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

[Nerd1000]

Here you go:

As a size reference, the lifters have a diameter of 12mm.

Side note: I originally designed the injection pump to couple directly to a control rod from the governor. To make this work the rod has to flex to follow the arm that extends from the pump fuel control sleeve, which is sure to create a bit of extra friction. I wonder if it might not be much more difficult to use a proper gear rack instead, might even make some aspects of the governor design easier to arrange. Any opinion?

 

[minh-thanh]

If I were to make that engine, I would do it similar to the one in the picture or I would use it to get other ideas

About the shaft for the lobe I can make it smaller, then the lobes will be smaller and I have more space, the lobes will be fixed with glue and dowels - of course the dowels I will make it smaller
I will fix the pump lobe at 20 degrees before TDC and an additional adjustment range of about 25 to 30 degrees is fine (12.5 or 15 degrees on the camshaft).
That idea gave me the ability to adjust the pump time and when I tested it it was fine -> adjusting the pump time was no longer a problem and I can concentrate completely entirely on other parts

 

[Roger B]

Using a rack to rotate the sleeve is quite feasible. I have made a helix pump using a MOD 0.4 rack with a 20 tooth pinion.

 

[Nerd1000]

If I were to make that engine, I would do it similar to the one in the picture or I would use it to get other ideas

View attachment 150375
About the shaft for the lobe I can make it smaller, then the lobes will be smaller and I have more space, the lobes will be fixed with glue and dowels - of course the dowels I will make it smaller
I will fix the pump lobe at 20 degrees before TDC and an additional adjustment range of about 25 to 30 degrees is fine (12.5 or 15 degrees on the camshaft).
That idea gave me the ability to adjust the pump time and when I tested it it was fine -> adjusting the pump time was no longer a problem and I can concentrate completely entirely on other parts

The roller is a nice feature, I went for flat lifters for simplicity but it did create constraints on the size of the cams, as well as the valve timing and lift.

 

[Nerd1000]

Made the piston rings and fitted to the piston.

 

[Roger B]

Made the piston rings and fitted to the piston.View attachment 150392

Did you heat treat them to get the 'spring'?

 

[Nerd1000]

Did you heat treat them to get the 'spring'?

Yes

 

[Lloyd-ss]

I have been doing some research on material compatibility and have found many different suggestions, plus the old automotive standby selections.

Just trying to remember what you are using. Gray cast iron cylinder (?), home cast piston (what alloy??), and the material for the rings (??).
The rings look very sturdy, like they are for a diesel, LOL. What are they, about 2mm x 2mm?

I am enjoying your progress!

 

[Nerd1000]

I have been doing some research on material compatibility and have found many different suggestions, plus the old automotive standby selections.

Just trying to remember what you are using. Gray cast iron cylinder (?), home cast piston (what alloy??), and the material for the rings (??).
The rings look very sturdy, like they are for a diesel, LOL. What are they, about 2mm x 2mm?

I am enjoying your progress!

Cylinder liner: ductile iron, grade FCD450
Piston: cast aluminium, grade AA337 (9.5% Si, 3% Cu, 1% Mg, 1% Ni balance Al)
Rings: grey iron, grade FC250.

The rings are 1.15mm thick, except for the oil control ring which is 1.5mm.

I have an unhealthy habit of using FCD450 for almost everything lol. It's also being used for the crankshaft, flywheel, cam gear and cylinder head. I like the easy machinability, and it is as strong as mild steel while also being slightly self lubricating. Makes a bit of dust when machining though.

 

[Lloyd-ss]

Cylinder liner: ductile iron, grade FCD450
Piston: cast aluminium, grade AA337 (9.5% Si, 3% Cu, 1% Mg, 1% Ni balance Al)
Rings: grey iron, grade FC250.

The rings are 1.15mm thick, except for the oil control ring which is 1.5mm.

I have an unhealthy habit of using FCD450 for almost everything lol. It's also being used for the crankshaft, flywheel, cam gear and cylinder head. I like the easy machinability, and it is as strong as mild steel while also being slightly self lubricating. Makes a bit of dust when machining though.

