Knocking Engine

C

cubby85

New member
Hi fellas. I have a 1956 Farmall Cub. Had the head gasket blow on me last fall. I replaced it over the winter and got all the water out of the crankcase which took some doing. Now it has developed a knock and I can't figure out where it's coming from. Oil pressure is good. Knock starts right away and doesn't go away when I throttle up, actually sounds worse. Also tried unplugging each spark plug to see if I could narrow it down but no change with any wire off. So I'm thinking it is not a rod bearing, but not sure what else could give me the knocking sound. There was alot of water in the oil after the head gasket went so I'm wondering if something rusted up in there. Any insights would be much appreciated.
 
I'd look at lifters/tappets, timing gears and wrist pins. I had something similar happen on an old engine after water got into the oil. Turned out to be a couple of stuck lifters that had rusted. Once I got in there and freed them up and replaced them, the knock was completely gone. Maybe try doing a few oil changes with fresh oil first just to flush everything out, then listen again to see if anything changes.
 
cubby85 said:
Now it has developed a knock and I can't figure out where it's coming from.
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Hi,
You could use an automotive stethoscope to check for noises, or a piece of garden hose, about 2 feet long, and go around the engine when it is running, hold one end against the engine, and the other end to your ear, and see if you can hear where the knocking is the loudest. You can hold it against the valve cover, and the oil pan too, in different places.
Be sure the Cub doesn't roll, while running in neutral.
 
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Glen said:
Hi,
You could use an automotive stethoscope to check for noises, or a piece of garden hose, about 2 feet long, and go around the engine when it is running, hold one end against the engine, and the other end to your ear, and see if you can hear where the knocking is the loudest. You can hold it against the valve cover, and the oil pan too, in different places.
Be sure the Cub doesn't roll, while running in neutral.
Click to expand...
I do the same thing only with a long screwdriver
 
Hi guys, finally back to looking at my Cub. I went through the valve train and everything was moving freely and adjusted right. From listening with a long screwdriver, the noise seemed loudest right above the oil pan. No noise from front cover so I left that alone. I pulled apart the rod bearings, a couple were slightly worn so I replaced them but no change. So at that point I was thinking maybe a wrist pin bushing or something wrong with piston, either way the head has to come back off. I didn't tell originally but I got a new head when replacing the gasket because the old one didn't want to seal up along the valve side, it was too corroded. Well I pulled the head back off today and the pistons and head are marked up like they've been knocking into each other. I will post pictures. Anyways they're dome top pistons and hitting on just the very side of the domes. So thinking I can maybe get flat ones to replace to avoid having to get the head machined. Part number on the pistons is 405008R1 and from searching around I'm finding they are .020 oversize. Seems like the mystery is solved now.
 
56 would not have dome pistons, so either someone installed those or changed the block, check the block #s, domed pistons used a different head for clearance
 
Yeah the engine was rebuilt in 2000, probably when it got bored and the domed pistons installed. I didn't think to use the grinder on it. I will surely give that a try to save time and money. Thanks everyone.
 
tst said:
56 would not have dome pistons, so either someone installed those or changed the block, check the block #s, domed pistons used a different head for clearance
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According to the parts list info the connecting rods to use with domed pistons are also a different part number. Stan
 
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