Big End Nuts

[Brian]

Does anyone know who can supply the nuts for the early big end bolts. These are a stepped nut and use a 1/4" BS socket to tighten unlike the later ones that use a 5/16" BS.

I have bought a couple of sets now but keep getting sent the wrong ones even after phone conversations in which they assure me they have the correct ones.

I havent tried SRM yet but thought I would ask the forum first as someone may know of a supplier.

[chaterlea25]

Hi Brian,
I had a poke through the SRM website and this is what I found

"SRMCR5    S/Journal end cap modified to suit later nuts (pair)    Â£10.38 "

I take it that this means they dont have the early nuts but spotface the caps to take the larger ones!!
2 thoughts!!
1 find someone local to you to modify your end caps
2 What about using Triumph nuts? I think the early 5T or T100 have nuts with a 3/8 hex and a circular disc on the face
the later ones have the bihex heads (beware of the late model ones with UNF threads)
I am fairly sure I have a couple of the early castellated BSA nuts somewhere (used of course)
But if you do not have any it might be better than nought!!

Regards
John O R

[Brian]

I thought about modifying the caps as I can do that myself but I am very reluctant to go that way. Big end caps are not something that should be played with, very risky.

I will have to keep searching and see what I can find, maybe a set of later rods will turn up or I can make the nuts myself when I decide what material to use. These early ones only have 8.5 ft lbs on them so a normal high tensile steel should be adequate.

Bit more research to do by the looks of it.

[muskrat]

G'day Brian, have you tried Modak in Melb'.
Cheers

[Brian]

I havent tried them yet. The more I think about it the more I warm to the idea of making my own, just have to decide what to make them out of.

[muskrat]

Holden axles or drill and tap a 1/4" HT nut to 5/16"bsf and make washers out of the axle.

[Brian]

It seems there are three different types of bolt/nuts.

The very early ones and I guess this includes the early longstroke A7's or maybe only them have 5/16" bsf bolts with the stepped nuts and a split pin. These require 10 ft lbs and a 1/4" BS socket to tighten.

The next ones are still 5/16" but C.E.I. (26 tpi) but still with stepped nuts and a split pin. These require 8.5 ft lbs and still a 1/4" socket to tighten. I think they used these from the start of the A10 but dont know for sure.

After engine no. BA10-13830 (somewhere in 1955) they where still 5/16" C.E.I. but had a different rod and used a normal 5/16" BS nut. The rod still carries the same part no. but is a slightly different casting and the cap is machined to allow a 5/16" BS socket to fit onto the nut. These require 22 ft lbs.

If I make the nuts myself I will make them one piece, the advantage of having a mill !

[trevinoz]

Brian,
         I would be inclined to machine the caps and use nyloc nuts as per late models.
This saves having to mess about with washers and files to get holes to line up for split pins when torque is correct.
Trev.