Mopar Muscle Association UK

Yep the very one Dunc. It should now be 8 thou PTW clearance. As Les recommended.

Carl wrote:Yep the very one Dunc. It should now be 8 thou PTW clearance. As Les recommended.

is this not excessive les ?????? i thought 4.5 -5 what make pistons are they, do some forged grow more than others ???

Cannonball wrote:

Carl wrote:Yep the very one Dunc. It should now be 8 thou PTW clearance. As Les recommended.

is this not excessive les ?????? i thought 4.5 -5 what make pistons are they, do some forged grow more than others ???

Duncan,
It's 0.008" on Diameter, which equates to .004" clearance

You sure about that Mark?
I thought piston to wall clearance is the difference between the piston skirt diameter and the cylinder diameter.
0.008" sounds too much to me, 0.004" sounds about right for a forged piston in a small block.

I was always taught 1 thou clearance per inch of bore 4 thou is about right.

Mick70RR wrote:You sure about that Mark?
I thought piston to wall clearance is the difference between the piston skirt diameter and the cylinder diameter.
0.008" sounds too much to me, 0.004" sounds about right for a forged piston in a small block.

As I understand the bore diameter is now 0.008" bigger than the Piston skirt diameter. Therefore the clearance is 0.004"

mopar_mark wrote:

Mick70RR wrote:You sure about that Mark?
I thought piston to wall clearance is the difference between the piston skirt diameter and the cylinder diameter.
0.008" sounds too much to me, 0.004" sounds about right for a forged piston in a small block.

As I understand the bore diameter is now 0.008" bigger than the Piston skirt diameter. Therefore the clearance is 0.004"

I'd say the clearance is 0.008".

Mick70RR wrote:

mopar_mark wrote:

Mick70RR wrote:You sure about that Mark?
I thought piston to wall clearance is the difference between the piston skirt diameter and the cylinder diameter.
0.008" sounds too much to me, 0.004" sounds about right for a forged piston in a small block.

As I understand the bore diameter is now 0.008" bigger than the Piston skirt diameter. Therefore the clearance is 0.004"

I'd say the clearance is 0.008".

I would too....

Well its 0.008 now so cant do anything about it now whether its right or wrong.

Confused?

Dave wrote:Confused?

Yep Im sure Les will clarify

Am I right in assuming that if the piston was perfectly centred in the bore, a 0.008 thou clearance would mean you could, in theory, run a 0.004 feeler gauge all round the piston. If the piston was pushed flush against the bore...180 deg opposite point where it touches would take a 0.008 gauge??

Yep that's about the size of it Steve

Gotcha....just trying to learn from your thread Carl as its really interesting....

so the discussion at the moment is whether you should be able to run a 0.004" gauge round or a 0.002" gauge?? Sorry if its a daft question mate but Im watching your build closely and want to stay with the plot....

Steve wrote:Gotcha....just trying to learn from your thread Carl as its really interesting....

so the discussion at the moment is whether you should be able to run a 0.004" gauge round or a 0.002" gauge?? Sorry if its a daft question mate but Im watching your build closely and want to stay with the plot....

And that clearence depends on the piston material. Forged pistons expand more. High silicon forgings less so. And cast pistons less again. I would be wanting 4 thou each side so a 8 though wider bore.