I am rebuilding a motor for my 1914 Touring and have bought a weigh scale. I now need to know what are acceptable limits between matching parts. Three of the pistons weigh in at 703 grams while the fourth is at 700 grams.
Is three grams close enough?
On the rods the differences are somewhat larger, 10g on the pin ends and 25g on overall weight. Is there a acceptable rule of thumb to determine weight differences?
I appreciate all input, there are no 'wrong' answers...
Tony I worked on my rods to get them all within 1 or 2g. Big and little ends. Pistons were all within 1g.
I did sort thru several rods to start close then started grinding and some drilling. don't get the grindings on the new babbit.
The biggest difference you will notice is in the flywheel and triple gears. There is a lot of weight spinning there. I recently did a Scat crank job and after dynamically balancing crank to flywheel drove the car down the road thought I would notice big difference in how it ran but it still sound like a Model T instead of new car. I guess it is still just a flat head engine.When Balancing crank to flywheel you can use the difference in weights of triple gears to your advantage on some engines, less drilling.
Joe, I'm surprised that after dynamically balancing the crank and flywheel, you didn't notice any difference. Did you insure VERY low run out tolerance from the front of the crankshaft through the transmission shaft and driving plate? The most perfectly balanced components will cancel a smooth running engine if they are literally lobbing around.
Especially important is the mating surface of the flywheel to the transmission shaft flange. Not many of these are true and require considerable effort to correct.
The 25 grams is unacceptable,it's going to cause alot of thumping and cause harm.
As Gene mentioned 1 or 2 grams acceptable.
On average I believe Ford had balanced the engines to within 6 grams.
If the rods are that far off I would suggest you have the crank taken to a balancing shop,have them weigh the rods/pistons and build a bob weight for each of the throws as seen in the attached picture. That way you can make the correction on the crank rather than the rods.
I know the average for new parts is about 4 grams.
Same with the flywheel,if magnets are now in a different position it will need balancing.
Our machine reads to the tenth of a gram so that's what we aim for.
A smooth running engine means two things,long life for the engine and happy customers.
J and M Machine.