Needle bearings in a model diesel ?

[Roger B]

This is the original oil pump design from ETW.

 

[Lloyd-ss]

Roger,
I see how the ETW pump works, but is it really a pump, or just a variable metering valve for pressurized oil?
Agreed, it is pretty straightforward.
Thanks, Lloyd

 

[Lloyd-ss]

I will be transitioning this discussion back over to the build thread of the model shortly.

https://www.homemodelenginemachinis...ke-will-it-ever-work.31110/page-7#post-393329
This post is to help clarify some of the original design details of the Detroit Diesel 71 series (71 cubic inches per cylinder, 2 stroke). It will show how I plan to deviate with what I am building, which is, "my interpretation" of the DD 2 stroke.

The model will be about 1/3 scale, but possibly smaller.... or larger.
The 71 cubic inch diesel will therefor become about 2.55 cubic inches or 41.8cc. But no promises, LOL.
The DD has a 4.25" bore x 5.00" stroke. The deck height is 16.18" and the conn rod is 10.20" C to C with full floating pin, and a drilled oil passage that also squirts oil onto the bottom of the piston. Injector fires directly into the center of the piston crown. There are either 2 or 4 exhaust valves, depending on config. There was also a turbo version where the turbo blew into the inlet of the roots blower.
The roots blower on the left ( a positive displacement blower with basically no boost pressure) feeds the intake air via slots halfway down, and all around the circumference of the cylinder liner. It also blows out the exhaust gases. The cylinder liner is 10.7" long. The crankshaft has 3.50" mains and 2.75" pins. The piston is 5.70" long and has 1.50" wrist pin. It has oil control rings at the top and bottom. The crank has the usual counterweights, but the camshaft at the top left, and the balance shaft at the top right also have counterbalance weights, fore and aft. The engine is designed to be assembled with left or right hand rotation, by switching the cam and balance shaft (and a lot more), mainly when used as twin marine engines.

The most serious way the model will deviate is with the open crankcase, so that the inner workings will be visible. (No fingers, thank you! ) The design will be such that a cover for the crankcase can be added if the oil mess becomes too much.

It will have a closed loop forced lubrication system, plus maybe metering some 2 stroke oil in thru the roots blower to add some lube for the cylinder walls.

Sounds easy enough, ha!
Lloyd

P.S.
Congrats to Minh-thanh . I noticed that he has some new credentials on the forum! He, like all of you, make this, most importantly, a fun place.

 

[minh-thanh]

P.S.
Congrats to Minh-thanh . I noticed that he has some new credentials on the forum! He, like all of you, make this, most importantly, a fun place.

Thank you very much !
I've just become a forum mod and I'm also learning...
But perhaps the easiest task is "Welcome to the forum" for new members

 

[Roger B]

Roger,
I see how the ETW pump works, but is it really a pump, or just a variable metering valve for pressurized oil?
Agreed, it is pretty straightforward.
Thanks, Lloyd

Yes it pumps and if you adjust the phasing of the ramp too far it also sucks. This is how I made it, not as elegant as the ETW version but it also includes a distribution manifold.

 

[Lloyd-ss]

Roger,
OK, now I see it better. The worm gear rotates the shaft item 6 at a speed proportional to the engine speed. The handle item 4 oscillates back and forth to move the piston (also item 6) up and down in sync with the opening and closing of the in and out ports in item 1. Adjusting the angular range of item 4 can also change the pump stroke volume. Similar to a diesel injector.
Got it! Thx

 

[Roger B]

Roger,
OK, now I see it better. The worm gear rotates the shaft item 6 at a speed proportional to the engine speed. The handle item 4 oscillates back and forth to move the piston (also item 6) up and down in sync with the opening and closing of the in and out ports in item 1. Adjusting the angular range of item 4 can also change the pump stroke volume. Similar to a diesel injector.
Got it! Thx

4 is fixed, the brass knurled bit on my version. It has an angled surface to match one on the drive gear which causes the piston 6 to reciprocate. The phasing of this to the flat on the bottom of the piston controls the flow rate. Easy to adjust down to small flows and no valves to stick/block.

 

[minh-thanh]

Hi !!!
Just my thoughts
Full control of the lubricating oil is not required.. If there is some lubricating oil involved in the combustion, it's fine
As long as it's not the primary fuel for combustion, it can take up 5, 10, 20 or 25% of the fuel's volume it's not a problem, and I don't mind.
My way: First I need the engine running - because when the engine runs I know I'm on the right track, then I'll perfect it or I'll perfect it with a 2nd version - if I can ( always with a single cylinder engine, of course)

 

[Steamchick]

Hi, Post #63. Thanks, as it explains the "non-crankcase" feed of combustion air. So really, unlike crankcase fed motorcycle engines, there is very little lube oil going to get into the combustion chamber. And I now appreciate why a feed and return arrangement for crank bearings is a practical alternative to "total loss" lubrication.
I have seen "ships' engines" with blowers that are 2 strokes and have side ports in the cylinder for either exhaust or inlet. - I think it depends on whether it is a "huge" slow-speed engine or "small high-speed" engine as to which way it is configured?
K2

