Needle bearings in a model diesel ?

[Nerd1000]

1000,
I am sure you have already considered this, but regarding the load on the bearing for the conn rod small end, the total motion of the small end bearing is only about 0.2 revs per one crank rev, with that movement being a rocking motion. This theoretically drops the PV value of that sleeve bearing significantly. That could explain the small end bearings performing better than expected.
Lloyd

Usually oscillating motion is considered harsher than continuous rotation, as it stops an oil wedge forming.

In a 4 stroke that might not apply because the load on the pin switches direction going from exhaust to intake. My understanding is that this allows the oil to get in under the pin and form a 'cushion' that has a similar effect. On a two stroke like yours however, the load on the pin is always 'down' so it is definitely a concern. The drawings I've seen for 2T diesel pin bushes always include oil grooves for this reason.

 

[GreenTwin]

I have always wondered about the big end and small end bearings on steam and IC engines, and puzzled about how much smaller the small end pin and bearing is compared to the large end.

So in layman's terms, is it fair to say that the small end pin and bearing sees much less stress/forces than the big end pin/bearing?

Since the small end just rotates a bit, but does not move side-to-side , but the large end gets flung side-to-side, and thus has a lot of lateral (is that the correct term?) forces on it, in addition to the forces pressing down on it from the piston-generated forces, then the big end needs to be a stronger bearing.

Or perhaps the big end bearing just needs to wrap around a certain sized crankshaft journal, and that determines its size.

I distinctly recall changing majors from Mechanical Engineering to Electrical Engineering, because things don't move in electrical engineering like they do in Mechanical. I heard the motion classes in ME were/are brutal.
Hats off to all the ME's and ME-types out there who understand dynamics.

.

 

[Nikhil Bhale]

I think for the wrist pin maximum force is that of combustion. The force is more or less acting in same direction. Big end has to deal with combustion force as well as mass of all the components, so It needs to be Big.
As nerd1000 has said load on 4 stroke engine component is cyclic in nature while for 2 stroke it is unidirectional. We have a maintenance system onboard ships where the connecting rod bolts for 4 stroke engines have to be renewed every 24000 running hours. This is to prevent fatigue failure of bolts.

Regards
Nikhil

 

[Lloyd-ss]

Bottom line so far, is that, for anything except conventional shell/sleeve type bearings, with constant lube at the small end of the conrod, everybody is hedging their bets. Needle bearings with lube might be in second place.
But basically, anything out of the ordinary is "try at your own risk."

So, how about some empirical test data. If you have looked at my youtube channel, you will notice that I am big on doing simplified tests, usually from materials on hand, that will produce conclusive results. The data collection and a little bit of analysis is fun. Too much analysis is not fun. Someone else can take the data and put it through their number cruncher.

I will have a piston pin (wrist pin) with its bearing(s), mounted with the top part of a conrod. The conrod will be clocked back and forth throughout the test in a +/- 20 deg oscillating motion. The bottom end of the short section of conrod will be supported by a solid pad, with some type of hard cushioning.

A drop hammer will repeatedly, but indirectly, impact the conrod bearing, from above, via the 2 ends of the wrist pin., or via the center section of the wrist pin.The impact force applied to the bearing will be combination of the drop height, the mounting and cushioning material, and the amount of attenuation that the cushining material provides.

Coming up with a way to do a primitive calibration and calculation will be difficult.
Some of the test bearings will be unconventional for the diesel application.
The results of the testing will be indicators, not quantifiers.
Lloyd-ss

edit, And of course, a hot box will be needed for the "business" area of the test unit.

 

[Nerd1000]

Bottom line so far, is that, for anything except conventional shell/sleeve type bearings, with constant lube at the small end of the conrod, everybody is hedging their bets. Needle bearings with lube might be in second place.
But basically, anything out of the ordinary is "try at your own risk."

So, how about some empirical test data. If you have looked at my youtube channel, you will notice that I am big on doing simplified tests, usually from materials on hand, that will produce conclusive results. The data collection and a little bit of analysis is fun. Too much analysis is not fun. Someone else can take the data and put it through their number cruncher.

