DennisB WiseAutoTools.com © Summary: Why it is so important NOT to drill or tap before making sure the valves are closed. When it comes to spark plug thread repair, a common misconception is that the piston "being down" is the only concern. Below is part of a recent email conversation I had with a customer preparing to fix his spark plug threads.
Dennis. I have a few more questions if you have the time. I don't have an air compressor so I won't be able to use the leak tester to find bottom dead center. Is there another method that would work? Maybe dropping something like a long plastic straw into the spark plug hole and rotating the crankshaft until the straw is at it's lowest point? I ordered a borescope, would that work too in finding bottom dead center? As far as blowing shavings out of the cylinder, without an air compressor I'm going to try rigging up a long thin flexible tube to a high powered leaf blower. It's all I can think of at the moment. I'm glad you include a tip sheet with the kit. Other than an old corded drill all I have are hand tools, so I need all the help I can get. Thanks again.
Jon. Bottom dead center is not exactly what you want. The piston does need to be down far enough so the tooling doesn't touch but it should be coming up on compression stroke. The valves have to be closed or you can bend them. One of our customers got a thread chaser stuck in the spark plug hole in a parts store parking lot. Since he couldn't get it out he drove home with it in there and bent his valves. By making sure the valves are closed: 1. The valves won't be bent by tooling. 2. When you blow the debris out, it will be exiting the engine through the spark plug hole and not blowing past the valves and going further into the engine.
I recommend renting a compressor so you can use the 389-4000 leak tester to help make sure the valves are closed easily. Another alternative is following one of Time Sert's suggestions, see the link below towards the top where it says " Stop: Check that the valves are not open!".
As you mentioned we do include tips that we've put together over the years answering a lot of questions like yours. When purchasing the Time Sert 5553, 5600 or Clavan 38900 others can just request tips in the comment section at check out. This is just for our customers. Keep in mind we don't sell on Amazon or eBay so the free tips offer is only valid when purchasing from one of our websites, WiseAutoTools.com or DenLorsTools.com.
We've been selling specialty tools and thread repair kits since 2005. Call for assistance in finding the best spark plug thread repair, head bolt thread repair, drain plug or other general thread repair kit for your application at 800-734-8665 x251 or provide your details by using our Contact Form.