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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #11  
Old 07-21-2006
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Un-connected water heater not it....maybe.

The Perkins diesel was originally designed to be a continuoulsy run engine for electric power production -- it has a 25000 hour design life. Because it sat out in the middle of a room it allowed for 360 maintenance -- which is why so many of the maintenance points are hard to reach in a boat. It was designed to operate in a space where spills etc didn't matter -- which is why it has a Lucas CAV style fuel filter. It was originally designed with a closed circuit single loop cooling system -- which is why when the marinized it they drove the water pump from the water circulator shaft -- which is why there are side-load problems on those bearings.

It was never designed to have a water heater. The engine cooling system is sized to keep it cool.

With a water heater in the system, it actually takes the engine longer to come to a stable operating temperature. In cold water operations it may never actually reach that temp to the detriment of the engine.

If the engine was operating with a water heater before rebuild and isn't now, the hose connections for the water heater at the engine must be completely sealed. If they are allowing even small amounts of air into the system, air blocks will form and the engine will not only run hot, it will have hot spots.

If those hots spots are severe, not only would they wreck the engine fairly quickly, they could cause enough thermal expansion to interfere to change tolerances and in duce vibration.

I'm not suggesting that is the case but it is worth making sure those connections are truly closed.

I'm inclined to think two things may be at play here. One, were the engine mounts replaced in this process? One may be weakened enough to allow vibration at high rpm. Second it may well be possible that the engine was rebuilt with an imbalance.

Last edited by DynaMeme; 07-21-2006 at 12:45 PM.
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  #12  
Old 07-21-2006
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Eleanna-
Don't confuse your two separate problems. (And I'll bet they are not related.)

If the rudder shakes there can be several reasons. On some boats, the design is simply poor and the prop is too close to the rudder. If someone replaced the rudder with one that extends too far forward, that could cause the problem. Sometimes the wrong prop (too big) or a too-long prop shaft has been used. Sometimes, a boat is simply designed with the engine and prop shoehorned in afterwards and it is a poor design so the prop vibrates the rudder. Sometimes the prop shaft support has come loose from the hull, which can mean you're about to flood and sink. Sometimes the cutless bearing (the wear tube that the prop shaft passes through in that strut) is simply worn.
All you can do is inspect for visible wear or motion, you should not be able to "shake" the shaft or support at all, they should be rigid. When you do this the engine should be OFF and the key should be IN YOUR POCKET or otherwise secured, so there is no chance of being hit by a moving prop.
Last of all it could be an unbalanced prop (damaged or worn) but the only way to tell that, aside from visible damage, is because there's no other reason for a shaft shaking so you take the prop off and have it checked for unbalance. If you run down the list one at a time, you'll find the answer.

You really need another owner (you may be able to find an owners' group online) to tell you if the rudder shaking is normal for that boat.

On the overheating...that can be so many things. Anyone who calls himself a mechanic, who can't find out why an engine is overheating, should go back to being a carpenter. Exhaust problems, fuel problems, timing problems, cooling system problems....it is a long list but a thorough tune-up and checkout can find many of them. After that, the cooling system can also be checked and the only "holy mystery" left is a blocking in the exhaust elbow, which should be checked and cleaned or replaced every decade or so anyway.

Yes, a bad prop (perhaps wrong size/pitch) might cause everything, so the starting point might be to dive with a light and try to get the specs from the prop, they should be stamped in the body of it someplace. If not, then at least measure the diameter across the blades, and try to find out if that is normal for your boat.

I find the hardest part of freediving on a boat is not smashing my head against the hull while I'm floating back up, so if you have anything to protect your head, even a wool watch cap, that really helps.
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Old 07-24-2006
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I did find the problem to my overheating and shaking rudder, one problem caused both. Cutlass bearing had drifted out to the middle of the prop shaft and caused vibrations and overheating. Not only do I now get 2600 rpm from before 2000rpm and no shaking and no overheating.
I want to thank everybody for helping and suggesting, this forum rocks..

E.
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Old 07-24-2006
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Hellosailor: Thank goodness you weren't the mechanic on this job....I would have worried for you splitting your head wide open! lol. Of course hindsight is 20/20. Its funny how mechanical problems always seem so obvious after the fact. Meanwhile, you have spent hours working on a solution.
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