On Tue, 22 Jun 2004 21:40:28 GMT, cb wrote:

Detonation. See if the clacking gets better with high octane gas.


B. Alexander wrote:
Hi,
I have a mercruiser 3.0 with an Alpha 1 outdrive. the engine runs great up
to about 3/4 throttle, but when I go to w.o.t. the engine still runs fine
but it starts to make a loud clacking sound. I sat beside the engine with
the cover off while someone else was driving to try to determine if it was
caused by something vibrating, but it appears to be coming from inside the
engine. Any ideas what this might be?
Thanks,



CB, you might try the 'screwdriver test'. Use a long bladed screwdriver and
while someone is operating the boat place the end of the handle against your
ear. Then touch the blade to various parts of the engine that you can reach.
You'll quick by able to locate the general source of the sound. I've used this
technique on motorcycles quite frequently. It works similar to a stethoscope,
which most of us don't have lying around.

Once you've pinpointed (as much as possible) the location of the sound, then
maybe some of the mechanic types in the group can help you more.

Good luck.

John H

On the 'Poco Loco' out of Deale, MD
on the beautiful Chesapeake Bay!