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

[Nerd1000]

Hi Nerd1000. Some of us talk the talk, others get on and do the job! - Excellent stuff! Don't worry about that odd nick from the tool, just make it the location for an oil drilling anyway! How fine did you linish the journals? I'm sure when crank grinding as a teenager, we were using finer than 600 grit, - I think the next may be 1200 grit emery? It was quite expensive stuff as I recall being told! - It came as a big coil of 1" wide... We had a special tool that had a fine adjustment then locking lever arrangement - it used interchangeable jaws that were usually the journal diameter plus a bit, so the linishing emery was clamped "just so" with not a lot of pressure, rotated a dozen or so turns slowly (100~ 200 rpm-ish?) - so on models I use Mole grips for the same task. But I have not made special jaws (Yet) as the "best of my grips" has good flat faces. But we NEVER ran 2 directions for linishing journals. I'm sure the crank grinding was always "clockwise" looking at the timing end (the direction of rotation of the crank in service), and we never had cranks returned (even from Haulage high mileage customers, or car racing guys) for Scuffed journals. We washed the journals (and rinsed oil-ways through) with paraffin before oiling when finished: the clean Paraffin always washed the "smokey" abrasive residue from the finished journal.
When I worked on engines for a major car maker, the Glacier company senior engineer explained the composition of aluminium-tin for the white- "Glacier-metal" shells was selected to have enough silicon (nodules) in the alloy to polish cast iron, without causing undue wear. But I wonder what bearing material you will use? Of course, you are right about the "grinding directionality" of the micro-structure of cast iron shafts. That was a key point about using the aluminium tin bearing shells instead of Phos-bronze metals on cast-iron cranks. - Or so metalurgists and tribologists at both Glacier and Welworthy - and my head office expert - taught me!

Well done on a proper job.
K2

Thanks K2.

At present I'm planning on using LG2 bronze for my bearings, mostly because it is easy to get and machine. I think I used 600 grit for the polishing, but I can always come back with finer grit to finish up.

The engine is to be splash lubricated so there's no need for an oil drilling in the crankshaft! My plan is to put a scoop on the big end cap with a drilling through to the bearing, this way the big end should get some oil force fed into it every time the scoop splashes into the sump. The mains are more generously sized so they should be able to subsist on the oil mist being flung about in the crankcase, so long as appropriate oil holes are provided.

 

[Lloyd-ss]

Nerd,
Impressive work. Keep that inner perfectionist on a short leash and keep doing what you are doing. Something to be proud of!
Lloyd

 

[Lloyd-ss]

Nerd, your analytical and research oriented nature is apparent in many of your posts. I have a thread going on a single cyl diesel also, but my approach is more design-as-I-go. But with decent research and experience. You must have considered a balance shaft for your single cyl, as am I. Would you be so kind as to share your thoughts? Thanks.
Lloyd

 

[Nerd1000]

Nerd, your analytical and research oriented nature is apparent in many of your posts. I have a thread going on a single cyl diesel also, but my approach is more design-as-I-go. But with decent research and experience. You must have considered a balance shaft for your single cyl, as am I. Would you be so kind as to share your thoughts? Thanks.
Lloyd

I think it's probably not needed for a comparatively small engine like this, but if you want to try it why not. Would certainly be nice to have an engine that ran super smooth and didn't try to shake itself off the table during demos. I think the usual arrangement for a single is to have two balance shafts geared to run in opposite directions, this way they can act together against the primary imbalance without introducing any side to side vibration or rocking couples.

My engine has displacement not far off that of a weed eater, I'm expecting it to shake quite a bit worse than one of those due to heavier internals, high compression and 4-stroke running. Should still be manageable, so long as the engine and its base together are heavy enough. I'm certainly not optimising it to be light, the block design has loads of excess metal in it... and I'm tempted to make the engine base from concrete, or fill it with sand if I make it from timber. That's still far in the future however.

 

[Lloyd-ss]

I think it's probably not needed for a comparatively small engine like this, but if you want to try it why not. Would certainly be nice to have an engine that ran super smooth and didn't try to shake itself off the table during demos. I think the usual arrangement for a single is to have two balance shafts geared to run in opposite directions, this way they can act together against the primary imbalance without introducing any side to side vibration or rocking couples.

