Small update on the Skyline.
I figured while I had the Rb30 in bits, I was going to lend my hand at balancing the innards. How hard could it be?
I managed to pick up a set of old school 'teeter' scales (18mnths back). Came from an old wrecking yard building where they were used to measure the weight of paint for colour matching on cars. Very well made, and able to read down to the closest 1/2 gram off the scale, and with enough scale separation to extrapolate to the tenth of a gram!
After weighing all the rods, pistons and pins, I did a little research into how things 'should' be done. According to all the info I could be bothered to read, after the rods had been weighed, the big end (or little end) needed to be weighed. From that, you are able to work out the opposing end by subtracting the end weight from the total.
Sound easy don't it!
Problem is 'in' the weighing of the ends. To weigh an end properly, the rod needs to be perfectly horizontal as not to load/unload the end being weighed.
The opposing end needs to be supported at its center pivot while not imposing ANY friction to it turning, or incorrect weight is measured.
And the end being weighed also needs to be 'weighed' from the center of its pivot.
O.k, attempt #1 at weighing big ends.
As the scales I have teeter from one side the the other, I couldn't support the rod directly onto the scale surface, as the scale movement would push against where the little end was being supported and imparting a friction onto the pivot. So I devised to hang a length of fishing line over the edge of the scale (as vertical as I could measure to cancel out loading, and as long as practical to help limit angle change) with a loop in the end to connect to the rod bolt between the beaing cap and it's mating surface, which happens to be the center of the big end pivot.
With this done, I also had to figure how to support the little end.
I figured that the piston pin would be great. So I used 2 pistons to support the pin and rod. But this proved to be non ideal, as it was inducing at least a 5gram friction loss due to oil drag. After the scale had settled, I would load the scale and let it osilate till it settled again, and it would show a consistant inconsistancy.
Try #2
I then substituted the piston pin for a short length of 20 od plastic conduit, which was lubed as best I could. It worked better, but was still giving a 2gram variation as it was turning and moving in the pistons as the scale settled.
Try #3
I then figured I'd need to support the little end the same way as the big end to eliminate friction. After a bit of thought, (light blub moment) I balanced the little end on the point of a screw as close as I could measure to the center of it's pivot. Bingo! I was now able to duplicate readings to the 1/4 of a gram, and if I was to load the scale the same way each time, the error was down to less than 1/10 of a gram!
At that point, I also realised that the rod had to be exactly horizontal for a meaniful comparo in the future. So I shimmed up the screw to get the whole thing spot on.
I started noting down readings I was getting. About halfway through the set, I realized that there was an inconsistancy in my method. The problem was without fully bolting the caps down (I had to leave a small gap to allow the fishing line to loop the rod bolt and still move freely) I was essentialy introducing a variance I couldn't replicate on all the rods equaly.
So, I fully removed the caps and nuts and placed them on the scale itself rather than on the rod. This allowed me to check all the weights much quicker.
But thinking about this more, this method was also inaccurate because the weight of the rod caps wasn't consistant either, and that would compromise all the readings I had already recorded.
And in reality, this is a problem which isn't/wasn't addressed in any of the info I had read on the net. Being a novice at balancing, I would have thought that this would have been something that would have been though of and sovled decades ago. But I couldn't find anything about it on the net.
So I had a friendly chat with my machinist bloke. I asked him a few Q's in general about balancing. He only balances to the nearest gram when he balances bits, as his setup is only repeatable to the 1/2 gram. (YAY, I win!)
He also doesn't balance the rod caps. I threw in the idea that even if the big end weights were the same, the weight arond them may not be evenly distributed. But he still maintained that it wasn't needed.
Weigh the rod first, then weigh the big end. Work out you little end and balance those first. Go back and weigh the big ends, then match them up.
(And the bit of advice which only comes with experience, GOLD!) Don't take weight off the pistons, take it off the corresponding little end. Far less steel needs to be taken off v's alloy from the piston. He is very reluctant to take any material off pistons at all. His words "Rods are inherintly far stronger than needed, esspesialy compared to pistons. So take weight from them instead."
So armed with this new knowledge I went back to the drawing board. To get my figures to fit 100%, I would have to balance the rod caps anyway. So I did. After they were done, I re-weighed rods without the caps and nuts, as now they cancelled each other out alltogether.
I then balanced the little ends, but found I fucked up an instead of taking .25gram off one of the little ends, I took off 2.5grams!!
So after fixing that, I balance the rod side of the big ends.
ALL DONE!
I will have to post up some pics to make the whole story a little more understandable.
Also, does anyone have an opinion about balancing the rod caps first? As I think its vital, but no-one seems to bother.
Damo