16H piston in an ES2

Previously andy_marks wrote:

I have got a NOS hepolite piston for my 1951 ES2 and I have a couple of questions, firstly what skirt clearance should I get it rebored with? In the past I have always bought new pistons that have had the relevant info in the box with them, but this one doesn't.

Secondly, I know I need to machine the skirt to clear the flywheels and probably need to put valve pockets in the top. What sort of clearance is reccomended between the valves and the piston when turning the engine over? Asearch on the internet has returned a huge variety of suggestions!

Finally, if I do need to put pockets in the top, I'm a bit concerned that the top of the piston is only about 0.2 inch thick and putting valve pockets in it could narrow this down to dangerously thin? Any idea how much I need to leave as a minimum safe thickness?

Thanks in advance

Andy.

hepolite pistons should have a clerance of 5 or 6tho..

Gpm pistons 4 and 1/2 tho.i think the ring grooves are thicker on a es2.

could this be because the side valve is lower compresion ?

i,m no expert so would ask mike pemberton for advise

he is always helpful...i think he would also suggest using a gpm piston

they work fine when bored correctly.as for cutting valve pockets.is it worth the trouble when there are pistons availible.

good luck.... tony.

Previously andy_marks wrote:

I have got a NOS hepolite piston for my 1951 ES2 and I have a couple of questions, firstly what skirt clearance should I get it rebored with? In the past I have always bought new pistons that have had the relevant info in the box with them, but this one doesn't.

Secondly, I know I need to machine the skirt to clear the flywheels and probably need to put valve pockets in the top. What sort of clearance is reccomended between the valves and the piston when turning the engine over? Asearch on the internet has returned a huge variety of suggestions!

Finally, if I do need to put pockets in the top, I'm a bit concerned that the top of the piston is only about 0.2 inch thick and putting valve pockets in it could narrow this down to dangerously thin? Any idea how much I need to leave as a minimum safe thickness?

Thanks in advance

Andy

Hi Andy

Normally the bore size is set and the clearance is on the piston. So 79mm (3.1102") is the standard bore, The WD workshop manual says the piston diameter is 3.106" at the skirt for the 16HThis gives a clearance of 0.0042 inches. (the old adage of 1.5 thou per inch of bore!).

The Franks book says that the clearance measured at the skirt with a feeler gauge on all models is 0.005". Not the most accurate ways of measuring though.

With regard to the valve pocket sizes, it would be worth doing a dummy build with some blue tack on the piston crown, slowly turn the engine and see what marks the valves make (if any) before machining the pockets.

I had to do the same with my pre-war ES2 using a later piston. Flycutting the underside of the piston on a Boxford lathe needed some (successful) lateral thinking

Colin

Previously andy_marks wrote:

I have got a NOS hepolite piston for my 1951 ES2 and I have a couple of questions, firstly what skirt clearance should I get it rebored with? In the past I have always bought new pistons that have had the relevant info in the box with them, but this one doesn't.

Secondly, I know I need to machine the skirt to clear the flywheels and probably need to put valve pockets in the top. What sort of clearance is reccomended between the valves and the piston when turning the engine over? Asearch on the internet has returned a huge variety of suggestions!

Finally, if I do need to put pockets in the top, I'm a bit concerned that the top of the piston is only about 0.2 inch thick and putting valve pockets in it could narrow this down to dangerously thin? Any idea how much I need to leave as a minimum safe thickness?

Thanks in advance

Andy

Hi Andy,

I run a WD 16H piston in my 1951 ES-2 without any need for valve pockets. I dry assembled the engine and covered piston top with plasticine. Spun the engine over several times and the valves didn't make an impression in the plasticine. Only thing I did was chamfer the top edge of thepiston to ensure it cleared the lip of the head. Advantage of the 16H piston is that the compression ratio is slightly higher due to the slight dome where as the ES-2 piston is a flat top.

regards, Ian