Q&A – Vibration – April 2007 - Soundings Online

Q&A – Vibration – April 2007

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Q: What are some simple things I can do to make everyday running vibration less of a problem?

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Q: What are some simple things I can do to make everyday running vibration less of a problem?

A: Vibration, even though it may be within “normal” limits, can cause many problems. You can never completely stop it, but there often are some simple, although not obvious, things to do that will help.

Think out of the box when looking for vibration problems. For example, if you have two components that are attached and that move but don’t move in sync, expect damage unless you take steps to rectify the situation. A good example of this type of problem is the connection of a stiff, heavy-duty marine exhaust hose to an exhaust riser. The riser is rigidly bolted to the engine, and vibrates and moves with the engine. The hose is anchored separately to the hull and/or other structure and to the transom. The hose is receiving the engine’s movement and is moving on its own because of the pulsing injection of exhaust and water. The constant working of the stiff hose against the riser can cause the metal in the riser to eventually fail, often on a weld seam. You may think it’s just a bad weld or weak area in the casting, but it could be a combination of that and the conflicting motions.

A “hump hose” can help solve this problem. You can buy them rated for wet marine exhaust, and they have one or more humps around the middle. They’re made of silicon material, and are quite flexible and usually easy to install. I use one marketed by Shields (a division of Sierra, which is a division of Teleflex Marine, www.teleflexmarine.com ) to connect my riser to my exhaust hose, and I’ve been very happy with the results. A typical exhaust hose will move to some extent back and forth, but it won’t stretch and compress. The hump hose will do both and help to remove this long-term strain on both parts of the system. These also can be useful in other similar applications on the engine.

Always look for clues. A little area (or worse, a mound) of rust under a joint or connection may indicate that vibration is wearing away at one or more metal surfaces and that a failure may occur unless remedial steps are taken. Often the only step that needs to be taken is greasing. Even if you don’t see areas of rust, always look for wires, hoses or metal parts touching metal on engines and generators. If you see this, secure, isolate or insulate the two components.

Unless I can securely bond the two pieces to prevent abrasion from vibration, I usually use a piece of rubber inner tube, cut to fit, with as many layers as appropriate. I secure the rubber with black wire ties. These are better than electrician’s tape because they will be less susceptible to degradation from oil. The electrician’s tape itself may not degrade, but the adhesive will, resulting in the tape unwrapping and loosening. Rubber itself will eventually degrade with oil and heat and may need replacing from time to time. You also can buy gasket material from hardware and automotive stores.

Regularly check areas where vibration over time might have loosened clamps, bolts or screws. Some aren’t very obvious. For example, the high-pressure fuel pipes running from the injector pump on a diesel to the injectors normally are secured in place by specially designed bracket clamps. If these loosen over time, they can allow the pipes to rub against each other or other parts of the engine or even the clamps themselves. This could cause a pinhole leak resulting in a high-pressure spray of diesel fuel, which could ignite.

Another inconspicuous example is the connection joints for the shifting and throttle control cables. Check at both ends and all along the route. Make sure that the cable is clamped to the engine at the point intended by the manufacturer and at all other design points. The bolts holding cable clamps can vibrate loose even at the helm station, far removed from the engine. The end connections often use ball-and-socket joints or another moving type of arrangement. These points can’t be tight because they must move in relation to each other, and the vibration of the engine eventually will affect them. Periodically apply grease and tighten the nuts that hold the moving assemblies together.

This is a problem without end, but you can usually control it if you’re ever vigilant.