Old Sckool 5 cc model Diesel engine build

[911hillclimber]

Afforded a few more hours on the engine this afternoon.
The 'elephant in the room' for me was cutting the ports accurately with what i have.

I've ordered a 1/8" dis slot drill to cut the ports, there are 4 of them, 2 x exhaust and the inlet and the transfer port. The Transfer and the exhaust ports are on the same height from the crank case deck, the inlet lower down.
All are at 90 degs to each other, exhaust the same size, the trans/inlet a smaller size.

Decided on the approach and confident it will work well; I have to wait for the cutter to arrive early next week, but I can make the cooling jacket/cylinder head in aluminium in the waiting time.

By using the Myford vertical slide the lathe becomes a small milling machine, and after marking out the square base in the cylinder flange the datum is set for all the ports.

The center line of the 3 ports at the same height can be picked up using a sharp dead centre, and I trust my 'micrometer eye' plus some arithmetic to set the height and centre to the datum.
I need to support the back end of the moving jaw of the small vice as it kicks over a bit too much for my liking, but some suitable wire will fix that.

I'm not good with words, so I hope the pics below will speak a thousand words.

[911hillclimber]

Today was to start the aluminium cylinder finned jacket that is also the cylinder head and seals the cylinder to the jacket so crucial to get this right to have good compression.

Looks simple on the drg but one hurdle for me and that is to cut a 24 tpi internal thread inside the jacket bore to match the thread on the cylinder. This means working quite blind.

The large bar blank just about fitted in the 3 jaw chuck but I was nervous of the overhand of the bar and the small grip area on the chuck jaws, but all worked out well, no flying objects across the garage, but i did move the 911 out of 'shot'.

Some careful boring out to the thread ID, then some relief to allow the thread tip to pass into after the thread cuts and also to get a good flat seal face for the top of the cylinder.

Won't bore you with all the details, but the thread in the jacket all came out well and the steel cylinder and the jacket thread together well and seal together at the head. Result!

First time since I was 16 that I had cut a male/female thread on the lathe.
Tomorrow (maybe) will be cutting the cooling fins using a sort of parting tool. This is hard to do and get a good finish so we shall see.

Going in:


Fully home:

[911hillclimber]

Daily updatetime.

Chattteereed my way through the cylinder cooling jacket/head this afternoon. To cut the fins is tricky as you use a parting off tool, but as i don't have one I ground one into HSS stock and set to very very gingerly 'cutting' the fins into the jacket which caused chatter no matter what tool angles I tried, but slowly-slowly got me there.
The fins could be thinner, but I think I will be ok with the cooling.

Added the top recess for the M6 compression screw and tapped the head in prep of making the comp screw itself probably tomorrow, should be a quick job.

The head top will be finned when the cylinder etc is all screwed to the crank case thus ensuring the cuts are orientated correctly and not angled which would look too home made...

No showing of the port cutters yet so will carry on with the other parts, plenty to make yet.

Hope I'm not boring you all!

[911hillclimber]

Spent all day in front of the lathe today, nice, but sure gets to your knees!

Made the contra piston compression screw first, just an M6 set screw, a length of 2mm spring steel and a blob of braze, oh so easy!

Next up was the dreaded inlet 'manifold' from the venturi spray bar (needle jet) to the inlet port when I've machined it. This is a small awkward part, drawn 2 x full size on the plan to make it easier. Taper machining on the bell mouth and similar taper internal machining inside to create a thin tapered wall.

Easy to type...but got there in the end with a bit of imagination. Finished the bell mouth (shape is more like the mouth of a rainbow trout) with a file, far to intricate to machine. Finished well.

So much for those bits, time for the crankcase.
Looks complicated but i hope I have started it the right way.

You need to machine the inside of the case for the crank shaft and the rod, but the whole lot is trapped in the case by a screw-in back plate and the crank runs onto a bush with a trust face to take the axia 'pull' of the propeller.

So, with my nice new 4 jaw chuck, got the casting as true as i thought right and faced the back of the casting, drilled the 7/16" dia hole for the crank shaft bushes and then opened out the inside to 1.250" dia.

This left me with just enough cast metal to take the 24 tpi back plate thread. Really could have done with off setting the casting 1/32" more to get more metal but all done now.

Threading tomorrow/Thursday and then deciding how to do the crank bushes and keep them in line for the crank. They are a 2 thou press fit. What can go wrong? (watch this space).

[911hillclimber]

Disaster struck the project this afternoon.

Cut the thread in the crank case ok. Then decided to make the screw-in rear cover which is aluminum extruded, not cast. All seemed to be ok, but was a battle getting the thread the right dia to mate with the thread in the cast case. After some effort I was there, the fit was nice and it all screwed together, BUT..

The two parts decided to gaul together and the threads picked up. Took a lot of persuasion to unscrew the parts and the cover was ruined and the first few threads in the case are wrecked.

However, have a rescue plan for the case and some more alum for a new cover.

