Tight rod bearing clearance
 

I am currently installing new bearings and rings in my ~150k 350. My crank bearing clearances have all been between .0015-.002 and rod bearing clearances have been .003, a little on the loose side but within tolerance. I am up to installing pistons 5 and 6, 6 went in fine with a .003 clearance, but 5 for some reason is very tight, only .001. It is so tight that the crank will not rotate when the rod cap is torqued down. I did not check it when I first disassembled, but the motor ran great. What could cause this?

i'd suspect you have the rod in backwards and not a clearance problem. how'd you measure it? with plastigage? if so i'd find a bore gauge and mics to check it with so you know what you really have. you're about .0008 too tight according to my manual. did you have the crank turned?

The tapered side is facing the crank and the flat side is facing the other rod, looks correct. The clearance was cheacked with plastigage, I might be able to get ahold of a set of mics to measure the rod journal but I doubt I will be able to come across a bore gauge. The crank was not turned.

#5 rod journal measures at 2.098, which is actually .0006 out of range according to Haynes. I installed 7 and 8 and they have no problems. Anything else that would help narrow this down would be great.

how about a snap gauge, or telescope gauge? measure the rod with the bearing in it. look for out of round. did you change rod bolts? have you tried swapping the bearings from one rod to another.

I got readings between 2.000-2.002 using dial calipers, only thing I could find. I have tried 3 different sets of bearings and one other rod cap. The rod bolts are stock. It seems like it should work going by the numbers. I redid the plastigauge and came up with between .0015-.002. I was hoping the have the whole motor finished on Sunday and running next weekend, it is not looking like that will happen.

guess i'd take the rod to a shop and have them resize it or at least check it.

you tried another rod cap, you mean from one of the other 7 rods in the engine? Just an observation, but did you keep the rods and caps matched when you dissassembled? they are machined together, to provide a perfect fit for the bearings. If its possible they got mixed up, I would be very cautious and re-check to make sure the right caps are with the right rods. that could cause serious problems in the not-too-distant future. I always mark rods on the cap and rod, and all on the same side, so I know right away is something isn't right.

The pistons/caps were all marked, I tried the cap from #6 just to see if #5 was damaged or distorted during cleaning. Like I said, all the other cylinders are fine. I guess the last thing I will try is the original bearings before I break down and go to a shop.

Trying another cap won't help. They're a matched set with the rod. The rod only goes in one direction and the cap only goes on the rod in one direction. Gotta make sure this is all correct.

When installing (jsut to get this absolutely right, with no possiblity of misunderstanding)....

Go by the little "bearing alignment notches" in the rod and rod cap and both bearing inserts. Both notched sides must point towards the OUTSIDE of the block for whatever bank of cylinders you have that rod installed on. i.e. the notches on 135&7 point towards the driver's side of the engine, 246&8 point towards the passenger side of the engine. The notches for the cap and the rod will both be on the same side when you do this- not on opposite sides.

If all else checks out you will have to have the rod's big end re-machined by a shop. Sometimes on a stock motor you'll find one or two that is a little tight or a little loose.

The piston notch is facing the front of the block and the bearing notches are facing the driver's side. I am confused to why this is happening. If the ~150k motor ran before I went through it, why am I experiencing this?

One of the rod caps got stamped wrong?
Actually you can NEVER have just ONE wrong.
If one is wrong there is another one wrong to go with it.

Pull them all back out and check them.
This is an area you CAN'T get wrong without wasting a LOT of time and money.

Jim is right, I had caps 5 and 7 mixed up because I had them both marked 5!:doh: Sorry for the wild goose chase guys.