The story continues....

I have a 1973 Triumph Stag.  Years ago I noticed an oil leak which I initially traced to a waterpump.  My clutch eventually glazed over and I parked the vehicle.  Fast forward 14 years...... I've obtained an air compressor, a hoist, and parts to change the clutch and replace the water pump.  While visiting my local community college I learned that they had a very nice automotive program.  I decided to attend classes and apply my knowledge to the Stag.  I learned that my compression was very low in terms of performance and decided to increase performance.  To date I have new custom high compression pistons which were reverse engineered by CP Pistons, Irvine, CA.  The new pistons are considerably lighter and are  40 over standard bore.    Here are the comparisons of the Old pistons to the new CP pistons.

Once the heads were removed I learned that there was  a crack in a sleeve.

Chipped sleeve - left side of block - rear

Block is Decked at 8.004 with a roughness adverage of  8.4  Sweet!

Compression

.40 over bore and high compression pistons have moved compression from 7.75:1 to 9.0:1



Crankshaft Balance


Old (Piston, pin, lock, rings = 608.5
CP (Piston, pin, lock, rings = 498.5

110 times 8 gives 880 grams or 1.94 pounds lighter!

CP Pistons			Old
Big End	475.5		Big End	475.5
Insert	39.5		Insert	39.5
Total	515		Total	515
Rod/throw	2		Rod/throw	2
Total	1030		Total	1030
Oil	4		Oil	4
Rotating Wt	1034		Rotating Wt	1034
Reciprocating	336.75		Reciprocating	391.75
Bob Weight	1370.75		Bob Weight	1425.75
Piston	379		Piston	456
Pin	94		Pin	127
Locks	2		Locks	2
Rings	23.5		Rings	23.5
Small End	175		Small End	175
Total	673.5		Total	783.5
	50.00%			50.00%
Reciprocating	336.75		Reciprocating	391.75

 Next the crankshaft has to be rebalanced to accommodate the lighter load.

Out of balance 106.1 in front and 232.8 in rear

After removing weight using a lathe

Back to the lathe

Out of balance 131.7 in front and 44.2 in rear

880 grams of weight reduction for pistons. At least 110 grams off the crank to date totals
990 grams.  31 ounces based on pistons and 4 ounces from the crankshaft.


Flywheel lightening

With 2 pounds of weight reduction some people wanted to know if I would be lightening the flywheel.  Based on my research the smoothness of the vehicle operation would be at risk. There is the potential for stalling at stop lights as the RPM's will spin up and drop quickly as lower speeds making for jerky operation and more attention to the vehicle than I want to give.  So no flywheel work absent other compelling information.