1939 Flathead six knocking

I just bought a non running 1939 Pontiac. I did some ignition work and fuel pump stuff and got it running. It does not seem to smoke and runs well, but has a very loud knock at the front of the engine. It has been sitting a long time and I am still working through issues. How much compression should I have in a 1939 six? Do all these flathead sixes knock? I am normally a small block Chevy guy. I was also wondering if no water is going through, and that is creating all the extra noise. The car has no brakes yet so I have been only running it in the driveway. I also did not want to run it long because of the knock. I ran out of time this weekend to see if I am actually pumping oil.

Thoughts?


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pull the plug wires from the cylinders 1 at a time, if the knock stops, u got a bad rod bearing. could also be a valve adjustment..

Back in those days the compression ratio was about 6 to 1 or so..Not much by todays stds.

Egge Machine if you are going to rebuild it..

Sam

__________________
I have tried most all of it and now do what is known to work..

My book says 6.20:1.

I pulled the plug wires off one by one and no particular cylinder is knocking. I have 40 psi of oil pressure. I am not real sure if water is circulating through the block. Could the complete lack of water be causing my noise? I have pulled the valve covers and nothing seems out of sorts. I ordered a shop manual so I can check valve clearances. I really do not think that is it. The knocking seems to come from the center of the engine. It is big time pronounced, almost sounds like a rod smacking the block.The engine starts immediately, idles and runs great. It has good compression an all cylinders but the knock is the worst thing I have heard, not like a rod knock. You guys have any other ideas? I really do not want to tear the engine down. What is the exhaust looking valve contraption right below the carburetor? It is some type of cam. Could that be it?

Possibly the heat riser flapper is banging inside the manifold.

That is what you're describing under the carb, I believe.

There should be a shaft with a counterweight at one end. See anything that resembles that?

Lack of water circulation wouldn't by itself cause the noise.

Water not circulating could be caused by a non working thermostat or plugged up radiator, or a bad water pump impeller.

There are a couple of possibilities. The oil pressure sounds great, but that only oils the mains, the rods are dipper lubed. The rod bearings on these can be adjusted by removing shims between the rod cap and rod. If there is no change when pulling the wires, you may have something embedded in the top of the piston, for example a lock washer or carb screw. It could also be part of a spark plug, pull them and look for missing pieces of porcelain around center electrode.

Good luck
Mark

I am waiting on a manual to go any further. I originally thought the noise was from the front of the engine, but now I am sure it is in the middle. It is near the heat riser. I need some type of exploded view of how that works. It sounds like it is beating on something. Does the heat riser have some type of arm that goes from its cam into the manifold. I mean is their something going inside the block that could be banging around as the engine rotates? When I bought the car it had a head gasket inside it. I think someone could have been into the top of the motor and did not put something back correctly. Is that possible with the heat riser?

I wanted to say thank you to everyone who has posted. Your input is greatly appreciated.

The heat riser is just a spring loaded shaft with a butterfly valve inside the manifold to direct heat to the carburetor, it has a counter weight on the outside to open it, when the spring is cold it closes, when it gets hot it gets loose and allows the weight to open the butterfly. If you think the noise is the heat riser just hold it still with a prybar or a pair of channel locks{they get hot} the noise would quit.
Mark

I got a manual and started sorting out my problem. Compression on all cylinders varies and is not perfect, but it is good for a 70 year old car. I pulled the valve covers and checked valve adjustments. Everything there is dead on. Oil is flowing well through the engine.The car fires immediately, idles well, and has great throttle response. The knocking noise is horrendous. It is definitely in the front bottom of the engine. It is not a rod knock. It has to be something internal so I am in for a rebuild. I might as well let the engine run a while and see if the knock goes away or the engine lets go.

After a few minutes I notice a puddle of oil near the front of the engine. The oil finally got hot an thin enough to flow through a small crack. Upon further inspection the previous owner hit something, or jacked the car up by the front of the oil pan. It is only smashed in about 3/16 of an inch in one spot, but it cracked the pan and has a small oil leak. It is such a minimal dent, but could this be the knocking noise? I spent the afternoon pulling the pan flat on my back in the driveway. Sure enough the bottom of the crank is hitting the pan in one little 1/8 inch round area.

I started the engine and ran for about 2 seconds with no oil pan. It was so quiet you could barely hear it run. All this time; something so simple. I couldn't be happier it is this easy. I thought I was in for a complete rebuild, and the kit alone is like $1300 bucks. Many thanks to everyone who helped me in this forum.