Issue is not just the mating sizes but the surface finish of the threads themselves, the rough finish on both parts caused the issue i think.

Limited time tomorrow, but it won't beat me.

[sladey]

Interesting stuff Graham

[911hillclimber]

Thank you, it has become a bit all-consuming at the moment.

Got out of thread trouble this morning with a Sh!t-or-Bust approach that saved the day, or rather the cylinder block and rear cover machined parts.

Got it all to screw together and tight.

Did my first Lathe/Miller cuts using the Myford cross/vertical slide which was satisfying and decided to call it a day until tomorrow when the rain will keep us indoors.
Need to borrow a 17mm reamer now and the block can be milled for deck height, rod clearance and induction porting.

Will cut the cylinder ports first thing.

A few pics:

Here, the block and the rear cover are in their chucks, hence the strange picture.





The flat face next to the thread is too large, it needs to be machined when the crank and crank pin are in place to set the float of the crank, so some more fitting needed later.

[impmad2000]

This is a tiny one my dad made whilst at college
Probably 0.25cc

[911hillclimber]

Looks great Tim.
The smaller the engine the harder it is to make to tight tolerances. There is a 0.5cc version of the engine i'm doing, and Hemmingway's say it is tricky!

Cutting the ports atm which is a bit nervey.

[911hillclimber]

Managed a few hours in the garage today.

The cylinder ports are all cut using a 1/8" slot drill which is the smallest I have, but new so keen.
Slightly juddery cutting due to the excessive back lash in the lathe's cross slide, but with a little help of a Swiss file, all done.

Borrowing 3 reamers off my mate on Monday to ream the crank shaft bushes out and also be ready for making the con rod which must be the most awkward part to make in the whole engine.

Bits of this engine slowly gathering.

A few pics as ever say more than my words:

[Kneeslider]

That's looking great. Not long till you will hear it run. Excellent progress.

I (mis) spent a lot of my youth making aeroplanes and playing around with tiny 2 stroke engines. My favourite had belonged to my dad in the late '40s or early '50s and wasa Mills 0.75cc, which went on to power a R/C motor glider for many flying hours. I also had a Cox 0.49 cu in engine and an ancient Davis Charlton which were both glowplugs, but the exra faff of carrying a battery about meant they were less practical.

Happy days!

[911hillclimber]

Yes, I have re-awoken my model plane days 3 years ago, and really enjoy it.
The windy weather ruins the flying days though.
I’m all electric, the buzzzzing engines so anti social..

Getting old now.

[911hillclimber]

I now have the reamers and awaiting the drills all under size by 1/64" which might be here tomorrow.

Had a few hours today making the crank bushes. The material supplied had a remarkably reluctant skin on the surface, but eventually the parts were made with about 2 thou interference fit (I guess) and were knocked in place with red loctite helping along the way.

The bushes can now be drilled and reamed to 5/16" dia and removed from the 4 jaw ready for machining the case mounting lugs , deck face and cylinder bore followed by the transfer port. All tricky on the compound slide and the cutters in the lathe chuck.
It is doing this that you realise how flexible even these old cast steel machines are even with light cuts.

I have no idea how to machine the crank yet, but that is for another day.

There are hours to be put into the crank case yet.



The crank bush is much smaller, the part you see is the crank thust bearing face that is part of the main bush:

[911hillclimber]

A few more hours today and a major (to me) step forward on this little project.

With my new drill sized for 'pre-reaming' the crankshaft bushes here drilled and reamed those rock 'ard bushes. This bearing material is a serious challenge to the machine tools I have, but got there.
This allowed at last the removal of the crank case from the 4 jaw chuck and onto the compound slide to machine the tricky bits on the case.

This all went to plan after a few hours of preparation a few days ago.
I made a close fitting mandrel and a stainless through bolt to screw everything tight to the vertical slide.

Managed to arrange the lot on the lathe's cross-slide to allow rotation of the casting and to mill the right surfaces starting with the engine mounting lugs before a very long thinking time before attacking the cylinder bore and more.

Made a pass or two on the one lug face (4 to machine) and it all cut well with very little chatter from the cross slide that (now) has near zero backlash (fixed 100 years of wear yesterday).

A few pics:

[911hillclimber]

Determined and productive day in the garage on this engine.

Wanted to finish the difficult machining on the crank case, the cylinder bore, the rod clearance slots and the transfer port plus the 4 tapped holes to retain the cylinder in place.

Nearly did it all. Just have to tap M4 the 4 cylinder holes and the 4 mounting holes for the lugs if this engine ever makes it into an aeroplane.

Had to make my own boring bar for the cylinder as i don't have the right size milling cutters or an adjustable internal boring bar, so spent 30 mins making one instead of spending and waiting for a 'real' one.

Few pics below. The surface finish leaves a bit to be desired, but a dremmel will sort that out. Big step out of the way, crank next when I've finished off the case and the cylinder details.