John Player Special restoration project

grandpaul said:
Rear brake hub guts cleaned and ready to re-install
John Player Special restoration project


Re-packed brake hub double-row bearing. This is officially the start of re-assembly!
John Player Special restoration project
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For me, it's such a great feeling of accomplishment and giddiness to know that the dirty work is done, and it's officially past the point of no return. I'm jealous!
 
grandpaul said:
Left these specs with the machinist to best determine the finish spec for the re-bore
John Player Special restoration project
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Your machinist will have kittens when he reads those numbers !?

That top line says the bottom of piston skirt diameter std has a 40+ thou range ?? (3.028 - 3.071).

The mm equivalents don't cover quite as big a range !!.

Thats a clear FAIL for whoever printed those specs....
 
Rohan said:
That top line says the bottom of piston skirt diameter std has a 40+ thou range ?? (3.028 - 3.071).
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The dimensions should be: 3.028 in. (76.913)* - 3.0271 in. (76.888mm).

* (My unit calculator tells me 3.028 in. is actually 76.9112mm).
 
Indeed, LAB.

So GPs machinist will have to trust that the guessing of the correct dimensions is indeed correct ?

Wonderful !!...
 
Actually, he just mic'ed the new piston, added .0045 and went with that.

(after we puzzled over that glaring error, AND the "A" and "B" spec numbers)
 
grandpaul said:
(after we puzzled over that glaring error,
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But you posted here, and didn't think to mention it.... !!!

grandpaul said:
AND the "A" and "B" spec numbers)
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Thats in the manual too isn't it.

The cylinders on a BM I had were stamped B, common practice across a lot of the bike world.
 
grandpaul said:
(after we puzzled over that glaring error, AND the "A" and "B" spec numbers)
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I'm surprised any competent machinist would be puzzled by the bore grade sizes!
Not that it matters when reboring as it only applies to the standard bores, as pistons would've been selected to give correct clearance in either an "A" or "B" size graded bore at the factory which was common practice rather than bores being sized to match the pistons when reboring.

BSA and Triumph bores were graded "L", "M" and "H" - Low, Medium and High, later Triumph just used "L" and "H".
Rohan mentioned BMW which were graded A-B-C.
 
I was the one puzzling, he was measuring both bores and writing down his findings. They were significantly different from each other.

Then he looked the photo of the book over and asked what clearance I wanted because he "couldn't make sense of these".

Then he mic'ed the new pistons, added the two numbers up, and wrote down the number he's going to bore them to. He did mumble something about "some of the old books".

It all makes sense. You MUST go by the new parts you intend to run, and the required clearance for them. Books be damned.
 
grandpaul said:
It all makes sense. You MUST go by the new parts you intend to run, and the required clearance for them. Books be damned.
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That is one confusing reply.
Especially for anyone reading here later.

Pistons MUST go by the clearance specs provided with them.
With that label all over the shop, its the values in other books that has rescued the situation...
 
I've always used new pistons + .0045, never stuck a piston in 25 years of Britbikes, and no smokers, either.
 
All the same makes and brands of pistons though ?

Forged pistons (generally) need more...
The old wire-wound pistons you could get (well pre Commando) needed less.
Some little Onda pistons I installed needed zero yes zero to run quietly and smoothly.
Or they rattled (not smoked).

It sure doesn't help ANYONE if the specs that came with those pistons had a huge typo in them....
 
Always Hepolite (now branded by JCC), Cycle Craft (JCC), or Emgo (JCC).

Specs came from the bloody NORTON SHOP MANUAL!
 
The piston/bore/clearance specs are correct in my 73 Norton Shop Manual for the 750 and 850.
What are you using ?

P.S. Why are you using old shop specs for newly made pistons, surely the maker should provide these.
It is by no means guaranteed that modern pistons will conform to the same measurements/specs/clearances as something made 40+ years ago...

Getting precise info on this forum sometimes is like pulling teeth. !
Bearing in mind leaving good info for later readers...
 
Where did you get the ignition switch bracket? I may need to relocate my ignition switch on my '74 850 and that looks useful.
 
Rohan said:
The piston/bore/clearance specs are correct in my 73 Norton Shop Manual for the 750 and 850.
What are you using ? P.S. Why are you using old shop specs for newly made pistons, surely the maker should provide these.
It is by no means guaranteed that modern pistons will conform to the same measurements/specs/clearances as something made 40+ years ago...
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I'll check which printing it is tomorrow.

Essentially the same materials for quite a while, always been .0045" clearance. As stated above, JCC under different labels.
 
cyclegeezer said:
Where did you get the ignition switch bracket? I may need to relocate my ignition switch on my '74 850 and that looks useful.
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Any Andover Norton dealer.
 
grandpaul said:
cyclegeezer said:
Where did you get the ignition switch bracket? I may need to relocate my ignition switch on my '74 850 and that looks useful.
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Any Andover Norton dealer.
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I don't see it on the parts pages of Old Britts, is there a more complete schematic online?
 
cyclegeezer said:
I don't see it on the parts pages of Old Britts, is there a more complete schematic online?
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Right, Old Britt's doesn't have the JPS supplemental Parts List.

Just call Ella and give her the part number 06-4111, she can get it. (It's not an "in-stock" item).
 
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