Connecting rod side clearances

[Mrbill426]

I have just installed my original crankshaft that was ground  .010" under-size along with the original rods that were resized and bushed for full floating pins.  I checked the crank end play and it is at .005" which is within spec.  However when I check the rod side clearances between the rods I get, from front to back, .007", .008", .010", and .005".  I think I will be ok with the .010 but the rest look pretty tight, especially between #8 & #7 at .005
Is there a optimum clearance for a street driven 340 that I could shoot for?

[1 Wild R/T]

Strange, normally your fighting to much side clearance... Stuff wears, it gets smaller not bigger.... Are these aftermarket rods?

[Mrbill426]

Kind of what I expected but no they are the original rods and so is the crankshaft.  I thought maybe I had reversed the rods but they are facing the right way.

Strange, normally your fighting to much side clearance... Stuff wears, it gets smaller not bigger.... Are these aftermarket rods?

[Mrbill426]

Does not make sense to me but I am obviously no expert.  Maybe I am measuring it improperly but it seems that either a feeler gauge fits between the rods or it does not.  I am getting readings so I must be doing something right.

Strange, normally your fighting to much side clearance... Stuff wears, it gets smaller not bigger.... Are these aftermarket rods?

[Chryco Psycho]

That is the correct way to measure it , slide in the feeler gauge , it fits or it doesn't .

[Mrbill426]

@Chryco Psycho ok I thought it was pretty straight forward.  This is the tightest pair.

That is the correct way to measure it , slide in the feeler gauge , it fits or it doesn't .

[1 Wild R/T]

Well my math sez there should be .011

.932
.934
-----------
1.866
1.877
-----------
.011

[1 Wild R/T]

However that means making a big assumption...  Are the sides of the rods 100% parallel and the sides of the journal also could vary...

[Mrbill426]

Yeah I know, maybe sloppy caliper work on my part but when they were together that pair allowed  .007".  I will check for sure before I sand off any material.  I didn't see any burs anywhere... you are right there could be a variance.  I guess the bottom line is there needs to be more room.
Wonder what a optimum clearance is?

Well my math sez there should be .011

.932
.934
-----------
1.866
1.877
-----------
.011

[Mrbill426]

They seem to be tucked up against the shoulder of journal ok

[1 Wild R/T]

FWIW I just did some searching & found the spec... .006-.014   I'd say run it....

One thing I was going to mention is since the crank has been turned the radius at the fillet could be effecting clearance but checking your photo shows undercut fillets so that shouldn't be an issue..

[Chryco Psycho]

  

[Mrbill426]

Meant to post this of the journal.

On a side note... I assume it is ok to be taking the rod nuts off and on (re-torqued) several times like this???  They are ARP bolts the machine shop installed when the rods were resized.

[1 Wild R/T]

As long as they weren't over torqued they will be fine....

[TGGodfrey]

Rod bolts on and off..... yes you can do that as long as you have moly or oil on the threads.  IF you torque them dry, you will gall the threads and snap on one off. Then you will have to go through weight matching a new bolt to the old one.

Calipers are not the best way to measure this.  there is a lot of room for error with them.  Stick with feeler gauge between the two installed rods. 

Something to take notice of..... as mentioned earlier, when a crank is ground, the machinest may leave a fillet at the end of the grind (corner of the rod pin to the weight).  If the bearing makes contact with the fillet, the bearing needs to be clearanced.  There is a specific tool for that.  This is also why many bearing manufacturers do not take the bearing material all the way to the edge of the rod.  Other bearing manufacturers will chamfer the rod bearings.

The rod set with the .005 clearance, check it with a feeler gauge, see if .006 will fit.  if it will, you are fine, factory spec is .006-.014 as mentioned.  I have built larger clearances in both race motors and restoration though.   

EDIT:  Did all these rods go back in the same location they came out of?  The .010 makes me wonder if a couple rods got moved between those two rod pins.
Terry