Rocker nut thread?

[67-2door]

Hi all.
Adjusting my valve clearances yesterday & one of the locknuts on a rocker has a stripped thread. Are they 1/4" unf? And are they a special nut or will one that fits do the job?
Thanks.
Neil.

[philthehill]

The original Minor rocker adjustment nuts are 1/4" x 28TPI UNF.
If you have replaced the rocker assy with the later sintered rockers the nut will be 5/16" x 24TPI UNF.

The nuts are high tensile steel and both sizes are 5mm thick.

If you cannot get the correct nut locally PM me and I will send you an adjuster complete with nut.
Please quote size required.

Phil

[67-2door]

My cars 1966 & the rockers are kind of pressed steel so I guess they're the 1/4 unf, if the originals were high tensile then I suppose it's not ok to replace with a standard 1/4 unf nut.

[philthehill]

So long as the nut is high tensile steel it will be OK.

[bmcecosse]

Pressed steel will be 5/16" I think. They are only to be 'nipped up' - how on earth did it strip?

[philthehill]

Just checked again the diameter of the adjusting screws fitted to several of the pressed steel rockers I have and they are all 1/4" UNF.

[bmcecosse]

Ah well -i don't have any left now....... but they will have 1/2" AF nuts.

[67-2door]

Just checked & they're not 1/4" unf. The thread measures (sorry for being metric) about 7mm so not 5/16 either. And they have a small hex,
Unfortunately the thread was damaged before I got to it, all the locknuts had been done up far too tight.

[philthehill]

Doing metric:-
The 1/4" UNF adjuster thread measures 6.95mm OD.
The 1/4" UNF nut has a across the flats measurement of 11mm.
If your nuts and threads do not match the original specifications I have given above you must have special rockers or non standard rockers fitted.
For example:- I have a set of 1.5 rockers with a 5.85mm OD adjuster thread and the nut across the flats is 10mm.
A photo of your rockers would be appreciated so as to clarify what you mean by pressed steel.

[67-2door]

With all due respect surely a 1/4 unf thread measures 6.35mm o/d? Quite a difference from the approx. 7mm mine measure.

[bmcecosse]

Stick to Imperial figures! Going metric like this is just confusing the whole issue.

[philthehill]

I have reviewed the information posted so far and examined and dismantled another set of early rockers.
The OD of the adjuster thread is 9/32"
The TPI of the adjuster thread is 26 threads per inch.
A 1/4" UNF tap will screw through the rocker with difficulty.
A 5/16" UNF tap will not even start.
I suspect that the thread is 1/4" x 26 TPI Unified National Special (UNS)
UNS threads are used in and for various functions on the 'A' Series.
The offer of a 1/4" x 26 TPI adjuster and nut still stands.
Phil

[67-2door]

Aah, that makes sense (kind of ). I couldn't relate the size of thread to anything I was familiar with. I guess 1/4 uns isn't a commonly used thread size.
I'd very much like to take you up on the offer of an adjuster & nut please Phil.
Thanks.
Neil.

[philthehill]

Neil
Hopefully we have got to the bottom of this mystery.
Just PM me with your address and I will put them in the post.
Phil

[67-2door]

Thanks Phil. Pm sent

[IslipMinor]

Phil,

I have the adjuster thread as 9/32" UNF in the list of threads - where I got that from now I am not sure, but 26 tpi sits exactly in the middle of 28 tpi for 1/4" UNF and 24 tpi for 5/16", so that would appear to make sense. There is no reference to a standard 9/32" UNF thread, so it would be UNS, in the same way that the big-end (rod) bolts are 11/32" UNS?

[philthehill]

Richard
Many thanks for the information reference UNS threads.

I have ordered a 1/4" x 26 TPI UNS tap and a 1/4" x 26 TPI UNS die nut.
When they arrive I will check them on the adjuster threads and post results on here.

There were at least two variations of the early rocker adjuster:- -
The (earlier?) adjuster was hollow drilled and had a waisted thread to allow oil from the rocker shaft (via a cross drilling) to get to the ball at the bottom of the adjuster, then onto the push rod and down to the cam follower.
The other (later?) had a straight non waisted thread and was not hollow drilled.

I cannot find reference to a 11/32" UNS thread.
I have checked the size of a small block rod bolt and they are 3/8" x 24 TPI UNF.
I have checked the size of a large block rod bolt and they are also 3/8" x 24 TPI UNF.
So not sure where the 11/32" UNS rod bolt comes from?
Phil

[BLOWNMM]

Hi guys
Phil - ARP refer to BMC 11/32 inch rod bolts but do not mention whether they are UNF or UNS.
Bob
http://arpcatalog.com/#34/z

[philthehill]

Bob
Many thanks for the link.
I still do not know where a 11/32" bolt fits on the 'A' Series - the ARP rod bolts BEB6001 (as fitted to my 1380cc engine) are 3/8" x 24 TPI UNF and are as specified in the ARP instruction sheet that came with the ARP bolt set.
No doubt all will become clear.
Phil

[philthehill]

After looking at various thread charts / thread profiles /trying different taps the only tap that fits perfectly is a 9/32" x 26 TPI BSCY (bicycle thread).
The 9/32" x 26 TPI tap screws through the rocker with ease and is a nice fit.
All other threads are either too small dia / too large dia / too many TPI or not enough TPI.
The cycle thread has taken me by complete surprise.

Phil