Big end shell bearing

[Docspaff]

Is it necessary to drill new big end shell bearings?

[Alan]

Is it necessary to drill new big end shell bearings?

What sort of engine? Splash or pressure fed?

[Docspaff]

Splash fed

[Alan]

It's probably the easiest option. My view is that they aren't there to lubricate the little ends, but to allow oil flow through the bearing. On my engines I do this by setting the side clearance in the big ends, but this needs access to suitable machinery, so if you don't have a milling machine, say, I'd drill the shells. Remember to debut the holes, though.

[Docspaff]

Thanks for that

[JonE]

My view is that they aren't there to lubricate the little ends, but to allow oil flow through the bearing. On my engines I do this by setting the side clearance in the big ends

revisiting old threads. I'd be interested to know what this meant in terms of clearances. Does this relate to the enormous Woodrow 60 thou figure for lateral movement on Austin big ends? I only ask as I note side to side movement of rods on all the journals (and the shells weren't drilled). Do conrods wear on their side faces and is there a figure they once should have been (or any way of returning closer to it)?

[Robert Leigh]

I can't see the need to set side clearance on three bearing engines. The shells are narrower than the rods which are already machined to a designed side clearance. As for drilling the shells it is only the top one which needs it, the hole being off centre to align with the holes in the connecting rod.

[Chris KC]

You could drive a quite small bus through 60 thou. On my 3-bearing (shell, pressure fed) engine side clearance is about 5 thou.
I'd venture that unless the side clearance is very tight it's anyway bigger than the flow path between bearing and journal.

Chris Gould successfully brazed 'washers' onto the sides of the A7 rods he used in the 10,000 mile record car (n.b. not the 'special' set which were used for the attempt itself). This was to compensate for the larger BE offset on a Reliant shaft. A bit outside the scope of A7 running repairs though!!

[JonE]

ok, well it would be interesting to know what others have found in a standard 3 bearing splash fed engine. These rods don't look worn in that area so I assume no contact has ever happened.. but on all journals I can move the big ends visibly side to side. I'm thus assuming the float is controlled by piston bore.

[Bob Culver]

That sixty thou suggestion has always struck me as far fetched. Would seem to be inviting a knock. was it meant to be sixteen?