I will have a piston pin (wrist pin) with its bearing(s), mounted with the top part of a conrod. The conrod will be clocked back and forth throughout the test in a +/- 20 deg oscillating motion. The bottom end of the short section of conrod will be supported by a solid pad, with some type of hard cushioning.

A drop hammer will repeatedly, but indirectly, impact the conrod bearing, from above, via the 2 ends of the wrist pin., or via the center section of the wrist pin.The impact force applied to the bearing will be combination of the drop height, the mounting and cushioning material, and the amount of attenuation that the cushining material provides.

Coming up with a way to do a primitive calibration and calculation will be difficult.
Some of the test bearings will be unconventional for the diesel application.
The results of the testing will be indicators, not quantifiers.
Lloyd-ss

edit, And of course, a hot box will be needed for the "business" area of the test unit.

The other thing you might try is to call someone at (for example) your local SKF office. Their engineers collect a lot of data from numerous applications, and might have some info on a similar use case.

 

[minh-thanh]

Question is the possible use of needle or roller bearings for the crank and pin to avoid some of the oil mess.

Hi Lloyd-ss !

Just my thoughts when I read your thread
The idea is a bit complicated so I dont meant to present it....but maybe it suggests you have another solution ...
So ....

 

[Lloyd-ss]

Hi Lloyd-ss !

Just my thoughts when I read your thread
The idea is a bit complicated so I dont meant to present it....but maybe it suggests you have another solution ...
So ....

Minh-Thanh,
That is a great idea. Maybe I have been looking at this all wrong. Instead of trying to find bearings that don't need much lubrication, I could use standard sleeve bearings that have already proven themselves in diesel-type applications, and then just control the oil.

You show o-rings, and those could be installed so-as to contain the oil. The crank and rod could be double drilled to have supply and return passages. The oil would need to be pumped into the bearings, and then the second passage, located in a opposite location on the bearing sleeve, would serve as the oil return passage to the oil tank. Like a variation on a dry sump system.

Viton o-rings are rated for 400 degree F and are easy to work with and they seal well, and PTFE is rated for 500 deg F, but can be difficult to keep everything leak-free because they are so hard.

The circulating oil might also help remove some of the heat from critical areas.
Great idea, minh-thanh! Thx!

 

[minh-thanh]

Hi Lloyd-ss !
More :

About O rings for Con rod
When I made the 12mm, 10mm shafts and I needed O rings for it, but I used up all of them, so I decided to cut the 25mm O rings to the length of the 12 or 10mm O rings - but 0.3 or 0.4 mm longer. , that allows the two ends of the O rings to press together and they are quite good at keep oil. I did it 3 times, if I remember correctly
Hope this gives you some ideas

 

[Vietti]

Been enjoying this thread. Just occured to me to wonder about a floating wrist pin. The pin is a tight fit in the rod but rotates in the piston. Larger bearing surface than just the rod bearing.. Aluminum or teflon buttons to keep the pin off cyl. walls.

 

[Bentwings]

. Many years ago I built a special machine for food industry. Lubrication is marginal on a good day corn oil being about the best you can use. Anyway this machine had a series of roller bearing lifters almost exactly like automotive roller lifters . It’s where I got the idea there could not be pressure lube only splash I made a test device mounted on a Bridgeport mill it very closely simulated load . In order to simulate cycling I geared it to run considerably faster than the Mach after some 100k hours simulated the test was stopped due to consideration the mill was taking a beating . The idea was to simulate about 5 years continuous running . The lifters survived perfectly with none ofvthe 20 failing I don’t Rembrandt all the specs but a million cycles was the goal . I only remained with the company about 5 years before I retired but as far as I knew the thing was still running when I left the thing processed Vienna sausages for a laugh . There are a whole set of rules for food mfg and processing equipment only certain materials can be used lubes have to be edible if you need to be cleaned out a glass of cORN oil will do nicely LOL. I NEVER WANT TO SE CORN OIL AGAIN. THE BEARING WERE QUITE SMALL ROLLER BEARINGS probably not suited for IC engine but I think many small IC enginges use them in wrist pins with 50 to one gas oil mixes. I’ve never had one fail. Small model airplane engine use plain bearing wrist pins. Castor oil is usually in the fuel mix I’ve had lots of these fail some rather spectacularly
Usually oscillating motion is considered harsher than continuous rotation, as it stops an oil wedge forming.