 

[Lloyd-ss]

Hi, Post #63. Thanks, as it explains the "non-crankcase" feed of combustion air. So really, unlike crankcase fed motorcycle engines, there is very little lube oil going to get into the combustion chamber. And I now appreciate why a feed and return arrangement for crank bearings is a practical alternative to "total loss" lubrication.
I have seen "ships' engines" with blowers that are 2 strokes and have side ports in the cylinder for either exhaust or inlet. - I think it depends on whether it is a "huge" slow-speed engine or "small high-speed" engine as to which way it is configured?
K2

Hi Steam,
The hope is to keep the speed of this model fairly slow, that is part of the reason I have agonized over the injector to get good atomization at low volume/stroke. The original DD had a 4.25" bore x 5" stroke but I plan to use a slightly longer stroke length ratio in the model, for 2 reasons: 1) to help keep the rpm down, and 2) to provide longer burn-time for the diesel fuel.

I will transition back to the original build thread now.
Lloyd

https://www.homemodelenginemachinis...ke-will-it-ever-work.31110/page-8#post-393470

 

[Rocket Man]

This is a TEST to see if my email to this forum works, I keep getting a message, email is now $69.95 sign up now.

 

[Lloyd-ss]

This is a TEST to see if my email to this forum works, I keep getting a message, email is now $69.95 sign up now.

Looks like it came thru like it is supposed to. Do I get the $69.95 now?

 

[kf2qd]

a bronze sleeve bearing will take a lot of use, and with a small amount of oil will last forever. I have an old K&B Model aitplane engine that I have had since the late 70's and the bronze bearings are still doing great. That is a 10,000 rpm engine that has a lot of hours and still runs great. Granted, it does have a supply of oil, but any bearing is going to need oil. Also consider the overall size of the bearing, because you need enough rod to surround the bearing for strength, and still fit inside the chrankcase.

 

[Steamchick]

One significant cause of models wearing bearings is shaft flexure. A major issue on full-sized cranks and related bearing wear. The parallel idea is the reason many motorcycle engines use a ball bearing on the drive end, and either roller bearing or bronze bush on the timing side where there is no side thrust. But if the crank is not stuff enough the bronze bush wears at high speeds when the crank flexes and effectively is not parallel with the bearing so touches ends and causes wear. Aeroplane and boat engines with propellers do not have the side thrust of belt or chain drive on a cantilever end of crank professing beyond the bearing, so can tolerate a bush for longer Without wear.
Just musings..
K2

 

[Lloyd-ss]

Gents,
Thanks for the latest posts. I (and many others I am sure) have wondered why there are just a sinful number of bearing choices from hundreds of catalogs and hundreds of manufacturers. When the answers for making a specific bearing choice are explained, they seem pretty much like common sense. But usually, it is that I didn't know what the correct question was. Learn something new every day or you have lost an opportunity.

 

[Ozwes007]

Have a look at outboard engine, some of those use split roller bearings.

 

[Nerd1000]

One significant cause of models wearing bearings is shaft flexure. A major issue on full-sized cranks and related bearing wear. The parallel idea is the reason many motorcycle engines use a ball bearing on the drive end, and either roller bearing or bronze bush on the timing side where there is no side thrust. But if the crank is not stuff enough the bronze bush wears at high speeds when the crank flexes and effectively is not parallel with the bearing so touches ends and causes wear. Aeroplane and boat engines with propellers do not have the side thrust of belt or chain drive on a cantilever end of crank professing beyond the bearing, so can tolerate a bush for longer Without wear.
Just musings..
K2

I think this is technically called 'edge loading'. It's a major factor for needle roller bearings too. Broadly speaking the longer the bearing is in relation to its diameter the stiffer the shaft has to be in order to avoid issues.

As I understand it the softer bearing materials like Babbitt hold up a bit better because they can 'conform' to the load. Perhaps this is part of the reason vintage engine designs often seem to get away with thin, flexible crankshafts and long, small diameter bearing journals.

 

[Steamchick]

Thanks Nerd. I am glad someone can expand on my limited knowledge. Teach us some more
K2

 

[Bentwings]

I have to agree with using bronze bearings I YHINK if you look up load ratings you will find a full cylindrical bronze bearing with oil lube will problem out last the engine. There is a specific bronze bearing material number but it escapes me. Full floating automotive steel connecting rods often have bronze bearings even heavy duty diesel Even with minimum oil they they are like the ever ready rabbit .

 

[Lloyd-ss]

I have to agree with using bronze bearings I YHINK if you look up load ratings you will find a full cylindrical bronze bearing with oil lube will problem out last the engine. There is a specific bronze bearing material number but it escapes me. Full floating automotive steel connecting rods often have bronze bearings even heavy duty diesel Even with minimum oil they they are like the ever ready rabbit .

There will definitely be some bronze bearings in this model, but maybe some ball and roller, too.