Trouble with Gearbox??

petehitch

petehitch

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I have a Gardner 6lxb turning a large 2 bladed prop through a SCG 4.5:1 box. This has worked well for 15 yrs. The engine is fine but now will not reach anything above half revs when manouvering or cruising. I thought it was a rope around the prop but have checked thoroughly. Would this be a fault with the gears??
Any advice would be appreciated.
 
IMHO I dont think it will be the Gearbox.....

I would check fuel filters and make sure that they are clean, it sounds more like fuel starvation than gearbox problem.

You will probably find that the engine will run at full revs out of gear but once load is applied there isn't enough energy (fuel) being delivered to turn the prop!

Lets us know what you find!

Tom

PS As always, diagnostics from afar are a little difficult!
 
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I agree with little ship - check the fuel system first. Gearboxes rarely cause power loss - usually they either jam up, slip or just dont do anything.

Is the prop shaft free to rotate - try turning it by hand. Check the inboard bearing after a run - is it very hot ? (careful - they can get hot enough to set the timber smouldering). Other power loss could be blocked exhaust - carbon can build up in the manifold and exhaust elbow. If you have a rubber 'diesel hose' exhaust pipe, the inner lining can perish and close off the exhaust causing power loss, particularly if it has been scorched by lack of coolant flow.
 
Trouble with gearbox??

Thanks for advice. I am pretty sure it is not the engine, but I will check. The engine was completely reconditioned 2 yrs ago and filters changed frequently. The shaft turns freely by hand. The boat is an old Danish fishing boat that we have converted back to sail. It did have a Hundested 2 cylinder 2 stroke with a VP prop. We have kept the prop and locked it in position. Hundested reccommend it turns at 300RPM hence the big reduction on the gearbox.
 
As others above have said. I would suspect the fuel filters or an exhaust blockage.
My other suggestion would be the injector pump "NOT" fully delivering.
I have personally experienced the main reason for loss of power in a sound running large diesel engine being the final fuel filter blocking . This has NO reflection on when the engine was last restored / reconditioned.
It is just something that can happen "at any time".
The very fine particles / gunge get though and it slowly blocks up it's then you notice the loss of power.
 
That is a very good point. I thought it would be impossible as the rods inside the shaft are locked in place. But that is what it feels like. I have now changed all the fuel filters, Racor primary and 2 on engine.
My worry is that I could damage or seize the gearbox, if it is the prop I can live with it until the end of season.
 
Any black smoke.

Just a thought

If the prop pitch had changed so that there was a greater load on the engine, I would have thought that you would see a lot of black smoke as the engine would be overloaded.

John
 
Many thanks to all. It has turned out to be the VP prop has changed pitch. The rod was locked into position, but either the rod has broken or the gearing in the hub. Has anyone any ideas??
The engine has white grey smoke presumably as it is trying to rev harder but the high pitch prevents it doing so.
 
petehitch said:
The engine has white grey smoke presumably as it is trying to rev harder but the high pitch prevents it doing so.
Click to expand...

That doesnt sound right either: overloaded engines usually give black smoke because the pump is delivering more fuel to try to make it go faster. White/grey smoke is usually a sign of fuel starvation where the atomised fuel is passing through the engine unburnt because of either overlean mix or failure to ignite due to compression faults. (rings, valaves, gasket failure)

The vast majority of white smoke complaints are actually steam from an overheating exhaust because of reduced coolant flow. The steam is tainted with diesel, so owners assume it is a diesel fault. True diesel 'smog' is very very pungent, one sniff and you know about it!
 
Thanks for your reply. This is driving me bonkers. The engine will give max revs out of gear with absolutely no smoke at all. When in gear it will only reach one third revs and starts to emit white grey smoke. The coolant supply is fine.
 
Thanks to all for your advice. Just a reply to let you know what is happening. It turned out to be a combination of faults. The VP had changed and overloads the engine in forward. The white smoke did turn out to be steam and have now increased water flow through the exhaust which helps.
Thanks again.
 
Good news.

petehitch said:
Thanks to all for your advice. Just a reply to let you know what is happening. It turned out to be a combination of faults. The VP had changed and overloads the engine in forward. The white smoke did turn out to be steam and have now increased water flow through the exhaust which helps.
Thanks again.
Click to expand...

Glad you got it fixed.

Lets have a picture?
 
petehitch said:
Thanks for your reply. This is driving me bonkers. The engine will give max revs out of gear with absolutely no smoke at all. When in gear it will only reach one third revs and starts to emit white grey smoke. The coolant supply is fine.
Click to expand...
Just to say, if you were absorbing half your engine output power in the gearbox it would seriously overheat and very quickly.
 
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