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401 nailhead compression help.


Todd H
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the compression on all piston except for #5 is 200psi. # 5 piston is 45psi. does any one know if its a bad piston, valves or rings... also a lot of air is being pumped into the crank case from whatever this problem is... if its a bad piston can i replace it with the motor in the car????? any info greatly appreciated... thanks Todd

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If it is blowing a lot of air into the crankcase, you almost certainly melted a piston. Been there--done that!<P>I don't think you can rebuild the entire engine in the car; however, if you can get the motor about 6" off of the motor mounts, you SHOULD be able to get the oil pan off. This will allow you to disconnect the connecting rod, but the piston will have to come out the top. You're still looking at removing the intake and exhause manifolds and removing the heads. <P>If you take the heads off, have a good machine shop go through and replace anything that is weak, including valve springs, guides and oil seals. If you have a high compression 401, you may want to have hardened valve seats and new valves put in. This will greatly extend the life of the engine and allow you to safely run on unleaded pump gas. <P>The good news is that after you tear it down this far and replace all the gaskets, oil pump and water pump along with anything damaged or worn, you'll have an engine good for another 100-150K miles.<P>Good luck!<P>Joe

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Hi, Yikes... sounds like the piston area is at fault try putting some oil into the cylinder this seals rings, pressure reading should come up, if not could be valves but air into crank case indicates piston trouble possible cause beside rings, piston burned through (overheat, improper timing) wrist pin let loose and dug up bore. You can do this in house but you will probably end up unbolting engine mounts and disconnecting so much it will be easier to pull engine and put on a stand, plus if high milage you may run into bearing problems etc...scott shocked.gif" border="0

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