Big End Oil Groove

[Steve Bryant]

Hi chums,
I have to put the groove back in my re-metaled big ends and I would like to know if the groove needs to be all the way across the bearing surface as was originally done:

  rod 5.jpg small file.jpg (Size: 51.95 KB / Downloads: 644)


or would there be any benefit to be had by not running the groove to the edge as in this photo shopped pic ?:

  modified pic.jpg (Size: 44.64 KB / Downloads: 643)

*pics are the big ends before being re-metaled.

Comments and suggestions welcomed.
Thanks,
Stephen

[Terrytuned]

Stephen I have never taken the groove to the edge and that's on a race/sprint crank but make sure you have 10 to 12 thou side clearance and the gudgeon pin sits central in the piston when viewed from below. Terry.

[Bob Culver]

Not sure if it lets oil in or out. From dirt grooves suspects a lot comes in. Often see them just drilled but not sure if ever this way originally. Based on the observation of pattern on bearing and book attitude to grooves under load I ran mine with no holes but altho not a racer suspect a mistake. Austin presumably had a reason.
Some sort of shallow relief at the parting line as original seems desirable/necessary. Dont think this ran to edge.

[Steve Bryant]

My current thought is to make this groove the same length as the chamfer on the edge of the separation face.

[Chris KC]

In the spirit of contributing opinion to things I know nothing about - I found the attached sketch on Formhalls' website which appears to support your general direction Steve. I would have thought the idea is to encourage oil to distribute itself evenly across the bearing without losing it all out of the end of the groove - whatever exits here doesn't contribute much. There should be enough running clearance at the ends to allow 'used' oil to escape and make room for fresh without adding a big hole. I guess a continuous groove is simply easier (& cheaper) to cut. I confess I've never used white metal myself so I'm only guessing!

   

[Bob Culver]

We have had just one really authoritative response based on racing experience so reliable. 
But what do regular rebuilders do? Do the later shells have grooves? Are these cut in shells for racing? How common are simple drillings? Were these ever the original, and any problems attributable? Transverse grooves in loaded areas are agin all theory, and in accord with this the wear pattern usually looks inferior on the leading edge, but this may be due to dirt entering.

[Colin Reed]

HI Steve,
Your thinking is right , only I would Block off the two holes in the rod end and only put the groove in the Cap but as you say Not right to the Edge
the Reasoning behind this is the load is on the rod and not the cap and the oil will flow out both sides of the rod this gives a solid oil film on the rod half
this is not a theory but from casting and machining a lot of rods and main bearings
Hope it helps

Colin 
NZ

[Steve Bryant]

Hi all,
 thank you for your comments.

This tends to leave me a bit puzzled as to why the factory did it the way they did. All your observations make perfect sense.

The factory drawing of the rod is not clear enough to see the details I'd like to see, although it does show the chamfers:
   

The rods were as made in 1929 when I disassembled the engine for overhaul, the pic  showing the groove and the two 1/8" diameter holes which I can only think are there to shoot a jet of oil on to the bore of the cylinders :
   

Cheers,
Stephen

[Colin Reed]

HI Steve,
If you think about it the two holes throw oil out sideways so it would hit the oil plate between the crankcase and block,
the last thing you need is losing pressure on the loaded side of the bearing.
something to think about.

Cheers 
Colin
NZ

[Bob Culver]

Trenches in high loaded areas, ie top or bottom are generally to be avoided.
 The Seven with its curious lube system is different. The oil spray is everywhere and I suspect quite a lot is slammed into the drillings on the upstroke. At the top of stroke oil would exit and serve to briefly vent oil and air from the main entries on the crank. 
Did the 3brg shell cars retain the rod drillings? Was the shell trenched?

(Incidentally blocking the holes did not seem to reduce oil consumption on my car)