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Very tight JIS screws

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26 Jun 2023 10:19 - 26 Jun 2023 10:19 #886458 by Michi
Very tight JIS screws was created by Michi
I've got to remove some screws to pop out the external shift mechanism, before I can split the cases on my knackered KZ440 engine. 
I've run into a spot of trouble though. The screws that hold them on are so tight it's crazy.

I can pick a screwdriver bit which seems to fit, but turning them would damage the screw heads, I think. Do you think a JIS screwdriver would help? I've also got one of those impact drivers where you hammer on the end of it and it loosens screws. However, I'd rather not use that in case of damage to the screw heads or to the engine case. From the look of the screws, this engine has probably never been opened up before, although I can't be sure. Do you think these screws might just be obscenely tight? And is there a specific, ideal tool to get them out or will I end up ruining them with heat or an impact driver?

KZ440A LTD (1980)
Last edit: 26 Jun 2023 10:19 by Michi.

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  • hardrockminer
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26 Jun 2023 11:08 #886461 by hardrockminer
Replied by hardrockminer on topic Very tight JIS screws
Do not try to turn a JIS screw with a Phillips head.  Use a JIS screwdriver, preferably a Vessel Impact Screwdriver.  Here is an example.  Be sure to get the right size head.


www.amazon.ca/Vessel-Megadora-Impacta-P2...a-422610599465&psc=1


 

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26 Jun 2023 11:09 #886462 by Nessism
Replied by Nessism on topic Very tight JIS screws
VESSEL MEGADORA IMPACTA (2PC. SET)
Brand: VESSEL

$35 shipped off Amazon.  These are the right tool for the job.
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26 Jun 2023 11:11 #886464 by Mikaw
Replied by Mikaw on topic Very tight JIS screws
If you have a hand impact driver I think the bit size is 5/16”. These should work I’m sure there are other available. 


rhinotools.com.au/product/jis-impact-screwdriver-bits/
 

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1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
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26 Jun 2023 11:34 #886465 by Michi
Replied by Michi on topic Very tight JIS screws
Very useful guys, thank you.

Impact rotation + probably Vessel then, since that's 3 recommendations.

KZ440A LTD (1980)

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  • Kelly E
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26 Jun 2023 16:57 #886474 by Kelly E
Replied by Kelly E on topic Very tight JIS screws
The other thing to have on hand is a set of left handed drill bits. If a screw head strips use a bit about the same size as the shaft of the screw and don't drill too fast. Most of the time the screw start to come out just before the head pops off. It does come off the shaft of the screw unscrews with your fingers.

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  • SWest
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26 Jun 2023 17:04 #886475 by SWest
Replied by SWest on topic Very tight JIS screws
Be sure to get a 3/8" drive impact. I use an extension long enough to reach from outside the frame using the largest bit that comes with it. Not JIS but fits well and a few hits the screws come right out. 
Steve

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26 Jun 2023 17:46 #886477 by ckahleer
Replied by ckahleer on topic Very tight JIS screws
I have learned to move to an impact tool at the first sign a screw will not turn with a reasonable amount of force. You are less likely to bugger up the screw head with an impact tool than a standard screw driver. I also have and use my #2 and #3 Vessel impact drivers, but they don't work as good as my 60 year old, solid steel, Craftman impact tool.

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26 Jun 2023 18:21 #886479 by JR
Replied by JR on topic Very tight JIS screws
I've bought this Vessel in the mid 70s. Made in Japan it came with JIS bits long before I knew what JIS was about. It has a half inch drive under the front end so I can attach (with a reducer) a 3/8 inch socket. An impact driver is a must have when it comes to an older bike.



 

1980 kz750E1, Delkevic exhaust
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26 Jun 2023 19:42 #886484 by sf4t7
Replied by sf4t7 on topic Very tight JIS screws
wow - my impact driver from 1979 has the same Vessel case!  25 years later I found out why the bits worked so well on my Z1 - when I learned about JIS screws.  

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1974 Z1A
1015
welded Z1 crank
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27 Jun 2023 06:28 #886506 by Michi
Replied by Michi on topic Very tight JIS screws
All good points, thanks. 

I've had a handheld impact driver for years. It will move anything, but I've only used it a couple of times. I just don't like the idea of transmitting direct lateral impacts into the engine case. I may have to end up doing that, but for now I'm doing nothing until I get my JIS screwdrivers and bits through the post.
I like powered impact wrenches more, because the hammering force they produce is only rotational. I think I should be able to use the detachable adaptor from the end of my impact wrench on my powered impact wrench, to fit a JIS bit on the end. 

There may be other issues when taking apart this engine. I'm not expecting it to go 100% smoothly. The bolts holding together the crankcase halves have brown heads... 
Worst case scenario: it will need replacement upper and lower crankcase halves. But that's thinking way ahead... First resort tool will be the powered impact wrench from here on in, I think.

KZ440A LTD (1980)

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27 Jun 2023 06:44 #886510 by Wookie58
Replied by Wookie58 on topic Very tight JIS screws
The lateral impact is converted to rotational by the internals of the impact driver, I would seriously recommend not using an impact gun as it will rip the screw heads.(the rotational force of the impact wrench will push the "bit" out of the screw) In many cases a sharp lateral knock on the screw head will release the tension in the threads allowing them to undo without damage
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