Rod journal oil hole diameter?

[ptuomov]

What’s the maximum journal oil hole diameter that is safe to run on a given length and diameter rod bearing?

[mag2555]

What motor are your talking about here?
How many square inches is the surface of the rod Bearing and what will the oil clearance be run at?

I think your question should be how much more oil pressure is needed to safely spin the motor to a higher rpm to allow oil to get to the rod journal in the first place and not get sent back to the main Bearings due to centerfuge pressure.

[ptuomov]

What motor are your talking about here?
How many square inches is the surface of the rod Bearing and what will the oil clearance be run at?

I think your question should be how much more oil pressure is needed to safely spin the motor to a higher rpm to allow oil to get to the rod journal in the first place and not get sent back to the main Bearings due to centerfuge pressure.

This is a general question after having read a number of piston guided rod conversion threads. It seems to be a relatively popular mod to take an existing crankshaft and convert it to piston guided rod setup with really skinny rods and short bearings. This got me to wondering about how do the existing crankshaft rod journal oil holes live up with bearings and whether the short bearings work with large diameter oil holes?

The topic is also somewhat relevant for my project in which we’re switching from soft but long 24mm bearings to shorter but harder 19.6mm bearings. The oil hole is 9.5mm diameter, so it’s big but I can’t see it causing any issues given that there’s over 10mm of support length even right at the hole. The journal diameter is 52mm and the bearing clearances on the tight side.

[Dan Timberlake]

We worked on a couple of british Riley engines 2 score years ago.
Converted the babbit rods to nice modeern insert type.
What struck me was the size of the oil feed holes in the rod journals.

I think those cranks were more conventional than this one. Is that a multi-roller center main bearing?
But the rod journal oil holes are similar to what I think I remember.
http://tiptopengineering.co.uk/services ... lding.html

[ptuomov]

We worked on a couple of british Riley engines 2 score years ago.
Converted the babbit rods to nice modeern insert type.
What struck me was the size of the oil feed holes in the rod journals.

I think those cranks were more conventional than this one. Is that a multi-roller center main bearing?
But the rod journal oil holes are similar to what I think I remember.
http://tiptopengineering.co.uk/services ... lding.html

Wow, that's small!

[ptuomov]

How about the largest oil hole you're comfortable running on a given length rod bearing?

[modok]

The bearing does need to cover the oil hole.
Minimum IMO at least 2mm overhang each side.

[ptuomov]

The bearing does need to cover the oil hole.
Minimum IMO at least 2mm overhang each side.

.

I’ve got more than 5mm per side and the oil holes are not at the spot that gets hit with the max combustion pressure. Thanks.

[Kevin Johnson]

... The oil hole is 9.5mm diameter, so it’s big but I can’t see it causing any issues given that there’s over 10mm of support length even right at the hole. The journal diameter is 52mm and the bearing clearances on the tight side.

It's raining outside so I did not go to the shed to look at the 928. The 944 crank that I have has 4.5mm ID rod journal oil holes. HTH.

[Kevin Johnson]

At least with the early 928 engine that I have here, the rod-journal oil-hole ID is ~3.7mm.