Thanks for that information. You seem to have a reasonable selection of materials to choose from, which is always nice, and of course we all have our favorites. I don't know if there is much advantage of ductile over gray iron for the liner, one way or the other. The high silicon alloy for the piston is definitely important. The long rod in your engine should greatly reduce the side thrust loading on the piston.

For the 2 stroke diesel I am working on, the piston has to be as long as the stroke to cover the inlet ports, which means a fairly long piston. Then, the cylinder liner has to be twice as long as the piston, which means the rod has to be extra long to give adequate clearance at the bottom of the cylinder liner. It all kind of snowballs.

I am debating with myself about the 2 types of pistons that the Detroit Diesels used. The trunk head is the standard one piece style of piston, with the taper and camber for differential expansion. Then there is the crosshead style piston (not crosshead style engine), where the top of the piston, all the compression ring grooves, and the wrist pin bosses are all made from a single piece of steel. Then the skirt is one long tube of aluminum or other material to take the side thrust and seal the ports, with oil control rings at the bottom only. It is usually a press fit (or maybe threaded) onto the piston head. The skirt handles the side thrust, sliding friction, but no compression. The head handles the compression, but no side thrust or sliding as it has full clearance from the liner. I am trying to determine/decide/guess if the steel head with some as-yet un-named bronze alloy for the skirt might work? Possibly the bronze might be compatible with a steel or chrome moly liner that could just be honed to size, instead of a cast iron tube. Mostly just thinking out loud, but wake-up calls are always welcome.
Thanks, Lloyd

 

[Nerd1000]

Thanks for that information. You seem to have a reasonable selection of materials to choose from, which is always nice, and of course we all have our favorites. I don't know if there is much advantage of ductile over gray iron for the liner, one way or the other. The high silicon alloy for the piston is definitely important. The long rod in your engine should greatly reduce the side thrust loading on the piston.

For the 2 stroke diesel I am working on, the piston has to be as long as the stroke to cover the inlet ports, which means a fairly long piston. Then, the cylinder liner has to be twice as long as the piston, which means the rod has to be extra long to give adequate clearance at the bottom of the cylinder liner. It all kind of snowballs.

I am debating with myself about the 2 types of pistons that the Detroit Diesels used. The trunk head is the standard one piece style of piston, with the taper and camber for differential expansion. Then there is the crosshead style piston (not crosshead style engine), where the top of the piston, all the compression ring grooves, and the wrist pin bosses are all made from a single piece of steel. Then the skirt is one long tube of aluminum or other material to take the side thrust and seal the ports, with oil control rings at the bottom only. It is usually a press fit (or maybe threaded) onto the piston head. The skirt handles the side thrust, sliding friction, but no compression. The head handles the compression, but no side thrust or sliding as it has full clearance from the liner. I am trying to determine/decide/guess if the steel head with some as-yet un-named bronze alloy for the skirt might work? Possibly the bronze might be compatible with a steel or chrome moly liner that could just be honed to size, instead of a cast iron tube. Mostly just thinking out loud, but wake-up calls are always welcome.
Thanks, Lloyd

Ductile is less slippery than grey iron, so grey would probably be better for the liner. I just already had ductile iron the correct size.

I wouldn't use bronze for the piston skirt, it's very heavy! An aluminium skirt should be fine against chrome molybdenum steel, thousands of aircraft radials were built with chrome moly cylinder barrels and aluminium pistons.

 

[Nerd1000]

Wow, more than a month since I last updated! My replacement engine block is almost done.

However, another complication has arisen: after an engineering consultation (my dad looked at my drawings while I was away) I've been informed that my main bearing mounts need revision, the 4 M3 screws each not having enough shear strength. He also advised me that my bolts between the top and bottom halves were too short, apparently for optimal performance a bolt should have at least 3x (preferably >5×) its diameter of length between the head and the start of the thread engagement in the mating part.

Some study of bolted joint theory later, I have decided on a solution. The bearing mounts and crankcase will have a new bolt circle drilled so we can have 8x M3 bolts per mount. This will allow enough clamping force to produce a 'slip critical' joint where the shear forces are handled by friction between the two parts. Such joints are much better in fatigue than pins loaded in shear. Also the bolts between halves will recieve sleeve spacers so they can be longer.

