Crank oilway mods - keyhole and radius

[litoslit]

Hi guy

I am Carlos from Spain, first af all i would like to thank you, all the help you give us.
I would like to ask you a question:
As you know the TC 131 type crank has 4 main journals, with 4 oil holes in each support. As I can see in the pictures one of them is not round. It is a hole with a shape of a teardrop. My question is. Do I have to the teardrop shape in all of the holes of each support?

Thank you very much again.

[litoslit]

Hi guy

I am carlos again, i Would like to ask you if it could be posible to do the tears in both holes of the rods also

[Guy Croft]

Hi Carlos,

1. Four of the main journal pickup holes take the oil from the main bearing housing and should be 'teardrop' shape (I call it 'keyhole) so they scoop the oil from the bearing in direction of crank rotation. The centre main of course has no holes.

2. The 4 crankpins (rod journals) should be given a circular radius. Do not do any other shape, the oil is exiting out of the crank - we want to try and distribute over the bearing.

The direction of the main journal 'keyhole' is critical, refer to the photo! It takes me 3 hours or more to do the early 2 liter crank. If it takes you less time it's not been done with enough care because I'm quick! It is essential that all the work is radiused and polished, sharp corners will take away any benefit from doing it all!

I use burrs followed by tiny grindstones, then small tapered abrasive points at 120 grade and then 400 grade carburundun by hand and then (!) finish all edges with fine ScotchBrite by hand before final polishing of all the journals contra-direction-of rotation with a crank lapping tool or in a lathe. Contra-direction: It is vital that any final polish does not 'raise the grain' (like stroking animal fur the wrong way).

I hope this is what you need.

GC

[Acki]

So the keyhole is on the right side? To make it easier for the oil to come in the oil bore?

[Guy Croft]

That is correct Martin,

if you click on the photo it will expand and show the crank nose nearest you, the keyhole extends right-wards so that the rotating journal will scoop the oil from the bearing. This does work -if coupled with reasonably generous 'polished' radii in the modified region. Any sharp edge or change of sectio/turn in any fluid flow line will reduce the feed and pressure.

GC

[Acki]

if you click on the photo it will expand and show the crank nose nearest you

That I never tried, should be a small hint "click to enlarge" or something.

Thanks Guy, I only asked to understand it ;)
I will test it on a old crankshaft (to see that I can polish it enough or not... when not I will ask my engine firm if they can polish it for me), I can make pictures... something like a "do it yourself guide" .