In a 4 stroke that might not apply because the load on the pin switches direction going from exhaust to intake. My understanding is that this allows the oil to get in under the pin and form a 'cushion' that has a similar effect. On a two stroke like yours however, the load on the pin is always 'down' so it is definitely a concern. The drawings I've seen for 2T diesel pin bushes always include oil grooves for this reason.

 

[Nerd1000]

Been enjoying this thread. Just occured to me to wonder about a floating wrist pin. The pin is a tight fit in the rod but rotates in the piston. Larger bearing surface than just the rod bearing.. Aluminum or teflon buttons to keep the pin off cyl. walls.

I'm using fully floating wrist pins that are free to rotate in both the piston and the rod. As you say, a button on each end stops them gouging the cylinder. Alternatively you could use wire ring retainers.

There have been some engines that use a pin shrink fitted into the rod and freely rotating in the piston, I don't think there is any problem with this other than it making it more difficult to assemble.

Bentwings, I think the quote on your post is messed up.

Anyway, I know that a lot of petrol 2T engines use rollers on the wrist pin (and also the mains and big end). I think the reason they do this is so less oil is needed in the fuel. I have a 1920s Johnson outboard in bits under the house. It uses plain bronze bearings, notably the conrods are made of bronze so the crankpin and wrist pin bearings are simple reamed holes in those parts. They seem to have outlasted the rest of the engine (one cylinder is cracked by rusting, I'll sleeve it one day and get the infernal thing working again). But those engines needed a 10:1 fuel to oil ratio, no doubt the smoke trail is rather impressive when running one! Glow motors are a similar story I think, they always run lots of oil so those plain bearings survive.

For a diesel of course you can't add oil to the fuel and have it lube the crankcase. So some other method is needed.

 

[Steamchick]

"Modern" 2-stroke motorcycles - many since 1970s - have an oil pump instead of pre-mixed fuel-oil. Roughly equivalet to 50:1 fuel oil ratio. The oil is simply pumped into the inlet tract, and inlet air drags it into the crankcase, so it passes through the crankcase to be burned in the combustion chamber, so could work with this diesel?
K2

 

[Lloyd-ss]

The Detroit Diesel 2 strokes, which my model is loosely based on, does have a full floating wrist pin. It is interesting that the rod has a bushing pressed into it but the piston is plain.
Another reqmt of the 2 stroke is that the holes in the piston must be sealed air tight to stop air transfer to or from the crankcase and blower circuit. The service manual says the pin in piston can have up to.010" slop.

 

[minh-thanh]

"Modern" 2-stroke motorcycles - many since 1970s - have an oil pump instead of pre-mixed fuel-oil. Roughly equivalet to 50:1 fuel oil ratio. The oil is simply pumped into the inlet tract, and inlet air drags it into the crankcase, so it passes through the crankcase to be burned in the combustion chamber, so could work with this diesel?
K2

Hi K2 !
If I remember correctly, the pump has an additional function for lubricating the bearings crankshaft.
But with a homemade engine - with what we have on hand, to make an oil pump with a ratio of 50 -1 is almost impossible. I think mixing oil with fuel is the best choice
( A 10 cc engine needs about 1 mm3 of fuel
50 cc = 5 mm3 , and the ratio 50 -1 = an extremely small amount of lubricating oil )

 

[Lloyd-ss]

The vision of the lubrication system is starting to solidify. It will be (mostly) a closed loop pumped system. The crank and rod will have 2 sets of oil passages drilled so-as to have pressurized supply and plain return. O-rings at each end of the bearings will contain the oil and force it to return through the appropriate passages. The overhead cam and rockers might have a simple sump to drip into and return. Not sure yet. Still looking at sealed roller bearings for the 2 main journals on the crank.

