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TIME-SERT 4212 Spark Plug Thread Repair Kit M12x1.25

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2.00 LBS
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TIME-SERT 4212 Motorcycle Spark Plug Thread Repair Kit 12x1.25 commonly used on Harley Davidson and other motorcycles. This kit can also be used on automtive applications when an M12x1.25 spark plug is used. Inserts are sold separately.


1. Wrench
2. Step-Tap
3. Insert Driver
4. Seat Cutter

 Remember to use Loctite PN 6020 especially on Harley Davidson's due to excess vibration. A common size for the insert is PN 42123 which is 15mm long. If there's room for a tap guide use PN 32125.

Question - I have a 1999 Harley Davidson that uses a Champion 6R12 spark plug. Will the 4212 spark plug thread repair kit work for my bike?
Answer - Yes, if it's a first time repair, because the Champion 6R12 spark plug is an M12x1.25mm so the 4212 is the right size. Remember to purchase the 42123 washer seat insert which is sold separately. Here's a cross reference for other spark plugs that are also the same size as the OE Harley plug 6R12 - Cross reference: NGK DCPR7E, DCPR7EIX, Champion RA8HC,DENSO IXU22, Autolite 4163, 4164, Harley-Davidson 6r12. More below.
Harley Davidson 6R12 equivalent spark plugs
Bosch 0242135515
Bosch YR7DC+
Brisk BR14YC-9
Champion 810
Champion RA8HC
Denso IXU22
Denso VXU22
Denso XU22EPR-U
Denso XU22TT
NGK 3932
NGK STK 3932
Question - I'm using this on a Fat Boy and only have about 5 inches clearance, do I have to remove the tank?
Answer - to use the wrench provided you would need to remove the tan, however some guys have said that they can use a small 1//4" drive ratchet and 12 point socket to to the tooling instead of the wrench provided.
Been repaired before and need an oversized? There's no specific Time Sert "Big Sert" or oversize for 12x1.25mm spark plugs. You can however use the 5212 kit.
 Mouse over the images above for a more detailed view of the kit components. Need more information on TIME-SERT thread repair kits? Visit our auto repair blog section on thread repair kits for tips, advice and all your thread repair questions answered. Just comment and we will be quick to respond.

See the pdficon-small.png TIME-SERT products pdf for more information on thread repair kits and inserts. Some are listed for certain applications on cars, trucks and motorcycles. The pdf is a partial application list so feel free to email or call if we can assist with your particular need. We also accept inquiries regarding our daily TIME-SERT specials. Remember TIME-SERT is recommended by leading car manufacturers like the General Motors Corporation. In fact TIME-SERT is GM's only authorized repair for head bolt threads.

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3 Reviews

  • 5
    Motorcycle spark plug thread repaired!

    Posted by Steven D on 1st May 2022

    Thanks to Dennis which helped me figure out which thread repair kit and insert to use on my motorcycle. I know some use 14mm so I was unsure. Anyway the kit works great! From Wise: Thanks for the feedback. Yes some motorcycle's use 14mm. Best to check the spark plug size before ordering. If it's not easy to find the size by the spark plug number, a digital caliper can be used to measure the OD (Outside Diameter) on the threaded part of the spark plug. Usually with metric sizes the measurement will be just under. In example a 12mm will measure less than 12.

  • 5
    Timesert on Harley

    Posted by Kevin K on 25th Apr 2016

    Tooling worked great. Took my time and was done in a hour. Took the extra time to use vacuum and a small hose to suck filings out of cylinder. Then for extra insurance I then blew through the same small hose right into cylinder that is when I saw the most filings coming out. I just used wd 40 instead of grease because of the chance of the grease and filings sticking to cylinder and not sucking or blowing it out.

  • 5
    great tool, easy to use

    Posted by BL on 20th Mar 2016

    Very easy to use

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