Possible New Idea for Pressure to Model A Mains?

W

Will Kimble

Senior Member
OK, I have a simple idea for pressure to the mains of an A block and am looking for some input on my idea. Please let me know what you think or if you know anyone who has already tried this.

My understanding is that the rod dippers supply significant pressure to the rod bearings - I have read as little as 40 psi and as high as 80 psi. My idea is to use a drilled crank to supply oil pressure from the dippers to the main bearings. Let's call it "reverse pressure" since it is flowing the opposite direction of a drilled B crank.

The pressure from the dippers would pulse a little, but as the RPMs come up I think things would smooth out. I think the babbit would have to be grooved with this in mind, I am thinking a single ring in the rod babbit that aligns the hole in the crank with the dipper hole. That way each pulse of oil through the dipper would be able to travel up the hole in the crank.

The babbit in the mains would require similar consideration, I envision a ring groove that lines up with the crank hole so the pressure is evenly dispersed through the bearing.

The center main would receive pressure from two dippers, which is good since it is the most delicate area.

To prove my idea works, I would need to measure the psi at the main bearings. I propose to do this by tapping the 3 tubes that connect to the main bearings and attaching an oil pressure gauge through the side cover. It is likely the pressure at the center main will be different from the front and rear since it will be supplied by two dippers.

Depending upon the psi readings, it might be desireable to attach a pressure relief valve to one or all of these tubes. It also might be useful to regulate the rear main pressure down so that it doesn't push too hard on the rear main seal. By the way, I think a modern rear seal would be a requirement with this setup.

So what do you think, am I onto something? Constructive criticism is welcome. By the way, I am not an engine builder and haven't been able to think of any way I could profit from this idea.
smile.gif


Will Kimble
www.kimblemandolins.com
 
Nope. You'll need a constant pressure so it will reach the mains, the pulsing you speak of is very real and once it's "off pulse" it will drain back towards the rod. Also, the dippers won't deliver enough volume to sufficiently lube the mains. Remember, the rear main has a bearing surface that's slightly more than 2" long.

What's wrong with the conventional methods for pressuring the rods and mains? It's proven over and over to work very well!

Once again, let's not over think things here!
 
Thanks for the input azmodela, the pulsing and especially the volume of oil is a legitimate concern. Here is some relevant math to ponder - at 2,000 rpm, those pulses would come 33 times per second or every .03 seconds. Twice as many pulses for the center main. Would the oil still appear to "pulse" at that point?

As to volume of oil, perhaps you could manipulate the size of the dipper or dipper hole?

Finally, I hear what you are saying about overthinking things. I see no reason to consider this with a B block, and no reason to consider it if good B blocks were easy to get. I also have no problem with a stock babbit rebuild of an A. But it is tough to pressurize an A block - I am not even sure there is a "conventional method" - and I have never seen a solution as simple as this.

Thanks again for your input, it is helpful and may very well be the fatal flaw in my idea.

Will Kimble
 
Yes, it will still pulse even if it's fed every .03 seconds, because there is .02 seconds in between with no positive pressure. You're asking the dipper to feed the rod, then work it's way into the rod journal on the crank, then into the crank throws that lead to a main bearing before it bleeds into the main bearing. Don't forget the rotational forces of the crank, without the constant pressure, who knows what the oil will do as it's whipped around in the rotation of the crank. It will most likely work its way out to the outer most part of the rotation, which is the rods.

This will just not work, physics are working against you.

The conventional method is to drill the crank and pressurize the mains, which will then pressurize the rods. This how your modern car is done.
 
OK, one more round of thoughts... The oil has to have some inertia if it is under 40-80 psi and moving, surely it can't start and stop that quickly? Unfortunately I don't have the engineering background to understand all the ramifications of this. At a certain RPM and psi the oil would not be able to flow back out the dipper hole - it would have to move towards the main bearing. I do not pretend to know where this point is, but I have read that dippers begin to lose their effectiveness at 4,000 rpm due to cavitation so that is probably the upper limit to consider.

By the way, fuel pumps pulse by design and can deliver satisfactory fuel pressure.

I had not considered the rotational forces of the crank, that would be substantial.

Will
 
If you try it, be sure that the dippers are shaped so that they pick up the oil without forcing most of the oil out of the tray. A lot of old dippers have been damaged or were not well shaped to begin with.

In my opinion, dipping will be very important (might not be very efficient) at high speed because oil might not be able to flow into the dipping part of the tray as fast as the dippers will splash it out.
 
Since the centrifugal force in the drilled tube is constant and outward, attempting to get oil to flow inward toward the center of the crank would require constant pressure. So the required pressure would need to be constant and of a pressure greater than the centrifugal force, which would increase with increase rpm of the motor.

