Pressurized center main bearing?

M

mcgarrett

Well-known member
Watching one of the Hagerty Model A engine rebuild videos, they show adding a copper oil line to the center main cap but didn't go into any of the details on how to plumb it up to the oil pump. What would be the reason for doing so?
Anyone ever done it to their engine? How does it connect to the oil pump? I'm interested in knowing more about this process.
 
Bob C. & Jim B.
Thanks for the excellent information. I wasn't aware of this modification. Just so happens, I am installing a counterweighted crank so this information is most welcome!

Jim, where on the oil pump do you drill and tap for the brass fitting?
 
Jim Brierley said:
I drill and tap a 1/8" pipe thread to the pump body and run a 3/16" tube to the main as shown in the link above.
Click to expand...

The link does not show to tap into the pump body, but to tap into the oil galley and run a tube to the center main bearing cap. Is there an oil pressure area under the lifter galley similar to when adding an oil filter?
 
I have posted here many times till some of you must be tired of hearing about how I drive long distances in my Model A while towing. The motor is working hard all day every day for weeks on end. Like you, I have installed a counterweighted crankshaft and I pressurised the middle main bearing. I tapped the oil pump housing just below the sump (pan) rail and restricted the oil outlet at the top of the pump which I modified like a B pump. I ran a short 1/4" copper line across to the bearing cap which was drilled and an elbow installed facing the oil pump. At a convenient place along that 1/4" pipe, I put a Tee with the right angled leg facing down. I made and screwed a pressure relief valve there but had to cut a hole in the side of the dipper tray to accommodate it. The valve regulated the pressure to a max of 25-6 psi. The relief valve points downwards to avoid the counterweights on the crankshaft. I tapped the top of the hole in the valve chamber where the oil used to run down to that bearing and plugged it.
I can be a bit of a fiddle to fit the pipe because it is so short but it can be (and has been) done.
BTW, I run insert bearings and an oil filter in the motor. The whole motor is getting a bit lose now but after 70,000 miles including about 50-60 thousand done while towing at 50 mph, I'm not complaining.
 
Synchro909,
Thanks for adding more clarification to this subject. If you have a moment, take a look at the link in post #2. Do you have any idea where the fitting and tube installed on the pan rail near the oil pump hole connects to? I looked at my block on the engine stand and I can't see where it would pick up any oil pressure from the pump. I don't understand what this would accomplish. Maybe someone else here on the Barn has seen this and could reply.
 
mcgarrett said:
Synchro909,
Thanks for adding more clarification to this subject. If you have a moment, take a look at the link in post #2. Do you have any idea where the fitting and tube installed on the pan rail near the oil pump hole connects to? I looked at my block on the engine stand and I can't see where it would pick up any oil pressure from the pump. I don't understand what this would accomplish. Maybe someone else here on the Barn has seen this and could reply.
Click to expand...

A pleasure! I can't see where the oil pressure would come from in that picture. Maybe we heed to see another angle or better still, the engine. Maybe someone else can fill in this gap.
 
Appreciate all the responses. I still need to know for sure exactly where to drill and tap the oil pump body for the oil line. I hesitate to move forward with this modification until I'm sure about that.
 
Synchro909 said:
Maybe but who would want to go to all that work when the main bearings in a B engine are already pressure fed?
Click to expand...

I have no idea, none of this makes sense.
Oh, and just to clarify, the mod B is not pressure fed, only directed oil to the bearings. It can be modified to pressurize.

J
 
Jim Brierley said:
Syncro, you restrict the outlet of the pump??? Sounds like that is defeating the purpose of it all except the center main.
Click to expand...


Maybe oil flow goes "back" in the traditional center main oil gallery thus feeding the valve chamber, and from hence everywhere else in the normal path?

I had to think about that as a possibility...

The Model A oil pump is generally considered to "not have much pressure." I've read somewhere less than 3psi. Which - without augmentation - is not enough to effect "hydrodynamic separation" of the bearing moving parts in the traditional insert bearing mode.

Or perhaps "positive" lubrication is more the goal rather than actual hydrodynamic separation?

My brother, who was into drag racing, told of dragster augmented oil pressure actually "blowing out" bearing inserts - 5000 rpm can do that I guess.

Joe K
 
Joe K said:
Maybe oil flow goes "back" in the traditional center main oil gallery thus feeding the valve chamber, and from hence everywhere else in the normal path?

I had to think about that as a possibility...

The Model A oil pump is generally considered to "not have much pressure." I've read somewhere less than 3psi. Which - without augmentation - is not enough to effect "hydrodynamic separation" of the bearing moving parts in the traditional insert bearing mode.

Or perhaps "positive" lubrication is more the goal rather than actual hydrodynamic separation?

My brother, who was into drag racing, told of dragster augmented oil pressure actually "blowing out" bearing inserts - 5000 rpm can do that I guess.

Joe K
Click to expand...


A stock Model-A oil pump can peg an 80# oil pressure gauge when the system is capped. ( I know this from firsthand experience with my old race car. ) The same thing with a garden variety water hose. Without a nozzle screwed onto the end of the hose, there isn't any pressure but put your thumb over the end to restrict the flow of water and it will definitely build pressure inside the hose.

As far as 'capping' a Model-A oil pump, when I have done this I used brass and brazed onto the end of the pump on the outside of the housing by the upper bushing. If you examine the pump, generally there are two flat areas that allow oil to bypass. I just put the pump housing in the lathe and machine the brass round to match the OD of the remaining portion of the pump. This just forces more oil out of the slots just under that upper bushing, and when there is a center main oil line, it creates a little pressure to force oil into the bottom of the bearing cap. FWIW, I never drill & thread the oil pump housing. Instead I just drill & thread the block itself. I think the pictures below show another way on how we do it.


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Glyptal on the engine block interior is a nice touch.

I just bought my first can of Spray Glyptal - cough-choke.


Joe K
 
Jim Brierley said:
Syncro, you restrict the outlet of the pump??? Sounds like that is defeating the purpose of it all except the center main.
Click to expand...

With a 25 psi oil pressure relief valve, oil is trying to exit the top of the pump at 25 psi. With the original arrangement, it exits at 3, maybe 4 psi. By leaving some way for 25 psi oil to enter the valve chamber, I have enough oil to lubricate the front and rear mains the conventional way.
An alternative (and my first method) was to allow the oil from the middle bearing to flow back UP the original oil hole, back into the valve chamber after going through the middle bearing. When I plugged that hole, I slightly enlarged the exit hole for the oil into the valve chamber.
I must have done something right - I have about 70,000 hard miles on that engine now and it's still going.

Brent, I understand your reservations about drilling and tapping the oil pump housing but I did it without a problem.
 
Last edited:
I have looked at the pics on the old Dennis Piranio website and Brents pics. The tube is actually connected at different locations in the block. How does each tap into the oil passage for pressure? Dennis's is tapped, (in what appears to the pan rail) and Brent's is inside the block. ??
 
Brent, I noticed you used flare fittings, that's much better than compression fittings. Good job.
 
oldspert said:
I have looked at the pics on the old Dennis Piranio website and Brents pics. The tube is actually connected at different locations in the block. How does each tap into the oil passage for pressure? Dennis's is tapped, (in what appears to the pan rail) and Brent's is inside the block. ??
Click to expand...

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.



katy said:
Brent, I noticed you used flare fittings, that's much better than compression fittings. Good job.
Click to expand...

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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