1940 Packard Engine Troble

[Guest ricko9]

I have a 1940 Packard 120 straight eight. The engine had a total rebuild and may have 2500 miles on. When driving on the interstate it started to develope a tap in the engine. The tap continued to get louder the faster I was driving. It did not effect the power, it continued to run smooth. I pulled the side plate off and it appears all the valves are working and turning freely. The sound seems to be near the front top of the head. I pulled one spark plug wire at a time and the noise did not change. I also removes the fan belting thinking it could be a water pump but no change.

I'm at a loss and looking for help.

[mrspeedyt]

what kind of oil have you been using? did you put in a new cam and lifters at rebuild time?

[Rusty_OToole]

Fuel pump?

You can buy an automotive stethoscope to help find funny noises. A wooden rod will do. Be careful to keep away from the fan or you might get a clip on the ear you won't forget!

[Alfa]

I have a 1940 Packard 120 straight eight. The engine had a total rebuild and may have 2500 miles on. When driving on the interstate it started to develope a tap in the engine. The tap continued to get louder the faster I was driving. It did not effect the power, it continued to run smooth. I pulled the side plate off and it appears all the valves are working and turning freely. The sound seems to be near the front top of the head. I pulled one spark plug wire at a time and the noise did not change. I also removes the fan belting thinking it could be a water pump but no change.

I'm at a loss and looking for help.

My first thought is that a big-end bearing is at fault, especially if it started suddenly on the Interstate. However, it would normally go silent with the plug lead removed on that cylinder.

You say that the noise sounds at the front/top. I would also be suspicious of a piece of trapped carbon being clouted by the piston, but at 2,500 miles there should not be any significant carbon build up. This leads me to think about a piston. It could be that a gudgeon pin has moved, or that a broken ring is allowing the piston to slap, or that an incorrect ring gap is causing the ring ends to meet.

It may be worth trying to ascertain if anyone in your area has a bore-scope (like an endoscope) with which to take a peek through the plug hole and check out the upper cylinder for any signs of damage. I hesitate to suggest reomoving the head !!

Have you checked the spark plugs? I have known an earth electrode to break off and to become embedded in the piston crown, hitting the head each revolution. I know that you say it still runs smoothly, but it is possible to have a misfire on an eight and hardly notice the difference.

I hope this helps.

Adam..