uscgjason

41 239 info needed

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So my father and I rebuilt the 239 in my 41 Streamliner Coupe (machine work done locally with seats installed by them) and it now has a (wooden) knock on the number one cylinder. I am not going to be home for another couple of months to troubleshoot further i.e. compression, looking for shaving in the oil, dropping the pan for inspection, etc. but was wondering if there is a source bigger parts like the cranks, etc. for these engines out there or anyone who has reman engines already done (real longshot). I am gathering information so that when I find out the culprit I can proceed with less delay. Any help is appreciated.

J

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If you look  in Smoke Signals mag (all pontiac) there are tech advisors  for all years. 

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What is a wooden knock?!!

 

When you get back with the car, run it as little as possible. Try disconnecting or shorting out spark plugs one at a time to see if the noise changes. A rod knock will probably get quieter or at least change when you kill the offending cylinder. If you open the throttle a little then close it suddenly, a rod will often rattle louder for an instant. A loose wristpin will usually make a double-knock. A main bearing knock could be more difficult, but usually gets worse under load. Piston slap (meaning loose piston skirt clearance here in my post) will get quieter when the engine warms up.

 

Could it just be a loose valve adjustment? A valve noise will be at half engine speed, and will be unaffected by anything you do with the ignition or throttle.

 

How is your oil pressure?

 

To answer your question, I have not heard of any source of exchange engines or large parts.

 

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3 hours ago, Bloo said:

What is a wooden knock?!!

 

When you get back with the car, run it as little as possible. Try disconnecting or shorting out spark plugs one at a time to see if the noise changes. A rod knock will probably get quieter or at least change when you kill the offending cylinder. If you open the throttle a little then close it suddenly, a rod will often rattle louder for an instant. A loose wristpin will usually make a double-knock. A main bearing knock could be more difficult, but usually gets worse under load. Piston slap (meaning loose piston skirt clearance here in my post) will get quieter when the engine warms up.

 

Could it just be a loose valve adjustment? A valve noise will be at half engine speed, and will be unaffected by anything you do with the ignition or throttle.

 

How is your oil pressure?

 

To answer your question, I have not heard of any source of exchange engines or large parts.

 

There is a metallic higher pitched knock (like two combination wrenches being struck together) that means trouble right away and a lower pitched wooden sounding knock (like two large wooden dowels/belaying pins being struck together) which is bad but you can keep the motor going for longer if needed.  That information is from being underway on boats for many years as a diesel mechanic and needing to know how long you can push an engine depending on what your situation is.

 

I have already determined that it is more than likely the main bearing on the crank. Spark removal from #1 makes the noise almost disappear. It is a single knock. I have adjusted the valves to ensure nothing is out of spec/stuck. Knock gets worse with load. Oil pressure is fine.

 

However, until I get back home in February I will not be able to get any further information on the true source.

 

Thanks for your input.

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Ouch. Well, yes I guess you know what you have to do then. Too bad it happened to a just-overhauled engine.

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