Connecting rod orientation

[ajwans]

Please set me straight! I think I have worked out what Nick Fulljames is explaining in the Peter Morgan video here: https://www.youtube.com/watch?feature=player_detailpage&v=9nG68Qgy_Ls#t=240s

If I understand correctly the bearing tangs on the connecting rods should be oriented away from the force on the power stroke.

Thus, the rods on the left bank looking at the pulley end should have their bearing tangs up and the rods on the right bank should have the bearing tangs down.



Please correct me if I'm wrong.

andy

p.s. that's not my crank, illustration purposes only

[Flat6pac]

The last one I took apart, 82, 930, with the nose bearing to the left, rods pointing toward me, all the numbers were up.
Thats the way I reassembled.
Bruce

[ajwans]

Originally Posted by Flat6pac

The last one I took apart, 82, 930, with the nose bearing to the left, rods pointing toward me, all the numbers were up.
Thats the way I reassembled.
Bruce

Were the numbers always on the same side as the intrusions for the bearing tangs?

andy

[Flat6pac]

I have to say no because I took pictures at work of rods where the stamping numbers were on the opposite sides from the recess for the tang. I looked for the pics but dont see them.
Bruce

[tom1394racing]

This diagram should help to understand the orientation for the rod bearing notches on the crankshaft



The gas load along the axis of the cylinder breaks down to a rod load along the axis of the rod and a side load side load perpendicular to the rod axis.

The bearing notches should be located on the unloaded side of the big end.

[ajwans]

Tom, thanks for you input. Your diagram shows the opposite orientation from explanation in the Peter Morgan video. Now I am more confused.

andy

[tom1394racing]

With the Porsche rods it is the bearing notches that are the stress risers. Orienting them on the non loaded side of the rod journal reduces the risk of rod failure.

[ajwans]

Originally Posted by tom1394racing

With the Porsche rods it is the bearing notches that are the stress risers. Orienting them on the non loaded side of the rod journal reduces the risk of rod failure.

I understand this part, but won't the inside of the rod journal be the loaded side?

In your diagram the gas force on the rod is pushing down on the crank and away from the crank centre line. By my thinking this should put the load on the 'inside' of the rod journal.

andy

[tom1394racing]

I think were are talking terminology.

For cylinders 1-3, the unloaded side will be closer to the top of the engine during the power stroke and thus the bearing tang should face toward the bottom of the engine.

The opposite is true for cylinders 4-6

[ajwans]

Thankyou Tom! Now I see, the tang should be *facing* down, I read that as the tang should be down, as in on the centre side of the journal.

Now I see we are in agreement.

Thanks for taking the time to educate me.

andy

[stokedforlife]

being that the connecting rods are not offset , does it really matter how they are installed as long as the numbers match up?

[Walt Fricke]

Last time this subject came up, the consensus of opinion of experienced folks was that it didn't matter as long as for each rod you had the cap and main numbers on the same side.

The factory manual is of no help here, as it doesn't even mention keeping the numbers on the same side of individual rods!

I'd guess you'd want any force trying to rotate the bearing to be reacted by the blunt (bent up) end of the bearing tang, as a force applied in the other direction could just try to straighten out the tang?

Wayne Dempsey (our host) in his book says that since our rods are symmetrical, it doesn't matter which way the numbers go.

[dannobee]

And if you call Carrillo and ask them how to install THEIR rods, they say that it doesn't matter at all.

And some modern engines have no tangs at all, and the bearings are installed by robots. So there's that.

[ajwans]

I don't know if it matters or not, but even the slightly reduced bearing load surface means that I set mine up with the tangs on the unloaded side.

Do what you feel with your own engines.

andy

[Walt Fricke]

It is widely believed that rods are most apt to fail due to inertial loads on the exhaust stroke. Rod bearings ought never to see bearing to journal contact, should they? So any loads trying to move the bearing shell would be transferred to it by the viscosity of the oil? Are those large loads? Large enough to cause the shell, which is clamped into the big end pretty strongly (the crush), to overcome the tang (and the tang of the other half of the shell, against which its end rests).

For sure there are cases of spun rod bearings. But were those due to anything other than an oiling problem, or rod bolts which were stretched?

Interesting subject, though. Are there any engines where the orientation of the tangs/cutouts in the rod is specified? Are the cutouts in asymmetric rods always in such a location that if the rods are installed properly, the tabs will always be as suggested here? I have zero experience with asymmetric rods.

[dannobee]

Older V8 engines often had a "spit hole" in the bearing shells opposite the side of the tangs. The purpose of the hole was to lubricate the opposite side cylinder wall and the cam lobes. This necessitated installing the rods both of the ways outlined in this thread.

[Mark Henry]

Originally Posted by dannobee

And if you call Carrillo and ask them how to install THEIR rods, they say that it doesn't matter

Doesn't matter, and I did email Carrillo and was told it doesn't matter.

Some rods are directional like VW type one (aircooled beetle) but it,s because there's an offset on the rod big end to center the rod in the bore. These T1 rods have a bump that goes up, which gives you tangs down. BTW This info is in every T1 repair manual, factory or not.

If you're worried about freaking out the next person who rebuilds the engine or your own OCD issues you could mount them tangs down.