Anyway I'm sure it won't work.
 
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I think you guys are over thinking Wills concept. Just how much constant PRESSURE do you think a stock Model A has at the mains anyway with gravity feed? This might work except for the consideration that Richard brought up in that the oil will at some point not be able to return to the pickup trough as fast as the rods could pass through it. This would cause oil starvation and failure. I believe this is why the pressure systems of today developed in the manner they did. The pump can serve a more constant flow and pressure than dippers. In the end, I believe it would work but only to the point that the oil would not return fast enough. This would probably be somewhere about 3500 RPM.
 
Why do you think that the engine needs an improved oiling system?

Ever notice when you take apart engines that have sat for 10 of years you find the mains are still full of oil?

Did you every notice the most worn bearing surface in the engine is the only pressure oiled bearing ( the cam center bearing)?

It does not take much to keep the A engine happy. People tend to be very worried about stuff that has just worked and ignore the stuff that need attention. Spend all your time precision machining the crank and such and even more time ensuring weights are all balanced. The factory oil techniques will keep even a fairly high compression engine quite happy for 10's of thousands of miles.

If the crank if slightly off balance or the flywheel is off center that will cause oil pressure variations. Certainly if you are well balanced it does not take much oil to keep the lubricating film and enough volume to carry the heat away. Vibrations in the crank will serve to move the oil in bad ways and work the babbitt.

I will also throw out some more to think about.

Where do you plan to drill the holes? If you drill hole that will be at a high pressure point in the rotation then you may cause the oil to push out of the bearing. The center main having the port drilled at the bottom is kind of a funny place. The ignition stroke is likely to cause the oil to be pushed back through the hole. Some of the modern chevy guys were having a problem when they drilled an extra oil hole for the cam. Seems it was drilled at a high back pressure point and it caused the cams to wear due to lack of oil.


Well anyway some thoughts to run through your head.
 
Will Kimble said:
OK, I have a simple idea for pressure to the mains of an A block and am looking for some input on my idea. Please let me know what you think or if you know anyone who has already tried this.

My understanding is that the rod dippers supply significant pressure to the rod bearings - I have read as little as 40 psi and as high as 80 psi. My idea is to use a drilled crank to supply oil pressure from the dippers to the main bearings. Let's call it "reverse pressure" since it is flowing the opposite direction of a drilled B crank.

The pressure from the dippers would pulse a little, but as the RPMs come up I think things would smooth out. I think the babbit would have to be grooved with this in mind, I am thinking a single ring in the rod babbit that aligns the hole in the crank with the dipper hole. That way each pulse of oil through the dipper would be able to travel up the hole in the crank.

The babbit in the mains would require similar consideration, I envision a ring groove that lines up with the crank hole so the pressure is evenly dispersed through the bearing.

The center main would receive pressure from two dippers, which is good since it is the most delicate area.

To prove my idea works, I would need to measure the psi at the main bearings. I propose to do this by tapping the 3 tubes that connect to the main bearings and attaching an oil pressure gauge through the side cover. It is likely the pressure at the center main will be different from the front and rear since it will be supplied by two dippers.

Depending upon the psi readings, it might be desireable to attach a pressure relief valve to one or all of these tubes. It also might be useful to regulate the rear main pressure down so that it doesn't push too hard on the rear main seal. By the way, I think a modern rear seal would be a requirement with this setup.

So what do you think, am I onto something? Constructive criticism is welcome. By the way, I am not an engine builder and haven't been able to think of any way I could profit from this idea.
smile.gif


Will Kimble
www.kimblemandolins.com
Click to expand...

Will,
So far,man has not reached the limits of possibility. Of course it is possible, maybe not exactly as presented here but creative thinkers like yourself could develope some variation that would work. I would submit that the idea may be impractical but certainly not impossible!
Rainmaker Ron
 
James Rogers said:
In the end, I believe it would work but only to the point that the oil would not return fast enough.
Click to expand...

This isn't your limiting factor. The capacity of the oil galley within the crank, mains, and rods would make up roughly a cup of oil. Once those are filled up they can't consume more oil from the dipper until oil is displaced at the main or rod bearings.

This just won't work, but I'll stand by and watch someone ruin a nice journal polish and a set of bearings trying.

The pulsing diaphragm type fuel pumps cited earlier do pulse, but they also dump into a bowl within the carb that levels out the pulsing, attenuating the flows.
 
As Mitch pointed out, you cant fight against Centrifugal force, and win! What ever the pressure is in the dipper, it is only one blast Per R.P.M., enough to keep the oil groves full, but it would Never climb a Rod throw, no matter if you had a circle groove or not, and just a circle Groove in a stock Rod, will not deliver the amount of oil that an X Grooved Rod does, or that is needed! Herm.
 
