Knocking Noise

[H. L. Chauvin]

Sounds like Monday morning you will hear that as a "minimum", you will need to provide new Babbitt.

Might add: One possibility that could have been worse:

Say nothing ..... do nothing ..... keep driving ..... throw a connecting rod which penetrates one side of your cast iron block.

 

[Marshall V. Daut]

Yup - George nailed it. Chunks of aluminum (actually, Babbitt) on the bottom of the pan or dipper tray invariably means a rod or main bearing has lost its Babbitt. It sounds as though in your case it's the center main, the one that normally goes first due to the crankshaft's whipping action. Shorting #2 and #3 as George suggested will confirm this. I would have also shorted each one individually, though, to eliminate a rod bearing in #2 or #3. The Babbitt chunks may look shiny like aluminum or be a dull gray, all depending upon the Babbitt's composition. I rather doubt that the pieces are aluminum, which if true would cast suspicion upon a damaged piston skirt. But a damaged piston's noise would not go away after 20-30 seconds, as you are experiencing. A center main's knocking might be reduced in this amount of time, but it won't go away on its own. In all likelihood, you have lost the Babbitt in the center main = re-pour time. 'Sorry.
Marshall

 

[harleynut]

Not to hijack the original post but I got the exact same symptoms. 20 to 30 seconds knock goes away. Tried George Miller's suggestion of shorting out cylinders two and three to confirm a bearing problem. In fact, I shorted out all four one at a time. Result is no change in knocking sound. Question is, do I drop the pan looking for pieces of Babbitt.....if none found, do I plasti gauge the mains and rods? Any suggestions would be greatly appreciated.

 

[J Franklin]

Not to hijack the original post but I got the exact same symptoms. 20 to 30 seconds knock goes away. Tried George Miller's suggestion of shorting out cylinders two and three to confirm a bearing problem. In fact, I shorted out all four one at a time. Result is no change in knocking sound. Question is, do I drop the pan looking for pieces of Babbitt.....if none found, do I plasti gauge the mains and rods? Any suggestions would be greatly appreciated.

It sounds like you may have a slight piston slap or just looseness until the oil gets to everything. Piston slap is fairly common and is not a grave problem. If you haven't dropped the pan in a long while it is always a good idea to check bearing clearances and dump any sludge buildup.

 

[taterjacksam]

Knocking Noise Update, complete engine rebuild done by Doug McPherson in Vero Beach. Boy does she sound different. I'm picking up today from mechanic. Babbitt worn slap out in all caps, cracked block and high compression head, bored 80 over with sleeves and one sleeve dropped down and something with valves.

 

[Curly]

Could the knocking be at your shop door? Sometimes I hear knocking when Im working on my A. Put out a sign that say, "Gone Fishing". Might fix your problem.