Race Engine Forum UK

Hi,

I'm about to balance my pistons and thought the best place to remove material was from the flat where the gudgeon pin is located. The pin is set back 5mm from the flat face and I estimate I may have to mill off 1.0 -1.5mm. The pin is loose in the piston and a press fit in the rod. I'll mill both sides equally.

I need to loose as much as 8gr on one of the pistons and after cutting 8gr off a piece of ali bar, it was easy to see that this was A LOT to loose from inside the back of the casting, where I originally thought was a safe place to grind.

Any thoughts would be greatly appreciated.

Thanks,

Ben

My thoughts:

1. 8gm is nothing on a reciprocating mass of over 900gm or so.
2. The piston and rod masses do not affect the crankshaft balance on a flat plane 4 cyl engine.
3. 8gm of alloy is a lot to remove, sure!
4. Milling in a redundant region may be OK, but depending on the piston design of course - it is more effective (higher removal rate) to remove metal by turning (lathe) around the balancing band region shown below (marked black top left just inside skirt).
5. I don't know what your piston looks like so publish a photo or 2 please showing the areas you are thinking of machining. That way others can see it all too.

I assume the pistons are not on the rods at present of course, else you would not have been able to weigh them..

Check your rod end-over-end weights too.

GC