compression ratio help needed 1966 200

[coronadon]

Trying to calc my compression ratio but have a discrepancy on the deck height portion. Classic Inlines small six specs for the 200 c.i.d. is .019. I measured mine using a dial caliper as a depth gauge and came up with an average of .052 per cylinder measured from top of block to piston top down the cylinder wall @ TDC. Why such a large discrepancy??? Also need to calculate the cc's of my stock (.040 overbore) dished pistons. Does anyone have a cc number for the dish volume? I measured the dish at approx. a 2 inch diameter by .1 deep in the dish center.
Current numbers as follows:
Cylinder diameter = 3.72
Stroke = 3.126
Combustion chamber volume 46 cc's
CC's of piston dish? Need to input negative number.
Head gasket crush thickness .053 per Classic Inlines Corteco gasket info, plus deck height measured @ .052 avg.=.105 total.

 

[CZLN6]

Howdy Back:

YOur engine has obviously been rebuilt at least once. A more typicall deck height for an OEM 200 is aproximately.025". Since you have replacement, overbore pistons they were likely built with a reduced pin height. aftermarket pistons will typically be down in the bores an addition .005" to .010". That might account for a deck height reading of .035". Yours at .053" is a bit of a mystery. IF the rod journal were turned down, the machinist could have done a .020" negative offset. Just for jolly's check the stroke on your engine from top to bottom. You already have the factory stroke number. It may be interesting to compare.

The dish on your pistons is aproximately 7 ccs. New factory pistons were rated at 6.5ccs, but volumes actually varied slightly. The best way to measure you pistons dish volume is to pack clay into the dish and level it off on the top. Then peal the clay out and drop it into a graduated cc beaker with a visable fluid in it at a specific number. The change after dropping in the clay is your actual dish volume. I can assure you it will be right near 7 ccs.

The 46 cc chamber volumes indicates that the head has been surfaced as part of a rebuild valve job. My guess is that the head was milled .030" to true the mating surface. What head gasket was in this engine when you disassembled it?

Hope that is helpful. Where are you headed?

Adios, David

 

[coronadon]

Thanks for a very concise answer on the isuue. I can't do some of your hints as the engine is back together.
The dish cc estimate you gave is a major help. Thx.
The head gasket I replaced was a Felpro,blown out between 3&4 cylinders. I previously had the head shaved .05 before the Felpro and this time .015 to offset the crush diff with the Corteco gasket.
As far as the deck height discrepancy goes, I'll use what I measured. You pose some interesting explanations as to why.
Thanks for your valuable input.

Don

 

[sctty1986]

if u goto walgreens get a medical syringe, the child oral suspencion syringe or at auto zone or pepboys they have 2 cycle mixing syringe get an old CD use some vaseline to seal the top of the piston to the cd and fill with water or trans fluid, it give a good measurment. i use both. the 2 cyle for the double digits and the smaller for the single digit readings.

 

[JackFish]

sctty he says the engine is back together

 

[CZLN6]

Howdy Back:

HEy Sctty. I like the old CD disc idea as a surface seal for checking volume. Walgreens along with your local ranch store are great places for graduated syringes and beakers. It may be too late for Don, but somebody is reading this who will appreciate the tips. Thanks.

Adios, David