Finding top dead center on the right stroke usually involves a thumb over the plug hole and a lot of guessing. This screws into the plug hole instead and whistles while the cylinder is coming up on compression, then goes quiet at the top, so you know both the position and the stroke.

Mr. Gasket 8016MRG Top Dead Center Indicator Features:

• Whistles on the compression stroke and stops whistling at approximately top dead center.
• Whistle is attached to a hose with 14 mm and 18 mm spark plug threads.
• Can be used to locate approximate top dead center for cylinder leak testing.
• Useful for distributor installation and timing chain inspection or replacement.
• Handy for individual cylinder valve adjustment.
• Not for use on diesel engines.
• Sold individually.