Spark Plug Rethread


| 10/23/2012 12:10:06 PM


Tags: MC How-To,

Spark Plug Rethread

One of the great things about old bikes is that they're typically pretty simple to work on. Tune-ups are generally fairly simple, with fresh spark plugs cheap insurance against poor running. And depending on your bike — especially if it's an old 2-stroke — you might actually need to replace your spark plugs quite regularly. That brings us to our present little How-To; repairing stripped spark plug threads.

Given the relative ease of replacing spark plugs, many owners are willing to give the job a try. But simple or not, like any project things can go wrong, usually because we get in a hurry. Getting in a rush installing spark plugs can easily lead to cross-threading a plug, resulting in stripped or severely damaged threads in the cylinder head. When that happens, your quick tune-up can suddenly turn into a major job.

If you're lucky and don't cross-thread the plug too far, you might be able to chase the threads with a plug hole rethreader. BikeMaster sells a couple different sized rethreaders; nice to have and only $12. But if you've stripped the threads and they're beyond chasing, the plug hole will either have to be welded up and retapped or repaired with a thread insert. Welding and retapping requires — at the very least — top end disassembly. But depending on your mechanical ability and the ease with which you can access the spark plug holes, you might be able to tackle installing a thread insert yourself, and without having to tear the engine down.

Sponsored by

 
BikeMaster 

We know that some people wince at the idea of inserts of any kind, but practical experience has proven them to be a secure, permanent fix for stripped spark plug threads. Importantly, there are engines — mostly newer overhead cam units — where inserts won't work because the plug hole is so close to the valves you can't cut oversized threads. Our subject bike for this How-To was pal Cailinn Drouin's 1968 overhead valve, 650cc twin-cylinder BSA Firebird Scrambler. A nice survivor currently receiving a little freshening up, it had spark plug threads so worn they would barely hold a plug. Given the ease of access to the BSA's spark plugs, we opted to install inserts.



There are a number of different spark plug rethread kits on the market. They mostly cost about the same ($20-$50), and they all entail the same basic process; clean out the old threads, cut new threads, install an insert and, finally, the spark plug.

Thomas
8/21/2016 12:16:04 PM

I have to say I had the same problem on my Yamaha XJ 600 Diversion (model N, 1997), and I followed all you tricks you described here. And it worked ! I did it nice and slow in about 1h30, and everyting went fine. Thanks fo this article and the pictures, you convinced me to do it myself, and it was a relly nice experience ! Thanks again !




The sound and the fury: celebrate the machines that changed the world!

Motorcycle Classics JulAug 16Motorcycle Classics is America's premier magazine for collectors and enthusiasts, dreamers and restorers, newcomers and life long motorheads who love the sound and the beauty of classic bikes. Every issue  delivers exciting and evocative articles and photographs of the most brilliant, unusual and popular motorcycles ever made!

Save Even More Money with our RALLY-RATE plan!

Pay now with a credit card and take advantage of our RALLY-RATE automatic renewal savings plan. You save an additional $4.95 and get 6 issues of Motorcycle Classics for only $24.95 (USA only).

Or, Bill Me Later and I'll pay just $29.95 for a one year subscription!




Facebook Pinterest Instagram YouTube Twitter

Free Product Information Classifieds