wjvail

My Feedback: (3)

Just a short note about something that needs to be considered... The acceleration on a piston with a stroke of about .53" and turning around 25,000rpm is in the ballpark of 200,000 ft/sec sqd or about 6,000 g's. These g loadings are also affecting the fluids lubricating the large and small rod ends. Any holes in the rod would be force feed lubrication with these g loads.

Bill

Hobbsy

My Feedback: (102)

On a rod bearing a groove would take up too great a percentage of the surface area.

Recycled Flyer

That's part of the issue here, the meaning of 'feed' - is it oil extraction or injection? My sources contend that it is extraction.

earlwb

Well the upper half of the rod journal has the highest pressure as that is the higher stress point on the rod. The lower half has the least pressure and is under the least stress too. So when a engine is running, and you have ignition, the piston pushes down on the rod which pushes down on the crankpin on the crankshaft. That would tend to push oil out of the rod on the upper half, but also tend to reduce pressure on the bottom half and you get a bit of suction there to pull in oil. The oil then migrates towards the upper half as the engine is rotating through its stroke.

There was a hand crank model of a engine and its connecting rod, where they had a couple of oil passages connected to a couple of glass tubes with a oil level in them. When you cranked the model around, you could see the oil pressure rise for the upper half of the rod and go down for the lower half of the rod journal. When a engine was running, the oil pressure on the upper half rose spectacularly due to the extra forces involved. I was trying to find it again, but I haven't had any muck finding it yet.

qazimoto

My Feedback: (1)

How would anyone know that Chris?

Is there any evidence or yet another appeal to authority?

Ray

qazimoto

My Feedback: (1)

I've loaded a pic of the dismantled front end of my Goodyear Tuned TBR PAW 15 Diesel. This has an interesting front bearing retaining system. But after the ball race has been removed a grove can be seen in the bearing surface from the venturi to the front race.

Conventional wisdom is that this "suck hole" or "suck grove", draws excess fuel leaked out the shaft bearing back into the venturi for recycling as the engine pressure cycles internally. I'd imagine that the one in the full length bearing mentioned by FFKiwi above has a different function.

The "suck hole" is a common "folk remedy" for "wet nosed" model engines.

I've only tried it twice, and in one case it seemed to be effective, and seemed to cure the problem

In the second case it didn't work at all.

I sense that model engine design is as much black art as real science.



I just checked out a spare piston/liner/rod assembly for a Nelson 15 Diesel racing engine.

The big end had two oil holes. Obviously Henry Nelson still believes in them.

I think I know the two Sydney engine tuners mentioned above. It's not too hard to work out who they might be.

I doubt that they are as absolute in their preferences as claimed.


Ray

earlwb

That groove on the front of the crankcase was a classic place for a air leak to develop on engines. You need to make sure the front bearing shield also seals it well too, otherwise it winds up being a nasty air leak with the engine. I have seen a number of engines that worked OK at first, but later developed a air leak there. New bearings just didn't seem to correct the problem either, but maybe it was the wrong type being chosen by the owners. Some guys filled in the groove with JB Weld epoxy to good effect and that usually cures the air leak problem. A shallow spiral groove on the crankshaft, that only goes part way forward, works much better as it works with or without the suction inside the engine. The spiral being made to pull oil away from the front. But then I do not mind oil oozing out of the front bearing. Most all of my engines have open bearings on the front anyway, and the bushed engines always ooze oil out of the front.

Here is a pic on a old engine rod where they use a shallow groove or slot in the rod bushing to help aid in lubrication. But in this case the rod was cast using a poor quality aluminum alloy though. But the rod journals are OK.

pe reivers

Roller bearings have a hard time when lubricated by a fuel mix. Methanol pretty much destroys good oil's lubricating ability. That is why so much oil is needed.
MVVS gas engines have rollers in the big end. The glow version of the same engine is bushed.

On oil distribution grooves:
As a ship's engineer I saw lots of plain bearings, and they all had them located just outside the load bearing section. They were running from about 10% to 90% of the shaft bearing length. The other thing they had in common was pressure lubrication, just like the bearings in an automotive engine.
Now, if you would make an oil collector ring on the face of the crank web, and drill suitable holes to guide the fuel/oil mix under centrifugal pressure to the big end, THAT would mean something in lieu of forced lubrication.

gkamysz

My Feedback: (19)

Pe, have you seen the cranks with an oil feed hole drilled through the intake passage to the crank pin? This was once popular, but I'm not sure anymore. I didn't think it was the best design as the hole exited the crank pin right at the top at 12:00 when at TDC. Of course this only applies to front induction. I might have a Picco crank laying around.

littlera

All I know about con rod oil holes is my experience that if they get plugged up, the conrod bearing will seize on the crank pin from lack of lubricatiion. This is exactly what happened to my Sait .50. I had to replace the crank and conrod.

gkamysz

My Feedback: (19)

quote:

ORIGINAL: littlera

All I know about con rod oil holes is my experience that if they get plugged up, the conrod bearing will seize on the crank pin from lack of lubricatiion. This is exactly what happened to my Sait .50. I had to replace the crank and conrod.

