I have a 327 in my 59 chevy. Last week when I got home from a 60 mile freeway trip I heard a horrible knocking noise coming from the engine compartment at idle but only when the car was in gear. I drove to my friends house who is also a mechanic to listen to the noise. When the car was in neutral or park the noise was not there, but in gear he heard the noise and identified it as the alternator. If you put you pull lightly on the alternator the noise went away. He thought it was a bearing inside the alternator, so today I put in a new alternator. As you guessed, the noise is still there. If I pull the noise goes away. So before I start chasing a problem throwing new parts at it, any ideas what could be causing the noise?
Did the water pump spin freely (by hand) with no play front to back and side to side before you installed the new alternator??? It's gotta be one or the other.....
So you pull on the alternator and the noise stops? Doesn't the alternator belt go around the water pump too?
Maybe real loose timing chain? pop the distribitor cap and rock the crankshaft back and forth to see how much play it has. Just a thought.
I'm not sure I have a grasp on why a noise caused by this would disappear when you pull on the alternator. Is there any other belt-driven stuff on the front of the engine besides the alternator and water pump? Loose water pump pulley or balancer pulley?
Back in the day, I had a 67 GTO, 400 engine that had a vibration between 50 and 60 mph. Eventually it got so bad I could duplicate the vibration in neutral and revving the engine. I was sure it was the water pump. As the car was under warrantee I took it to the Pontiac dealer and told them I thought it was the water pump. They said it wasn't the water pump but the torque converter was causing it and set up an appointment for its replacement. When I got to the dealer to pick up the car they said it wasn't ready as they were still changing the water pump. I said I guess I was right after all. They replied no it was the torque converter but we're changing the water pump precautionary. Yeah, right.
Two projects back, I got a trade, SBC, the valve covers were on backwards, { they do bolt up- but also will use the rockers to ventilate the covers as you drive }, also during thier rebuild {?}, when they put the harmonic balancer on, they didn't know or realize the stock retaining bolt and "cupped" tension retaining washer, the key word here is "cupped", was also on backwards. The concave side of the washer was out towards the radiator, instead of in towards the balancer. My point is, soon after the engine runs for the first time, the bolt backs off, the balancer loosens, starts to wobble, destroying the hub, and you sometimes ear a slight knocking sound. The sound of the hub and its attemting to absorb harmonics beating on the snout of the crankshaft. Pull tension on the alternator, which in turn pulls tension on the crank pulley, also taken up slack on the worn hub of the balancer. Just a POSSIBILITY, not saying this is exactly what's wrong, but you should check it. As far as only hearing it in gear, thats because in gear you have slightly loaded down the engine. I am assuming a stock converter, nuetral or park equalls no load on the engine other than drive belts and accessories. BDM
A mechanics stethescope (sp?) is a cheap and a very useful tool for locating bearing noises. With the engine running you touch the probe to the possible noise locations...alternator bearing, water pump, etc. etc. You can do the same thing with a long screwdriver pressing the handle to the ear. Just watch out for the fan!! They are only 10-15 bucks.
Here is an update, may help somebody in the future. Spent a hour searching for the source of the noise, and we determined there was harmonics coming through the upper alternator bracket. We decided to build another bracket to attach to the upper bracket to support it, and we were going to bolt that bracket to the drivers side front exhaust manifold bolt. After undoing the lock tab, we found that the tab was actually broken, and the bolt on the exhaust manifold was loose. After tightening up the front two exhaust manifold bolts the noise went away. Guess I was wrong when I said everything was tight. Thanks for all the ideas, I really do appreciate it and all that this board has to offer.
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