Oil feed to Rocker box

[Gavin]

Just a random question I'm pondering:

There are 2 different sized holes in the bolt through which oil passes as it's fed to the rocker box. (65-306) How does one know if the engine requires the larger or smaller holed bolt? As far as i can see neither Roy Bacon or Haynes covers this wonderful detail. obviously there have been changes to the rocker box oil feed over the years. Any insights would be appreciated. thanks.

[Brian]

These bolts come with two different size holes, the small holes are oil feed to the rockers of the A10/7 series and the ones with large holes are oil drain bolts for the B33/31 series.

In the attached pic you can see a pipe running from the rear of the cylinder head down in front of the magneto, that pipe attaches to the crankcase and lets the oil in the cylinder head drain back down. The bolts with the large holes are used on both ends of this pipe.

[Peter in Aus]

Hi Gavan, use the ones with the small holes that gives more than enough oil up top, from memory they are about 1/16" holes, quite small any rate, some where in the forum there is a bit about them.
See you at Kal.
Peter 

[RichardL]

I believe this post from dpaddock (what happened to him?) may be the definitive answer regarding rocker feed holes:  https://www.a7a10.net/forum/index.php?topic=592.msg3432#msg3432  Also, if you choose, you can read my meanderings from 2008 leading up to learning this answer.

Richard L.

[Colsbeeza]

More here too Gavin.

https://www.a7a10.net/forum/index.php?topic=17105.0

My measurements verify that the standard size is 3/64".
Col