Jap 55 twin stationary engine

[paulivey]

Hi All. Have recently aquired a jap 55 twin. Doe’s anybody know what size the nut is that holds the flywheel on so I can get a socket to remove it.
Thanks
Paul

[trusty220]

Most British built machinery will be Imperial sizes; measure across the flats of the nut (in inches, of course) and that will give you the size socket you need.

[paulivey]

Thanks for that. Very much appreciated

[davidbliss]

Most likely awkward and would be Whit-worth but like earlier post measure the AF size to give both imperial and metric should be something to fit, I have old sockets and fit exactly, oddly new ones are a bit loose although marked the same and some marked with two sizes they fit, well they may fit one size but its ether going to be tight or loose, 3/4 inch whit roughly the same as 24mm but if correct the whit-worth should be a tight fit but made to fit 24mm so loose on the imperial size, typical of that will do engineering today.

[trusty220]

All of the JAP engines that I have rebuilt over the years have had very hybrid bolts- threads are British Cycle Thread (CEI) but the heads have been A/F sizes instead of Whitworth or BSF, hence the hybrid description.

Cycle Thread is a constant 26 threads per inch irrespective of the diameter and was used as an industry standard by many small engine manufacturers whose existence began in the bicycle industry. J.A.Prestwich had originally began by building bicycles, then motorbikes and then stationery engines; having one set of threads for the whole production would be a sensible way to go and would save buying different taps and dies for different applications- and prevent mistakes with the wrong threads being put on the wrong parts.

I hope that makes sense!
Happy Christmas, everybody!

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