7 Piston Shuffle

Mick at John Sidney Racing referred me to another workshop when they realised that they were not able to push the pins out of the pistons.  This morning I drove about 40 mins to go and get the pistons swapped over on the rods.  The guys in the workshop were real nice fellas.  First step was to separate the pistons from the rods.

IMG_2048  IMG_2049

After cleaning the pins and piston I reordered them to match the cylinder sizes as calculated.  In order to get the pins back in you need to heat them with an oxy acetylene torch.

IMG_2054 IMG_2055  IMG_2051 IMG_2052

They made it look so easy.  It makes a difference when you know what you are doing and have the right tools!

Balancing Act

Time to balance the Piston/Rod assemblies.  First I weighed each assembly.  I also then made a jig in order to weigh each end and measure the weight distribution.  The actual values are not important, but rather the relative values to understand the where the weight is for each assembly.  I found the only way I could get a consistent reading was to place a steel weight on top of the piston to hold it frim in the Vee Block.

When it came to weighing the Piston end, I really struggled to get a repeatable result.  I found that any twist or torsion on the scales affected the reading.  I placed a couple of skewers under the Vee Block on the scales (to act as rollers) to eliminate any stress, and the numbers became repeatable!

IMG_2068  IMG_2066 IMG_2065

The results were as follows (all weights in grams):

Cylinder Total Big End   Piston End   Adjustment
1 1459 440 +3 1164 +6 -3 Piston
2 1461 444 +7 1162 +4 -5 Big End
3 1458 445 +8 1161 +3 -3 Big End
4 1461 447 +10 1161 +3 -5 Big End
5 1457 440 +3 1158 0 -2 Big End
6 1455 437 0 1163 +5
7 1460 445 +8 1166 +8 -2 Both Ends
8 1461 443 +6 1170 +12 -4 Piston

I worked out the adjustments required as shown in the right hand column of the table above.  For the Piston end adjustments I enarged the drilled holes in the bottom of the pistons and also ground a little off of the webs.  The Big Ends were pretty easy to adjust – I ground metal off using an angle grinder.

IMG_2069  IMG_2070 IMG_2071

Once all of the adjustments were made, I weighed everything again.  I can’t believe that I actually got them this close, but here it is.

Cylinder Total Big End   Piston End  
1 1456 441 +2 999 0
2 1457 441 +2 1001 +2
3 1456 439 0 1001 +2
4 1457 440 +1 1001 +2
5 1457 449 +10 1002 +3
6 1455 442 +3 1001 +2
7 1456 442 +3 1003 +4
8 1457 442 +3 1001 +2

It is interesting that number 5 is heavy at the Big End.  Number 5 Piston and Rod were untouched so this is as it left the factory.  I will take a couple of grams off of the Big End of number 5 to improve its balance.


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