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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rex on July 04, 2026, 07:42:57 PM »
A metric spec, but clearly not a metric thread.
I read somewhere many years ago that the early US loco's (the ones always featured in Westerns) used Imperial threadforms until US manufacturing and standards caught up.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on July 04, 2026, 02:01:53 PM »
Oh, this bike has everything on it. Including proper metric, not just BA (which is metric thread believe it or not!)
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by 33d6 on July 04, 2026, 06:52:07 AM »
Learning about various thread forms is one of the great entertainments of ancient machinery (not just motorcycles). In the early days of the automotive industry there were three great centres of industry, USA, UK, and Europe. Of which Europe had several major subsets, France Germany and Italy with activity elsewhere on top of this. None of these areas really spoke to each other. They couldn't, there was only surface post and ships, let alone all the different languages, even friendly and helpful communications took months so all played alone. All had the same problems. All had much the same knowledge base, machinery, metals and men to work with and all invariably came up with much the same answers to their problems but not quite hence the weird mixture we find today.
Everyone has known the need for standardising these things for over a hundred years but we haven't managed it yet and I doubt we ever will. Human beings can be remarkably contrary.
Working on an old motorcycle is just a pleasant way of learning all this history and ain't it fun.

PS
Just be glad you haven't had to dive in to metric stuff. That's another world of mystery all of its own.
   
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by cardan on July 03, 2026, 08:23:53 AM »
Weirdly I was working at my bench this afternoon when I noticed a banjo fitting on the (very messy!) windowsill. I measured it: 1/8 BSP on the screw-in end and 3/8 BSCy on the nut end.

I have an Australian-made bike with a Spacke De Luxe engine, made in the USA. One of the fittings the oil pump is 1/8" NPS, which is major diameter 0.405", 27 tpi.

So 0.375", 0.383", 0.405"... 26, 28, 27 tpi... you've got to love a good thread.

Leon
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on July 02, 2026, 03:26:47 PM »
Interesting conversation with the Guru this afternoon....

I hadn't realised it, but that banjo "post"  fitting has a counterpart in the Pilgrim pump outlet, which is BSP as standard, and the Rocker box fitting is BSC as standard.

Here's photos of the 2 parts from the supplier...





Apart from the machined channel on the upper part.... they're both nigh on identical banjo fittings.  It's quite within the bounds of probablity that the BSP pump outlet part (the lower photo) has been modernised to have the channel cut into it to improve oil flow and that photo is of an older style part, so the parts would look virtually identical when you're just picking them up and throwing them into a package.

So it's quite likely I've just been sent the wrong part...  hey ho, I can easily see a mistake like that happening, we'll see what they say at the suppliers....
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on July 01, 2026, 07:49:24 PM »
BSP confuses everyone. The belief is that it refers to the pipe I/D, but that's likely a myth, too. ???

That's what it says on the Wikipedia page I found earlier...

All I can think is that the Edwardian engineers were an odd lot...
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rex on July 01, 2026, 04:55:41 PM »
BSP confuses everyone. The belief is that it refers to the pipe I/D, but that's likely a myth, too. ???
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on July 01, 2026, 04:17:31 PM »
1/8" BSP (British Standard Pipe) is 0.383" major diameter, 28 tpi. (There's also BSPT which is a tapered version)

3/8" BSCY (British Standard Cycle) is 0.375" major diameter, 26 tpi.

Both are commonly found on pipe fittings on old British bikes.

Leon

Interesting (I was hoping someone here would be more knowledgable about threads than I am, which isn't particularly hard I'll admit...)

In the BSP specs... what does the 1/8" measurement refer to?? because the outer diameter of the threads on the new oil-fitting is indeed as close to 3/8" as I could measure it.  So I'm confused slightly.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by cardan on July 01, 2026, 02:39:26 PM »
1/8" BSP (British Standard Pipe) is 0.383" major diameter, 28 tpi. (There's also BSPT which is a tapered version)

3/8" BSCY (British Standard Cycle) is 0.375" major diameter, 26 tpi.

Both are commonly found on pipe fittings on old British bikes.

