Date: Sat, 7 Dec 1996 17:31:42 -0800 From: Mike West Subject: Rod Balancing etc. Doing your rods. Finding the long ones and balancing. It's raining again. . stil actually, but particularly hard and constant. So you get another of the "how to" suckers. I've pulled the rods back off the crank for reasons that will become apparent and was determining the long ones from the short ones. The differences are fairly negligible but there is always a few thousandths of an inch variation. I just used the calipers between the bores and then "miked" the bores. Half the bore diameters plus the distance between the sides of the bores is the center to center distance. Now I have my "long, shorter, shorter still and shortest. It doesn't matter the accuracy of your calipers as long as they will be in error the same amount all the time. Then I thought of another way a blind man could do this. Put the rods on one of the gudgeon pins, well three anyway. Take the bearings out by the way, They are narrower than the boss. Now line up the big bores side to side. Now just feel along the bottom of the bore toward the wrist end and see if there is a difference of height. Or if you can see, run a staight edge across them. Any variation can be seen as light. You don't really care what the number is just which is higher or in the useage we are putting it, longer. When you've worked out long, medium and short, you put the odd rod that hasn't been measured in the middle of the two long and short ones and measure it against them. So with little or no tools you can "gauge" the four rods for long, thru short in no time. While playing with the rods I was running the scenario of balancing them thru my head. How can I do this in my shoddy hovel without "proper" equipment. Two shoestrings and a stick, so to speak. What you want is the same center of gravity or moment on all four rods to be the same. And also they should weigh the same. "No problemo, CG's of irregular shapes are one of my specialties!" Easy, even girls can do it. I learned it from a girl. :-) A trick I learned while launching sundry articles into space. The space boys want the CG of everything. I think they do that in planes too. Here's the trick: get something like a triangular scale that engineers and architects use. That's a ruler to you non-teckies. If you can't find something like that, then get a triangular scale. Now we need a balance beam scale of some dubious accuracy. You could use a stick with two shoe-strings as mentioned above. All you really want is something that balances evenly with the two strings out on the ends to tie rods to. Now me, I have a neighbor who has a triple beam Ohaus scale. Since I fix stuff for him, I have a little credit. So armed with my three sided scale and some rods and the Dremel, we are off to the neighbors. Beer, don't forget the beer. I forgot the scribe to make sharp lines on metal, we need that too. Uhhh, forgot the little six inch scale(ruler) for a straight edge. Alright, we're fully armed and at the neighbors. Clean the triple beam, oil it and zero it. He doesn't know about stuff like that. Weigh all the rods. Find the lightest one. VW says they may vary by weight 8 grams, they then turn around and say that they can be 10 grams difference in matching. Unaccepatable, you have any idea how much a gram weighs when you're spinning it at 5 or 6 thousand rpm? Bunches. OK, we have the lightest rod now we set up the triangular thing. Lay the light rod at right angles to the scale and find the point where it just balances there. This "right angle should be within Angstroms,so use your "good" eye". Holding it in place, put a scribe mark at the point of the scale on the side of the rod. Now - now - we forgot a gudgeon pin. Back to my house to get a gudgeon pin. OK, we're really fully armed now. :-) Take the rod you just marked the CG on, put it on the gudgeon pin with two more rods one on each side. Transfer the scribe mark to the other two and then take one off and put the odd one on and mark it too. "John, have you got an adjustable square I can use?" He has one. :-) Now we have the CG we want them all to adhere to when we're done and they all weigh the same. Put the light one aside, or if you're using the "stick n' string" method, tie it to the beam. Balance each of the rods in turn across the triangle and put a light mark there. They should all be heavy on the big end but maybe not. On the big end, there are areas where you can take off metal that won't affect the strength. These are shown in the Benley manual, but in case you don't have one, it's on the wrist of the rod where the flat spots are cut out for the bolts. The area on the wrist there is useless as far as strength of the rod is concerned. The Bentley says leave that little nub on the side of the rod up in the middle alone. It's an assembly reference. It should also be figured in on the logitudinal balance, so I'd do what they say. If you have to remove metal from the small end, I'd start by removing some of the casting flash they left up the sides. Then perhaps radiusing corners. So mine was all in the big end as mentioned and I just ground a little from each side of the wrist evenly, stop, check weight and re-balance to see how much the CG had moved. It doesn't take a lot to change either the weight or CG since this is steel and weighs a lot more than aluminum. There was 5-1/2 grams diff. in weight and 1/2"(12.5mm) diff in CG when I started. When I got done, there was no appreciable difference in weight, and the CG's were within a scribe line of each other. Approx. .010". (0.025mm) I'd say it was a 2 beer job, a lttle over an hour, maybe two, John drank them all tho. He did hold the dust pan when I cleaned up tho so that counts. :-) Considering the equipment, I don't think it was too bad a job. And the price was right. :-) If you look at the 10 grams as max, then the possible 1/10 gram I got, is 100 times better than a worst case stock part. When you think about it, you can beat VW at this, in the jungle with nothing but rocks, sticks and your boot laces. And a guy named John who drinks beer. :-) west "still pushin' back the darkness"