My engine has displacement not far off that of a weed eater, I'm expecting it to shake quite a bit worse than one of those due to heavier internals, high compression and 4-stroke running. Should still be manageable, so long as the engine and its base together are heavy enough. I'm certainly not optimising it to be light, the block design has loads of excess metal in it... and I'm tempted to make the engine base from concrete, or fill it with sand if I make it from timber. That's still far in the future however.

Nerd, thanks for sharing your thoughts and encouragement. I will see if I can design that into my model without making it huge. I think "super smooth" will have to be a relative term, LOL.
Lloyd

 

[Nerd1000]

And that's a finished crankshaft! Just wrapped up machining the ends. I did most of this between centres, plus a bit of milling to make the keyway (for the flywheel) and flat on the nose.

The flywheel will have a simple parallel bore and will be retained by a big nut on the crank. The way I've made it is slightly cursed, it's a 15mm diameter... with a 18 TPI thread cut into it. I'm probably going to engineer hell for that one.

Anyway, on the topic of hellfire I think my next move may be to try casting the crankcase again. Stay tuned!

 

[Nerd1000]

Rapid progress today. Here's the block casting.

After removing the gating system and the bigger bits of flash:

Certainly not the worlds best casting here, but I haven't done many before especially with the use of cores. There are a few spots where the surface finish is very rough (probably due to my crappy home made greensand dropping bits into the bottom of the mould), I'll fill those with bog before machining and, ultimately, paint the block to cover them up. Two more castings left for this project (the lower crankcase and the piston), but that's a mission for another day.

 

[Lloyd-ss]

Nerd, so what's wrong with a M15x1.4 thread?

 

[Nerd1000]

Nerd, so what's wrong with a M15x1.4 thread?

My lathe is imperial and thus far less convenient to cut metric pitches. I have to put a special transposing change wheel on and figure out the right combination of stud gear and QC box positions to get the pitch I want. Then once I start threading I cannot disengage the clasp nuts, or I will go out of time with the thread.

Imperial pitch by contrast I can just set the desired pitch on the QC box and use the threading dial to pick up the timing of the thread. Way easier!

 

[minh-thanh]

Hi Nerd1000 !
A mistake of mine hope it helps
For high compression ratio diesel engines, make the valve seat very tight tolerance with the head and press for assembly. You can use a little glue when assembly but don't rely on glue
Or at least have tight tolerances on the part as shown in the picture

 

[Nerd1000]

Hi Nerd1000 !
A mistake of mine hope it helps
For high compression ratio diesel engines, make the valve seat very tight tolerance with the head and press for assembly. You can use a little glue when assembly but don't rely on glue
Or at least have tight tolerances on the part as shown in the picture

View attachment 144640

Hi Minh-Thanh,
I think this is very good advice.

I've actually changed my mind a bit since that iteration of the design. I decided I would make the cylinder head from ductile iron (mostly because it has low thermal conductivity, which i think will help keep sufficient heat in the cylinder for running). Then I realised, with this material the valve seats can be machined directly into the head, no bronze cages or seats required. So I have altered the design with integral seats and pressed in guides.

 

[minh-thanh]

About heat, I don't know if it's better and I'm not too bothered about it, but the cast iron head is a better choice.

 

[Nerd1000]

Some wins and some losses today.

As you can see, the lower crankcase casting did not go as planned. This is my fourth try and I'm still getting misruns! Seems like I need to revise my mould setup to get more pressure pushing the metal into the top of the casting.

However, i had another pattern and core to try:

I had a go at casting the piston, and this came out well. After some clean up on the lathe the blank looks like this:

I cast this in an alloy called AA337, which I bought an ingot of for this project. It is 10% silicon, 3% copper and about 0.75% each of magnesium and nickel, and is sold as an alloy specifically intended for making pistons. The high Si content makes for good wear resistance and low thermal expansion, while Ni increases hot strength. As with most Al-Cu alloys this stuff achieves full strength by age hardening. I don't have a heat treating oven but I did make sure to quench the casting asap after solidification, so with some luck (and the kitchen oven) we should get something like a T5 condition after baking for 8 hours at 180 Celsius.

