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dinkum1 11-18-2006 04:10 PM

Engine/Drive Train Noise
We recently purchased a 1975 Bristol 27' with an Atomic Four. During
our initial cruise we noticed that at RPMs above 600 there was a
knocking sound. This sound is not heard with the engine running in
neutral or increasing the RPMs while in neutral. With the engine in
forward gear and upon acceleration (more than 600rpms) the knocking
sound becomes apparent and increases as the rpms are increased.

Question: Does anyone know if this is normal for the Atomic Four or
Bristol 27 or if there might be a particular problem that needs to be
addressed? Any input or help would be appreciated. Thanks.

Michelle and Harley

erps 11-18-2006 07:40 PM

Knocking is usually bad. I would work on identifying the source before I ran the engine too much more. You can use a big screw driver as a stethoscope (sp?). Hold the handle against your ear and put the tip of the screw driver on different parts of the drive train to try and isolate the source. Might also temporarily disconnect v-belts to accessories, uncouple the drive shaft shaft to further isolate the source. Main bearings and rod bearings are an expensive source of knocking noise and hopefully you can rule those out.


capn_dave 11-18-2006 08:11 PM

Ahoy Dinkum1
It's not normal for the A-4 to make a knocking noise. The only wierd noise you should notice is a noise like a crunching whine while in reverse. That said, It sounds to me like the accessory drive is causing the problem. You didn't mention the if the A-4 was an early or late modle. It could also be the transmission. As noted before use a long handeled screwdriver or a stehascope, and stick it to various places on the engine while it is running and making the noise.
Contact Myoyer Marine and get the A-4 bible to start. Don is very helpful and is known as the A-4 Guru.

Fair Winds

Cap'n Dave

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