[sdbob]

I'm dealing with a 16hp Kohler engine that previous owner damaged threads and put an insert in it(not a helicoil). I have replacement head ready for end of mowing season.Just for my tool box would one of these adjustable back taps be worth buying? The taps say USA made. I've read couple different prices. High was about $30.00 low was about $20.00 for same part number. Thanks

[JSchmitz]

Never used, or heard of, a back-tap. Sounds vulgar! LOL! Looks like a good idea in principle. I'm not sure why it's necessary though. Supposed to keep chips out of the cylinder? What are you trying to repair? Thread inserts are extremely hard. Do you just want to chase/clean up the threads? I would use a regular tap with some grease in the flutes. That's the best way to control chips.

[sdbob]

From video. Insert back tap all the way into cylinder in the retracted form. The tap has 4 external fingers that are threaded.With a tapered internal threaded rod.Piston down .Expand threads by tightening internal threaded rod and slowly screw tap out.From theory threads on inside are still good. I've never a had a cross threaded plug.Always been careful with aluminum head on small engines. It's one of those tools I thought might come in handy at my age ,yeah right(75).

[JSchmitz]

Originally Posted by sdbob

From video. Insert back tap all the way into cylinder in the retracted form. The tap has 4 external fingers that are threaded.With a tapered internal threaded rod.Piston down .Expand threads by tightening internal threaded rod and slowly screw tap out.From theory threads on inside are still good. I've never a had a cross threaded plug.Always been careful with aluminum head on small engines. It's one of those tools I thought might come in handy at my age ,yeah right(75).

Understood. Can't have too many options when it comes to tools!

[Nobuddy]

I have one that I bought to also repair a mower. Worked well on the original aluminum threads but they were only buggered for maybe the top thread. Sure beat pulling the head off and using a regular tap from the chamber side. I suspect in iron threads or an insert it would require some patience and a few passes to clean up.

[carbking]

Never heard of this, and Bob, I am older than you.

Was taught at a very early time in my lessons in mechanics to put 90 weight grease in the flutes if chips were a concern.

Not only does the grease catch the chips, but the resultant thread seems better than without the use of the grease.

Jon

[sdbob]

Jon my grandfather showed me. The only advantage I see with this back tap is using the threads that arent damaged. Tool for tools sake when younger I made do with I had on hand.

[limejudge69]

I use them regularly on aircraft engines and they work great. Start down low where the threads are good and the trash comes out the end. I use a nickel based antisieze and usually make 3-4 passes, just barely opening enough on the first pass to get it in the correct groove. I then open slightly more each pass. I use the Powerbuilt brand

[limejudge69]

These are lifesavers on Rotax engines where a heli-coil is not an option, as well as Lycoming and Continental where the plugs are baked in. I find the first couple of threads are the ones most likely to be boogered up, and the back tap solves that issue, allowing the new spark plugs to thread in much easier

[Sirrotica]

I had to look up "back tap" because I've never seen one. The idea apparently is to collapse the cutting edges, push the tool into the combustion chanber, expand it to cut the threads as you unscrew it out of the cylinder head. Basically tapping it from the inside out.

I've never seen , or heard of the tool, but I'm sure it would start straighter from the bottom, undamaged threads, so as not to cross thread if a conventional tap was run in from the top. I'm sure it has a limited use, and is usually being used to straighten out threads that were cross threaded inadvertently with a spark plug change. If the threads were pulled out of the head from overtightening, you're only choice would be to restore the threads with an insert, or a Heli Coil.

I have a tap that both ends can be used depending what size threaded hole your working on. It fits into a sparkplug socket so you use the socket as the tap wrench. I've used it a few times to fix the top threads when they got crossthreaded.

Wisconson engines are classic for people ruining the plug threads, they take a 14 MM plug, but are aluminum, as well as the theaded area is thin, so a very limited area is threaded. If you mess up likely you're looking at a new head, or removing it for an insert installation. Those engines usually are exposed to rain water, and it pools around the plug further causing corroision problems when the plugs are in there for many years. Removing a plug sometimes also means the threads are coming out with it.