Connecting Rod Offset and Pistons

[IBob]

Grumpy,

After a long pause, we are back working on our 383 project.

I have a couple questions re SBC/383 rotating assembly installation.

I read through many of the links, but could not find an answer.

As I understand it SBC 350 5.7 factory rods are offset. If installed with the offset wrong damage will result.
If the rod bearings are installed correctly, doesn't proper orientation of the rod bevel to the crankshaft radiased bevel insure proper offset orientation on installation?

It would seem then that with the rod bevel to the front on odd cylinders and to the rear on even cylinders, exclusive of piston requirements, that any rod could be used in any cylinder and the offset will be correct?

Following on that, with center pin pistons (KB134), with equal size valve reliefs for intake and exhaust, (flat top) no dome or dish and no front indication on the piston, that any piston/rod unit could be used in any cylinder and rod offset and piston orientation would be correct?

Thanks

 

[Indycars]

As I understand it SBC 350 5.7 factory rods are offset. If installed with the offset wrong damage will result.
If the rod bearings are installed correctly, doesn't proper orientation of the rod bevel to the crankshaft radiased bevel insure proper offset orientation on installation?

It would seem then that with the rod bevel to the front on odd cylinders and to the rear on even cylinders, exclusive of piston requirements, that any rod could be used in any cylinder and the offset will be correct?

Thanks

I'm not aware of any directionality except the bevel on the rod bearings. You are right, they would have to be correct if the bevel is installed right.

 

[IBob]

It is my understanding, from what I have read, that these rods are not aligned. There is a difference from the center of the small end to the center of the large end of some thousandths on the bearing axis. I am guessing that the bevel alignment on the crank puts this offset in the proper position on each rod.

 

[Indycars]

Not sure I can put in words, but the offset would be in the piston, not the rod. The rod is only works thru the centerline of both holes, putting more material on one side would not effect it's operation.

Now the piston is a different animal. Moving the pin offset in the piston would change the side loads on the piston. I think they do this to keep the piston from slapping the cylinder wall when it goes thru TDC or BDC.

I'm not trying to say that I'm right and that's the only way it could be, just my understanding at this point. I'm sure Grumpy will set us all straight shortly.

 

[grumpyvette]

I think your discussing two totally different things,
(1)

the tab on the bearing tang keeps the proper alignment of the bearing shell in the lower big end of the connecting rods crank journal bearing.
the connecting rod is beveled on the outward facing surface to provide clearance for the radius where the crank rod journal meets the crank counterweight,and so is the matched bearing shell
(2)

pistons can have off set pin locations that effectively change the way the piston side loads occur

http://www.motorcycleproject.com/motorc ... ffset.html

http://www.epi-eng.com/piston_engine_te ... basics.htm

http://www.hastingsmfg.com/ServiceTips/piston.htm

http://www.federalmogul.com/NR/rdonlyre ... cript2.pdf

http://www.engineparts.com/publications/CL77-3-402.pdf

http://www.mahleclevite.com/it_crankinstall.asp

http://www.aa1car.com/library/ar797.htm

http://www.scribd.com/doc/42259464/Dyna ... ecting-Rod