Re: Speaking of Compression Ratios...

[James Montebello <jamesm@domain.elided>]

Measure the chamber volume with the head off first, by greasing the valves
and filling the upside-down chamber until it's full (you might use a flat
plate with a hole in it if you're really anal about accuracy.  Then 
measure the swept volume directly (bore x stroke) using obvious methods
like a rod down the plug hole for stroke and calipers for bore (or just
trust the published figures).  

The crown volume is the same at BDC as it is at TDC, so just measure it
once, using a greased liner and a piston flush with the top of the liner.
Measure the bore of the liner with calipers, and with the engine partially 
assembled, measure the stroke with a straight rod.  Subtract the crown
volume from the measured swept volume and the measured chamber volume to
get the ratio.

Much easier than trying to measure the total volume.

james montebello

On Fri, 15 Feb 2002 formeister@domain.elided wrote:

> I'm in the middle of swapping out the pistons on my 1750 and due to the complex shapes of the combustion chamber and 
> piston crown want to physically measure the actual compression ratio by accurately measuring the total cylinder volume at 
> TDC and then again at BDC with the head temporarily in place.  I have an accurate (to 0.1ml) titration burrette but can't 
> seem to find an easy way to seal the piston to the liner so that the liquid I add doesn't run down past the rings.  Anyone 
> have any ideas besides smearing grease in the the space between the piston crown and top ring groove?
> 
> Regards - Frank Formeister
> 
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