balancing pistons

gvisconty · #1 (**permalink**) 03-09-2004, 11:47 AM

I am refreshing (rebuilding?) a 1973 2-liter engine, and I have 4 new piston/cylinders. I read that you should weigh the pistons with the rings, rods, bearings, etc and if you need to reduce the weight of a set of these you grind off a bit of the rod. This seems just wrong to me, or is it? If not, where is the correct place to remove (add?) metal to adjust the weight?

Lifer · #2 (**permalink**) 03-09-2004, 12:12 PM

I have never ground on rods, but I've ground on pistons quite a few times. I just ground on the bottom (inside) part of the piston and try to get them with in 2 grams of one another. Keith

geh458 · #3 (**permalink**) 03-09-2004, 02:06 PM

To add to Keith's reply, it's best to determine which piston is the lightest and bring the rest down in weight. I would never try to add weight to a piston for fear that the added weight breaks loose and does nasty thing to the motor. Also, if you want to balance the rods as well, you will need a fixture of some sort that enables you to measure the weight of both the large and small ends of the rod seperately. Then there's the crankshaft, it can be balanced based on the weight of the rod/piston combination.

My suggestion therefore is to take everything to a top notch machine shop or engine builder and spend a few dollars to have the balancing done right. You might contact the Cope Brothers Machine Shop in Tacoma, they did some excellant work for me during my boat racing days in the 1980's when I lived in Port Orchard.

There is also a good book from HP-Books dealing with engine balancing and blueprinting, a definate must have if you intend to do this yourself.

Good Luck.

gvisconty · #4 (**permalink**) 03-09-2004, 03:09 PM

Thanks. I figured that adding weight was not a very good idea, and was not looking forward to it.

The only problem with taking the whole mess to a macine shop is the "few dollars" (and the time lost), but I have been considering it.

Any other suggestions for a machine shop in the Seattle area (perhaps a little closer than Tacoma, and maybe even one that has worked on Alfa engines before?).

Thanks again.

**George Willet** · #5 (**permalink**) 03-09-2004, 09:36 PM

The Shop that I have been using for years to do the machining and balancing on the Alfa race engines I build, is in Stanwood, Wa. They are familiar with what needs to be done, and most importantly, what doesn't need to be done. Their prices are reasonable. They have a people that live in the Seattle area, and might be able to arrange a pick up.

ABCO Machine, Jim Harter, 1-800-822-3176.

I understand he will be moving the shop to Bothell in the near future.

Contact me if I can help. George Willet