Where is the best place to remove material to balance pistons? I need to remove 11 grams. PK
11 grams is a lot on an aluminum piston. The bottom inside edge of the skirt is the usual place- tape up the ring lands and grab in a lathe chuck and bore the id of the skirt. The bottom of the pin bosses is another place you can remove some material. Weigh your pins 1st and see if that is where the difference is. Depending on your shop equip, it is possible to bore a chamfer on the id of the pin to remove material at the ends. this will not weaken the pin. Good luck.
Thanks for the reply Dan. The pins are within 1 gram. I have one light piston, the others are all the same weight. I have a lathe and can cut the inside if the skirt. Cutting the pins might be the best option being steel. PK
The pins are hardened.
You might be able to cut the pins with a carbide insert, but you will probably be better off grinding them.
A nickel weighs about 5 grams, so about the same volume of material that is in two nickels would have to be removed from the pin to equal 11 grams. If you removed that much material from the inside piston skirt, it may get a little thin?
11 grams is quite a bit, can you exchange the pistons for a different set?
A carbide or CBN tool will definitely be required to bore the end of the pin. To clarify, I suggested boring the inside of the pin on a taper, not grinding the end- suppose you could grind the id tapered, but it will be very tedious
Dan McE is one person who's opinion I respect in regards to balancing (and a number of other things).
One advantage (as if there really are any) to being broke and trying to accomplish something good while cutting corners. I find that wrist pins from over the years have varied a lot in weight.. When I am putting an engine together, I mix and match pistons by fit and condition first, weight second, then adjusted the weight by swapping wrist pins. Generally (there ARE exceptions out there), the fit on wrist pins is very precise and standardized (but always check their fit when swapping them around).
I don't know what Dan McE would think of swapping old and new wrist pins around with newer pistons?
Drive carefully, and enjoy, W2
I'm using the old pistons. They are .060 over Jans from the 60's. I'm putting in new rings only this year. What are your thoughts on adding weight to the one light piston using the pin? Like pressing a weight inside the pin? Thoughts? PK
I've pressed weights inside the pins. A rod bolt was the right size for my pins. Just a matter of cutting the bolt to the right weight and pressing into the center of the pin. Just to be sure I slathered the bolt with Loctite. Overkill I suspect.
I have heard of people putting weights inside of the wrist pins. BE VERY CAREFUL that it cannot move to either end of the pin and start cutting the cylinder wall! Remember, the piston and pin get hot enough while running that things like epoxy and Loc-Tite may not hold it.
So far, I have been able to do okay by using pins of different thickness and weight.
Wayne, yours is a better idea (usings pins of different weights) if you can get the right amounts of weight to balance the pistons. I was also concerned about the weights moving and scoring the cylinder walls but the bolts I mentioned were a very tight press fit. I did notice the pins swelled a tiny bit with the bolts inside. Clamping the pins on the rods also helps keep the bolts in place. The use of loctite made for high heat application should be fine as the wrist pin area doesn't get that hot. In my case, I was working with a survivor car I wanted to keep original, so keeping the iron pistons was a priority.
If you add weight in the pin, i would put aluminum plugs in the ends just in case the weight shifts.
Just a little too much press will swell the pin od and cause other issues. plus most pins have a terrible surface finish on the inside, making an accurate press fit a little difficult. I recall that the Jahns pistons had a rib around the inner face of the pin boss that really does not do much strength wise, so I think I would whittle away on those ribs to get the weight off.
You remember right Dan. There is a lot of material in that boss rib. I might stick them in the mill tomorrow and see what I can do. PK
Just don't use the "nickel" comparison to remove aluminum. Nickel has about three times the density of aluminum. You would have to remove three nickels of aluminum.
For adding weight, use copper plugs in the pins. It's soft enough to conform to irregular surfaces and is more dense than cast iron. You can even cast it in-place and drill it for fine tuning weight. You can melt copper in a stainless steel cup if you don't have a crucible. Do NOT try to melt it in a cast iron ladle.
Ken - why not melt it in an iron ladle? I won't be doing it, just curious.
Have anyone tried to melt lead into the pin?
Lead melts at 327.5 degrees C.
Would that be enough for it to stay solid within the pin?
Walt - Sorry I missed your question until this thread popped up again. The melting temperature for cast iron is too close to that of copper. You'll end up with a blob of cuprous-iron on top of your work surface. Don't ask how I know.
Niels - I think lead may be too soft and start to roll/hammer itself into a loose rod inside the pin. You could try it. I'd prefer zinc over lead. It melts ~420C and is much harder than lead. The drawback is that zinc has a high shrink rate. It might be better to cast a plug and press it in. (I use pure zinc for making sheet metal press dies--It's pretty hard.)