Can anyone answer this question, or does it matter other than drill filings ending up in the oil gallery requiring removing the valve chamber cover, etc. ?
Center Main Oil feed
- Thread starter SAXBY2
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Can anyone answer this question, or does it matter other than drill filings ending up in the oil gallery requiring removing the valve chamber cover, etc. ?
David in San Antonio
Well-known member
The earliest MG four cylinder engines had just two main bearings to minimize parasitic friction loss (and, presumably, lower the cost.) A roller and thrust bearing at the crank nose, and a poured Babbitt at the rear, with nothing supporting the crank in between. The Packard straight eight had nine main bearings. I guess parasitic friction losses and cost were not a great concern.
Synchro909
Well-known member
The two main bearing engines more more successful in competition than the later 3 bearing ones. The whip in the crank shaft meant the middle two cylinders had longer strokes so the engine capacity was increased and the compression ratio was higher on those cylinders.
I doubt I will cut the middle main bearing out of my Model A just the same.
old ugly
Well-known member
i don't think it matters which direction you drill into that gallery. i would pick the direction that is the easiest to drill and tap and which leaves you enough room to direct the plumbing. clearance from rotating parts.
if you are drilling it you most likely have the engine upside down. the filings are going to go into the oil system.
there is a tube that directs oil to the front of the side chamber, it fills the chamber. filings could end up in there. filings will for sure end up in the distributer hole.
i would not drill into there without flushing all the openings. there is no filter up there. so you better make sure it is cleaned out.
i would do it with the engine apart. you would not want filings entering any of those oil holes or areas especially the ones that go to the mains.
Going to do it this way per other posts.3/16"tubing, brass pipe threads to pump body at ridge and cen main cap
BRENT in 10-uh-C
Well-known member
Do as you wish, but I don't think you will like doing it that way, ...and I am unsure who said to drill & thread the Oil Pump housing, but that is NOT the way most of us do them.
It's to the side of the oil pump similar to the way Piriano's used to do it. Since the valve chamber cover would have to be removed (with engine in the car) to access the bearing nuts, the new hole appears to go up into the oil galley and no hole sideways in to the oil pump housing shaftway. Any drill chards could be suctioned and cleaned out. By the way, evidently the steel tubing can be the same as Model A carb 1/8" fuel line with compression fittings. One I suppose could use semi permanent thread locker on the brass threads.
The other photo is from an engine with 4000 miles on it, supposedly with no issues, that Brent in tenn says could be suspect due to vibration and pump housing failure. Just trying to find the simplest way to do this with engine installed in the car.
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gilitos
Senior Member
The idea of extra oil to the center main sure sounds good, but is there any evidence that the extra feed actually extends bearing life? For example, something like: "The center mains on five engines I built with the stock oiling system all had to be readjusted at 10,000 miles, but the next five I built with the extra oil feed all went at least 20,000 miles without needing readjustment." The modification sure doesn't look like it hurts anything, but does it help?
After following this thread, I also would like to see an answer to the question about empirical evidence . The later Service Bulletins showed the lower oil pan tray and oil pump shield that supposedly lowered oil consumption, but did it help with overall lubrication as well to the mains, etc. ? Also, does the oil pump move around that much that the drilling of a small hole in it for an oil line would crack it ?
alexiskai
Well-known member
I talked to a knowledgeable engine builder who said he doubted that "pressurizing" the center main would help much with one of the primary causes of center main wear, which is the crank flexing at high rpm. He thought the Model A crankshaft design is just too thin with too little support, it's gonna push through the oil barrier at rpm above 2k or so. I said that might be the case, but I thought it might help with one of the other causes of center main wear, which is lugging. If you're running in third gear at low rpm and trying to climb a hill, it is possible to apply enough torque to overcome the oil wedge when there's not a lot of oil being forced into the bearing. Having a direct line into the bearing from the pump might reinforce the wedge enough that a momentary dip into the lugging zone wouldn't result in bearing contact. It's all just speculation though.
gilitos
Senior Member
When Ron's Machine Shop poured my babbit back in the mid 90's, they added the oil line to the center main. When the rear main failed a few thousand miles later due to contact with the flywheel bolts (crankshaft had been set too far back), I had Herm Kohnke pour the next set. He took out the center main feed, calling it (not in his words) 'of questionable value'.
