Trying to figure out my compression ratio. Could I just use a straight edge and a steel scale and measure from the highest point on the piston to the deck? Anyone done this before?

 

try feeler gauges and a straight edge for a low buck way of doing it

 

Steel scale isn't very accurate. Typical deck height is anywhere from .030" to .050" so feeler gauges and a straight edge work best. I've used a digital vernier caliper and used the depth gauge on it.

You want to measure to the flat part of the piston. Valve cutouts or popups are part of another displacement measurement. Typical valve cutouts are 3cc's each.

 

Chris,

Make sure the piston is at TDC.

I know that doesn't sound right at the first reading, but it isn't meant as a joke or insult. If the crank is off even 2° the piston is already at a point below the deck by a couple of thousandths. Factory tolerances for the crank keywaycut are wider than you might expect, and you shouldn't rely on factory timing marks for a TDC indication. A dial indicator is the easiest/most accurate way to determine true TCD, and a dial or digital caliper is a close second.

However, if you are looking for an inexpensive method, the feeler gauges and a straightedge will work fine as long as you also use them to verify TDC by moving the crank a degree or two in either direction, then re-measuring with the feelers. The tightest point is the true TDC for that cylinder (or more accurately, crank throw). That should give you an accurate deck/depth measurement.

You see - it wasn't a dumb-*** response, but more of a smart-*** one. Hey! At least I'm still and ***, so I'd rather be a smarter one...