Model Diesel: 32mm bore, 38mm stroke, indirect injection

[Lloyd-ss]

Good save on that "minor" issue.

In the software development world, they would call that a "special feature" of the piston.

But I am always curious to know. A good percentage of the time when I break a drill or tap, I am telling myself just before it happens: "C a r e f u l....... don't mess uuuuuuupppppp." SNAP.
Did you see it coming?

 

[Nerd1000]

I was more or less the same. Gently does it... *tic*. Did I just break my drill?

Being Australian, I then followed my cultural traditions by saying something that doesn't bear repeating in polite company.

I'm pretty sure that the problem was a result of not backing out to clear chips often enough. I was peck drilling, but wasn't fully retracting the drill often enough. The really tiny drills and taps seem to be worse for such issues, compared to their larger brethren.

 

[Nerd1000]

Here's a bit more progress:

Gudgeon pin and its aluminium buttons.

Assembled with piston and rod.

Making the cams for the camshaft using the mill indexer. Here I'm drilling the cross hole for pinning them to the shaft. The lobes were cut as 72 facets using a table of cut depths, then smoothed with a file.

Completed cams prior to heat treatment

Finished camshaft.

I made the cams from 4140, which I oil quenched to harden them. The 4140 must have been on the low end of carbon contents, as the end result was still soft enough to cut with a file. So I re hardened them with cherry red case hardening compound, which put a thin case on the surface over the hardened 4140. We shall see how it holds up!

The cams are pinned to the shaft with No. 3 tapered pins. One could also use dowels, but the taper pins will be easier to take out if I decide to change my cam timing.

 

[Scott_M]

Hi Nerd
Thanks for the update I have been enjoying the build !
If it was indeed 4140 it should be able to get hard enough to resist a file. Judging from the other stuff in your photos and the print I am guessing the thickest part of the cam would about a 5.5mm ?
4140 would need to be held at temp for 1 hour per inch of thickness, so about 10-15 minutes for 5-6mm before quenching. Do you have a furnace or did you use a torch ? Holding at temp with a torch is much harder to do. Doable but not much fun.
The case hardening should do the trick though.
Thanks again

Scott

 

[minh-thanh]

Hi Nerd .
How can you change the cam timing when you use a pins ?
And Thanks for the update I

 

[Nerd1000]

Hi Nerd
Thanks for the update I have been enjoying the build !
If it was indeed 4140 it should be able to get hard enough to resist a file. Judging from the other stuff in your photos and the print I am guessing the thickest part of the cam would about a 5.5mm ?
4140 would need to be held at temp for 1 hour per inch of thickness, so about 10-15 minutes for 5-6mm before quenching. Do you have a furnace or did you use a torch ? Holding at temp with a torch is much harder to do. Doable but not much fun.
The case hardening should do the trick though.
Thanks again

Scott

Not far off regarding the size, the shaft for reference is 8mm. I used a torch, which is adequate for the silver steel I'm accustomed to but 4140 is a different beast I suppose. Oddly it did harden enough to resist a file when i tried quenching a scrap piece in water rather than oil. I was worried about cracking if I subjected the real parts to such an aggressive quench, so I went for case hardening with an oil quench.

Hi Nerd .
How can you change the cam timing when you use a pins ?
And Thanks for the update I

The pin bores in the shaft are all in line, so by making a new cam lobe with different timing I can simply swap it in place of the old one.

 

[minh-thanh]

The pin bores in the shaft are all in line, so by making a new cam lobe with different timing I can simply swap it in place of the old one.

I don't know your design, but if it were me, I would find a way to adjust the pump timing a little simpler, like bolts or clamps..., because with a small diesel engine there are a lot of things ....to adjust and discover . Changing the cam lobe with a new cam lobe requires disassembling and assembling many parts...which adds complexity and increases fatigue over time..
I always like to do something a little simpler .
Personal opinion !
Each person, each way ...

 

[Nerd1000]

I don't know your design, but if it were me, I would find a way to adjust the pump timing a little simpler, like bolts or clamps..., because with a small diesel engine there are a lot of things ....to adjust and discover . Changing the cam lobe with a new cam lobe requires disassembling and assembling many parts...which adds complexity and increases fatigue over time..
I always like to do something a little simpler .
Personal opinion !
Each person, each way ...

It's also possible to change the timing by varying the clearance between the pump cam follower and the pump plunger, a larger clearance will delay injection (it will also reduce the quantity of fuel injected, but my pump can deliver far more than is needed anyway). There's an adjustment screw for this in the design. I also wanted a way to make larger changes if required.

