SOHC.co.uk Forums > CB750
Vacuum screws
McCabe-Thiele (Ted):
Ah but did they still put a dot on the head of the screw as I understand it they do not need it anymore to indicate a JIS head?
To clarify my status I must have bought probably 10 JIS screws in the last two years - does this make me credible though?
Oddjob:
--- Quote from: Trigger on September 04, 2023, 07:54:42 PM ---I know I am not wrong. I went to Honda technical collage in Japan, where I was taught that the JIS bolts and screw thread changed in 1966 to 1967.
The question was about a CB750 and the 750 was not made in !966/67 ;)
--- End quote ---
You seem to ignore the fact that IF that were the case Honda would have had no reason to post a bulletin stating the thread pitch problem.
Oddly on all my Honda courses not a single mention of JIS was made. They just assumed we all knew what it was and what it meant.
And yes Ted, they still made them look like JIS screws and bolts, I suppose that was the point of the bulletin, to point out that they were not JIS thread pitched. The dot was to show the recess was made for a JIS screwdriver for example and not a Phillips screwdriver
Laverdaroo:
--- Quote from: Oddjob on September 04, 2023, 08:01:07 PM ---Paul posted a picture of a Honda bulletin which says that motorcycles like the CB750 were fitted with what are essentially a mixture of both ISO and JIS standards Ted. In order to try and avoid stripping threads Honda decided to keep the look of the JIS screw and bolt BUT they threaded them to the ISO standard and not the JIS standard. The JIS standard for an M5 screw or bolt is 0.9mm, whereas the ISO standard is 0.8mm.
Graham in his usual, I know everything manner, incorrectly said the JIS standard is 0.8mm and the Honda bulletin clearly shows he's wrong. Now for some reason he can't read bulletins any longer and when he does he clearly misreads them, or as is more likely, he pretends to misread them and continues to argue a losing point.
So to clarify, all bolts and screws fitted to bikes like the 750 are threaded to ISO standards not JIS standards, the shape of the head is irrelevant, as it's the thread pitch that counts not what it looks like.
Roo, ;)
--- End quote ---
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Trigger:
--- Quote from: Oddjob on September 04, 2023, 08:01:07 PM ---Paul posted a picture of a Honda bulletin which says that motorcycles like the CB750 were fitted with what are essentially a mixture of both ISO and JIS standards Ted. In order to try and avoid stripping threads Honda decided to keep the look of the JIS screw and bolt BUT they threaded them to the ISO standard and not the JIS standard. The JIS standard for an M5 screw or bolt is 0.9mm, whereas the ISO standard is 0.8mm.
Graham in his usual, I know everything manner, incorrectly said the JIS standard is 0.8mm and the Honda bulletin clearly shows he's wrong. Now for some reason he can't read bulletins any longer and when he does he clearly misreads them, or as is more likely, he pretends to misread them and continues to argue a losing point.
So to clarify, all bolts and screws fitted to bikes like the 750 are threaded to ISO standards not JIS standards, the shape of the head is irrelevant, as it's the thread pitch that counts not what it looks like.
Roo, ;)
--- End quote ---
The whole post is about a CB750 and CB750 have JIS post 1967 M5 with a 0.8 pitch thread which are Japanese Industrial Standard after the change over in 1967. It was not about JIS pre 1967 which are M5 with a 0.9 pitch thread.
Both are classed as JIS. It is just pre and post pitch size.
Trigger:
--- Quote from: Laverdaroo on September 02, 2023, 10:08:13 AM ---
--- Quote from: Trigger on August 31, 2023, 05:42:13 PM ---
--- Quote from: Pauarc on August 31, 2023, 04:05:50 PM ---Does anyone know what size the vacuum screw on carb on cb750k are like to change them they are a bit damaged
--- End quote ---
M5 with a 5mm thread ;)
--- End quote ---
Not entirely correct that….
Surely if it’s an M5 bolt, it’s telling you it’s 5mm, the pitch of the thread is what your after in that question in which case it’s only one of two options .08 or .09, that’s all it can be. Not in the workshop so can’t check but if you have a tap and Dye set use your thread gauge and find the matching pitch in that particular screw. Simples
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--- End quote ---
I would like to remind that only one option for the SOHC bikes which this thread was about and to say that it is one of two options is incorrect ;)
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