Packard Forum Index » Post-War (1946-54)

1951 288. What metal nuts/washers for head and manifolds? Thinking stainless. What grade? I don't like acorns. Nuts/washers won't be painted.

If you take one of the head nuts and washers to a place that specializes in fasteners, for me it's Calgary Fasteners, they will be able to tell you what grade the originals are and get you something equivalent. I would guess around a #8.

I would use Grade 8 also except I'm thinking stainless steel.

Fromstsindustrial.com/products/grade-8-stainless-steel-heavy-hex-nut-domestic/:

"Grade 8 SS Heavy Hex Nut Domestic

Domestic ASTM A194 Grade 8 heavy hex nuts are manufactured from AISI 304 grade stainless steel, tested to meet ASTM A194 Grade 8, and are melted and manufactured in the USA. Dimensional specifications are governed by ASME B18.2.2. Grade markings for A194 Grade 8 heavy hex nuts consists of the number 8. Grade 8 stainless steel heavy hex nuts are intended for use in high-pressure and/or high-temperature service with ASTM A193 bolting of similar material, such as B8 and B8 Class 2. Heavy hex nuts provide increased bearing surface area over finished nuts."

It sounds like in other words, 304 is equivalent to Grade 8.

Any thoughts?

My thought is that stainless steel, as long as it's hard enough will be fine, if they are dimensionally the same size. If the nuts or washers are a different size, or softer metal, then I would be concerned about them not torqueing down correctly, and/or not maintaining their correct torque.

When I put my head back on I torqued it, warmed it up and retorqued it. After a couple of drives I retorqued it again. This was on the advice of a couple of of the forum members, the service manual does not say to do this. I found it was probably a good idea and may retorque the head again this year.

I really doubt you would gain anything by using 8 grade unless the studs are also 8 grade. Also, as I recall, the nuts had a larger hex size than those with that thread size usually have but I’m not at my shop so can’t give the sizes off-hand. Prewar manifold nuts, at least on junior models, were actually brass although they were much longer than usual.

As for acorn nuts, I don’t think they’re attractive at all but that’s just my own taste.

Both the studs and the washers are listed in the Utility section of the parts book, but they do not have a G prefix part number. So not necessarily common, but not too special either.

A standard hex nut is 3/8" tall (same as listed) but 5/8" tall ones are also available.

That being said, referencing a torque chart gives Grade 8 as 60 ft-lbs for 7/16 x 20 TPI. So I would use Grade 8. Remember that automobile torque charts generally assume "wet" torque not "dry" torque. I would apply some thin oil to these connections before tightening, otherwise the clamping force will probably be too low.

It's worth noting that elsewhere in the manual, a 7/16 x 20 TPI connection is given as 45-50 ft-lbs, such as for the clutch release lever ball nut, which is a Grade 5 torque (in between wet and dry).