 

[Steamchick]

My concern with any cross-pinned cam is the torsional load on the pin. Basically it tries to "waggle" the cam on the shaft and the pin takes oscillating shear loads. Hardened pins are probably OK, but the unhardened shaft and cam holes apt to fatigue and wear, so I should have silver soldered or bronze brazed the cams to shafts, relying on the pins to hold everything accurately while brazing. Then case hardened the cams before a final polish. The finer the polished surface the better IMHO.
Obviously, it doesn't disassemble though!
Only time will tell if the pinned cams are adequate for fatigue long-term?
But well done so far!
K2

 

[peterl95124]

I too obsess about cam hardness, but have found that I run my engines so infrequently that my not-very-hard 4130 cams are holding up just fine, though am switching to A2 just for the heck of it

 

[Nerd1000]

My concern with any cross-pinned cam is the torsional load on the pin. Basically it tries to "waggle" the cam on the shaft and the pin takes oscillating shear loads. Hardened pins are probably OK, but the unhardened shaft and cam holes apt to fatigue and wear, so I should have silver soldered or bronze brazed the cams to shafts, relying on the pins to hold everything accurately while brazing. Then case hardened the cams before a final polish. The finer the polished surface the better IMHO.
Obviously, it doesn't disassemble though!
Only time will tell if the pinned cams are adequate for fatigue long-term?
But well done so far!
K2

In this case the pins are softer than the shaft and cam; taper pins are usually just mild steel. They shouldn't be seeing torsional stresses though? Just shear at the joins.

 

[Steamchick]

Sorry, the torsional stresses are the transfer of torque from cam to pin to shaft. My text wasn't clear (As my brain is often torsionally stressed - I.E. twisted - too). The pins are in shear.
An alternative fixing would be to use an interference fit between the cam and shaft, and shrink-fit the cam onto the shaft. The high frictional forces generated should greatly improve cam security from torsional stresses at the interface between cam and shaft.
Just an idea for the experts to advise?
K2

 

[Lloyd-ss]

1000,
I love the progress reports, and the picture of the assembled piston, rod, and bearing almost gave me goose bumps. (OK, I confess, it did give me goosebumps, ha ha.

The discussion of the cam attachment is interesting. I think I tend to trivialize that sort of thing because in my previous life, I couldn't trivialize anything. So now, gut feel, and a few calculations if there is reason for such, seem to be sufficient. The power of the engine might be the cube root of the real thing, but the strength of the parts and fasteners might be the square root of the original, so mostly plenty of strength to spare? I do understand the concern for the unique dynamics of some of the internal parts where fits might be an issue, and pay attention to that too. Do you think your engine will have to make it past 10 minutes or 10k miles?
Just in an odd mood and joking.
Very nice!
Lloyd

 

[minh-thanh]

Personally, I think that shaft is fine, at least with the model engine
But with my little experience, changing the lobe to change the pumping time seems a bit too complicated
Making a diesel engine is a difficult task so why make it more complicated !!??

 

[Nerd1000]

Just felt like doing some turning today, so I made the valves.

Minh you must have missed my reply where I said the pump timing can also be adjusted by other means (namely the clearance between the pump lifter and the plunger). Being able to change the cam lobes is probably more useful for experimenting with different valve timings or different lift profile of the pump cam. Which is not a priority, but might be fun if the engine works.

 

[minh-thanh]

Hi Nerd !
I don't miss your answer. I know those things
Pump lobe, timing, amount of fuel ... they are closely related to each other.
When you adjust the clearance between the pump lifter and plunger and you have a amount of fuel injected is fine and you want to change the timing a little you have to make a new lobe, remove - reinstall...then test run - no okay and you make the new lobe... So why not make it simpler by making a lobe that has the ability to adjust as needed!?
With DIY engines, I don't object to the way people make a part or an engine. Just make it a little simpler if possible, save time, effort...and increase the likelihood of success.
Once the engine is running you can change things up if you want to learn more...
Just a personal opinion.
DIY engine - do it the way you want.

 

[Nerd1000]

Hi Nerd !
I don't miss your answer. I know those things
Pump lobe, timing, amount of fuel ... they are closely related to each other.
When you adjust the clearance between the pump lifter and plunger and you have a amount of fuel injected is fine and you want to change the timing a little you have to make a new lobe, remove - reinstall...then test run - no okay and you make the new lobe... So why not make it simpler by making a lobe that has the ability to adjust as needed!?
With DIY engines, I don't object to the way people make a part or an engine. Just make it a little simpler if possible, save time, effort...and increase the likelihood of success.
Once the engine is running you can change things up if you want to learn more...
Just a personal opinion.
DIY engine - do it the way you want.

Well I did consider making the lobe just held on by a setscrew. But didn't trust that approach, they always seem to loosen and then spin on and gouge the shaft, have fixed many machine tools and other things with such symptoms. Or I could have used an external pump, but it seemed like a lot of extra parts to make compared to just putting the pump lobe on the camshaft.

The clearance method is used on even full sized diesels. So I think it will work, but I might have to also adjust the governor to achieve the same running speed, as changing the timing will also change the fuel quantity. Though that would probably be the case with any timing change regardless.

 

[minh-thanh]

Do you have a 3D image of the design at the location of the lobes ?

 

[Nerd1000]

Do you have a 3D image of the design at the location of the lobes ?

I can take a screenshot from my CAd software. What parts do you want to see?

 

[minh-thanh]

I want to know the location of the lobes, the space for them,