Pressurized center main bearing?

Garden variety compression fittings on copper tubing tend to crack at the point where the ferrule bites into the tubing so they are not the best fitting for inside an engine where they are unaccessable. Generally flare fittings are a much better choice. Inverted flares are not the best, but where there is not much room to make a connection, they are still better than compression fittings. If you must use compression fittings, instrumentation fittings such as Parker, Gyrolok or Swagelok are preferable but are not inexpensive.
 
Dan,
You make an excellent point about not using compression fittings; I hadn't thought about the inherent hazard of the copper tube fatiguing and breaking where the ferule bites into the tubing. I'll look for the brass fittings that Brent uses.
 
Jim Brierley's book 4 Bangers and me has a photo on page 39 where the tube is feeding all 3 mains. I'd think an orifice in the line would be desired to make sure the other areas still get enough oil.
 
ModelA29 said:
Jim Brierley's book 4 Bangers and me has a photo on page 39 where the tube is feeding all 3 mains. I'd think an orifice in the line would be desired to make sure the other areas still get enough oil.
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An orifice is a restriction, not recommended. Bendix air brake fittings support the line very well, available at truck parts stores. The system shown in my book are used with a full pressure system, so everything gets oil.
 
BRENT in 10-uh-C said:
I install mine into the same Cylinder Block passage as the Oil Pump end and the Oil Pump Drive Bearing slip into. I use a ²¹⁄₆₄" drill bit in a 90° right angle drill to bore the hole. Then I use a tapered reamer followed by an ⅛" pipe tap for the block fitting.





I guess I should start by saying these aren't my design. I have been purchasing these from Ron's Machine over the years. They are flared however they are not double-flared as hopefully you can see in the picture. The tubing is copper however it appears to be the same material as used in industrial instrumentation work. Although copper can vibrate and fracture over time, I think because of the short length and gentle bends, it stays pretty rigid. Because of the orientation of the fittings on each end, and the rigidity of the tube, it may not be that big of a deal if ferrules were used.


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Brent, how in the world do you get that fittings' shoulders to pass (rotate) without hitting and stopping you from threading it into (installing after threading) the block. Those surfaces, or boses, aren't they hitting the shoulder of the fitting? The throws on the crank look very close? Is this a kit you guys sell?

When you drill and tap the car, how do you do that? Do you lay the cap over a big dowell rod, or a wood fence post or something? What if you drill a smaller hole for that last little bit of the cap, so you can leave more babbit? Also, seems like a bigger bit might "snag" the babbit, whereas a 1/8" might be less likely and still provide oil. Lets face it, "a little dab will do ya". LOL
 
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So how is this passage (pictured) not giving oil to the center main? Meaning why do we need another feed?
 

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Gene F said:
So how is this passage (pictured) not giving oil to the center main? Meaning why do we need another feed?
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That passage is just a dribble feed-gravity flow from the valve chamber. Mains are starved for oil until oil warms up on a cold day. The center main is stressed the most, so needs the most oil. Adding this line direct from the pump gives the extra oil that the center main needs in a quick, cheap and easy modification.
 
Gene F said:
Brent, how in the world do you get that fittings' shoulders to pass (rotate) without hitting and stopping you from threading it into (installing after threading) the block. Those surfaces, or boses, aren't they hitting the shoulder of the fitting? The throws on the crank look very close? Is this a kit you guys sell?

When you drill and tap the car, how do you do that? Do you lay the cap over a big dowell rod, or a wood fence post or something? What if you drill a smaller hole for that last little bit of the cap, so you can leave more babbit? Also, seems like a bigger bit might "snag" the babbit, whereas a 1/8" might be less likely and still provide oil. Lets face it, "a little dab will do ya". LOL
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I drill the block first, then I have a small tapered reamer to create a hole that a tapered pipe tap like, then I thread the block. There is room to rotate the fitting. The throws of the crankshaft are close, but not too close to cause concern,

Ron's Machine in Shandon, OH will likely have everything you need.

I just set the cap in a Mill Vise and plunge thru it with a drill. If you are worried about the Babbitt material breaking loose from the cap, then the cap was not properly tinned. I use a drill and then a tapered reamer before using a pipe tap. The hole thru the Babbitt is the same size as the pilot drill size. I have a small countersink that I use to flare the end of the bearing material. The thing I would not care for is if you are using the bearing material as a orfice, then the oil may find its way tunneling between the bearing material and the metal cap.



Gene F said:
So how is this passage (pictured) not giving oil to the center main? Meaning why do we need another feed?
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It is giving oil to the Center Main. The main difference is the oil entering the top of the journal is gravity fed to the crankshaft, whereas the oil entering thru the bottom is pressure fed.
 
Just one comment. Joe K in post #14 made a comment that the pressure was not enough to force hydrodynamic separation (of the journal to the bearing). The hydrodynamic separation is caused by the rotation of the journal in the bearing. There is a wedge of oil formed that is dragged along with the journal and this actually does the separation. The pressure that is formed is many times more than the oil pressure, even in a modern engine.
 
nkaminar said:
Just one comment. Joe K in post #14 made a comment that the pressure was not enough to force hydrodynamic separation (of the journal to the bearing). The hydrodynamic separation is caused by the rotation of the journal in the bearing. There is a wedge of oil formed that is dragged along with the journal and this actually does the separation. The pressure that is formed is many times more than the oil pressure, even in a modern engine.
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Neil is quite correct. The sole purpose of oil in the engine is to keep the bearings cool. The fact that it is slippery helps. Guys who race these engines set their bearings with a wider clearance than most of us so that the oil can flow through quickly, carrying heat with it. By supplying oil under pressure to the bearing, more oil flows through it while the engine relies on hydrodynamic pressure to keep the crank journal from contacting the bearing. There is a relationship between the two but they are different.
 
