brand new build ...broke in by the book....about an hour on the motor now....was purring like a kitten...and then a knock started....narrowed it to #1 by grounding out the cylinders...soon as i ground out one the knock goes very faint...no change when i ground others ok so i dropped the pan....pulled the rod cap on #1...bearing wear is normal and uniform....mic'ed the journal and got...2.079...with "MY" caliper..it was ground .020...and the bearing are .020 over.....double checked the rod itself without the bearing...its dead on....but when i clamp the bearing in the rod with the cap to get the i.d...im getting 2.083 so diff. of .004....my book says .0017 to .003 so why is this not working out.....the math works....am i missing sumptin....i grately apprieciate the help fellas _________________
I'm not sure that a clearance of .004 would even knock, sure it isn't a wrist pin issue, or cracked piston?
I am NOT a machinist but I read someplace that the space between the bearing and the crank should be .003 . If it's .002 it's too tight and the oil won't flow in between and if .004 it's too loose . I would take that up with the machinist to make sure you have the correct bearings . I have heard of this before from some other HAMBers . Glad you found out before it was too late ! Let us know what you find out !
Many engines call for a rod bearing clearance from .0015 to .003. Did a rebuilt 400-M Ford engine that had clearances on one rod that mic'd and and Plasti-Gaged at .0008. Rest of them came in .0012 to .0025. Ran fine, no knocks, lasted a long while. Wrist pin issues? Piston to cylinder clearance? Plug wires running parallel with one another for a long run? That'll induce voltage in the opposite wire and create a soft knock in one of the cylinders at idle.
Might want to try a compression test. Had a slight knocking sound in my 440 a while back, thought it was a lifter. Then I did a compressions test and found out #1 cylinder was leaking down real bad. Turned out the #1 wrist pin had come out and was slamming into the cylinder wall and causing a slight knocking sound. New piston, wrist pin and a sleeve and its back on the road.
They can be run a lot tighter than .002. The type of material, journal diameter, bearing type all come into play. For most of the engines we run on this board, .002 would be a nearly ideal clearance. What you read may have been for a specific application, which can't be applied to all.
If I read your post correctly-------------, .004 won't knock. It's loose, but won't knock. CAN YOU GET UP IN BETWEEN THE PISTON SKIRT AND CYLINDER WALL WITH SOME FEELER GUAGES? BTW, is the knock/noise temperature sensitive?
From your description it looks like the big end is not the problem. I hate to say this, and this has happened to me and I was cussing for a few days, but I just said the hell with it and popped the head and pulled the piston. I think you'll find the little end gimped in some way. That's almost always a noise maker up there. I felt bad about buying new gaskets and doing all the backtrack work, but I feel so much better today driving down the road in the middle of no-where without a tow-truck in sight...
I would also have to say it should be something else. I would plastigage the rod just to be sure, but I would be ready to open it up and pull at least that one ***embly out. Could be a loose wrist pin or if they are free floaters, clip that popped out. Any number of things, but I would open it up and be sure.
My God man. You said a KNOCK started in your initial posting. THAT loose spark plug would sound like an exhaust leak!!!! Jesus, step away from the car sir, and slowly put the tools on the ground.. Sorry Boss, I don't sugar coat anything
At least he was man enough to admit it.we have all done it at least once.you know how excited you get with a new motor!every little noise or knock.........some guys would let it go.kudos for paying attention!and searching the answer!
Wow, a loose spark plug noise? Glad you found a simple cure. Wish all my car problems would end so simple.
Brain Fart Syndrome. We all get it sometimes. Atleast you got it figured out before you went further into the motor.
Wow, a major league problem with an easy no-buck solution, aside from practicing a little oil pan R & R. In the future, measure cranks with a decent micrometer and not a caliper. Plastigage is also good to use when ***embling the engine just to ward off big problems before you start it. Bob
I had a 350 that would start knocking, the #1 plug would be loose. Sounded like a rod knock! Did it every couple of thousand miles, until I changed heads. Weird **** happens!
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