Engine knock

My 1927 Model T engine knocks at idle. I replaced the timing gear with a fiber gear that fits tightly and I tightened the connecting rods. It still knocks the same. It only knocks at idle. Does anyone know what causes this? Retarding the spark doesn't help. Shorting out the two center spark plugs doesn't help. Email me if you know what causes this. Thanks, Ken



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Ken:



There are a lot of things that will sound like a rod knock. One of the most common things is the front bearing on the cam shaft can have the thrust worn out so it sounds like a rod. Another thing can be piston slap. I have had to hone the wrist pin holes on all new piston as they are way too tight. Just opposite is if you have a set of old iron pistons the wrist pins may be too loose. Another thing to check is the crankshaft pully loose and hitting the pin that holds is on to the crankshaft. A good dose of JB Weld will cure that knock. There are other things as well but I believe these three are the most common.



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When you had the pan off, did you check the mains, particularly the rear? However, a main would be more of a "thump" than a knock, and would not go away upon an increase in engine RPM.



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Check the "fourth main" for cracked or broken babbit. Also, loose nut on the cam gear. This can be checked by removing the generator and prying against the gear with a long screwdriver to see if it is loose.



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Ken:



There are a lot of things that will sound like a rod knock. One of the most common things is the front bearing on the cam shaft can have the thrust worn out so it sounds like a rod. Another thing can be piston slap. I have had to hone the wrist pin holes on all new piston as they are way too tight. Just opposite is if you have a set of old iron pistons the wrist pins may be too loose. Another thing to check is the crankshaft pully loose and hitting the pin that holds is on to the crankshaft. A good dose of JB Weld will cure that knock. There are other things as well but I believe these three are the most common.



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When you had the pan off, did you check the mains, particularly the rear? However, a main would be more of a "thump" than a knock, and would not go away upon an increase in engine RPM.



<table><tr><td><font face="arial">

Check the "fourth main" for cracked or broken babbit. Also, loose nut on the cam gear. This can be checked by removing the generator and prying against the gear with a long screwdriver to see if it is loose.



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