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4.0l connecting rods question?

Mdub

NAXJA Forum User
Location
Gilbert, AZ
Long story short, but looking at the connecting rods on the old engine from my 94 and the #1 and #6 look bent. Are those rods different from the others from the factory?

p.s. I took the motor out because I thought I had a bent rod, but the bend in #1 and #6 looks identical. Like they were made that way.
 
Mdub said:
Long story short, but looking at the connecting rods on the old engine from my 94 and the #1 and #6 look bent. Are those rods different from the others from the factory?

p.s. I took the motor out because I thought I had a bent rod, but the bend in #1 and #6 looks identical. Like they were made that way.

They should not be different.

Quick check - use a thick glass plate and lay the rod down flat on the plate. Try to slip a feeler gage in between the rod and the glass plate. I don't recall the "bend/twist" spec offhand, but I know it's in my book and in most FSMs.
 
You are the exact person I was hoping/expecting would respond. Thanks.
 
Max Twist--0.001 in per inch
Max Bend-0.0005 in per inch
Wayne
 
Wayne Sihler said:
Max Twist--0.001 in per inch
Max Bend-0.0005 in per inch
Wayne

Ah - thank you.

"Bend" would be noticeable by being able to fit the feeler gage under both sides at that point, while "twist" would only show up on one side.

A granite surface plate is idea for checking bend/twist, but I've found a thick glass plate to be an acceptable substitute. I used to have a 1" glass plate, about 8" on a side, with a wooden base plate and cover that I'd made to fit it. Had it checked by a machine shop for flatness.

Probably broken by now - definitely not in the same state I'm in! I should probably get another one, or just get a metrology-grade small granite plate...
 
From the sounds of it, the rods should lay pretty flat. The #1 and #6 rods have an "S" shaped bend in them. I'll try to take a pic today for your amusement.
 
Ok, so guess which ones are bent !

WiringHarness010.jpg


WiringHarness012.jpg


WiringHarness011.jpg


WiringHarness013.jpg


Glad I did that motor swap !
 
OUCH!

Those first two pictures (#1 rod, then #6, I take it?) are not good. That's the sort of bend that would lead to ultimate failure - with or without hydrolocking (the grain flow of the metal has been significantly disturbed.)

So, how'd you do that? Overheat, casting/forging fault, what?

Everything else, however, should still be salvageable - but I'd check the crank for taper wear and see if it wants grinding.
 
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