Whitey's New Pistons

The Valves

While reworking the head I decided to put in new valves since the originals were a bit burned. I'm fairly sure #3's compression problem was in part due to a burned valve as well as a stuck ring.

75w_worktable.jpg (31276 bytes)

I purchased a set of stainless steel valves from BPNW. Why? Stellite is too hard and has problems, and the price is well, a joke. The stainless steel valves were barely more expensive than stock units at just around $30 for a set of four. The stainless shouldn't burn nearly as easily as the stock metal ones did. They supposedly won't let contaminates stick to them as much either. .... We'll see.

After cleaning up the old valves, I used them to lap in the seats before doing it to the new valves. I figured I'd wear down the seats of the old valves rather than the new.

75w_valvesoldnew.jpg (8929 bytes)
old exhaust new exhaust old intake new intake

75w_lappingcompound.jpg (13584 bytes)

Lapping the valves makes sure the full circle of the seat is concentric and touching. The lapping compound came in a kit of two grits. 280(fine) and 120 (coarse). It's a bit like tooth paste, that has sandpaper grit in it. A small dab on your finger and lightly spread a bit on the seat face. Stick the suction cup of the tool on the valve face, and twirl the stick between your hands, lifting and rotating to spread the grinding compound evenly.

Start with the 120 grit, clean up a bit and repeat with the finer 280 grit. You should end up with a nice concentric 'ground' surface around the seating face of the valve. In the photo above, the old valves had been lapped, but not the new. You can just see the 'grayish ring' area of the seating face which has been ground to match the valve seating area of the head.

The New Pistons
The new pistons I'm putting in are the flat top 9:1 units as used stock in 1976. The original '75 engine would have only had around 7.5:1 compression. Since I was buying the stainless steel valves from BPNW, I figured what the heck, and bought most of what I needed all at the same time. The aluminum piston 'set' came supplied with rings and gudgeon pins and clips. The packaging, and casting marks, say County. The ring sets supplied are AE. The interior casting marks are nearly identical to the originals. The bare piston is nearly 20 grams lighter than the original Stanpart unit, and out of the box, all are matched to with +/-0.8 grams.
new aluminum piston original Stanpart unit
The new pins though are quite a bit heavier than the originals. They also vary in weight by as much as 0.5 grams. As can be seen in the small photo above right, the inner diameter of the old pins are tapered. I think this could easily be the weight difference between old and new units.

The initial weighing/balancing checks of the pistons revealed:

	#1	#2	#3	#4
Piston	258.22	257.71	258.41	258.07
gudgeon pin	99.19	99.08	99.12	99.59
totals	357.41	356.83	357.53	357.66

This match meant a weight variation of 0.8 grams between
piston sets. So I swapped pins on #2 and #4 and ended up with:

	#1	#2	#3	#4
Piston	258.22	257.71	258.41	258.07
gudgeon pin	99.19	99.59	99.12	99.08
totals	357.41	357.30	357.53	357.15

a weight variation of only 0.38 grams.

Weighing the AE rings (supplied with the pistons) revealed

1st compression ring	7.8 grams	+/- 0.07 grams
2nd compression ring	7.56 grams	+/- 0.01 grams
oil ring sets	8.7 grams	+/- 0.02 grams

So what's all this mean? I'm not going to attempt to balance any of this and just leave well enough alone for once.

©1987-2010 All material copyright© Teglerizer 1996-2008	last edited 3/15/08	hits since last reset

Whitey's Engine Rebuild New Pistons, Valves, Rings

The Valves

The New Pistons

Whitey's Engine Rebuild
New Pistons, Valves, Rings