06-11-2017, 02:52 AM
Hi, I have a question that I have been pondering regarding machining a piston. It occurs to me that this operation has been done millions of times before so I thought I would ask on here as I am sure that some of you guys will have done this before. Note that this is a first for me.
I have what we in the UK call a vintage motorcycle and you guys in America call an antique motorcycle. It is about 100 years old and the original pistons are cast iron. I need to replace the pistons to suit larger bores and pondered as to whether I should go for more modern aluminium pistons or cast iron ones as per the original. I have opted for cast iron ones.
The castings have been sized to suit the new bore sizes whilst maintaining the same wall thickness as the original pistons.
The machining operations themselves are simple enough but I do have one query regarding boring the wrist pin/gudgeon pin holes.
The holes obviously need to be through the centre of the internal cast bosses. Locating the centre of the boss in a line from the bottom of the skirt to the top of the crown seems to be straightforward. However I have been pondering on the best way to locate the centre line in the direction 90 degrees to this. Obviously these lines have to be translated onto the outside of the piston.
Any ideas on this question would be greatly appreciated along with any tips on workholding.
Here is a picture of a new casting alongside one of the original pistons.
![[Image: Build%20250.jpg]](http://i375.photobucket.com/albums/oo198/jpwbrookes/Harley%20F/Build%20250.jpg)
Thanks, John
I have what we in the UK call a vintage motorcycle and you guys in America call an antique motorcycle. It is about 100 years old and the original pistons are cast iron. I need to replace the pistons to suit larger bores and pondered as to whether I should go for more modern aluminium pistons or cast iron ones as per the original. I have opted for cast iron ones.
The castings have been sized to suit the new bore sizes whilst maintaining the same wall thickness as the original pistons.
The machining operations themselves are simple enough but I do have one query regarding boring the wrist pin/gudgeon pin holes.
The holes obviously need to be through the centre of the internal cast bosses. Locating the centre of the boss in a line from the bottom of the skirt to the top of the crown seems to be straightforward. However I have been pondering on the best way to locate the centre line in the direction 90 degrees to this. Obviously these lines have to be translated onto the outside of the piston.
Any ideas on this question would be greatly appreciated along with any tips on workholding.
Here is a picture of a new casting alongside one of the original pistons.
Thanks, John