Leon
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on July 01, 2026, 01:21:30 PM »
When was I last here... sheesh.... I need to pull my finger out.


So: I bought myself a new cam-follower.


And today I tried it out to see if it made any difference to that annoying "clickety-clack" noise I'm getting.

It didn't. (ffs)

However the follower DOES sit on the spindle MUCH tighter, so I'm going to use it. It also seems to fit nicely when the cover is on, ie the float of the cam-followers along the spindle is well within the desired tolerance (ie there's a tad of movement :D), so I'm happy to use it.  Next job with that is to try assembly "wet", with some oil dribbled onto it.

I also want to file a notch into the lug of it - I noticed that one of the old followers has such a notch (see below), and what it does is allow oil to get onto the spindle.  There's no direct oil feed, the oiling is done by "splash".  Having said that - the cam-follower-spindle actually has a channel cut into the top of it, which I can only assume is an oil "trap" to keep the spindle lubricated.  Cutting a notch into the cam-follower-spindle lug will allow the oil that is splashed about to get into that channel, and from there it would lubricate the cam-followers on the spindle.  So - I kinda wonder why the followers don't have that notch as they come, but it is easily something that could be missed when making up a pattern part, especially as it could well be that (like my engine) only 1 of the followers in the engine the pattern maker had, had a notch.


Job for the next visit anyway, because while I was pondering the clickety-clack, I decided to have a go at refurbing/remaking the push rods.

First I took some highly accurate measurements, to ensure that I had the original lengths of the two push rods BEFORE I took the caps off.

(ahem :D).



I decided to try "safe" heat first to remove the caps, I wasn't sure exactly how they were secured, the normal method is soldering, but the Guru told me that it's also perfectly valid to use epoxy, so these could be either.


This one was epoxied!


The other end was soldered! go figure!


Re-usable push-rod caps, steel.


Did my best to give everything a good clean up


New pipe on left... old on right.
These new ones should be a tad stronger by the looks of it!!

The new pipe came a tad long, 12", but that's cool


Precision marking for cutting (ahem)


And some hack-saw action


More high precision measurements.... :D


Close enough for government work?


I always like to dress a hole nicely.... (ahem)


Using Meths to clean up the dust and dirt


The original plan WAS to try to solder the  caps onto the push rods, I promise you.  However... I never been good at soldering, but I did give it a try with a propane can (and yes, I DID burn my $%^&&ing finger tips, again), unsuccessfully... so err...

i cheated.


Trigger clamps for the win.


The second one was a bit of a bugger, for some odd reason the upper cap (the "cupped" one) refused to go onto the rod easily, no matter how much I cleaned up the pipe, or scrapped out the fitting on the cap.  In the end I just gave it a bit of a bash...  :D



They're roughly the same length, visually anyway.

To be fair, the "exact" length isn't terribly important, as long they fit between the cam-follower and the rocker arm within the range of movement of the adjuster on the rocker arm - there's at least 1/4" of play in there..... :D  And now I know how to do the job, I can disassemble them, file a bit more off the ends and re-glue them if they're too long. :D

While I was in the workshop I figured I'd also swap the oil feed fittings which I bought replacements for. :)

First I pulled the old, utterly knackered fittings off: using my "new" flare spanner found and bought specifically for this job! :D


Shiny new fittings installed!


I gave the feed tubes a clean while I was here.  They feed an oil dribble from the rocker box to the valve stem.


Fitted the dribble-tubes.


These are the old fittings for the dribble tubes, they're utterly shot.


As is the main inlet feed fitting, new one behind it with the oil feed banjo being tested.




A couple of these should fit..... (despite being metric!)


But.... and here's the rub.... the sodding main thread is wrong.


They're both 3/8" diameter thread, but the OLD one is 26tpi (and so BSC), the new one is 28 tpi... and I can't for the live of me figure out what that is supposed to be. It's not BSF, it's not BSW, it's not UNC and it's not metric (I don't think ? ).  So I may well be phoning the supplier tomorrow to find out just what tf it is!

Tune in next time for some lubed up action! :D
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