F: Frame Part # 327

[Magnetoman]

To add (or subtract…) to this topic, the first photograph shows the shape of the seat stay brackets on my 1950 C Black Shadow.

The larger hole has a 5/16" nominal diameter the smaller has a ¼". There is no sign of remnant threads inside the ¼" hole on any of the four "ears," but there wouldn't be if it was originally tapped 2BA.

The second photograph shows the outside-facing surfaces of the seat stays.

Those of you who are observant and have calibrated eyeballs will have noticed that both of the off-center holes on the right stay are ¼", while one of the holes on the left stay is smaller, sized for 2BA.

The third photograph shows the inside-facing surfaces.

In this case, two of the off-center holes are sized 2BA.

However, if your eyes are super-calibrated, you will have noticed that the center holes aren't exactly 5/16" (0.3125"), they're slightly smaller at 0.310". Since nominal 5/16" fasteners have shanks that are 0.305"–0.308" they are a nice slip fit, but what the size means is the holes couldn't have been drilled (or reamed) with standard 5/16" tooling. Typically, holes are made with standard-size tooling, and what goes in them is turned to the necessary size to fit, since turning is less expensive than custom tooling. This isn't the case on the Vincent.

 

[Magnetoman]

The holes in the damper drums that I have are just over 3/16,

The holes in mine are just under 3/16", at 0.310". Also, in looking up the part number for the drums I discovered an "anomaly" in The Alternative Spares List. Note that the two drums in the "exploded" portion of the list are shown with one off-center hole, while the assembled drum is shown with two.

 

[chankly bore]

Er, MM, your mensuration is faulty or you've done a typo. We are probably overthinking this. A factory in desperate financial straits would not hesitate to re- use an otherwise sound component just because of one redundant hole. They would more likely use up whatever was to hand, or modify it, just to get bikes out the door.

 

[Magnetoman]

your mensuration is faulty

Them's fightin' words, fellah. Since we're only dealing with crudely-made Vincents I didn't deploy precision instrumentation when writing my previous post. A punch marked 5/16" would not enter the hole, but a letter punch marked N would, so to get the measurement I reported I used calipers, crude though that instrument is.

But, since my quantification now has been qualifiedly-questioned, I got serious. The next photograph shows I first confirmed the calibration of my 3-point internal micrometer is accurate to 0.0001".

The next photograph shows the ID of the hole is 0.3117", which unqualifiedly is less than 0.3125".

The next photograph shows, using a calibrated micrometer, that the OD of the shank of the bolt is 0.3074", so it goes in the hole with clearance of 0.0043" (nb. the final photograph provides circumstantial evidence for this claim of the relative sizes).

This means the crudely-made Vincent's seat can rattle up and down by 0.002", which I'm sure would be unacceptable by even BSA Bantam standards. Personally, I'm shocked by this shoddy workmanship.

For those who question whether 0.3074" actually is less than 0.3117", the final photograph shows the bolt does indeed go into the hole.

 

[Cyborg]

Your post is kinda half baked…..What about the holes in the RFM? Probably some additional thrashing going on there.

 

[Magnetoman]

Your post is kinda half baked….

Only half? You’re too kind.

 

[chankly bore]

To quote "the holes in mine are just under 3/16" at .310" ". That's a beer you owe me, only I don't drink! These clockwork toys are all the same, wind 'em up, and away they go----------.

 

[Magnetoman]

"the holes in mine are just under 3/16" at .310" ".

Everyone knows 3/16 is another way of writing .316, and .310 is under that…

 

[chankly bore]

To quote #45, "not many people know that---"