sandcast 750 oil return pills (jets?) in head

[K0Kid]

   Many years ago I rebuilt my crashed SC and used a number of later model K4, I think, mostly cosmetic parts. One of the few engine parts, I changed were the little oil return jets in the head. At the time I had a choice as the holes were different sizes. The later ones were larger or could have been smaller. I assumed at the time that since the later model had the larger jets that Honda decided this on purpose opening them up for easier oil drain back so I switched them. I also assume their purpose was to retain just enough oil in the valve train as needed but the manual didn't discuss them ( I'm not even sure I used a manual as the engine was so simple and intuitive that it went back together without a hitch.
   Who really knows about these jets, their purpose and optimization. I need to reassemble the motor once again and wonder if I should change them back. Engine had lots of miles and obviously has had little effect on the engine as far as wear is concerned.
Ross  

[tomcourtney]

One big problem the early heads had was people that did not do regular oil and filter changes.
I have seen numerous broken engines where one of the two oil feed hole to the cam boxes would block up with crud and deprive oil to that cam box and then half the cam would run dry and seize, the camshaft would often break in half.
Often the engine would still run on two cylinders at reduced power.
I followed a friend home about 20 miles with his engine running on two and when we pulled the engine apart and found a blocked oil feed hole and a dry cam box with a seized broken cam we were amazed.
Revisions to the head were made with modification with a removable oil feed orifice feeding each cam box.
 These can be removed for cleaning and changed out on reco, the later larger type have a strainer and will let engines run longer with dirty oil before they blockup.

This would be on the list of the top ten killers of CB750 engines along with broken drive chains busted crankcases and Cam chains, bent valves, and others  

[K0Kid]

Tom,
Bungee cords being eaten do a good job of busting crankcase don't ask how I know!
i'm curious to know more about strainers as the "pills " or orifices were quite small in diameter and the oil holes even smaller.
Could you rephrase your comment as it is a little hard to understand due to something being left out?
thx ross