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Oil passages to main bearings - different diameters


Bryan

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Confirmed what I was seeing last night.  The horizontal passage from the main oil galley to the main bearings are about .33", but this stops before it gets to the main bearings vertical passage. It has a step and decreases to about .25.    On the front and rear mains, why didn't they continue .33 to the vertical going to the main, and decrease it to .25 starting the passage to the cam bearings?  On # 2 & 3, since the vertical passages are smaller, why not just make the entire horizontal passage about .25" diameter?

 

Was thinking, oh I could drill all of them out to the vertical passages,  BUT  look at the engine block pictures of # 2 and #3.  The cylinder bore is cut up into the oil galley passage.  Might not be a good idea drilling those out unless you knew the wall was plenty thick.   Still I could maybe drill the front and rear out to .33, but hesitant to do that.

 

Edited:  Pictures made it confusing. ALL passages are like that  Front, 2nd, 3rd and rear mains.     .33" to about 1/2" before vertical junction, then .25" to cam bearings on all.

 

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Oil passage sizes.jpg

Edited by Bryan
Pictures were misleading.
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8 minutes ago, kencombs said:

From the last drawing it appears that they increased passage size as the destination became further from the pump.  Probably intended to equalize pressure and volume end to end.  Just my uneducated guess.

That would make sense but why did they decrease the last 1/2" to .25 before the vertical junction to the mains on the front and rear? Oversight?

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If you take a look at the cam bearings you will see two sets of holes.

One set is smaller than the other set. I will let you ponder that a moment.

 

The oil pump is on one side of the block and the oil galley is on the other, it takes a cross over tube to connect them. The oil passage doubles back with thru holes to the other side. Now look at the crankshaft. The front main feds oil to cylinder #1 and the rear main feds cylinder #6 all the other mains feed two cylinders each. If you were to guess which rod bearings might suffer from oil starvation, you’d say #2,3,4 or 5. But theres more, because the rods are fed by one hole drilled in the crank, there is a timing issue as to when they get a full shot of oil. 40 lbs of oil pressure does a good job of lubrication and the pump has enough volume, especially when you consider what Chevrolet gave their engines. Pressure to the mains, cast iron pistons and dip fed rods!

 

Many after market parts makers have noticed on OHV V8s that the oil goes to areas where it really isn’t needed.

Smokey Yunick made oil pans, timing covers, valley covers and rocker covers out of clear plastic so he could study where the oil was going.

He started putting restricters in the oil lines to the cam bearings and lifters as a means of directing more oil to the mains & rods.

 

In our case that is why the cam bearings have two sets of holes. Standard practice is to use the small holes on number 2 and 3 cam bearing.

The front bearing feeds the timing chain and one rod bearing. There is no rear bearing as the cam runs directly in the bock and feds only one rod bearing.

I talked to one old boy who said they used to cut a short piece of lamp wick and insert it in oil galley and push it over to the cam bearings as a used car lot fix for worn bearings. I don’t think I’d recommend that but you get the idea.

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5 hours ago, Bryan said:

That would make sense but why did they decrease the last 1/2" to .25 before the vertical junction to the mains on the front and rear? Oversight?

By the time your engine was built in the mid-1940s the basic design had been in service for over 10 years. Chrysler employed smart engineers and my guess is that if something was giving problems in the field they would have addressed it by the 1940s.

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45 minutes ago, TodFitch said:

By the time your engine was built in the mid-1940s the basic design had been in service for over 10 years. Chrysler employed smart engineers and my guess is that if something was giving problems in the field they would have addressed it by the 1940s.

That's the only thing that making me hesitant from boring the front and rear ones out.  Just usually a step in pipe size messes with flow.  Even wonder why they didn't taper the bore down gradually?   Trying to understand the reasoning behind it. 

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1 hour ago, Loren said:

If you take a look at the cam bearings you will see two sets of holes.

One set is smaller than the other set. I will let you ponder that a moment.

 

The oil pump is on one side of the block and the oil galley is on the other, it takes a cross over tube to connect them. The oil passage doubles back with thru holes to the other side. Now look at the crankshaft. The front main feds oil to cylinder #1 and the rear main feds cylinder #6 all the other mains feed two cylinders each. If you were to guess which rod bearings might suffer from oil starvation, you’d say #2,3,4 or 5. But theres more, because the rods are fed by one hole drilled in the crank, there is a timing issue as to when they get a full shot of oil. 40 lbs of oil pressure does a good job of lubrication and the pump has enough volume, especially when you consider

I know from other posts about using the small holes on the two middle cam bearings.   If they figured the front and rear were getting less they would set it up to feed less rods.   My main question is about why they bore from the side galley .33" diameter passages but stop right before the vertical passage to the mains, and change it to .25" diameter abruptly with a step.

