Piston stroke: piston stops and finding top dead center

Tom writes:

Hi Sajeev, I am the original owner of a 1973 Chevy Camaro with all original drivetrain. The engine is 350ci and the car underwent a frame off restoration. During the engine rebuild a breaker kit was installed. Shortly after I got the car back the breaker kit module failed. I reinstalled the breaker and condenser. (I did not remove the distributor.)

I set the dwell to 30 degrees and checked the timing (with the vacuum line plugged). The timing mark was about 3/4 inch past the timing tab. I set the timing to 12 degrees. After that the engine misfired through the carburetor. I checked the spark plug wire routing and everything was correct. Then I set piston #1 to TDC on the compression stroke. The rotor was pointing to wire #1 on the cap. (Wire #1 was at about the 6:30 position on the cap.) I set the timing back to 3/4 inch from the tab.

The misfire has stopped but it is not where the ignition should be. I am afraid of damaging a newly rebuilt engine. Any ideas?

Sajeev Answer:

Hi Tom, thanks for this detailed question, it helps me give you a better answer. The ignition timing was the right decision and I doubt you damaged the engine if you kept the misfires to a minimum.

There’s something wrong with the vibration dampener (or maybe the timing mark?), but I’m absolutely not qualified to isolate that problem. Instead, I shared your question with Brandan Gillogly from Hagerty, and his response cleared everything up in a jiffy:

“It sounds like his new balancer is out of alignment with the timing tab. I think he should use a piston stop and find out where top dead center (TDC) is and make sure everything is in line.”

Bingo. Let’s take a step back and learn how to use a piston stop tool (which you can make yourself) with this video of an early Chrysler Hemi from our friends at Holley.

I hope the markings you made on the balancer match the timing tab on your engine. Or maybe not, because that would indicate a bad balancer.

I suspect the timing mark on the balancer is not in the right place (as in the video above) due to a manufacturing defect, probably due to the connection of the two metal pieces and the elastic band between them. Aftermarket balancers can be of dubious quality and I hope that is your problem. Considering the quality of the point elimination kit that came with your engine, there’s a good chance I’m on the right track.

Far too often today, bad parts end up in our engine bays. It’s usually not the repair/machine shop’s fault, as most places have the best intentions. However, the quality of the supplier is a little harder to confirm, and often it’s situations like this that bring problems to light.

I hereby pass the torch to the Hagerty community. Does Tom’s Camaro have a faulty balancer or is there something else wrong with the ignition system? Your comments are always welcome.

Do you have a question about Piston Slap? Send your questions to [email protected]—Give us as many details as possible so we can help you! Remember, this is a weekly column, so if you need a faster response, please let me know in your email.

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