Harley Davidson Spark Plug Thread Repair – How to Fix

DennisB WiseAutoTools.com © 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 solutions for stripped spark plug threads. Determine the size of the spark plug and we can help get the right kit. See below for more Time Sert repair kit information as well as the FAQ’s (Frequently Asked Questions). Need some assistance in getting the right kit? 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. If doing a second time repair see our article called Harley Davidson Second Time Spark Plug Thread Repair. 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. If your bike has an M10x1.00, the kit to use for a first time repair is the Time Sert 4010 and the most common insert which is sold separately is the 40103 linked from the 4010 product description. Finally, some motor cycles use M14x1.25 which are the same size that most cars use. If doing a spark plug thread repair for 14mm see the Time Sert 4412 kit.

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 200-300 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.