1970 A65 Firebird Fork top nuts

Started by Ian C, 11 Jul, 2020, 11:09

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Ian C

11 Jul, 2020, 11:09
Would anyone be able to measure the OD of the 1 1/16" X 28 thread on any top nuts they may have lying around? I bought some 'LF Harris' ones (part no. 97-2245) and I'm suprisingly disappointed at the fit into the stanchions.. 1 1/16" = 1.0625" and the OD of the thread on these top nuts is 1.049" so they are 0.013" undersize. I realise they don't have to do much of a job when fitted to the bike, but you'd expect a better fit than that. :-\

chaz

#1
11 Jul, 2020, 12:44
the size of a thread is measured at the effective diameter , around half way down the thread. It could be that the thread has been "topped" or truncated, ie it is not a full point to the crest . this is often done to allow clearance.
the other possibility is that the modern screw cutting tip may be a metric one.

AWJDThumper

#2
11 Jul, 2020, 13:10
As far as I can see, the OD tolerance allowed for this unified thread is about half the 0.013" measured. The thread might be ok but it would depend on whether the inside diameter was also out of tolerance - unfortunately, this is difficult to measure. I'll measure the top nut on my A65 for comparison and see how this compares.

Ian C

#3
11 Jul, 2020, 13:21
Thanks Chaz for your insight and AWJD.. Yes the 28 TPI adapter for stanchion fitting I have is much better (as the top nuts should be) with approx 0.007" clearance..

AWJDThumper

#4
11 Jul, 2020, 13:25
Just measured one of top nuts on my A65 and the outside diameter of the thread measured 1.062" or 1 1/16" and is therefore spot on. I think the top you have has just been poorly machined. If it is not a tight enough fit in the top of the fork leg then you might risk stripping the thread when you tighten it.

Ian C

#5
11 Jul, 2020, 13:32
Quote from: AWJDThumper on 11 Jul, 2020, 13:25
Just measured one of top nuts on my A65 and the outside diameter of the thread measured 1.062" or 1 1/16" and is therefore spot on. I think the top you have has just been poorly machined. If it is not a tight enough fit in the top of the fork leg then you might risk stripping the thread when you tighten it.

Thank you AWJD, your help is much appreciated!!  :)

Ian C

#6
13 Jul, 2020, 12:53
Just to complete this thread, I contacted the vendor and he agreed to refund me, so alls well that ends well..  :)
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