Thanks for all the responses.
One issue that has been discussed with some A owners is that when the engine isn't run for a week or more, oil runs to the rear of the block in the valve chamber and with oil not flowing via the oil holes to the 3 mains. Perhaps this slight starving requires the motor to be turned over with the ignition off in order to prime the pump. Another option would be to turn down the oil pump shaft per the Service Bulletins ('32 B motor, etc.) to get more oil flow.
Gilitos, do you recall where Ron's Machine added the oil line , to the block, pump housing, etc ?
One issue that has been discussed with some A owners is that when the engine isn't run for a week or more, oil runs to the rear of the block in the valve chamber and with oil not flowing via the oil holes to the 3 mains. Perhaps this slight starving requires the motor to be turned over with the ignition off in order to prime the pump. Another option would be to turn down the oil pump shaft per the Service Bulletins ('32 B motor, etc.) to get more oil flow.
Gilitos, do you recall where Ron's Machine added the oil line , to the block, pump housing, etc ?
BRENT in 10-uh-C
Well-known member
Colin, you as an engineer should have debunked his theory. To begin with, it is the micro-scratches that move the oil onto the bearing. If the oil wells are installed correctly, there will always be an adequate supply. Now next thought about his theory, ...if the Flywheel and the Crankshaft were properly balanced (-many if not most olde-time Model-A engine rebuilders did/do not do that operation) then exactly where is this "flex" originating from? Could it be the 'flex' was due to improper line boring where each Main Bore was not in perfect alignment? (hint; Likely!) The biggest cause of failure is torsional 'twist' created by the combustion pulses however this does not affect the center Main if it is truly parallel and in perfect alignment with the front and rear Main bores.
To begin with, if the Crankshaft location was set too far back (thicker rear thrust surface) then this would not have affected the Flywheel Bolt clearances. The likely reason for failure of the Rear Main Cap thrust surface was due to the incorrect Flywheel fasteners used during the assembly. It has been my experiences, that if the correct 27/32" long bolt (Ford #: A-21113) is used, but even if the Dowel Retainer is omitted, there still is enough clearance.
Let's be polite since Herm is no longer around to defend himself, ...but it has been discussed by many others that if something was not Herm's idea, then even if it was Jesus Christ himself who came up with the idea, it still was no good.
FWIW, even if the center supply line was of little or no value in his opinion, what would it have bothered if it was left in place? Afterall, the machine work was already done and all Herm had to do is reinstall the line. Oh I forgot, ...I should re-read the previous paragraph for my answer.
Some Model-A owners do not understand the engineering and the reality of real-world. Instead, I think many just use the 'He Said/She Said' method of spreading false information. To help correctly answer this myth, I am going to suggest you crawl under a Model-A engine that has sat for 3 months or so. Begin by removing the Engine Splash Pan and then remove the Oil Return Tube. Next, make sure you are directly under the Valve Chamber Cover and begin loosening all of the fasteners around the perimeter of the cover. Once all fasteners are loosened a couple of rounds, use a small screwdriver and pry the Cover away from the block beginning at the front of the Engine Block. Now again, the key to making this experiment successful is to make sure you are directly under the Cover as it is being pried away from the Block so you have a good visual vantage point. After doing this, please report back to us on this post and let us know exactly what happened!
Bonus Points will be given if you post a video of you doing this experiment exactly as described. 
To answer your second question, Ron's always threaded the port into the Block and not the Pump. It is MUCH more stable there.
David in San Antonio
Well-known member
Does this whole discussion about pressure oiling the center main only apply to babbit bearings, or is it equally as relevant to insert bearings?
Information about pressurized front main and middle main bearings has been around for many years . The first one that I am aware of was by Terry Oberer, St Louis ,Missouri . I modified my pump and caps for my engine with bearing shells ,even though the article was written for Babbitt bearings. System still working after many years,but if I had known about tapping from the block as Dennis Pirano did in 2017 I would have done it that way. Less worry about the connection with the pump housing,and possible vibration damage.
Don S
Don S