7880 14mm Thread Top Dead Center Indicator Switch, Shift Indicator Replacement Part, 6" Long

Worked extremely well. Tdc as easy as 123. Great product

The threads were not the correct pitch for a 14mm spark plug hole in a GM Big Block 454. The brass ends are so loose they need to have thread locker or epoxy to prevent them from falling into the cylinder. Any angle other than perpendicular to the piston, the operation of the tool was not smooth, hangs up on the graduated scale. For all the above reasons; I did not use the tool and returned it for refund.

So reading other reviews that used on plugs at angle to piston. It clearly states not for that use. Decided to try it anyway. What I did was switched the rod end so the notches weren't sliding out when actuating. Also put some shrink tube on part of spring that is exposed sliding. Between the rib marks and spring it was catching up and not smooth action. Added some light oil and it became very smooth. Used a dial indicator to find true zero. Borrow one or buy cheap one if you don't have. Totally worth it. Found TDC very easily. Just a note. Ends unscrew extremely easy. Recommend low strength loctite and tighten. Not worth risking leaving part in cylinder

As others have noted, the unit can work very well, however, the threaded parts unwind quite easily, and can lead to lost parts in the cylinder. The unit states it's not for plugs coming in on an angle, so what I did with my BBC was turn the motor over until #1 was a couple degrees BTDC going by the engine indicator bracket and balancer, this may or may not work for everyone if the bracket is off, or the balancer has slipped, but it's a good place to start. This allows for the very minimum of the tool going into the cylinder, and helps to mitigate possible binding or bending of the tool. It worked great for me, I only had to turn the motor a few degrees to see the gauge rise, and then lower.

Works as it should

Throw of piston too long, actually hit fender well in my application

Used properly this was a helpful tool to locate TDC on my 351w SBF. I would recommend using a bit of white paint once it's at TDC so when you rotate the motor you have a mark to monitor as it hits it's peak at TDC. Also, add a bit of oil to the threads before installing it in the number 1 spark plug port. Would recommend.

This tool is poorly made. For something that requires great precision this is not the answer. The plunger to barrel fit is poor. The brass measurement surface had a pip in the very center from poor machine work. The grooves on the plunger were all sharp edged and would catch on the barrel when the piston moved. FWIW I was using this to measure TDC on a hemi head so the tool movement was parallel to the piston. This tool will forever occupy a dark corner of my toolbox.