Now I just need to fix that annoying lower crankcase casting, and all foundry work for the project will be finished assuming I don't mess up a part and have to re-cast it.

 

[Lloyd-ss]

Nerd, Again, I am impressed by your perseverance. You might just need to use a stiff wire to poke a few 2 or 3mm vent holes in the sand where the mis-run occurred. Just to let the steam and gasses escape fast enough. No pressure, LOL.
Lloyd

 

[Nerd1000]

Nerd, Again, I am impressed by your perseverance. You might just need to use a stiff wire to poke a few 2 or 3mm vent holes in the sand where the mis-run occurred. Just to let the steam and gasses escape fast enough. No pressure, LOL.
Lloyd

Oh no, there's no issue with venting, that was the first thing I tried.

I cast the whole part in the cope, as a result there's only about 12mm of sand on top of that part of the casting. By the end of the pour there is very little 'head' to keep the flow going.

I do use a tapered sprue and a pouring cup, I find that the sprue does a fantastic job of controlling the flow rate so I'm not filling too fast (and thus entraining air or eroding the mould) at the start of the pour.

 

[Nerd1000]

Ok, here's a conrod.

That took way longer than planned, many mistakes were made. I'm waiting on some reamers I ordered to do the small end, but in the meantime here goes with the big end.

I made the shells full round but with the circumference oversized by 2x my slitting saw kerf, plus a little extra for crush. After cutting in half the circumference of the paired shells equals that of the bore plus the crush allowance... they are then pushed down into place, bending to conform to the bore shape as they go. As it turns out I miscalculated a little so they needed to be skimmed after installation.

For now I'm setting the clearance with shims. You can also see the oil hole in the lower shell, this connects to a passage in the oil slinger that should scoop some oil up and force it into the big end when it dips in the sump.

This is the point where I discovered a flaw in my crankpin (taper I didn't notice previously), which may be worth reworking. If I do that I'll probably make new shells to match.

Finally, here is the rod assembled on the crank.

 

[Lloyd-ss]

Extremely nice design and machining. I know the discovery of taper in the crank pin was disappointing. The setup to rework that will be time consuming and stressful.
You said you are waiting on a reamer. Do you have a boring head for your mill? I rely heavily on one, just as I do boring to final size on the lathe.
But again, very nice.

 

[ajoeiam]

Ok, here's a conrod.View attachment 146655
That took way longer than planned, many mistakes were made. I'm waiting on some reamers I ordered to do the small end, but in the meantime here goes with the big end.
View attachment 146656
I made the shells full round but with the circumference oversized by 2x my slitting saw kerf, plus a little extra for crush. After cutting in half the circumference of the paired shells equals that of the bore plus the crush allowance... they are then pushed down into place, bending to conform to the bore shape as they go. As it turns out I miscalculated a little so they needed to be skimmed after installation.

View attachment 146657
For now I'm setting the clearance with shims. You can also see the oil hole in the lower shell, this connects to a passage in the oil slinger that should scoop some oil up and force it into the big end when it dips in the sump.

This is the point where I discovered a flaw in my crankpin (taper I didn't notice previously), which may be worth reworking. If I do that I'll probably make new shells to match.View attachment 146658
Finally, here is the rod assembled on the crank.

 

[ajoeiam]

Hmmmm - - - - it was IIRC more for grease situations but I was taught to use a small groove on either side of the bushing with a spiral that went through the oil hole and connected both grooves. (Something that was put in as a final roughing stage with the last fine cuts, maybe 0.010 a side or so, then leaving you with no ridges. (Sorry don't have any pics)

 

[Nerd1000]

Extremely nice design and machining. I know the discovery of taper in the crank pin was disappointing. The setup to rework that will be time consuming and stressful.
You said you are waiting on a reamer. Do you have a boring head for your mill? I rely heavily on one, just as I do boring to final size on the lathe.
But again, very nice.

I don't have a boring head, mostly because my mill is really small and the commonly available ones are very bulky. I have done boring operations on the mill using a flycutter.

I'm still mulling over the rework setup. Presently I'm thinking I might lap the taper out, will have to make a special lap in two pieces.