| Author |
Message |
    
Mike Carter
Visitor
| | Posted on Sunday, August 05, 2007 - 10:55 pm: | 
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I have a 1984 model 4-108 that has suddenly developed a problem with low power. The engine was running happily at 2800rpm (around 6.5knots in our yacht) and then suddenly it reduced speed to around 2400 revs and now that is the maximum speed it will do under load. It revs to over 3000 rpm in neutral and runs smoothly. The injectors and fuel injection pump (it had developed a leak) have since been rebuilt and the compression is good on all cylinders. Any suggestions - I am wondering if it is possible that the valve or fuel pump timing has somehow changed - is that a possibility?
Any bright ideas welcome! |
Dwight Brooker
Member
Username: sailmaster
Post Number: 57
Registered: 05-2006
| | Posted on Monday, August 06, 2007 - 07:38 am: |
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Is there exhaust smoke? How are the gear box, stuffing box, and cutlass bearing? If there is increased drag through these components it will slow the engine down and reduce fuel economy. If all is OK I would look at the fuel source i.e; fuel tank pick up line and return and the fuel line themselves. |
Mike Carter
Visitor
| | Posted on Monday, August 06, 2007 - 08:25 pm: |
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Thanks Dwight
There is a small amount of white smoke.
When the boat was out of the water last (this is since the the problem started) the prop-shaft turned easily by hand so I am sure the cutlass bearing and stuffing box are not an issue here. However I suppose the gearbox is a possibility, it is a velvet drive hydraulic gearbox as fitted to many 4-108s. Any suggestions as to how to check it? I will check the fuel lines in any case.
Thanks, Mike |
Ed Heckman
New member
Username: beachboy
Post Number: 2
Registered: 08-2007
| | Posted on Monday, August 06, 2007 - 11:10 pm: |
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I had a similar problem with my Yanmar 2GM. It was primarily due to the injection pump, which I had rebuilt, and the exhaust system, which was almost totally blocked and was completely replaced. |
Dwight Brooker
Member
Username: sailmaster
Post Number: 58
Registered: 05-2006
| | Posted on Tuesday, August 07, 2007 - 07:47 am: |
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The Borg Warner gear box would most likely be making noise if the bearing were gone and causing the drag. As Ed indicated, the exhaust system would be suspect at this point since you have already dealt with the injector pump. Pull the exhaust riser out and see if it is plugged with carbon. Check that you have free flow through the entire exhaust system. Check the pressure drop (∆p) over the exhaust system with a monometer. If it is higher than recommended the exhaust system needs servicing. Do not run the engine until you determine that the exhaust system is OK as this will burn out valves and cause other damage if it is restricted. Good luck. |
Mike Carter
Visitor
| | Posted on Thursday, August 09, 2007 - 08:07 pm: |
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Thanks Ed and Dwight
I'll be having a go tomorrow, the muffler is very old so that is a possibility, I'll let you know how I get on.
Mike |
Bernard Knight
New member
Username: baknight
Post Number: 2
Registered: 08-2007
| | Posted on Tuesday, September 04, 2007 - 06:16 pm: |
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I had a similar problem and experiences similar to yours - rebuilt/cleaned entire fuel system on a right new Volvo MD-2030 which has a Perkins label on the block. Problem was, exhaust elbow was almost completely blocked with rock hard carbon/iron oxide. Who'd have ever thunk it...only 750 hours on motor. |
Michael Carter
New member
Username: mike_carter
Post Number: 1
Registered: 08-2007
| | Posted on Monday, September 17, 2007 - 06:29 am: |
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Hi Dwight, Ed, Bernard
I wanted to let you know what transpired with my engine. Having checked all the external stuff, fuel system, exhaust etc and checked the fuel pump timing and compression I finally concluded that the problem had to be in the transmission. I lifted the motor and split the gearbox from it to find that the drive plate between the flywheel and gearbox input shaft had partially collapsed. Some of the discarded springs had wedged between the flywheel and bell housing causing friction and hence the power loss.
A tricky one to diagnose but at least simple to fix.
Thanks for your suggestions.
Regards
Mike |
Ed Heckman
New member
Username: beachboy
Post Number: 3
Registered: 08-2007
| | Posted on Tuesday, September 18, 2007 - 11:17 pm: |
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Mike,
Glad you found the problem. I have never looked inside a tranmission so if such a problem developes on my boat, I'll call you!
Ed |
