Spark plug hole striped 1968 cl175
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Thread: Spark plug hole striped 1968 cl175

  1. #1
    Member Adamgs340's Avatar
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    Spark plug hole striped 1968 cl175

    So today I threw some new tires my 1968 cl175. I got that done and decided to take it for a ride. I a made it around the block and heard a pop and the bike stalled. I looked down and on of the plugs blew out of the cylinder. So I pushed it home and checked the hole. The threads are gone. So I am looking for ideas on how to fix it. It was originally a 12x1.25 thread. I looked a heli coil kits and various others threaded inserts. The problem is the original plug only has a 1/2 inch reach the shortest insert I have found is 15mm. So I thought what about drilling and tapping to a 14mm plug. I have found a ngk plug that looks like it will work a B8HS. Is this a good idea or should you guys use an insert. Thanks for the help. Here is a picture of it
    Attached Thumbnails Attached Thumbnails Spark plug hole striped 1968 cl175-20190908_173232_1567990365756.jpg  

  2. #2
    Senior Member Alan F.'s Avatar
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    You'll probably get opinions on both sides. For me if the 14mm threads don't interfere with valve seats I'd go for it.
    But I'd probably do them both and put a note of the new plug number somewhere with a handheld engraving tool. ☆Even if you're planning to keep the bike forever.☆
    CB250 Nighthawk projects 92,93,92.
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  3. #3
    Member Adamgs340's Avatar
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    I was going to do both I will check they valve seat thank you

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  5. #4
    Senior Member Twowheelrich's Avatar
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    When I got my Sloper I found one spark plug hole had been enlarged to accept the larger plug *without using an insert* with the same heat range. The PO did a decent job and the threads were in good shape and I would have been okay running it that way, but I needed to tear into the motor anyway, so when I pulled the head I had it the plug hole welded, drilled and tapped to fit the original plug size. It's a more expensive option for sure...
    Last edited by Twowheelrich; 09-08-2019 at 08:22 PM.
    1973 CB 450 - Sold!
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  6. #5
    Member CDan185T's Avatar
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    Why not reduce the insert from 15mm to 1/2inch before inserting it?
    colvfrfg likes this.

  7. #6
    Member mikemo's Avatar
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    I would pull the head and use a helicoil insert, trimmed to size. I might even install an insert into the good plug hole while the head was out, just to keep things the same.
    You _can_ install the helicoil with the head in place. The thought of all those metal shavings inside my motor would keep me up at night.
    I would not enlarge the hole unless I was desperate. Some day, someone will curse you for your actions.
    Last edited by mikemo; 09-09-2019 at 06:50 AM. Reason: add info
    1982 CB450SC Nighthawk
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  8. #7
    Member Adamgs340's Avatar
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    What's the best way to reduce the helicoil? Just grind the top since the bottom has the tang to thread it in. The run a tap through it and a die over it?

  9. #8
    Member Adamgs340's Avatar
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    Oh and thanks for the reply's guys

  10. #9
    Member mikemo's Avatar
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    The helicoil is just a coil of wire. Measure the depth of the hole accurately and trim the top side of the helicoil (the part without the installation tang) to end just below the top surface when it is installed. It is stainless steel, so it may be hard to cut with clippers. After you cut it and before you install it, dress the cut end with a file so it is smooth and without any burrs where you separated it.

    Good luck
    Mike M>
    1982 CB450SC Nighthawk
    2 x 1988 Toyota MR2 Supercharged (one finished, one under reconstruction)
    2018 Honda Civic SI

  11. #10
    Member CDan185T's Avatar
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    I would use this type of insert

    https://www.ebay.co.uk/itm/Spark-Plu...4383.l4275.c10

    there is a 1/2 inch repair piece in the kit.
    colvfrfg likes this.

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