[Guest]

alright i still have a knocking tapping in my engine and was wondering about this. when we got the pistons put on the machine shop did not center the wrist pins. meaning if u were to center the wrist pins in the pistons the connecting rods were about 1/8 to 1/4 inch off center. so when the connecting rods were moved to be in the center one side of the wrist pin would be sticking out of the piston. i hope i explained this good enough to be understood. but ive been wondering about this since we put them in. the machine shop said it didnt matter. but i was wondering if this might be the knocking sound. what is piston slap anyways? and if it was a bad valve spring making the noise, would it run good because it runs great. also. on one of the connecting rods the main bearing was a little too long, but on the other side the bearing was a hair short so it compensated. being the impatient idiot i am i said to use it. could this also be the origin of the knocking sound? sorry for so many questions.

 

[Guest]

It is obvious that the machine shop knows your engine is together and they didnt take the care to center everything. The knocking probably isnt caused by them being slightly off center, but they need to to very close to centered. You are not getting the bearing surface that you should if it is too far to one side.

 

[camachinist]

Off-center pins, in the amount you spoke of....sloppy but likely not a major problem on a stocker...if the engine went together OK, it's not the pin that's causing the noise you hear...

That's why I float my pins....no centering problems....the race car uses a tool steel pin floating in the stock rod hole...

Piston slap is caused by excessive piston skirt to cylinder wall clearance, usually when the engine is cold...
I run the pistons in the race car a bit loose because of the expansion characteristics of the pistons but any piston slap at cold startup is masked by lifter clatter and the loud exhaust...

Your engine shouldn't have piston slap if new...

Bearings should fit the rods precisely and you should've checked the rod to journal clearance on all bearings with Plastigage or the correct precision instruments....rod bearing halves are exactly the same size; one side is not longer than the other...

If your knocking sound is at the speed of the crankshaft, then it is likely bearing related or a piston....if at half crank speed, it's probably valvetrain...

Oil pressure??

And, since the shop was a bit sloppy, did you double check to make sure the chamfers on the rods faced the right way (towards the radius on the crankshaft journal)? There's a method to making sure the piston goes on the rod right so the rod goes into the engine right and the chamfer points where it's supposed to and the valve reliefs or dome ends up in the right place too....

Pat
http://albums.photopoint.com/j/View?u=1570936&a=11937754&p=42910787.jpg

 

[Woodchuck]

Since the pins are pressed in the pistons, the pins should float in the rods small end and center itself. IIRC, SBF rods are offset, and when properly installed on the pistons, there are usually notches on the pistons which should all face in the same direction (I can't remember whether it's front or rear). I did hear that one of the reasons for the offset is to reduce piston slap when cold, and that by reversing the offset (facing the notches in the opposite direction from typical install) will allow cold engine piston slap, but also free's up about 40 horses (don't know if this is really true or not).


'66 A-code Fastback (therapy)
'89 Town Car (SWMBO D'driver)
'87 Caprice (as req'd by Hagerty)

 

[Hottarod]

Ok, you are saying that one of your bearing sets was odd and different than the others? Did you look at the stamping on the bearing shells for that one set and verify that they were both std, .010, .020 or whatever your crank is ground to? The size is stamped on the bearing halves. It sounds like to me that somebody shuffled your rod bearing and you got a std with a .010 or .020 or just got one that is wrong. That would be pretty much a DISASTER to run your motor with a bearing like that.





You can see my 65 fastback at: http://hottarod.stangnet.com/
http://members.aol.com/macstang/Gifs/macstang3.jpg

 

[Guest]

odly enough i dont think it was the bearings because we tried fitting other in there and it did the same thing. my dad (who was helping me and doing alot of the work since this was my first engine rebuild) has never seen anything like it and thinks maybe it was a connecting rod from another engine maybe. or just a strait up deformed connecting rod. i dont know but i fear it may be the root of my problem. and to camachinist, how do i know what if its crank speed or half crank speed¿ ok would the spark plug be fireing at crank speed¿ give me something i can compare to. thanx

 

[HoosierBuddy]

Could have busted one of the rings when putting the pistons in.

Phil

'65 Convertible (with many mods.)
http://www.blueriver.net/~finite/Pony.htm