I have just spoken to the previous owner (an old friend of mine) and he told me that during his ownership he took a light skim off the cylinder head/exhaust rocker box mating face to remove some pitting to the surface that was causing oil to seep.He assured me that he was still able to set the exhau...

I purchased new end caps but they proved to be thicker than the existing ones which only exacerbated the problem.

I seem to be getting out of sync with my responses:I apologise for that,I am new to this!
The inlet side appears to be fine with,as you mentioned, some threads remaining underneath. I think that my next move is to check the pushrod lengths.

I did take care to ensure that the pushrod end was correctly located.

The new gasket that I used compressed very badly so next time I employed one of the Aluminium type. I now have two of them in place and that just about allows the adjusting screw to protrude far enough through the rocker arm. It works, but it isn't right!

Just to make certain I even removed the lifter entirely!

It was fine before I removed the head. I was sure that I replaced them in their original positions but, just to be sure, when I next removed the rocker box I measured the pushrods and found them to be the same length

I have been a club member for more than a year but this is the first time to seek advice. I have a 1938 NH which was running well when it came to me. Recently I removed the cylinder head in order to replace the pushrod tube rubbers to cure a niggling oil leak. When everything was back in place I dis...