I always worry about that and never run an old four stroke without cleaning the insides.

Recycled Flyer

Sounds like the Cyclon 10cc stunt engine.

Recycled Flyer

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Hi Ray,
just follow the logic trail Ray, when a cross is provided on the front of the rod, the rear wears less.
Circumvent that with a central hole and it fails, so logically the flow is from the unworn to the worn - or from front to back.

Those comments from the engine builders were done in earnest and were unsolicited so what you are angling at is mischievous behavior at best and down right lies at worst.

You just lost me in this thread mate, but its an interesting thread at that.

P.S. What gets me here is that you 'think' that you know who I refer to and go on to doubt their (who ever 'they' may be) claimed resolution.
It just may surprise you to whom I am refering too!

pe reivers

No, have not seen that. It does however not make sense to have the crankpin exit hole on the outside (pointing outwards). It should be on the inside or perpendicular to that (trailing in rotation direction) to allow a flow of oil every time the piston goes through top dead center. By rotary surface film drag, this oil is drawn into the bearing squish space as soon as the combustion load relaxes. A study of the wear pattern of the crankpin will clearly show where not to make the exit hole.

gkamysz

My Feedback: (19)

I have a Picco 3.5cc FISE with this kind of crank. The rod big end also has two holes in the normal location. I know Cyclon used crank oil holes in some engines. They also have seemingly odd locations for conrod oil holes.

I'm calling BS on oil exiting the oil hole. Simple experiment. I took a rod and put it on an electric motor with appropriate shaft size. Held such that the oil was facing up(little end down), I put oil into the hole, while running. With no load on the rod the oil just sat there. As soon as I put a load on the rod, pushing in the direction of the oil hole as typical, the oil was quickly drawn in. Loaded the other direction oil was pushed out of the hole. This coincides with any text an experiment I've ever read. This experiment came to mind yesterday, but I just now tried it. I simply did not believe oil was exiting the holes.

There still remains the issue that there is very little oil to fill the hole in an engine. How does it collect oil? Mist settling on it? Scraping off the crankcase walls?<hr style="font-family: Verdana, Arial; font-size: 13px; background-color: rgb(251, 252, 255); " />gkamysz

gkamysz

My Feedback: (19)

BTW, Earl, thanks for the photos. I was sure somebody had used a groove like that. You must have a pretty impressive engine pile. I'm trying not to add to my pile lately.<hr style="font-family: Verdana, Arial; font-size: 13px; background-color: rgb(251, 252, 255); " />gkamysz

Recycled Flyer

So as I understand this, you simply wet with oil the outside of a hole and observed a pumpimg action?

Perhaps it may be different when the entire assembly is equally wet with oil and one side is faced with the centrifuge of the crank web doing 10,000rpm + and the other side is faced with the drag of the back plate.
Don't you think that its highly possible that the plausible pump system you evidenced could work in reverse?

How does the engine collect oil? The fuel/air mix coalesces upon contact with any surface and there will always be a reservoir of fluid inside the workings of any run or just run two stroke.
Pull the back plate of any IC model engine just after it has run dry of fuel and watch what drips out of it, and this is when it is in its driest condition apart from storage! When its running I would envisage that the internals would get a whole lot wetter again.<style type="text/css">@font-face { font-family: "ï¼*ï¼³ 明æœ�";}@font-face { font-family: "Cambria Math";}@font-face { font-family: "Cambria";}p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Cambria","serif"; }.MsoChpDefault { font-family: "Cambria","serif"; }div.WordSection1 { page: WordSection1; }</style>

gkamysz

My Feedback: (19)

We can guess and assume many things and many different answers will come of it. You can guess whatever you want if you put the burden of proof on somebody else to prove you wrong.

Maybe you can find an oil pressure plot for a journal bearing that suggests oil might exit at the lowest pressure point (below ambient). Maybe you can do the math to see if the volume of oil in the oil hole at 10,000G is enough to overcome the negative pressure. Maybe I can put the burden of proof on you.

