Jowett 7 piston rings

[k. rogers]

This evening, managed to break a new oil control piston ring on the Kingfisher's engine while assembling one cylinder, despite using a special tool I bought instead of my fingers! Needless to say, I won't bother with the tool again as I assembled the other cylinder successfully without. Among my spare pistons and rings, I found a new replacement (or so I thought) and set about filing the gap to size. When I fitted it to the piston I found the clearance in the groove was 2thou as opposed to the 1thou on the other rings. Would any of you expert engineers out there know if this is excessive in which case I will have to source a replacement from somewhere - club spares reckon they are a bit thin on the ground!

[Tony Fearn]

Hi Ken,
I'm not ignoring you, I just don't know.
Perhaps a call to Pre-War Registrar might help.

Tony.

[johnairey]

Item 4. of instructions on fitting Deves replacment piston rings.
Check for wear in the top grooves by installing a top compression ring, holding the face of the ring flush with the ring land and inserting a feeler gauge between the upper side of the of the ring and groove. If the clearance is greater is greater than .006" the groove has excessive wear and the piston should be replaced or possibly regrooved.
Hope this helps.

[k. rogers]

Thanks for that, John. Since placing this request on the forum I have done a little research on the net and through some books. It would seem that although the measurements vary from make to make the acceptable clearance is anywhere between 1 and 6 thou! However, access to a Wellworthy catalogue of 1930s pistons and rings indicated 1.5 to 2 thou as being ok, therefore, mine should be fine!