COMP Cams 4795 Top Dead Center Stop, 14mm Bolt-Style

I give the quality, and utility of this tool 5 stars, but it cannot be used on Ford 4.6, and 5.4 engines, as the tool is too short. The 4.6 & 5.4 have deep spark plug holes, and this tool won't work, as it won't even begin to thread into the cylinder head. The threads on the the spark plugs for these engines, are from the beginning of the threads, to the shoulder of the spark plug, 5/8 of an inch long, whereas the threads on the tool, from the beginning of the threads, to the shoulder of the tool, are only 3/8 of an inch long, which means, the tool is 1/4 of an inch too short. If you need a piston stop tool for one of the above mentioned engines, you will need to go to a specialty tool company, such as Modular Motorsports. Hope this helps.

Worked great on a Pontiac 400.

Ahh the joys of classic car ownership !got the 84 vette, was running rough, turns out gm harmonic balancers are bonded with rubber in 2 pieces, the outer piece slips due to age, and your timing marks are way off, to determine where TRUE TOP DEAD center is you need a piston stop which is waaaaay more accurate than using a screwdriver or straw or whistle to know where exactly true top dead center is on the compression stroke.Fit like a glove and i was able to re mark on the balancer true top dead center using this tool and i was able to time my engine to factory spec of 6 degrees before top dead center with the est wire unplugged. Car runs great now !!!Great price, super fast free shipping !

Great product

Used it on motorcycle, with a degree wheel, to check ignition timing.

Did not fit my 14mm Vespa.

Really, this is the ONLY way to determine what you TRUE TDC of your engine. And this is essential.On my old Dodge Ramcharger the actually timing mark had shifted. I had previously set the timing by that and it was low on power so I suspected there was a issue. Timing using the piston stop I found the stock timing mark had shifted several degrees retarded.I use some timing tape and set the advance to a reasonable 8* and the sleepy (stock) 360 woke up!

but otherwise it does its job. If you're trying to find TDC within range of a timing chain/belt tooth, you should be fine. After that you can use valve timing marks to get a good mark for a timing light etc. for ign. timing, or a trigger wheel, hall sensor, pos sensor what have you. I used it very far from TDC, and bracketed interval, going from both sides, narrowing it down, making sure marks on both sides spaced similarly, just as a sanity check.Don't use it extremely close to TDC, you could damage something, spark plug hole, piston etc. Just go halfway between your final marks.