Bearings and oil pt#2

[Ol' Ron]

Bearings vs oil pressure Pt #2

Ok Now you know how and where the oil goes, and thanks to walts help, have a visual of how all this happens.
Notice that all the clearances in a stock engine are very tight. Main and rod bearings run from .001/.002". Cam bearings even tighter, but no more than.003". An important one Rod side clearance, .006/,010. Now you know where all the pressure comes from, resistance to the oil pump output.
Now trying to shuve some heavy oil through these clearances, forces the relief valve to open. The relief valve is only so big and can't reduce the pressure below #50 if the oil is too thick, thus forcing this heavy oil through the small spaces. However the pressure of the oil coming out of the small spaces is much higher that 50 or 60 lbs. More like several hundred lbs. This is the principal of water jet, cutting steel with hi pressure water. This high pressure also contains small particles which blast the bearings and surrounding materials. One thing we've forgot is: why we put oil in the engine anyway? I have a hit & miss engine that doesn't have any oil in it, but a drip system for the cylinder and rod. Yes, it lubricates the bearings and most everything else. But it also cools the bearings by removing the heat generated by the force of the connecting rod being driven down by combustion pressure. To cool these bearings we need flow, the more flow the better. In fact all the bearing mods are designed to increase flow.
WE do this by increasing the bearing clearances to .oo2/0025,both crank and rods, and increasing the rod side clearance to .015.
I'll end this now, Food for thought. If you're contemplating building a 276/284/294, this might be the way to go. Next: the all out competition, blown, nitro burning beast????
Gramps
I gots rest now

[Mart]

Thanks Ron, very interesting information. Thanks for taking the time to put it down "on paper".

Mart.

[Tim Ayers]

'Ol Ron,

Thanks for the right ups. I've been thinking about this lately. Is there any reason if one was to have a tight, fresh engine with metric ring packs to use a lighter oil like new cars?

Seems like most guys are running 15W-40 or 20W-50. How about 10W-30 or 5W-30 to reduce some of the "water blasting" effect you mentioned?

I would think heavier oil is needed in a worn out engine, but what about one that is built with clearances in mind?

[tubman]

I run 10W-30 in my freshly rebuilt 258" 8BA. After I swapped in a genuine Ford pump with a new relief spring, it has 20 psi at idle and 59 psi at 2000 RPM. This is with a fully warmed up engine running 180 degree thermostats that settles in at 175 on the (aftermarket) temp gauge. When rev'd higher, it exceeds 60 psi. This is consistent with the 57 psi figure from my 1960 "Motor Manual". I am quite satisfied with these numbers.

[flatjack9]

I'm still running 10W-30 in my engine with over 60,000 miles on it.

[Kahuna]

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I use 5-30 in my 290 inch flathead.
Oil pressure about 50 cold startup.
Hot idle about 30.
Max 60# at relief point

[tubman]

Kahuna, I'd say that we have pretty consistent readings. (I also have slightly over 50 psi on a cold start.) One question; what kind of oil pump are you using?

[Kahuna]

I use a stock early long pump

[Ronnie]

Originally Posted by flatjack9

I'm still running 10W-30 in my engine with over 60,000 miles on it.

And it will go another 60,000 with no problem.


R