Connecting Rod Balance

[IH3444]

Have balanced a few engines. Made all the pistons weight the same by removing material under the piston from the wrist pin boss. Then also balanced the connecting rods by removing most of the material from the connecting rod big end, and by using the rod balance fixture shaved the small end until they were in balance big end to small end, then made all connecting rods weight the same. I would finish up with just taking a single stroke off the rod with a file, then re-weighting then until all weighted the same to within 1/4 gram. It does make a difference. Did a Porsche 2.7liter engine 911 engine this way also. Hot rod friend commented on how the engine spooled up like it was electric. Used 906 sprint cams, 296 duration, 444 lift, 107 overlap I remember. Opened the ports up to 37.5mm also. All flowed and matched ports. 5 angle valve job, all new valves. All 6 assemblies weighted to within 1/4 gram of each other, and to within 1/4 gram to each bank. Heaviest assembles go closest to flywheel, then next heaviest, finally the two last lightest assemblies. Good luck on whatever you decide. Mostly all production rods should be within 10 grams of each other.

 

[TractorGuy]

I am trying to become a little less OCD as I age but it doesn't always work out for me. How much was the salvage rod? Were it's matching rods available and in like condition? These are the first two questions I would consider before moving forward.

Here is a listing with 3 available on that auction site for around a 100 bucks each. You might ask this seller if they have matching casting numbers and are all good.

 

[CincyFlyer]

I am trying to become a little less OCD as I age but it doesn't always work out for me. How much was the salvage rod? Were it's matching rods available and in like condition? These are the first two questions I would consider before moving forward.

I was thinking exactly that; snag the rest of the set, maybe the pistons, etc. We always balanced things—even for low-speed engines ("truck cams")—quite a bit more closely than 11 grams.

 

[TimberHole]

An interesting development in my quest for rods which are reasonably close in balance. I’ve been studying the parts diagrams to see if the 1050 uses the same rod because the salvage yard has a 1050. It appears the early 850, 950 and 1050 all use a CH10683 rod and the later machines all use a CH10682 rod. I need a CH10683 but am starting to wonder if my salvage rod is a CH10682. It is dimensionally correct but a touch heavier. Hmmmmm. I don’t suppose anyone knows the difference in the early/late rods or engines?

 

[Barry 1]

An interesting development in my quest for rods which are reasonably close in balance. I’ve been studying the parts diagrams to see if the 1050 uses the same rod because the salvage yard has a 1050. It appears the early 850, 950 and 1050 all use a CH10683 rod and the later machines all use a CH10682 rod. I need a CH10683 but am starting to wonder if my salvage rod is a CH10682. It is dimensionally correct but a touch heavier. Hmmmmm. I don’t suppose anyone knows the difference in the early/late rods or engines?

Go look again- 682 is for 850 only

 

[TimberHole]

Go look again- 682 is for 850 only

I don't think I misread it. There are 3 parts diagrams:

Early 850
Early 950 and 1050
Late 850,950, and 1050

The 682 Rod was used on the early 850 and all late models. Still don't know what the difference in the rods is. Went back to the salvage yard today and found a Rod that is very close in weight but a different casting number. I'll have to inspect it but I'm pretty sure it is my solution. After all, even if I buy a new Rod the casting number isn't going to match.

I'll report back after firther research.

 

[Tractor Seabee]

My deceased FIL was a master mechanic specializing in engine rebuilds. He would never replace only one rod or piston. He always procured a balanced set. Said labor wise it was cheaper to buy the set that mess around trying to match up stuff by trimilation (my dad's word for trimming till it fit).

In my industrial machinery days I overhauled/rebuilt large air and refrigeration compressors. Even in the days of hand fitted babbitt bearings for 1 and 2 cylinder compressors running at 300-500 RPM we balanced pieces by weight. Most of those had a 3 piece rod; journal box, wrist pin box, and the rod with a flange on each end. Shim packs for each bearing box and the flanges. A lot of heavy hand work. A 2 cyl 24" X 24" compressor each component had to be moved and handled with a chain fall. Crank shafts had 3 bearings within the body plus 1 or 2 outside on both sides of a huge flywheel. A lot of stuff to balance and align before the days of lasers and computers. Cost of labor finally pushed that work from the field into machine shops. Still had to fir and align it all on site.

Those were the days when craftsmen were proud of there work and abilities. We enjoyed what we were doing and loved to hear a smooth running machine when done instead of whump! whump!. When high speed machines; rotary and piston type the whole industry changed. A rebuild was a complete kit from the factory. All pre balanced and fit.

Ron

 

[TimberHole]

I am trying to become a little less OCD as I age but it doesn't always work out for me. How much was the salvage rod? Were it's matching rods available and in like condition? These are the first two questions I would consider before moving forward.

Here is a listing with 3 available on that auction site for around a 100 bucks each. You might ask this seller if they have matching casting numbers and are all good.

The salvage Rod was $50.00. As mentioned I found a Rod that weighs between the two original rods being reused. All rods are within 6 or 7 grams. I'm calling that good. The guy at the salvage yard offered to trade this new Rod for the heavy Rod. I intended to purchase the second Rod but he insisted trading rods was ok. Good people! I pressed out the old bushings tonight. Hopefully install the liners, pistons and rods this week. Should go fast after that.