Would like some advise regards the oil feed banjo bolts used on iron head B31 and B33 engines.
Are these the ones with the 1/32" small hole Part #65-306.
Can the same bolts, but with the 1/8" hole, be used in the same application, or will there be too much oil fed to the rockers, and not returned to the tank. ie (less restriction)
The larger hole bolts are used on the oil return pipe, just wondering if the small hole bolts are specifically used on the feed side on these iron head engines. May-be they are used post 1952.
Thanks in advance
Keith Atkinson

email (option): keithatkinson@hotmail.com

Small holes for feed, large hole for drain. Otherwise if guides are a bit worn you'll get lots of smoke. If all you have is large, fill holes with solder or Araldite and drill hole smaller.

Hi Kieth..The banjos with the small hole are used on the feed side and the ones with the large hole on the return...

An increase in the oil supply is beneficial to these engines but the return banjos deliver too much oil..

When building these engines I drill out the feed banjos to a 1mm hole size...

Another point to note is a change to the rocker feed pipe to reduce 'bias' in the oil feed between the inlet and exhaust spindles...

Early engines (up to and including ZB) used an oil pipe that fed into the brass 'boss' on the inlet side of the supply and then went from there to the boss on the exhaust side of the supply...

This was found to bias the supply to the inlet side...Later engines had a pipe that fed into a 'T' fitting positioned centrally between the inlet and exhaust bosses and from there to each boss...Ian

Thanks for your reply;
Interesting information regards the different rocker feed pipe up to and including ZB. I thought there was only the T type used.
I would think the T type eliminates any bias.
I will drill the small hole banjo's to 1 mm for the feed, and only use the large hole banjo's on the oil drain.
Keith

I have checked my XB31 engine running with the covers removed.
I find I have used the larger hole banjo's on the rocker spindle feed.
That's why I have a strong stream of oil coming out of the rocker drain holes, just under the pushrod arms.
Still though, there is oil spitting out of the return pipe inside the tank.
I think maybe a fair amount of the oil is being recirculated, rather than if I had the correct small hole banjo's, and more oil would be returned to the tank, and hence through the filter.
Opening up the small hole to 1mm makes a lot of sense, approx. 8 or 9 thou bigger than 1/32"
These feed banjo hole sizes would have been designed in conjunction with the size of the hole in the tank return pipe surely.
Thanks for your advise.
Keith A

email (option): keithatkinson@hotmail.com

If your running both holes the same large size the problems will be oil burning due to oil going down the guides when the oil builds up in the rocker box and cannot return properly.

It may be that with the later rocker pipe fitted larger feed holes are not required...

However, on more than one occasion I have come across engines that have had new guides fitted but then have an oiling problem (deficiency) to the guides (via the rockers)..

The resulting dry guide can be heard squeaking and one old boy told me to put my finger over the return pipe in the tank to get a bit more oil up there...

I should note here that in each case the valve to guide clearances were correct and that this problem only occurred after new parts were fitted and the valve to guide clearance was at its minimum before any wear took place...

An .008"-.010" increase in size doesn't sound much but remember the cross sectional area of a hole increases disproportionately to its diameter..

Anyway...My own 1951 700cc plus ZB33 is still running its original 'in line' rocker feed pipe which may produce a bias but with the increase in feed hole size I've never had a problem with that...

I used to do the mod. only on tuned engines but for the last 20 years or so I have done it on all the engines I have rebuilt...

This won't result in 'over oiling' of the top end or cause any other identifiable problems...but it does ensure an adequate supply under all conditions...Ian