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OK, I think I have it figured out. I don't think whoever rebuilt my engine (20 years ago) figured out the whole two different rod part numbers thing. There seems to be no rhyme or reason which face of the connecting rods has the most babbitt. I pulled the #6 rod/piston which had the rod that was riding the farthest forward on it's wrist pin. The top of that rod looks like it is right up against the inside of the skirt. I see that the front of that piston has some scuffing. To be precise, the scuffing is directly over the wrist pin hole that faces forward. The scuffing is even, top of the piston to bottom of the skirt.

I think that what must be happening is this: I push on the clutch it pushes the whole crankshaft assembly forward the .005" of available play (the spec is .002"). That pushes the connecting forward which is making the piston knock.... I can't figure out why else the thing would be knocking when I push in the clutch and then only when it's cold, before everything has expanded. Once it's warmed up you can't make it knock.

Short of rebuilding this engine I am thinking of pulling all the off kilter rods, measuring the journals and having the babbitt re cast and machined on those rods so they will be centered or at least not too off centered. I will probably have to de-glaze the cylinders and put in new rings too. A complete rebuild just isn't in the cards at the moment...

Comments are welcome.

Scott

PS Packard V8, The slots are all on the passenger side of the car, all the pistons are the same.

Can't tell for certain w/o a side or interior view, but that piston just above looks like an autothermic strut piston and if so, it wouldn't need a "T" slot, just a simple expansion slot. This type of piston uses a steel strut separating the skirt from the head, the benefit being that the head, which runs the hottest, is somewhat insulated from the skirt and thus tighter skirt-to-bore tolerances are possible, running quieter in part by eliminated piston slap when cold. Perhaps the strut also somewhat controls the expansion characteristics. Cast and forged pistons are normally one-piece affairs and as the heat from the head travels more directly to the skirt, the skirt runs hotter, expands more, and requires more clearance when cold-fitting. At least this is my understanding of the matter.

Scott,
Looking at your pictures of the rod inside the piston, it seems that the wrist pin bushing is central in the con rod. I have just done a rebuild of a 34 and a 35 standard 8 and I don't know if these engines are exactly the same but in my case the bushing is not centralised and there is a difference between the 1,3,5,7 rods and the 2,4,6,8. I can't remember which is which but it would be obvious when you look at the rods when fitted. One set has the bushing flush with the rod on one side and projecting out the other side. The other set is the opposite. With this arangement the bushinging is centralised in the piston even though the rod is not. This is the way these engines were when I took them apart. Unfortunately I don't have any pictures to show you, but if I find any thing that I can photograph I will post it for you.
Wade

Wade,

There are different part numbers for odd and even numbered rods and I am pretty sure that the difference is how much babbitt is on each side of the rod bearing. The trouble is I don't think the guy that rebuilt this engine figured it out. There doesn't seem to be any pattern to how much babbitt is on which side of what rod. Some have substantially more babbitt on one side than the other and some are centered and it doesn't seem to follow the odd/even rod numbers.... I don't know how they have to machine these crankshafts. Do they have to disassemble them? Could somebody have messed up the spacing on this crankshaft?

I'm slowly figuring it out thanks to all you guys

Thanks,

Scott

To do a proper job, you remove the counterweights from the crank before grinding. They are bolted in with extended head bolts and after tightening the protruding head is cut off and welded. So to remove you have to mill the bolt head from the countersunk recess in the weight. Make new bolts and reverse the process to reinstall, then balance the crank.