Thanks for the input everybody - even the guys who say it would never work. :) You may be right, but I am not yet convinced.

I am most concerned about the centrifugal force and I am hoping somebody might be able to help me with some math. Centrifugal force would increase as RPM goes up and as you get farther away from the centerline of the crank. So the centrifugal force would be highest at the rod journal, and lowest at the main journal. By using the throw of the crank we should be able to calculate the centrifugal force at a given RPM - let's say 2,000 since we have already mentioned it.

I would like to know what PSI would be required to overcome that amount of centrifugal force? If it is 150 PSI then we know it is impossible. If it is 20 PSI then it might be possible and we shouldn't rule the idea out because of centrifugal force.

I have a feeling this equation is too complicated for me to sort out, can anybody help with this? Does anybody know the throw of the crank offhand?

Thanks,
Will
 
Another thing I want to add after re-reading azmodela's most recent comment - why would this ruin a crank polish and set of bearings? Other than my suggestion to cut the bearing grooves differently (point well noted Herm) this is really a stock Model A engine with a drilled crank. If you had a drilled B crank that was ground for A mains you wouldn't think twice about dropping it in a stock babbit rebuild, right? Or would you weld the holes closed to make sure nothing funny happened?

Thanks,
Will
 
Yea, it will work, but, you are going to have to do some redesign of the system.
First, Boyles laws state that pressure will be equal in all parts of the system
and volume will depend on pump delivery pressure and size of the delivery lines.
You will have to have a pump that will keep the dipper trays full at the design rpm.
By directing the delivery nozzles directly at the dipper it is quite possible to make this system work. The ammount of oil in the system will be large enough to negate any effect of pulsation.
While you are doing all this, you might as well just direct the pump outlet into a manifold and have it supply the bearings directly as is already done with current designs.
But to answer your question again, yes, your idea will work fine.
 
Hey Pete, thanks for chiming in. I am going to paste one of your posts here, I found this while researching this topic and I think it is very relevant:

Years ago an SAE engineer did some testing on his own on a stock Chevrolet 6 with babbit bearings and dip oiling. He was trying to determine at what rpm the groove cut in the oil by the dipper would not refill between revolutions. With the oil he was using it was about 4000 rpm and the oil pressure generated at the bearing surface was 40 psi.
This was all noted in a paper he presented at an SAE meeting.

Any idea where I could find this paper? Do you remember the engineer's name?

Thanks,
Will Kimble
 
Will Kimble said:
Hey Pete, thanks for chiming in. I am going to paste one of your posts here, I found this while researching this topic and I think it is very relevant:

Years ago an SAE engineer did some testing on his own on a stock Chevrolet 6 with babbit bearings and dip oiling. He was trying to determine at what rpm the groove cut in the oil by the dipper would not refill between revolutions. With the oil he was using it was about 4000 rpm and the oil pressure generated at the bearing surface was 40 psi.
This was all noted in a paper he presented at an SAE meeting.

Any idea where I could find this paper? Do you remember the engineer's name?

Thanks,
Will Kimble
Click to expand...

Good luck on finding that paper.
Here is the SAE url..There are thousands of papers to look through but there is a search function. I'm not sure how well it works though.
http://www.sae.org/search?searchfield=dip and splash oiling&typ=paper
 
I'm with Herm on this one.

As far as the Chevy, remember they also have jets of oil pointed at the dippers, and not just the dip trough to gather the oil.
 
I say go for it! Don't forget the aeronautical engineer who said that it is mathmatically impossible for a bumblebee to fly. It's just that no one told the bee!
Your biggest expense will be your time (and getting the crank drilled). Start with a used engine with good babbit-no matter if the valves are burned or the rings are shot. Assemble it the way you like and mount in a test stand with plugs out and side cover off. Devise a way to spin the engine and watch for oil coming up the tubes from the mains. If this works, add your gauges and go from there.
An idea for spinning the engine: install the trans with U joint attached. Borrow a farm tractor that has PTO (maybe a local antique tractor club has a member who could provide one). Go to a farm supply store with a Model A driveshaft in hand and find a PTO coupling that you can adapt to the driveshaft and plug the other end into the trans. Presto! By varying the tractor RPM and shifting gears in the A trans, you can spin your engine at whatever RPM you want. (This assumes the PTO turns in the right direction; for the life of of me I can't remember at the moment! If not, run the trans in reverse.)
The spray nozzles Chevy used may be necessary. Again, the main cost would be fabrication time. Check an old shop manual (up to '53) for pictures.
 
Why not just pipe the oil from the valve chamber outlet to the 3 tubes to the mains and have a spring loaded bypass to let the overflow go to the valve chamber.

OR.........just wait for the new 5 bearing block to reach production.
 
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