Crank bearing oil feed hole chamfer

[reclino]

Discussing my engine build with Fred Apgar, he suggested cutting a small chamfer on back of the crank bearing shells. He indicated this was done on race built engines to improve oil flow.
I got out the old bearings today to see how difficult this was. Using a new 118 deg drill bit (9/32") it was very easy to lightly chamfer the backside. I was initially concerned the drill bit would grab and self feed, but with this large a bit it's very easy to control. There was more chatter in the cut than I liked, so I tried a small carbide Burr by hand and it left a very smooth finish, and took almost no pressure to form a chip.
My case is still wrapped up and clean, are the oil feel holes only on the bottom case half?

[otto_kretschmer]

I wouldn't do this on the back side of the bearing but I guess it can't hurt. The hole in the bearing has to be inline with the hole in the block. I would think a better argument would be made for a chamfer on the crank side of the bearing.

[Neil Harvey]

Before you do anything look at what is in front of you. Then the decision of what to do will become obvious.

Hint, look at the galley hole in the bearing housing. Then look at the hole in the bearing shell. See anything that seems odd and could be changed and why?

[dannobee]

^^^^this^^^^

On every race engine that I can think of, we always followed what Neil is saying.

And use a countersink bit instead of a drill bit to get the chamfer. Drill bits are for drilling holes.

[faapgar]

Neil said it is obvious if you look.In 1977 Porsche changed the oil delivery to the main bearings.When you look at the left bearing it shows a shiny aluminum disc around the feed hole.They did this 1st on Carrera 3.0 & 3.0 Turbo.If you look at the saddle boss it looks like you stuck your pinky into a cake and left a depression.The oil delivery hole is also increased in size.Oil delivery hole sits about 4-5mm below the bearing.I will try and get a case off the shelf tommorow.I have a 77 turbo case.On bearings that are older and have a dark stain around the delivery hole in the back of the bearing the need for the chamfer is obvious.Maybe Neil will expound on the change to the main bearing saddle for the change of delivery.Fred

[reclino]

From a manufacturing engineering point of view the large feed hole in the case makes it cheaper and easier for the feed hole.in.the bearing shell to always line up. It will also allow a change in flow rate up or down by changing the size of the hole in the shell, instead of changing a case.
It seems to me Neil is suggesting drill the oil hole in the bearing out to.the full size of the case.
I guess my question is, should I make the chamfer a bit bigger Fred or do you think this is good? It's maybe 1 mm on the one shown above.
The first few done with a drill bit were larger.



Neil, I respect the wisdom and experience you bring to this forum, but your above response didn't really hit the mark for me. Carefully rebuilding a Porsche engine is not obvious or simple. Your answer while interesting was a non answer because no details about your preferred bearing hole were provided.

I don't plan on putting this engine together based on my best guess of some half described detail. I find it's always better to ask questions and practice something you have never done before, especially when your following verbal instructions from a subject mater expert, thanks to Fred Apgar and Peter Dawe for providing me with some very helpful suggestions.

[356911930]

What were their suggestions?

Rahl

[reclino]

Reverse engineering and selling wastegate parts for the 930 has really been a rewarding experience. My car hobby expenses are somewhat offset by the steady sale of rebuild kits. A completely unexpected side effect of selling these kits to so many different shops that are experts on the 930 is I am able to chat with these guys about my project goals. Yes it's taking me a very long time but forward progress on the 930 happens from time to time. Every engine builder I have talked to has been helpful in some way or another. Peter Dawe went above and beyond over the course of a couple of phone calls discussing my build and how to do much of it myself, but which parts to job out. I haven't had a chance to meet him yet, but did find out about a machinist he uses,.and was able to get all my engine parts to him last year.
Fred Apgar is "local" here in North Carolina and pointed me towards a number of shops in Mooresville NC,
H M Elliot Mooresville for REM finishing cam sprockets and cam shafts, and coating skirts on my pistons.
Piranah ultrasonic Mooresville, cleaning.the oil coolers and oil tank.
Bagshaw fabrication Mooresville for welding a bung on the oil cooler for the fan temp sensor
Stratford metal finishing for CAD plating a bunch of engine parts.

It's also interesting listening to the different methods one builder uses vs another builder. They are all experts but sure do not all follow the same process once you get down in the weeds of the details. At this level engine building is definitely a craft, or an art, blended with good engineering principles. My engine goals are tame, limited to bolt on mods to get maybe 325 HP out of an engine that's hopefully durable, and fun to drive.

[faapgar]

In all the world Reclino makes the best kit.Crosses the T,s and dots the I,s.Also a nice person as well.I will try to help him make 375 HP good for 100k at .8 bar.At our age that is our lifetime.

[faapgar]

Recino makes the nicest waste gate rebuild kit I have seen.Very complete.A few pics of the saddle with oil hole.Oviously the hole is a few mm,s lower than the bearing journal.The relief above the holeis about 1/4 inch across.The champher is just help the oil guide into the back of the bearing shell for smoother feed.Hope these pictures help.Fred