The hydrodynamic pressure in car engines needed to keep the bearing surfaces separated is far in excess of oil pump feed pressure. Anywhere from maybe 1000 to 6000 or more psi depending on engine speed, bearing load, clearances etc etc. Spark advance has a big effect on bearing load, the ideal maximum piston load from combustion being at about 17 deg ATDC for best power (usually quoted at 15 to 20 deg ATDC) for petrol engines. This maximum oil pressure occurs a bit after bottom dead centre in the bearing, since the journal runs a bit off centre from the bottom of the cap.
One can calculate the bearing load per square inch from engine torque and the angle at which it is maximised for a given engine. And hence the hydrodynamic oil pressure needed to keep the bearing surfaces seperated to avoid "boundary lubrication" such as occurs during engine start up before the high pressure hydrodynamic film has formed. But too involved to do here!
So an interesting question is how does oil from the pump at 45 psi manage to feed into an area where hydrodynamic pumping of the bearing is generating at least 600 psi and a lot more at higher revs?
I don't doubt that feed into the bottom high load area helps, since it has been proven many times practically. But i feel intuitively that feed pressure into the top of the bearing where gravity normally supplies it would work even better. Does any one feed oil pressure here?
SAJ in NZ
 
Yes Beth is still in business but has moved from Denton to Celina Tx. Phone number is still the same.
 
SAJ said:
The hydrodynamic pressure in car engines needed to keep the bearing surfaces separated is far in excess of oil pump feed pressure. Anywhere from maybe 1000 to 6000 or more psi depending on engine speed, bearing load, clearances etc etc. Spark advance has a big effect on bearing load, the ideal maximum piston load from combustion being at about 17 deg ATDC for best power (usually quoted at 15 to 20 deg ATDC) for petrol engines. This maximum oil pressure occurs a bit after bottom dead centre in the bearing, since the journal runs a bit off centre from the bottom of the cap.
One can calculate the bearing load per square inch from engine torque and the angle at which it is maximised for a given engine. And hence the hydrodynamic oil pressure needed to keep the bearing surfaces seperated to avoid "boundary lubrication" such as occurs during engine start up before the high pressure hydrodynamic film has formed. But too involved to do here!
So an interesting question is how does oil from the pump at 45 psi manage to feed into an area where hydrodynamic pumping of the bearing is generating at least 600 psi and a lot more at higher revs?
I don't doubt that feed into the bottom high load area helps, since it has been proven many times practically. But i feel intuitively that feed pressure into the top of the bearing where gravity normally supplies it would work even better. Does any one feed oil pressure here?
SAJ in NZ
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SAJ, you are spot on with that post. I have seen pictures of modifications done to an A engine where plumbing is added tot he valve chamber to force oil down the original oil passages to the main bearings. That plumbing is not an easy task.
 
True, but she just recently sold the shop in Denton and moved back to Celina. Still selling parts.
 
[ModelA29;2289017]Jim Brierley's book 4 Bangers and me has a photo on page 39 where the tube is feeding all 3 mains. I'd think an orifice in the line would be desired to make sure the other areas still get enough oil.]

I have a few questions about this thread.
If you pressurize the center main bearing why not all three?
Is there any advantage or disadvantage to doing all three?
Would the oil tubes in the valve chamber going to the bearings need to be plugged? Or could the pressurized oil be run through the valve chamber tubes?
How would either affect the oiling to the camshaft.
I have not had a Model A engine apart in 30 or so years so I am a little rusty on the internal workings.
Sorry if I ask stupid or too many questions.
Thanks
 
1928 Sport Coupe said:
[ModelA29;2289017]Jim Brierley's book 4 Bangers and me has a photo on page 39 where the tube is feeding all 3 mains. I'd think an orifice in the line would be desired to make sure the other areas still get enough oil.]

I have a few questions about this thread.
If you pressurize the center main bearing why not all three?
Is there any advantage or disadvantage to doing all three?
Would the oil tubes in the valve chamber going to the bearings need to be plugged? Or could the pressurized oil be run through the valve chamber tubes?
How would either affect the oiling to the camshaft.
I have not had a Model A engine apart in 30 or so years so I am a little rusty on the internal workings.
Sorry if I ask stupid or too many questions.
Thanks
Click to expand...

You'll get several different answers to that series of questions. Oh, and BTW, there cannot be too many questions.

If you pressurize the center main bearing why not all three?
In my case, I was lazy. I did the middle one because it is the one that is the first to fail. I figured pushing more oil through it would increase the flow of oil through it, helping keep it cool.

Is there any advantage or disadvantage to doing all three?
IMO, the front and rear main bearings are robust enough that while pressure feeding them might increase their life, the effort is not worth it.

Would the oil tubes in the valve chamber going to the bearings need to be plugged? Or could the pressurized oil be run through the valve chamber tubes?
I've seen it done both ways but as I said above, the plumbing in the valve chamber to force oil down all 3 of those holes is not easy to squeeze in there.

How would either affect the oiling to the camshaft.
Oiling though the original tubes would affect the cam shaft bearings unless provision was made to still have the floor of the valve chamber flooded with oil. If oil were pressure fed through the bearing caps and then exit UP the oil tubes, the cam bearings would be fine.
 
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