Big end nuts

[Bob Culver]

Barely relevant to the small rigid parts of a Seven but for anyone interested, in early edition of Ricardo, he maintained that big end failure often contributed to by the bearing closing on the shaft under tension at top of stroke; a wide seating at the joint resisted.

[Howard Wright]

Hi All

Just for the record I’ve found a supplier (GWR fasteners) selling Grade 10.9 8mm button head bolts with a 28mm shank (they are 60mm long and will need to be shortened).

Thanks for all of the replies

Cheers

Howard

[Chris KC]

Well done Howard - sounds like a good solution; thanks for sharing.

[Colin Wilks]

One thing I noticed when fitting my M8 bolts into the rods was that there is a very slight radius between the bolt head and the shank which can lift the bolt head off the flat on the rod. Putting a minute countersink into the hole in the rod gets around this.

[Colin Wilks]

Just for completeness, these are a couple of the original sports big end bolts from my engine:

[Howard Wright]

Thanks Colin

That’s quite a complex casting (?) and it does look as though the bolts are a quite close tolerance fit.

The button heads I now have do need a very fine emery paper finish and I will countersink (very slightly) the rods as you suggest.

Cheers

Howard

[David.H]

The bolts look like a cold forging (probably two blow from wire) to me. The keyway would not be a problem, not the head shape, although that could be a second op. Difficult to tell if the threads are cut or (better!) rolled. The shank could be ground as a second op.
David