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Why even think about re-inventing the wheel. Chrysler made tens of millions of these engines. If there was a problem, which I doubt, Chrysler would have made alterations. 
 

My ‘53 Plymouth has 102,000+ miles. It had rings, one burnt valve replaced, and the rest lapped 30,000 miles ago. Main and rod bearings were plastique gauged at the time and were in the middle of factory specs so were re-used. The bearings, camshaft, pistons are all original. Only things replaced were the rings. To this day the car does not burn oil, has great compression, and great oil pressure. 
 

Just saying, don’t over-think things and have faith in the great engineers who designed these engines. 

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5 minutes ago, RobertKB said:

Why even think about re-inventing the wheel. Chrysler made tens of millions of these engines. If there was a problem, which I doubt, Chrysler would have made alterations. 
 

Just saying, don’t over-think things and have faith in the great engineers who designed these engines. 

I have faith in the engineers.  I've worked in a factory before and knows how that goes. The passages are drilled. I know because you can see the spiral markings.  If some new guy bored the .33 part too short..then oops.  As of yet nobody has confirmed this is how it is designed, and is the same on all 230 Dodge engines.

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If it is engineered that way, then somebody here would have the knowledge why it was done that way. Should be based on some kind of science, right?  Fluid mechanics? Flow of viscous fluids?  Maybe the engineers that we trust lost out to the economics majors..

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Having spent several decades in manufacturing I can tell you drilling holes in metal isn’t as simple as you might think.

Engineers talk about the diameter vs depth ratio and the types of drills required to achieve deep holes.

The problem is getting the chips out of the hole while drilling.

Deep hole drills have one cutting surface (your typical jobber drill of course has two) made of carbide brazed to a tube that looks like a quarter pie sliced cut out of it when viewed on end. The tube is connected to a high pressure pump which forces coolant out of a hole in the carbide. The coolant literally blows the chips out of the hole. ( what I am trying to describe is called a “gun drill” if you’d like to google it)

What the various diameters are may be a function of how they drilled the holes. It must be remembered that Plymouth and Dodge made their own engines in their own factories and thus could have used very different methodologies. I have only dealt with Plymouths and never noticed the different diameters.

I am thinking it can’t make much difference.

It could be that it was done as a two step process with two different drills. The larger diameter for clearance of the second drill on a rapid approach. Even with a gun drill there are limits to how much torque can be applied to the drill with chips coming out of the hole. Finishing with a smaller drill makes sense in that case. The hole that I am impressed with is the one running the length of the block.

I am not sure boring out the holes would be of much value.

The more volume the pump has to fill on cold start up is more time the bearings are not getting pressure.

 

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factory machining limitations may very well be what ya have here, also there may have been some calculations and empirical evidence that showed that the step bores acted as a dampening device for the oil pump to deal with high rpm oil pressure variations during engine operation.  I don't know for certain, but Chrysler cranked out these flatheads for decades, so if they have some unexplained quirk in their oiling design, I accept it as something them guy did cuz they knew what they were doing.  Ultimately, any flathead could be compared to its last iteration, as that would have the best lubrication, compression ratio, cooling design, etc. but who has time for that these days...clean'm up, fix'm up, run'm till the wheels fall off :cool:

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4 hours ago, Loren said:

 

I am not sure boring out the holes would be of much value.

The more volume the pump has to fill on cold start up is more time the bearings are not getting pressure.

 

I'm talking about the front and rear mains, drilling 1/2" further on each to reach the vertical passage going to the mains.  Difference between .33" and .25" diameter.  .02 cubic inch volume difference total.

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4 hours ago, JBNeal said:

factory machining limitations may very well be what ya have here, also there may have been some calculations and empirical evidence that showed that the step bores acted as a dampening device for the oil pump to deal with high rpm oil pressure variations during engine operation.  

I was studying last night fluid flow at T junctions to no avail. At least in water flow there can be stagnant areas near the junction.  Oil flow don't know.   Adding a step to a smaller size would cause turbulence.  With water the velocity would increase.    Plus still  don't know if this is unique to my block or standard.

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Didn't you have a second block, mostly apart? Checking that may be your best bet for comparison. 

