in neutral.

Tony-B
Tony-B

Posted: Tue Dec 02, 2014 9:19pm

Post Subject: Engine losing revs

I agree that from what you say it does sound heat related but I think it would be a good idea to check the fuel pump delivery. The pick up pipe in the tank may have a strainer on it and there is a faint chance that it may be clogging as the engine draws fuel and when the engine is stopped some of the muck floats away until it is next started. However I do to see how that squares with clean fuel filters. If the electric fuel pump is like a long cylinder with a bayonet cap on one end take that cap off and make sure the small filter in there is clean (unless you have already done this. It woudl also be worth taking the return to the tank pipe off near the engine, running the engine while directing the return flow into a canister. In that way you will get an idea about the fuel flow and how much air is being returned to the tank. This woudl give some idea if you have an air leak on the system. Make sure all the valve clearnesses are correct. Sometimes a tight valve clearance will hold a valve open when hot and that could explain the loss of revs and the rough running. Too loose is far better than too tight. Apart from that I fear that you may be suffering a partial engine seizure, but why I have no idea. I suspect it may be time to talk to and possibly pay Barrus to sort it out. They should know all the little foibles of their engines and it may well be cheaper in the long run. I have known injectors jamb when hot but if that was it I would expect you to have mentioned excess or more smoke. Its the fact it does it in neutral that bothers me. When some drive plates break up they can cause misalignment between gearbox and engine giving rise to similar problems, likewise an over-tight stern gland or a broken engine foot but again they should not do it in neutral.

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