How do you weigh a rod? With bearing and bolts or not?

[Ho Hum 74]

hi all,

How do you weigh a rod? Do you weigh it with small end bearing and bolts and nuts or without?

Thanks

tristan

[911pcars]

Weigh it with all the pieces that will go into the engine (rod, cap, bearings, fasteners).

If you're referring to weighing for balancing. You also have to determine the big and small end weights, then calculate this with the weight of the pistons, rings and wrist pins, retaining clips and the crankshaft.

Sherwood
http://members.rennlist.org/911pcars

[Ho Hum 74]

Weel, Wayne has the weights in his book but doesn't say how those are measured. Do you mean with ALL the bearings, even the big end ones?

Thanks for your help.
Tristan

[911pcars]

The connecting rod bearing (big end) is part of the rotating weight so this must be factored into "balancing" the engine.

If I may ask, what are you trying to accomplish?

Sherwood

[Ho Hum 74]

I'm trying to replace a rod that was damaged and was asked what weight group the rod was from. My machine shop weighed the rod at 660g including small end bearing bolts and nuts. Is this the correct way?

[911pcars]

Triston,
Yes. In this case, you weigh the connecting rod and fasteners except the bearing shells. What would be more important is to get it as close as possible to the opposite con rod.

Sherwood

[Ho Hum 74]

Thanks Sherwood, I should have been more clear!

[Fishcop]

So the Poms got up Tristan....

I am sad

[Ho Hum 74]

Damn. Damn. Damn! Here in the US we get it 3 days delayed. So I was hoping to tape the game and watch it this weekend thinking I was isolated from the rest of the rugby world. Oh well, I was hoping for wallaby win. What the hell. How the heck can the poms have taken it? You guys played so awesomely against nz. What happened?

[Fishcop]

I'm really sorry I spoiled it for you then!

I won't say any more until you watch it.... it was a simply an awesome game and the poms played better. Jonny Wilkinson won it for them with that amazing kicking ability.

[snowman]

On a flat 6, opposed engine, or even a straight 6 the process for balancing is the same. Unlike a V type engine where the rotating and reciprocating weights are needed to calculate the necessary bob weights, a flat 6 needs only to have everything the same weight, the opposed weights can also be matched if there is some discrepency in weights.

First the pistons, with wrist pins, rings, clips are measured for weight. The lightest one becomes the "standard". All other pistons are machined in some non important place on the back side, and or the inside of the wrist pins is ground out until all are equal to the lightest or standard one.

Next the large end of the rods are weighed, just the rod with fasteners. The rod is placed in a horizontal position with bearings supporting both the big end and small end. The big end is held on a scale, the small end is just held. That way the weight of just the big ends is obtained. Again the lightest one is found and becomes the standard. Next all the big ends are ground or sanded on the boss on the bottom of the big end. Additoonal info on the "bearings" that hold the rod for measurement. The bearings are NOT the ones used in the engine. They are high quality ball bearings that allow the rod to be supported without any lateral friction. They should be just small enough to fit into the rod openings (fixed bearings with round pieces pressed on them). Once the rod is horizontal it is lifted at one end, just a little. The support must not wiggle when the rod is lifted from it. This insures that the rod has no lateral force on it. You just have to see a picture to understand this setup. See ref at end.

Finally the rods are weighed with the fasteners. the lightest becomes the standard. The small end is ground or sanded until the weights of the entire rod, with fasteners are equal to the standard one. Note this process combines the total rod weight and weight of the small end in one single process. The small end can also be weighed just like the big end, but it is much more difficult to do the same way accurately. Using a little simple math it can be shown that weighing the total weight is exactly the same thing as measuring the small end seperately, but much simpler and more accurate. (note this is ONLY TRUE if the big ends have been matched first).

Bearing shells are generally not weighed because they are almost always exactly the same weight. In a V type engine the weight of the bearing shells is important, in a flat 6, it is not needed for anything just because they are all the same. If one were anal about it the bearing shells could be included in the big end and smalll end steps of the process.

The crank and flywheel are balanced togather or seperately. The weights of the rods and pistons are not needed for this type of engine. Only V type engines need consider the rod and piston weights. All straight types, flat opposed types need not.

A good referance is "Engine Blueprinting" by Rick Voegelin, ISBN 0-931472-21-0 Part No. 21-0. Mostly chevy stuff, but applicable to any engine. The book has good pictures of all the steps, machining, balancing, porting, all are good for any engine.