Con rods

[spike123]

Hi guys
Just reading the workshop manual on my a65 1967 engine and it states the con rods have to go a certain way round , I've fitted the caps to the corresponding numbers but didn't know they go a certain way round . So how do you identify which way is the right way
Mark

[DAVE BRADY]

Hi Mark,

Does one of your rods have small hole through from the journal to the side of the rod?  This is the lefthand or drive side rod.  The hole faces the crank so the numbers will be to the left and to the rear looking at the crank with the drive side to the left.  The hole is meant to allow a bit of oil to squirt on to the crank which then gets flung up to help lubricate the piston, small end and bore to some extent.
I think it is also intended to equalise the pressure in the big ends.  The timing side journal will get the pressurised oil first and by the time it gets to the other side the pressure has reduced so by putting the hole in it reduces the resistance to the oil pressure thus balancing it between the journals, well in theory at least.

Dave.

[Allan G]

It started as a theory to stop motors breaking, it wasn't until they got rid of the 4CA points (or rather the 4CA points cam) that this stopped. I don't believe A10's ever had this hole and it's never been an issue. My Lightning has the hole in for the left side rod (thunder engineering rods) but the rods for my bored and stroked A65 doesn't. But if yours have the drilling the hole should go to the drive side as Dave mentioned.

For orientation, obviously the caps need to line up and the numbers help here, the numbers in theory should face forwards (I say in theory in case they have been stamped on the wrong side) to be more precise the tangs on the shells should be on the same side of the rod as each other and both tangs should be at the rear side of the crank.

[idie]

Except for the very early A10s all A10s and A7s had the small hole in the drive side con-rod. It was to force some lubrication on to the nearside bore after problems with that side nipping up.

[DAVE BRADY]

Hi,

The A10s had this hole and if it was later considered unnecessary then it was just carried over to A56s as a just in case.  There does seem to be tendency for left hand journals to wear a bit more than the right.  This is  made worse when the sludge trap starts to get blocked and the flow to the left hand journal is potentially reduced. 
I used to have a camping stove with a grill and in order to get even grilling the holes in the burner started off being like a pin prick and gradually got bigger as the burner got further from the gas inlet. 
I suppose, in theory, if the hole is not there then an extremely small amount of wear on the left journal would have the same effect as there would be little less resistance to the oil pressure.

Dave.

[Bess]

Hi,
     Worth a read, I guess it would be prudent to have a rod with a hole installed correctly:

Best wishes...

[spike123]

Thanks fellas I've looked and I can't see any holes but I'll make sure the numbers face backwards when fitting

[spike123]

Sorry numbers facing forward

[Bess]

Hi Mark,
             Engines after Feb 1965 should have the lub hole in the con rod when supplied by BSA. If not it is suggested a hole is drilled when being overhauled.

Best wishes...

[Ian C]

Just for Information only.. I'm NOT saying you should do this but I've previously re-built my 1971 OIF A65L and now I'm just working on my 1970 Firebird and I've found the drive side rods on both to have 2 holes drilled. Pictures are of both sides of the Firebird DS rod which was removed yesterday.

[DAVE BRADY]

Interesting.  It looks like BSA put a single hole as discussed, then stopped and then started again but with two.  Obviously to make sure enough oil gets to the left hand side.  Having these holes would also increase the   centrifugal effect of the rotating crank drawing oil through regardless of oil pressure.  Higher revs means more centrifugal force so more oil drawn through.
Perhaps not quite so important with an end feed conversion but with the standard bush I would think a definite plus.

Dave.

[idie]

If you are thinking of drilling a hole in your con-rod, the hole size is 3/64". You will need to drill at an angle to finish up in the centre of the big end eye so as to line up with the hole in the bearing shell. Good luck with that!

[Bess]

Hi,
    The second hole added to the OIF models lubed the roller bearing on the drive side:

Best wishes...

[ChrisG]

My A50 is a 1970 (last in the line) and that has two holes.

[Allan G]

I'm still not convinced with the oil holes benefits to be honest. An example of a new rod not having a drilling is MAPs H beam rods, these types of rods are used in NASCAR but a lot of racing guys (BSA and Triumph twins) use these rods. They don't have the hole... they do have the small relief on the side of the rod which is supposed to do the same thing, but that is more for oil spray direction, there is plenty of oil flow through the journal/shell, there has to be otherwise the oil sandwiched between the shell would fail very quickly.