Ive got a 65' CL77. Some of the screws are I.S.O. and some are J.I.S. I need new point cover screws and stator cover screws, J.I.S. . Nobody local has them. Case screw kits may not be the right pitch... What do you do? Drill and tap? I can't be the first guy to get screwed.
jcspc
SCREWED BY J.I.S. SCREWSI believe that only the 5mm and smaller screws are a differnt pitch. I have scounged tohrough my trays of bols, and found correct ones for stator cover, which are 5mm x .90. I have also just ran a atap into the holes, 5mm x .80 and the screws went in securely. The case screws should be standard 6mm x 1.00
davomoto
the good news is that 6mm is unchanged ! i believe most of your case screws will be this size. they are on my ca77 305. also, anything over 6mm is typically available new as 'fine' thread - 8mm, 10mm, 12mm ... not sure about anyhting bigger than that.
anything under 6mm you're outta luck - as best as ive been able to find. for applications of short thread length and no real holding requirements @ 3mm you can substitute standard 4-40 threads ( although they'll be somewhat sloppy ). 4-40 equates to 2.85mmx.635 . on short thread lengths the lead discrepancy will be rectified by the smaller diameter. i believe the tank badges is the most applicable area for this. the old JIS size is available widely in taps and dies, if that would help you any. i ran them through all my old hardware to clean out corrosion and clean up and thread form that got bunged up. made assembly go nicely. i've heard of alot of people retapping the 5mmX.9jis with the new 5mmX.8. i can't advise it. in short threading scenarios it probably works fine, just nudging a thread or two into place. on longer thread it would inevitably nudge the material right out of place. thread size- newISO - oldJIS 3mm-.5-.6 4mm-.7-.75 5mm-.8-.9 6mm-1.0-1.0 8mm-1.25-1.0 10mm-1.5-1.25 12mm-1.75-1.5 matt Thanks Davomoto and 3BeanCrispy. Both useful info. At this point it seem the easy option is to just retap it to the 5mm 8 pitch. Since it's just holding that stator cover on and a short tap... no pressures or leaks to worry about...
If anyone else has an idea I wouldn't mind hearing about it Thanks jcspc
for retapping these make SURE and retract the tap often and <if u have> compressed air to blow the chips off of the tap and out of the hole. make sure to oil the tap to help it cut rather than tear. i drew up a quick sketch of what happens when you retap .9 to .8 showing the alignment of the threads and what it 'hopefully' will leave for intact thread form.
additionaly, metric drill size is the nominal thread size minus the pitch. a 5-0.9 would use a 4.1 mm drill, where the 5-0.8 would use a 4.2mm drill. not a bad idea to check the hole size before you put the tap to it. granted it should be only .004 inches difference, everything is manufactured with tolerances, and assuming what it is based off of what it should be will burn ya when ya least expect it.
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