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Leak-Down results great - except for 1 cylinder. Would you run this engine?
Been lurking here for a while and searching my butt off, but I have been unable to find quite what I'm looking for.
I bought a junkyard motor for my 03 F150 4x4 w/ 4.6L Romeo because of an oil starved head (bought the truck this way). Truck has about 140k miles and is in decent shape.
I did a leak-down test on the very cold new motor (on a stand) and got 2-3% on all cylinders except #5 which tested at 15-17% (rings). It's supposed to have about 67k miles on it. Looked at the pistons with a bore scope and this one has a kind of odd clean spot on one side.
Here is a crappy pic of the #5 piston:
Plugs looked ok (going to replace them before installing).
It is about can't-feel-my-face degrees here right now, so I don't know if that temperature would affect the rings being able to seal correctly. My gut says it's not that simple.
Should I be concerned about these results? Would you guys run this motor without more work? It makes me uneasy having that much difference between cylinders but I'm not very familiar with these motors. I'd hate to do all the work to get it in the truck and then have misfires or other weird problems.
If you want to use the engine you bought I would first look under all the cam caps to make sure there is no groove that could catch your fingernail. Replace headgaskets and timing set if engine is useable. On the leaking cylinder I would make sure the ring ends are not lined up allowing the compression escape. If there is a hole in the edge of that piston then it will be more complex but perhaps you might use one from the junk engine if the micrometer measurements and the balance weight are close to the replaced rod/piston but that is stretching it. Anytime you have access to the internals on a modular engine I think you should re-gasket and use the early iron chain tensioners if not the entire timing set.
The Modular's are not as forgiving as the small blocks so I don't think it is a good idea to get too involved. The bolts are TTY and suppose to be replaced if un-torqued (rod bolts, head bolts, even cam cap bolts, etc.).
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