“What I Learned Today” With Jeff Smith — Improvising A Piston Stop

When installing new components like a timing chain cover or balancer or when building a new engine, it’s always a good idea to double-check TDC with the balancer and pointer you will be using. With the heads off, this is easy with a piston stop. But with the heads in place, some flat or dished pistons may not work with a spark plug style piston stop. The easiest way to create a piston stop is to use the valves in the head.

The timing marks on a new balancer aren’t always dead on with your engine and timing pointer combination. By knowing how to accurately verify where TDC actually is, you can adjust the components so that everything is spot on, and you can once again trust your tools.

In this case, we used a Moroso over-center style valve spring compressor (P/N: 62370) with a steel plate laid across the valve tip to hold the exhaust valve open. The over-center operation will lock the valve in a given position. We then very carefully rotated the crankshaft first clockwise then counterclockwise until the piston contacted the valve. We marked the balancer at each stop location and then measured the distance between the two marks with a machinist rule and divided it by two. In this case, the TDC mark was within 1/64-inch, so we can be confident that the TDC indicator is accurate.

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