Not sure that I made this clear, but the bottom of the piston and the crank will all be exposed, and that is the driver for my "no oil-drip" quest. But the quest will probably get it to "clean enough for a work bench", but not "clean enough for a kitchen counter", LOL.
It is evolving..... slowly.
Lloyd-ss

 

[minh-thanh]

Not sure that I made this clear, but the bottom of the piston and the crank will all be exposed, and that is the driver for my "no oil-drip" quest. But the quest will probably get it to "clean enough for a work bench", but not "clean enough for a kitchen counter", LOL.
It is evolving..... slowly.
Lloyd-ss

I think it's okay if there's a little oil
Conquering challenges and satisfying passions is important !!

 

[Nerd1000]

The vision of the lubrication system is starting to solidify. It will be (mostly) a closed loop pumped system. The crank and rod will have 2 sets of oil passages drilled so-as to have pressurized supply and plain return. O-rings at each end of the bearings will contain the oil and force it to return through the appropriate passages. The overhead cam and rockers might have a simple sump to drip into and return. Not sure yet. Still looking at sealed roller bearings for the 2 main journals on the crank.

Not sure that I made this clear, but the bottom of the piston and the crank will all be exposed, and that is the driver for my "no oil-drip" quest. But the quest will probably get it to "clean enough for a work bench", but not "clean enough for a kitchen counter", LOL.
It is evolving..... slowly.
Lloyd-ss

Don't forget that you'll need to oil the piston and rings!

Two ways I can think of for doing this would be to introduce some 2 stroke oil to the intake (being careful that it isn't enough for the engine to run on alone) or to drip feed into the lower part of the cylinder, rather like the Webster engine does. Either way some oil will be thrown out of the bottom of the cylinder, perhaps a sheet metal shield could catch this so it doesn't go all over the bench.

 

[BWMSBLDR1]

First recall that antifriction bearings are used on both ends of the rod because the combustion loads and the inertial loads combine to give
a continuous compressive load which prevents developing a lubrication wedge in the bearing gap. Some engines can be designed with weighted pistons allowing the compressive load to be relieved thus allowing oil to enter and the wedge to develop.
Secondly I remember that the suppliers of needle bearings supplied hardened sleeves allowing the use of needle bearings on soft steel shafts. This could allow a wider choice of materials for the crankshaft. But carefully check the upper limits on needle bearing rotation rates before designing them in! A famous Ferrari engine, the MM 125 of 1948 was designed with needle bearings in the main crankshaft that failed. Tony Vandervel of Vanwall Engineering bought two of the cars, rebuilt the engines with his companies trimetal bearings, and raced them as the Thinwall Specials. Their success popularized the use of these bearings in England, saved Ferrari's bacon and set Vanwall on a successful career in Formula One racing.

 

[Roger B]

Most of the clag that comes from my diesel is unburnt fuel that gets past the piston.

It has a low pressure, low volume pump system for the plain main bearings and big end. The crankshaft is drilled through from both ends and oil is fed via both main bearings to the big end. The little end and piston seem to survive on splash lubrication.

The oil pump is a modification of an E T Westbury design with a worm driven reciprocating and rotating plunger. There are no valves to block or stick. The oil flow can be adjusted by altering the position of the wedge piece. To prime and adjust the system I can disengage the worm and spin the pump with a battery drill.

 

[Steamchick]

An odd couple of thoughts.... Lloyd, Am I correct thinking the crankcase takes the (supercharged./blown) intake air and through transfer ports feeds the combustion chamber? - like most 2-stroke petrol engines?
I would recommend lip seals instead of o-rings. As the contact surfaces are fine narrow lips there is less heat, better cooling and much better sealing and durability with lip seals. - you don't want to replace o-rings after but a few runs.
Any surplus oil in the crankcase region, that is transferred to the combustion chamber, should burn as does the diesel fuel. It is a hot engine during combustion, and fine oil droplets are the same chemistry as the atomised fuel. The oil mostly burns in motorcycle 2 strokes with large throttle openings, so should burn much better in a diesel at higher temperature and excess air.
Minh, on motorcycle 2 strokes the oil pumps are small and geared down to one stroke every 100 revs or more, to meter the small oil delivery. Worms and wheels here. No pressure. Also, the oil is introduced via a small hole close to the carburettor. With Lloyds engine having a supercharger/blower, it could be advantageous to feed the crankcase oil - if mist lubrication is a solution - before the blower, to help lubricate the supercharger/blower as well?
Just crazy ideas. . .
K2