con rod oil holes

[Guy Wilson]

the Haynes manual is ambiguous....

'...connecting rod with oilhole must be in the left-hand side , oil hole facing engine..'

The drawing in teh manual suggests the oil hole on the conrod face the centre of the engine on the primary side.. is this correct ?

thank you
Guy

[RDfella]

They both say the same and are apparently correct.
However, I happen to disagree with loading oil onto a flywheel, so put mine facing out towards the crankcase. But that's just me .....

[trevinoz]

The easy way to remember is the matching numbers on the rods face the camshaft.

[Rex]

They both say the same and are apparently correct.
However, I happen to disagree with loading oil onto a flywheel, so put mine facing out towards the crankcase. But that's just me .....

I did the same, because Drag's daft diagrams show it this way. I don't suppose it matters a jot anyway.

[Colsbeeza]

Another great discussion plus Julian's relevant Service Sheet.

https://www.a7a10.net/forum/index.php?topic=12113.msg98449#msg98449
Col

[Swarfcut]

 I'll offer a different opinion to Trev. The forging numbers on the rod's can't face the camshaft, but they can face the (centre of) the crankshaft.

 Now here's my take. On the power stroke the forces act on the rear face of the piston and on the big end bearing eye, both on the side to the rear of the engine. As such I would give those shells the most support in the eye of the rod, so would fit both rods with the shell locating tabs away from the major thrust, in other words tabs to the front. So the forging numbers on both rods face to the left, primary side, and the oil hole in the left hand rod faces the flywheel.

 Now whether this makes the slightest difference in the grand scheme of things I don't know, so if you folks have done different it will still keep going until it stops.......All I know is from experience  that's how the unmolested motors that I have seen were assembled.

 Swarfy.

[trevinoz]

Swarfy, the numbers that I referred to are the numbers stamped onto the rods and caps for matching purposes.

[Swarfcut]

  Apologies Trev. The cap and rod 3 digit stampings will indeed end up facing towards the cam. The old brain skipped over the word "matching"...forging numbers sometimes match, more often they don't on that bargain project. But rods and caps are stamped as a unit, and assembled with the numbers together on the same side of the rod and always match unless the rod has been made up of random bits and then rebored to the nominal size. A trap for the unwary, always a good idea to check rods for ovality of the big end eye.

 Swarfy.

[bikerboy]

I have always put that hole facing inwards towards the flywheel

[muskrat]

G'day Fellas.
When I rebuilt the A7 for the first time in 1981 (no internet) I thought the hole was to squirt oil at the roller bearing. Many years (20) and thrashings later I learned the truth and on next rebuild I couldn't find any ill affects of my error.
Cheers

[Slymo]

It goes on the primary side facing inwards to provide oil to the flywheel and thence to the bores. Seems like a sound plan to me.

[raindodger]

Hello.  I have just installed a set of Thunder rods, they were supplied without oil holes.
I fitted them as they were, no problems.
I guess that lubricants have inproved over the years.

[RDfella]

Why would one squirt oil onto a flywheel to lubricate one cylinder only? Why not drill both rods?
My understanding is that engine failures were not piston seizures but rod failures, probably caused by lubrication failure to the big end. Let's face it, the oil goes past the RH rod to get to the LH rod - the side that usually failed - (OK, the tube may help to even things out) so that's a possibility.
Hence my belief that oil hole was not to lubricate the cylinders, but to help oil flow through the big end, If that's correct, it really doesn't matter which side the hole is.
I fitted Thunder rods too - they arrived undrilled and so I drilled the LH one. What a pig of a job - those rods are so hard (presumably work-hardened) as to be virtually undrillable - especially with such a tiny drill. If you believe the rod should have an oil hole, make sure Thunder do the drilling!

[berger]

as RD says improve oil flow, i have read somewhere but forgot where that the hole is to improve oil flow, as for thunder rods i got MWAS to drill mine in the mill and he said it was tuff stuff.

[JulianS]

I bought Thunder rods over 10 years ago, one was supplied drilled. Before that I bought R and R rods, they were not drilled and were 40 thou over length between centres. I chose not to use the R and R rods I was concern about them as they could not get a bsaic dimension correct.

This is the 1950 BSA service sheet about the drilled rod.