Mon-Fri. 10am - 5pm EST or order online anytime. We ship from the closest stocking warehouse.

    Recent Posts

    Harley Davidson Spark Plug Thread Repair – How to Fix

    Harley Davidson Spark Plug Thread RepairDennisB © Summary: In this article we cover motorcycle spark plug thread repair using the best kits available. Harley Davidson spark plug thread repair as well as other motorcycles made by different companies all share the same solution’s. Determine the size plug and we can help get the right kit. See below for more Time Sert kit information as well as FAQ’s (Frequently Asked Questions). No time to read? No problem give us a call at 800-734-8665.

    We answer a lot of questions on spark plug thread repair everyday. Many times our customers have already tried a parts store kit that didn’t withstand the heat, compression and vibration and blew the spark plug out. A common mistake is to use a Helicoil which is only held in by using a wedge tool to hammer down on the topside of the insert. This is a weak way of holding in a repair insert that has to hold up under so much compression, heating (expansion) and cooling (contracting). The Time Sert kits we sell use inserts that are held in by using an installation driver that cold rolls the bottom threads. This  expands and spreads the BOTTOM of the insert holding them place. This is a much better way to hold a repair insert in. It doesn’t take an engineer to realize this. Permanent red high temperature Loctite is also used as an added measure to secure the insert. So which kit does your Harley take? The kits we sell come in many different sizes. So the first thing to find out is what size the spark plug hole is from the factory. One of the most common sizes for Harley Davidson motorcycles is; metric – M12x1.25 millimeters. If that’s what your motorcycle uses, the kit will be the Time Sert 4212. If this is a second time repair, meaning that an inferior type parts store type thread kit has been used and has failed; Use Big Sert, which is Time Sert’s name for oversize. There’s no specific Time Sert “Big Sert” – (oversize) kit for M12x1.25mm spark plugs. You can however use the 5212 kit along with the 52121 insert. Read on to learn why the Time Sert solution is a wise choice to repair motorcycle spark plug threads when they are cross threaded or damaged in some other way.
    Question – I have a 1999 Harley Davidson that uses  Champion 6R12 spark plugs. 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 6r12 – Cross reference: NGK DCPR7E, DCPR7EIX, Champion RA8HC,DENSO IXU22, Autolite 4163, 4164, Harley-Davidson 6r12.
    Question –  Will the motor use the same size spark plug after I use the Time Sert thread repair kit?
    Answer – Yes. It accepts the same size, original spark plug as before. Be sure to verify the size is correct before using the kit.
    Question – The manufacturer, Time Fastener, says that I only need to use Loctite on taper seat plugs, not washer seat. Can I skip the Loctite?
    Answer – That is technically correct in most cases. You don’t have to use Loctite if you’re using a washer seat insert and plug. However as extra insurance we recommend it.
    Question – Why is your Red Loctite so expensive? I have red Loctite already so why can’t I just use that?
    Answer – Red Loctite is NOT all the same. Our Loctite is high temperature. As you can imagine the threads for the insert will get very hot since it’s located at the combustion chamber. Regular Loctite like 271 and 277 will burn away at around 200 degrees, which will make it useless in this application. Our Loctite 266 will withstand temps up to 500 degrees so it will continue working even under extreme conditions.
    Question – I thought I read that the insert is held in by spreading the bottom somehow. How does the bottom get expanded?
    Answer – The installation driver which is used to put the insert in the prepared hole is the key. While other brand insert kits instruct you to use their cone shaped tool and strike it with a hammer! Time Sert uses a driver tool that cold rolls the bottom threads finishing them while spreading the bottom of the insert locking it into place. This along with the use of the Loctite 266 mentioned above is a far superior way to lock the insert into the engine.


    Comment from Dennis Bandy
    Time August 7, 2015 at 7:59 am

    FYI, the 4212 kit is used for plugs on older Harleys that use the M12x1.25, see the following link Time Sert 4212.

    Comment from david o’connor
    Time March 18, 2016 at 10:25 am

    I have a Kymco zing hipster 125 it has a 9.5 or a 10mm size plug what type helicoyle would a need for it?

    Comment from Dennis Bandy
    Time March 18, 2016 at 11:07 am

    David, from what I see, your bike would use a 12mm spark plug, Please verify your spark plug number – I’ve listed a cross reference below. If it is M12 then the 4212 is the correct kit. And I know when you say Helicoil you really want a Time Sert kit since they are superior to Helicoil, even though most people refer to thread repairs as Helicoil.

    Thread diameter: 12mm
    Thread reach: 19mm
    Seat type: washer
    Hex size: 18mm

    Replacement spark plugs for NGK DR8EIX cross referenced below:
    Brand Number
    Autolite 4163
    Autolite XS4163
    Champion A6G
    Champion A6GC
    Champion OE112
    Champion R6G
    Daihatsu 99906-910X9-014
    Daytona 61488
    Denso 4167
    Denso 5372
    Denso 5730
    Denso I72
    Denso IX24
    Denso IXU01-24
    Denso X24ES-GU
    Denso X24ESG-U
    Denso X24ESGU
    Denso X24ESR-ZU
    Denso X24ESRZ-U
    Denso X24ESRZ-U9
    Denso X24ESRZU
    Denso X24ESRZU9
    Denso X24ESZ-U
    Denso X24ESZ-U9
    Denso X24ESZU
    Denso X24ESZU9
    Denso Iridium IX24
    Denso Iridium stk 5372
    Kawasaki J4520IX24
    NGK stk 6681
    Suzuki 99000-69835-DR8
    Suzuki 99000-79K24-X24
    Tacti V91105372
    Toyota 90098-74037
    Yamaha 90793-20011
    Yamaha 90793-20022
    Yamaha 90793-20152
    Yamaha 90793-22107
    Yamaha 90890-78118

    Comment from Mel Taylor
    Time March 22, 2016 at 10:10 am

    My Harley panhead uses a Champion J12YC ( 14 mm x .375″ reach). Wire helicoil failed, need a timesert-type sleeve. What kit part number do I need?

    Comment from Dennis Bandy
    Time March 22, 2016 at 12:07 pm

    You need an oversize repair. Big Sert is TIME-SERT’s oversize repair. The 5141S is a BIG-SERT kit. The shortest insert available for that kit is the 9.4mm reach p/n 51401. The 9.4 is .37″ which should make it the right size barely. Call if you’d like to order since we currently don’t have the 51401 listed on our site although it is available. 800-734-8665.

    Write a comment