Author Topic: Fastener Thread Pitches on Fours - I am in need of info and help  (Read 201 times)

Offline paulbaker1954

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As I do more and learn more I get more confused with life in the Honda Fours lane  ;D ;D ;D

Having just helicoiled a number of my carb float bowl threads with M4 x 0.7 inserts I got to wondering why these threads were stripping - I have had the float bowls off so many times and wondered if this was why as the carb bodies are pretty soft alloy.

I had earlier replaced the float bowl original M4 screws with M4 capscrews  that I "borrowed from work" without any real intimate knowledge of thread pitches and Japanese variations used on these bikes. So I got to wondering if the capscrews I used were a different pitch to the original JIS screws and maybe that was what was causing the threads to strip.

I am not a purist and prefer to use capscrews where I can as opposed to the original slotted head screws (even though I do have a good set of JIS screwdrivers)

So I started on a Google quest trying to figure out what was what and really didn't get very far.

The parts book is no help as it will simply state size and length (eg M4 x 20)

I do know that on the Hondas often the larger fastenings use the finer pitch but not sure on some of the smaller fastenings

Any gurus out there ever looked at this issue and found any useful data

I did find one post that threw some light on the issue but I am not sure it's a definitive source.

http://www.xt225.com/forums/ubbthreads.php?ubb=showflat&Number=93395
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Offline Trigger

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #1 on: June 11, 2019, 11:47:41 AM »
It is so simple, spend a couple of quid on a thread gauge  ;) ;)

Offline AshimotoK0

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“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline paulbaker1954

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #3 on: June 11, 2019, 12:14:03 PM »
It is so simple, spend a couple of quid on a thread gauge  ;) ;)

Graham I now have one !! That said trying to differentiate between 0.7 and 0.75 with my aged eyes is challenging Ha Ha
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Offline paulbaker1954

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #4 on: June 11, 2019, 01:07:27 PM »
https://www.dropbox.com/s/egrrzvo1yx6clbl/TL27_Change_of_threads%20%281%29%20%282%29.pdf?dl=0

Thanks Ash thats really interesting - so from 1967 on fasteners moved to ISO standard.

Having said being a bit anal I still see some weird stuff. For example when I last put my head back on I misplaced one of the flange nuts so temporarily used an M8 nut whilst waiting for the replacement correct flange nut from DSS. Weird thing was the M8 nut used a 13mm socket whilst the correct flange nut need a 12mm socket
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Offline Rob62

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #5 on: June 11, 2019, 01:08:42 PM »
if you try to use a screw of the wrong pitch it will become very tight very quickly that's for sure... so if it fits it will be correct, you shouldn't have to force it.

Offline Oddjob

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #6 on: June 11, 2019, 01:53:57 PM »
https://www.dropbox.com/s/egrrzvo1yx6clbl/TL27_Change_of_threads%20%281%29%20%282%29.pdf?dl=0

Thanks Ash thats really interesting - so from 1967 on fasteners moved to ISO standard.

Having said being a bit anal I still see some weird stuff. For example when I last put my head back on I misplaced one of the flange nuts so temporarily used an M8 nut whilst waiting for the replacement correct flange nut from DSS. Weird thing was the M8 nut used a 13mm socket whilst the correct flange nut need a 12mm socket

That would be correct Paul, the ISO standard that Honda used was an 8mm size which used a 12mm head, however most nuts of that era in metric used a 8mm with a 13mm sized head, seem to recall Yamaha were guilty of this, it seemed only Honda used the 12mm headed size which made working of different makes of bikes a little confusing.
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Offline ka-ja

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #7 on: June 11, 2019, 02:32:29 PM »
12mm spanner sizes instead of iso standard 13mm was/is a weight and material saving exercise that was first used by the Japanese during WW2
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Offline Trigger

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #8 on: June 11, 2019, 02:37:51 PM »
On the Honda design and practice sheets, number 13 is not used as it is unlucky   ;)

Offline AshimotoK0

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #9 on: June 11, 2019, 02:46:51 PM »
The M8 nuts with 12mm AF I was told were introduced in WW2 in Japan to save metal... dunno how true that  is. The 12mm AFs are pretty easy to find in bulk these days aftermarket but some M8s are 14mm (e.g. fork bottoms) and I have searched everywhere for a source in bulk but alas can't find em. Cheapest is probably Yamiya but once you have imported still much more than the 12mm AFs
« Last Edit: June 11, 2019, 04:46:03 PM by AshimotoK0 »
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline taysidedragon

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #10 on: June 11, 2019, 04:19:15 PM »
Some fasteners use small head sizes so that it's easier access for a socket or spanner in tight locations but you still have the required strength of the bolt.
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Offline Bryanj

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #11 on: June 11, 2019, 08:35:28 PM »
There is another thread on hondas that uses a non prefered spanner size, one of the 17m spanner size i think

Offline Bryanj

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Re: Fastener Thread Pitches on Fours - I am in need of info and help
« Reply #12 on: June 11, 2019, 08:39:15 PM »
 You will find that many iso thread diameters will have 3 different pitches available fine, course and non preffered.
The makers can use the non preffered if they wish and still call it "standard"