Top Dead Center Tech

To Read The Full Article, Go To

How To Make A Piston Stop Tool

Article And Photos By: Daniel Donley –

Orignally Published In The July 2018 Issue Of Cycle Source Magazine


TDC? Stands for Top Dead Center. TDC Happens when the piston in your engine is at its highest point. Yes, you can pull the spark plug and watch your piston come up and say yep that’s TDC. That is not very accurate. The best way is to use a piston stop in conjunction with a degree wheel. By using this method, you can accurately find true TDC. So, you ask yourself, why do I need to know this. It is necessary to know True TDC for proper valve adjustments, setting ignition timing, and if you’re a hot rod gearhead it is necessary to find TDC when you are degreeing in your cam shaft. There are a lot of piston stops available on the market for purchas, and they work great. But there is always that great satisfaction when you can make something yourself, So, for this month’s tech I am going to show you how I made a piston stop. With a cool little feature that is not available for purchase.

To get things started you need a random spark plug of the size for your application. Some scrap solid round bar. The round size will vary per application. We are using 3/8” here.

You will want to chuck the spark up in the lathe. If you don’t have a lathe you can put the spark plug in a vice. Then cut it with a hacksaw. Just cutting the steel portion only. So, you will have to rotate when doing so. If using the hacksaw method, please read the entire article first.

What we are after here is to remove the porcelain part of the spark plug from it’s base. Using the lathe to turn this down makes quick work

of its removal. You want to leave approximately an 1/8” above the spark plug washer. Different plug manufacturers and or sizes will vary.

Here is a picture of before and after to give you an idea of what you want to achieve. The spark plug tang can easily be removed with a pair

of pliers. Touch up the end with a hand file to make smooth. For you guys that are using a hacksaw this is approximately where you want to cut. You will want to rotate the spark plug around as you are cutting through only the steel portion.

The next step will vary per spark plug size. For, this we chuck the spark plug base back into the lathe and drill through with a 3/8” Drill bit. You can also use a handheld drill here.

Next, is the piston stop. Slide the 3/8” round bar through the spark plug base. I like to make these with approx. 1 ½ to 1 5/8” of sticking out from the crush washer base. I am also going to leave some length here on the other side, so I can install a small “T” handle to make for easy installation. The length of this handle can be at your discretion.

Here is part of that cool feature that you don’t get with ones that you purchase elsewhere. Right above the spark plug base approximately an 1/8” or a little more make a mark. Remember this is your tool, you can make it how you want!

Take the 3/8” rod and install back into the lathe and center drill a hole that will extend just past the mark that you made above the spark plug

base. This hole is going to be part of our compression release hole. Now

you can drill into one side with a hand drill to complete the compression release passage. Wait a minute… compression release passage…? Yep! Pretty cool huh! All of this can be done with a hand-held drill. You will also want to put a nice rounded surface on the end because it will be making contact with your piston.

So, this gives you an idea of what I am making mine look like. The length and whether or not to have a handle is up to you.

If your installing a handle do so now. With whatever metal melting together, device you have!

Lastly weld on the base, making sure that you keep the stick out between

1-1/2” – 1-5/8” from the crush washer base.

Piston Stop to find “TDC” COMPLETE! This was a fun little project that honestly happened out of necessity, the piston stops that I have used have proven to be very lackluster. With the addition of the compression release, it makes rolling over the engine by hand very easy. For next month’s tech we are going to get into how to use this piston stop in conjunction with a degree wheel to find TRUE TOP DEAD CENTER! Stay Tuned! If there is something that you would like to see me do a Tech article on please call me or email me with your idea. If you have any questions, please feel free to call me at the shop anytime 419-576-6812

Daniel Donley – Pandemonium Custom Choppers

Facebook- Pandemonium Custom Choppers

Instagram – pandemoniumc2

Leave a Reply

Your email address will not be published.