My initial take would be that step would/should be after the mains , but I think it is unlikely to be "by mistake"

However 

As yourself and others have said, what is on the engineering drawing and what happens on the factory floor are two different things. Tim Kingsbury has lots of period documents, you may reach out to him and see if he knows.

 

I have done oil passage mods on Ford FE engines, but only stuff already pioneered by Ford and other racing teams. 

I suspect they figure out what is needed by crafting a sort of "oil system Dyno" where they can measure results of their mods.

 

Almost everything is a balance, although we need to remind ourselves that sometimes that balance is between performance and production cost/time.

If you can identify things that saved the company $00.15/peice, and you can do for cheap or free, that is where you can gain without sacrifice.

Oil passages are large near the pump, where volume and pressure are highest. As oil gets consumed, passages get smaller to keep pressure at needed levels. You don't want passages so large that they take time to fill, or reduce pressure.

 

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One thing to also remember, camshafts move at half engine speed.  So they don't need as much oiling.  I seem to recall reading somewhere that the cams in our applications are over oiled.  Not sure where I read that.  Might have been the AoK boys there.

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1 hour ago, FarmerJon said:

Didn't you have a second block, mostly apart? Checking that may be your best bet for comparison. 

My initial take would be that step would/should be after the mains , but I think it is unlikely to be "by mistake"

However 

As yourself and others have said, what is on the engineering drawing and what happens on the factory floor are two different things.

 

Forgot about that. Let me crawl out there in the old wood shed and see. Been burning a brush pile this morning. 

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  • Bryan changed the title to Oil passages to main bearings - 48 Block different- somebody explain?

The 48 Dodge (49 Plymouth replacement block) has large .330 holes going all the way to the camshaft for all main bearings.   The 2 middle cam bearings were turned slightly so the holes were 2/3 open.  Somebody knew back then.

 

Sorry I keep calling it a 48 Dodge, that's my car. The guy cracked the block (pure water) after owning it a year and had the block replaced. Story my father told me.

 

Okay, NOW WHAT?   It has the same dished out galley sides (from the cylinder bore) on the 2 middle cylinders.   Probably safe to bore but still would like to know the logic.

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1 hour ago, FarmerJon said:

What year is the block with the stepped oil galley? 

 

Did either engine show abnormal wear in the bearings?

 

It's a D46 which I think is 53.   On my original 48/49 it had dirt stirred up in it so everythings worn.    The older block does have the same size holes in the main journals.  .31 front and rear, about .26 for #s  2 & 3.

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Best explanation of laminar flow I've come across..  Viscosity and Laminar Flow; Poiseuille’s Law – College Physics (opentextbc.ca) 

Radius of the tube DOES matter.    Engineering doesn't change.

 

In the factory, boring holes, like getting rid of casting sand, is left to the workers and quality control.

Flow 1.jpg

Flow 2.jpg

Flow 3.jpg

flow 4.jpg

Flow 5.jpg

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The rear cam "bearing" being the block itself is known to wear. Back in the day there were restriction devices that were sold so that oil pressure would not drop off due to that wear. They come up on ebay now and then.

 

I would spend more time, money and effort into making sure that the diameter of the rear cam bearing was correct than worrying about the gallery size. When I do my next flathead, I plan on drilling and busing the rear cam "bearing" area so it is back to factory spec. I have wondered what that "slop" at the rear of the cam is going to the valve geometry over time. I know it is not a lot, but the pressure of the valves on the cam must cause the ass end of the cam to "wobble" a very little bit due to the clearance.

 

I have measured a couple of blocks and some at almost at spec and some are way over.

 

My 2 cents worth.  James

 

*******

Related: One of my blocks that had a rod failure hot the block right on the oil gallery. It did not go through, but it did take a little block out when it hit. To be paranoid, I drilled the gallery out just a little and put a sleeve in it. I did the opposite of what Loren talked about. I got a three flute bit as I was taking a very small amount off. It worked fine.  I pounded in the sleeve and the block it sitting in  a corner.  The old automotive engineering block that was first in the 1949 Desoto that had the oil pushing into the water system is waiting for me to go looking to find out where. It is a shame as that engine ran well as has very low miles on it. Either there is a gallery problem or more likely a rust through on the floor of the water jacket above a gallery. In any event, I would pressure test both the oil gallery and the water jacket on any flathead block that I had not been running to make sure.

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2 hours ago, Sniper said:

Ok, Prefessor, what's that in English, lol.

Decreasing the gallery size has a large increase in resistance and decrease in flow. Flow is what lubricates and cools bearings, not pressure. 

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  • Bryan changed the title to Oil passages to main bearings - different diameters

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