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Piston Rods to tight.. any help?

2K views 10 replies 6 participants last post by  BstMech 
#1 ·
I am rebuilding a small block 350. I just had the engine bored .030 over, putting in a new set of probe pistons with eagle rods. The crank was checked and was fine. The problem I'm having is when putting the number 3 connecting rod on against the number 4 connecting rod, they are to tight. It's like the connecting rods are a little to wide for the journal and it locks up the motor if I try forcing the # 3 connecting rod on the journal beside the number 4 journal. When I say tight the width of the rods seems to be too wide. They aren't locking up on the journal itself the width is the problem.

Any help would be greatly appreciated.
 
#2 ·
Was the crank turned down?

Is there a large fillet on the crank journels?

Mic the inside width of each crank throw journal and mic the thickness of each rod large end. This will take time but, you may have to have some milling done to the rods to pair them and be within your rod side clearance. Since the rods are not the original set with the crank.


Fill
 
#3 ·
Pull it out and see if it will fit when the piston isn't in the cylinder. If it does then I'll take a stab in the dark and suggest that maybe the pins were pressed in too far and when you have the piston in the cylinder the pin is butting against a wall and creating a side pressure that appears as if the rods are too wide. As I said check to make sure that the rod fits the crank when it is out of the cylinder. If it doesn't one of the 2 rods must not be machined correctly, I haven't seen too many though and I think Eagle has a pretty good reputation. One other thing that occurs to me is that the chamfer on the rod may be facing away from the cheek instead of against it, that will make the rods "crowd" each other and tear up a good crank.
 
#4 · (Edited)
The pistons do not have pressed pins. So I can exclude the pressed in to far. As fopr the crank being turned it wasn't and it mic -ed out good so that wasn't a problem. The rods aren't specific are they. You talked about the chamfer on the rod. I mean there aren't even or odd cylinder rods correct? they are all the same????

I appreciate the input so far guys thanks. :)
 
#6 ·
Sounds like you have a rod backwards. I know on a stock application the little relief grooves for the bearings face the panside........... I'm having a brain fart at the moment, but compare the two rods in question with all the other rods and you'll see what I mean.
 
#8 ·
Rods have a specific way they go in. Usually there is a large chamfer on the side that goes toward the cheek and that allows clearance on the journal radius. Since you are unaware of that ,I would start there. Get a Motor's manual or similar and they will tell you how the bearing tangs are supposed to be in relationship to the block.
 
#9 ·
Vince, BST Mech, Crazy Larry, WoodZ428, Fill.

Guys thanks for all the help. It's been 20 years since I put a motor together and things are coming back to me little by little. I checked the chamfer on the inside of the rods and I had 4 of them backwards so thats why it was binding up on me. Seems I'm back on track again. :drool:

I've had a 1957 Chevy 2dr Hardtop sitting in the garage for 20 years, along with a 1970 Corvette I bought back in 1987. SO after getting rid of the Wife (now EX) I've finally been able to get back to working on them again.

On a side note the 57 has a small block 400 in it I ran back in the early 80's went 12.90 with street tires. I'm putting back together the 350 for the vette which has a Muncie 4 speed. I Ported and polished the heads trying to decide on a camshaft right now to go back in it. Hopefully I'll have it back together by the end of next week. Thanks again for all the help I'm ready to to put the cam in next :D
 
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