Scott Gardner wrote:
> In regards to engine balancing, I understand the idea of balancing
> the crankshaft and flywheel, but am a little unclear on balancing
> the piston/rod assembly.
The piston and rod are weight matched seperately ... Barney Gaylord
wrote on 1/12/97:
> Pistons are also critical to good balance, and the specification
> here is also usually all weighing the same within 1/2 gram.
> Material can be removed from the bottom edge of the piston
> skirt, or from the interior surfaces around the large boss that
> holds the wrist pin. I would not recommend removing any
> material from the interior in the vicinity of the ring grooves, as I
> have personally witnessed a piston failure because of this.
> For my MGA 1500 I just bought a new set of +.020" pistons.
> These are Aerolite 4-ring and came from Moss Motors inventory.
> Inside the cover of the box is printed the proclamation that these
> pistons are weight matched within 1/2 gram.
> Is it just a matter of removing metal from one or more piston/rod
> assemblies until all four are the same weight, or do you have to
> make sure the new center of gravity of the assembly lies along the >
>longitudinal axis of the rod?
Barney Gaylord wrote on 1/12/97:
> The connecting rods are the next critical item to balancing an
> engine. These are statically balanced on weighing scales.
> Two scales are used, placed under the extreme opposite ends
> of the rods (one rod at a time), and carefully located in the same
> position for each rod. The method here is to weigh all the rods
> first, find the rod with the lightest big end, also find the rod with
> the lightest small end. Then you remove weight from the ends
> of the heavier parts until the big ends all weigh the same and the
> small ends all weigh the same. Again material is removed from
> the non-contact surfaces. Maximum imbalance here is usually
> specified as all parts to be equal within 1/2 gram.
> From where is the extra metal usually removed? What is considered
> to be "good enough" when weighing the pistons and rods?
See Barney's post above.
> The pistons in the 1950 cc kit that Brit-Tek sells appear to have
> "eyebrows" cut into the otherwise flat surface of the pistons.
> These don't seem to be of any use, considering the face of the
> valve is parallel to the piston, and any collision would involve the
> entire face of the valve colliding with the piston at once. Perhaps
> the pistons in the 1950cc kit were originally designed for a
> different engine?
Exacty ... they are Lotus Twin Cam pistons.
Safety Fast! ... larry.g.unger@lmco.com
'61 MGA 1600 MkII
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