 

[Steamchick]

Hi N1000. It's the simple case of long spring in tension versus short spring in tension. And compounded by the differential expansion of the aluminium block versus steel bolts. I had to study "why" a steel tube fitted into an aluminium block was failing at either -30C or +55C ambient, and this interference fit was a similar problem. Long bolts are simply better than short bolts, especially for Aluminium cylinder heads, con-rod big-end bolts, etc. where the cold to hot condition applies the differential expansion most. Your Dad will explain better than I... I first encountered this "differential expansion" discussion at a job interview, from a question relating to sliding clearances of "Very hot objects" sliding in much cooler "steel tubes" (Cannon shells in gun barrels, and shell casings in breaches!) - Then at another job interview about long versus short engine cylinder head bolts - re: cast iron and Aluminium cylinder heads!
K2

 

[Nerd1000]

Another belated update. I've been busy tinkering with my new mill, notably scraping in the vise and knee gib, and making a 22mm horizontal arbor. The reason for the latter is that I was very spoiled this Christmas, and I'm now the proud owner of a vertex BS-0 dividing head. It's very nice, and I used it to cut the timing gears for the engine.

These are fairly beefy gears for this size of engine, module 1 with 10mm face width. The small gear is 1045 steel, and its partner is ductile iron. I've temporarily assembled the engine so I could mock them up and check the mesh. This also meant installing the camshaft and its bearings, semi permanently as the bearings are pressed in on either side of the cams.

The next step is to mill the hub of the camshaft gear and drill it for the retaining pin and the governor flyweights. Once that is done, we'll need to make the rear cover plate and gear housing...

 

[ajoeiam]

Another belated update. I've been busy tinkering with my new mill, notably scraping in the vise and knee gib, and making a 22mm horizontal arbor. The reason for the latter is that I was very spoiled this Christmas, and I'm now the proud owner of a vertex BS-0 dividing head. It's very nice, and I used it to cut the timing gears for the engine. View attachment 152705View attachment 152706
These are fairly beefy gears for this size of engine, module 1 with 10mm face width. The small gear is 1045 steel, and its partner is ductile iron. I've temporarily assembled the engine so I could mock them up and check the mesh. This also meant installing the camshaft and its bearings, semi permanently as the bearings are pressed in on either side of the cams.

The next step is to mill the hub of the camshaft gear and drill it for the retaining pin and the governor flyweights. Once that is done, we'll need to make the rear cover plate and gear housing...

Nice - - - you must have been a 'very good boy' last year (chuckling!!).

Good on you there - - - looking forward to more 'interesting' bit and bobs from your shop in the future!

 

[Nerd1000]

Ok, as promised almost 2 months ago, here's the gear after milling, and the backplate on the engine!

Not the prettiest outcome unfortunately, I had a few boo-boos on the way. But it assembles ok and won't be visible when the engine is finished. Speaking of boo boos, I fumbled and dropped my flywheel right onto a heavy steel part of a power hacksaw I've been restoring for my brother. Naturally it landed on the edge and left a substantial dent in the flywheel's rim... nothing that will compromise the function, but enough to remind me to be more careful in future

 

[awake]

I've heard the term "upset" used for displacing metal through a blow. Seems apropos in this sort of situation ... which I have caused far too many times!

 

[ninefinger]

I recently somehow got an itch to design and build a 2 stroke uniflow diesel model so any model size diesel info is appreciated. I see Lloyd is looking into those too. Anyway carry on. Looking great so far.

 

[Nerd1000]

Work is now in progress on the cylinder head.

For now that basically means I milled the stock to size and drilled some holes. The corners are for the M5 head bolts while the two small holes in the middle are reamed to 6mm for a press fit of the valve guides. The larger, offset hole forms the roof of the swirl chamber and was drilled using a ball endmill. Plenty of work still to go!

Fun fact, I milled the gasket face of the head using a CBN tip. Can't really say the finish is any better than I was getting from carbide, so maybe I was running it too slow.

 

[Lloyd-ss]

Nerd, I have been away for a while, but see that you have not. As always, nice, steady, progress.
What you are doing (and many others, too) is inspiring.
Thank you,
Lloyd