To my mind there are answers if you want to find them.<hr style="font-family: Verdana, Arial; font-size: 13px; background-color: rgb(251, 252, 255); " />gkamysz

qazimoto

My Feedback: (1)

I'm pretty sure that this is the engine that Recycled Flyer is really talking about (see pics below). It's a Rothwell R250 Vintage A Team Racing engine. It's a very good development of the Oliver Tiger mk3. It's a much better engine and has been developed well beyond anything ever produced by the Olivers.

I have three of the R250 diesels. The pictures below show the rods of two of them. One has the modification that Chris (RF) has described the other doesn't. Note the picture of the hardened steel plate on the backplate and the other picture shows the backplate in place and the fine clearance between end of the crankpin and the plate.

During operation if the rod tends to migrate backwards against the crankpin taper and bears against the BP the movement is limited.

I have no doubt that the rod with the front face treatment and no oil holes is 100% effective.

The other one with the oil holes is effective as well. If SMR says, as RF claims (I suspect), that the former is much better then I accept that.

Is it the greatest innovation ever in model engine conrod design?

Well it first appeared in the 1960's in ETA 15 team race diesels, it wasn't a secret, and there are equally as good engines that don't use it.

It certainly works in the R250. That's all I know with certainty. The rest is opinion or conjecture.

That also applies to what goes on within a running model engine. You can offer up theories.

This topic was offered up as a religious discussion.

It started with a dogmatic statement of belief with a claim to a higher authority as proof.

For the past six years I've been trying to teach first year undergraduate students the notions of the Scientific Method.

FFKiwi has touched on these above.

Anyone with some Science or Engineering training expects nothing less.

qazimoto

My Feedback: (1)

The grove pictured is put there by the manufacturer and runs to the venturi. The front bearing is unshielded on the PAW 15 TBR GTS diesel.

A Nova Rossi .21 I stripped down last year had the same feature.

Ray

gkamysz

My Feedback: (19)

You'd be surprised at how quickly the rod in my experiment became too hot too hold at only 10-12kRPM, without any load. I think the temperature stabilized though. I didn't have a handy way to measure temperature.

Why don't more model engines locate the rod in the piston such that it doesn't rub the backplate? Especially removable cylinder designs that allow installing the rod over the crankpin without the need for clearance in the piston like a one piece crankcase with slip-in liner?

Back to the Picco crank. In addition to the oil hole in the crank pin there is a groove in the passage right at the hole. I have to think this would assist in collecting oil.<hr style="font-family: Verdana, Arial; font-size: 13px; background-color: rgb(251, 252, 255); " />gkamysz

Recycled Flyer

Well worded Ray, and thanks for going to all that trouble with the pics too.

Actually .......... that was not the engine example I had in mind at all!
In fact no specific engine was discussed with those engine guys but let it be said that both had extensive team race experience and leave it at that.

This was all sparked by off the cuff conversations (one a few years ago) and me trying to 'fill in the blanks' over time and believe me there are a few blanks left for me to fill.

If nothing else, I have learned something here and hope others can take something away from all of this too.

I find modellers who dare to do diesel VERY knowledgable and a pleasure to talk to but they sometimes need prompting, hence the somewhat contentious stance I took at the onset.

Thanks.

earlwb

Interesting.
Several engine designs used a spiral groove to draw oil away from the front bearing so it didn't get too muh oil.
The Fox Quckie .40 engine used a deeper spiral groove on their engine. Fox used the spiral groove on a number of engines.


The groove on this engine actually resulted in an air leak there causing the engine to lean out. But then maybe there were aggravating conditions occuring too, such as the crankshaft may have had too much of a gap between the crankcase and the crank there too.


This example was a interesting air leak situation, where they had drilled a hole instead of cutting a groove to the front of the engine. It would be easy to miss this one as you have to pull the front bearing off to see it. What is puzzling is the anti-oiling groove and anti-oiling hole seem to work Ok when the engine is new, but after it is used a lot, the problem starts to manifest itself. So maybe it isn't the anti-oling method but something else causing it to become a problem.

earlwb

gkyamyz,  That oil hole passage in the crank on the Picco engine is certainly pretty neat. I can see that working out pretty well too. The high RPMS would tend to push oil into the gap of the crankpin and rod fairly well too.

earlwb

There have been several studies done, but most of them are behind a pay to view website though.
Here is a nice article where they were studying the oil film pressure in rod journals and it is free to look at so far.
http://lib.tkk.fi/Diss/2009/isbn9789...9522481627.pdf


Here is another interesting article too.
www.google.com/url