Al2011

I'm asking because I want to buy new pistons and install them without balancing the motor. I picked the motor up and it has been rebuilt and balanced, but they used the stock 72 pistons with the big dish. Is there a piston out there that weighs exactly the same or about the same to the stock pistons that I can swap out for a compression of 9.5 to 10.1. I'll be running pump gas and add octane booster if necessary. The heads are stock Ga heads. I was going to rebuild the motor but when I took it apart everything looks clean, the only thing is the timing chain looks new (double roller) but feels loose. Any help will be appreciated. Also is this swap worth it for a weekend burnout cruiser? Or should I just put in a better cam & leave the pistons alone?

Run to Rund

24.057 oz. without pin or rings

coppercutlass

if i remember correctly most cast pistons are manufactured within factory specs forged ones are usually lighter . an older olds guy told me if you stick with cast pistons you wont need to balance the bottom end if you go forged you will need to balance it . i think keith black makes cast pistons that yeild good compression also check out egge machine they make cast units too with smaller dishes on the piston. a nice towing rv style cam with a good intake carb and headers will make gobs of tourqe it wont need alot of compression and drivability will be near stock but with more hp and tourqe

Kennybill

Is it still standard bore? Back in the day it was pretty common to overbore using a cast piston. Along time ago when I switched over to Oldsmobiles from Chevy and I believed the compression ratios I built a street engine using Ohio cast pistons that were 60 over 8.5 CR. If it is a factory pistons then the engine was probably reringed, new bearings and if it was balanced is questionable. Look at the rod caps, any grinding? Is the bearings std? If the engine has been aline honed then a "standard" timing chain install and/or just a stretched chain would be the reason for a loose chain. I would start measuring and looking for answers. Mondello book, Olds service manual, BTR's book have the specs so you can tell if the heads/block have been decked, bore tolerance, centerline. If it was Aline honed the main caps will be milled. If it was, you can get the undersized timing set from the Olds performance guys. What cam is in it, aftermarket? go to Harbor Freight, they have a battery operated digital scale cheap that reads lbs/grams up to 11lbs. Weigh each of your rods/pistons, if balanced they should be +/- a couple grams. If more then forget the balanced story. You can "balance" them while your at it. For your needs "street" this engine with a torque cam and lifters, probably new valve springs will be more engine than you need. Plenty of torque.

Kennybill

About the timing chain. The average stock measurement between the front main bearing housing bore and the front cam bearing with cam bearing installed is 2.430"-2.432". Without cam bearing 2.366"-2.368. That may help you with the timing chain question.

74sprint

Engines are not normally balanced at the factory, except the prototype production engine. They then use the weights from that engine to make the production runs. If you read about my engine build you'll see that I swapped rods and stock high compression pistons into my motor and didn't balance it, also it kicked *** on the street with a Sig Erson TQ30 cam. https://classicoldsmobile.com/forums...tml#post982565 1-2 shift is at 6,500 rpm and 2-3 shift is at 6,000 rpm.


Ray