Engine Rebuild Wrap up.
Ok, here is what I found during the engine rebuild.
Remember back when I started working on adjusting the valves? I found one of the head nuts laying in the valve covers. This prompted me to question virtually everything with this engine. What was torqued and what was left un-done. I couldn't trust it. Out it came. Much to my delight, I discovered everything else in the engine was torqued up just right. The only thing that wasn't torqued correctly was the head nuts on the #3 and #4 cylinder head. The builder must have gotten distracted and missed the final round of torquing on that side.
The only other thing I found that wasn't to spec was the deck height. As I mentioned, someone had been in there adjusting things. There was a 1.25mm shim at the base of each cylinder that was not stock. I found that odd, everything else was stock. After much consternation, I decided to measure the compression ratio. This is the ratio between the cylinders uncompressed volume and the compressed volume. The only tricky part is that you need to CC the heads. This is where you mount the head so the sealing surface of the head to the cylinder is facing up and level. You then add water or fine oil to the head to determine how much volume it has. This head volume is needed in the following calculation to determine the compression ratio:
(Note: These numbers are not from my engine, just an example!)
1. Determine the displacement of your engine. Displacement formula is:
BORE X BORE X STROKE X .0031416 = DISPLACEMENT
Example: 92 x 92 x 82 x .0031416 = 2180cc
2. Determine the swept volume of one cylinder:
Example: 2180cc divided by 4 = 545cc
3. Determine the deck volume of each cylinder. The deck volume is the distance from the top of the piston to the top of the cylinder rim when the piston is at top dead center. Measurement is made in thousandths.
Example: on cylinder #1 you measure and find you have .020" deck height.
BORE X BORE X DECK HEIGHT X .01996 = CC"s
Example: 92 x 92 x .020" x .01996 = 3.378cc's
Measure each cylinder.
4. Measure the volume in each cylinder head. To do this, use a piece of plexiglass cut to fit in the cylinder head to cylinder mating area. Drill a 1/4" hole in the center of the plexiglass. Lightly grease the edge of the plexiglass and install in the head. (Spark plug and valves have to be installed) with a syringe graduated in cc's fill the cylinder head chamber up with a light weight oil. Record the measurements. Repeat for other three chambers. Average cc volume of a new head chamber is between 47 and 51 cc's.
5. You now have all the measurements to determine your compression ratio.
one cylinder swept volume + deck cc + head cc
deck cc + head cc
Example: 545 + 3.378 + 48 = 596.378
3.378 + 48 = 51.378
So: 596.378
51.378 = 11.6:1
Now the original VW 1600 dual port engine was designed to run at about 7.5:1 . The original calculation I came up with for my engine was 6.63:1 Oddly enough, when I took out the shim at the base of the cylinders, the new compression ratio came out at 7.48:1 It looks like someone add the shims which lowered the compression ratio. This would not cause any harm, it just would make the engine a bit under powered. The lower compression ratio would make the engine run a bit cooler, but the 7.5:1 ratio is in a very comfortable range. This new ratio should work out quite well. More importantly. I found out the engine is completely stock. Good to know.
Ok, here is what I found during the engine rebuild.
Remember back when I started working on adjusting the valves? I found one of the head nuts laying in the valve covers. This prompted me to question virtually everything with this engine. What was torqued and what was left un-done. I couldn't trust it. Out it came. Much to my delight, I discovered everything else in the engine was torqued up just right. The only thing that wasn't torqued correctly was the head nuts on the #3 and #4 cylinder head. The builder must have gotten distracted and missed the final round of torquing on that side.
The only other thing I found that wasn't to spec was the deck height. As I mentioned, someone had been in there adjusting things. There was a 1.25mm shim at the base of each cylinder that was not stock. I found that odd, everything else was stock. After much consternation, I decided to measure the compression ratio. This is the ratio between the cylinders uncompressed volume and the compressed volume. The only tricky part is that you need to CC the heads. This is where you mount the head so the sealing surface of the head to the cylinder is facing up and level. You then add water or fine oil to the head to determine how much volume it has. This head volume is needed in the following calculation to determine the compression ratio:
(Note: These numbers are not from my engine, just an example!)
1. Determine the displacement of your engine. Displacement formula is:
BORE X BORE X STROKE X .0031416 = DISPLACEMENT
Example: 92 x 92 x 82 x .0031416 = 2180cc
2. Determine the swept volume of one cylinder:
Example: 2180cc divided by 4 = 545cc
3. Determine the deck volume of each cylinder. The deck volume is the distance from the top of the piston to the top of the cylinder rim when the piston is at top dead center. Measurement is made in thousandths.
Example: on cylinder #1 you measure and find you have .020" deck height.
BORE X BORE X DECK HEIGHT X .01996 = CC"s
Example: 92 x 92 x .020" x .01996 = 3.378cc's
Measure each cylinder.
4. Measure the volume in each cylinder head. To do this, use a piece of plexiglass cut to fit in the cylinder head to cylinder mating area. Drill a 1/4" hole in the center of the plexiglass. Lightly grease the edge of the plexiglass and install in the head. (Spark plug and valves have to be installed) with a syringe graduated in cc's fill the cylinder head chamber up with a light weight oil. Record the measurements. Repeat for other three chambers. Average cc volume of a new head chamber is between 47 and 51 cc's.
5. You now have all the measurements to determine your compression ratio.
one cylinder swept volume + deck cc + head cc
deck cc + head cc
Example: 545 + 3.378 + 48 = 596.378
3.378 + 48 = 51.378
So: 596.378
51.378 = 11.6:1
Now the original VW 1600 dual port engine was designed to run at about 7.5:1 . The original calculation I came up with for my engine was 6.63:1 Oddly enough, when I took out the shim at the base of the cylinders, the new compression ratio came out at 7.48:1 It looks like someone add the shims which lowered the compression ratio. This would not cause any harm, it just would make the engine a bit under powered. The lower compression ratio would make the engine run a bit cooler, but the 7.5:1 ratio is in a very comfortable range. This new ratio should work out quite well. More importantly. I found out the engine is completely stock. Good to know.
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