Blower Motor Noise
 

The first trip out this summer I spun three main bearings and a rod bearing in my motor from detonation. I pulled the motor and had it rebuilt. I put it back in the water two weeks ago and I noticed a noise, when I first started it up it ran fine, I got into open water and opened it up and it seemed to do fine but when I came back down to around 1200 rpm I noticed a hollow knock coming from the engine compartment. If I whent above or below 1200 the knock whent away. I never ran the motor past 3800 due to breaking it in and I kept a eye on water temp and oil pressure and it stayed right where it was supposed to be. To give you a little background on the motor its a 454 bored .30 over with a stroker crank and a wieand 177 blower. My question is does anyone think its the blower making the noise and if not any suggestions on where to look. Thanks for any advice.

A couple of things you can check

Disconnect the blower belt and free spin the blower and see if you feel any rough spots

At 1200 rpm is the engine in gear? if it is does the motor do the same thing a 1200 in neutral? could be coupler

Recheck compression , see if one cylinder is out
Did you pull the plugs and read them ?

Starting point. If I can be of further help give me your number and I call you.

You could be right about the coupler I did notice that it didnt make that noise in neautral. I will check it this weekend and let you know. Thanks for the help.
Mike

I had a similar noise on a B&M250. I had the blower bolted down too tight to the manifold. It was distorting the blower. I loosened the 4 bolts and the noise went away. I think B&M calls for 15lbs of torque on the bolts.

I had a low RPM knock about a month ago. I could only hear it with the hatch open under 2000 rpm. Spent about 20 minutes feeling and listening around and discovered that one of the satinless flappers inside my exaust tips was the culprit. It really sounded like a universal knock when it resonated through the transom.

Thanks for all the help guys I am going to check all of this stuff this weekend when I take it out! I wish I could have taken it out today but I had to go to a wedding instead. Life just doesnt seem fair, oh well I will let you know this weekend.