Big stroke 55 cc one cylinder ICE

[AlexS]

Thanks me too 

[AlexS]

Cylinder

Machined outside diameter with sharp P30 10x10 Carbide. Better surface quality. Had some problems with making the cooling fin grooves. Had a 1.5mm HSS bit but it tend to bend and make not good cuts. Had an old carbide tool but tool is weared out. Continued with boring internal diameter to 28 mm.

Piston

Very nice to machine the piston. printed an support block inside the piston of PLA for counter supporting. Turning on the lathe, not much off centric movement of raw 3d printed part.
Played with different tools. Ended with chinees carbide for soft materials. And last cut need to be =+- 1mm depth for good surface quality. Piston is a bit to small now in diameter, but this is a test piston. 2nd piston would be send from supplier because this was off on given sizes (quality check).

Put the piston afterwards in the cnc at home. And modified the 3d model to fit the smaller cutted diameter of current test piston. Trying to milling the ovality of the piston. Width piston is 0.25 less in diameter than perpendicular to piston pin. Draw a elipse pattern so cutted angle is around 90 degrees if you look from topside of piston.
I think by this time the piston 2nd test is done. I have rotate the piston 90 degrees for 2nd test. Changed stepp over of 2mm flute from 0.75 to 0.15 mm. Video is of 1st test, 2nd I already saw better surfaces.

Forced Cooling

Well. Lets make it more complicated! Today it was heavy snowing and got a idea when heading home on a bicycle middle of the snow.

Cooling is now only concern of this engine.

Have some raw idea's to make a shroud around the cylinder and axial helix cooling thing (bottom to top exit around cylinder). Printed fan placed mounted right (backside view) of cylinder. One balance shaft axis have some room for a V or flat belt to power an mixed flow type fan. Raw idea 1:3 ratio gear. And fan and pully in 1. Belt on outer diameter and internal the fan blade structure. bearings supported in printed shroud.

Stay tuned!

[AlexS]

Preparation ready, tomorrow girlfriend at work so whole home for my self. Pre paired for boring cylinder to size 38.8 and stone hone to 39.000 and then fine hone brush short. Could use Kroon Espedon cutting oil for honing, that what also did in 2017.

Cooling

Cylinder lacking of proper heat cooling fins. Why not add a top section. I remember some were at workshop laying PC cooling pasta. Could use that between cylinderhead and top fin.

Cylinder surface 21 cm2. Additional fins add 37 cm2.

Modified cylinder fins before it was 2.5 mm gaps and cut to 12.5 depth. Now 3 mm width and 15 deep. 62 to 72 cm2

Total increase theoretical surface 55%

Later would design the forged cooling shrouds. Helix pattern 8mm heigh channels 4-6 mm wide helix 8-9mm should be fine for prototype.

Other things

Cylinder head bolts M5 are currently A2 or A4, guess A2 stainless steel (a50?). Calculated needed tension force applicable to 50 bar combustion pressure. Better to have 12.9 bolts. Modified cylinder with top and bottom side 7mm thick threaded holes.

[AlexS]

Cooling

Preview of raw concept forced cooling shrouds of "snake" type of cooling channel. Mass around 150 gram.

Need to reinforced around intake for adding an bearing or shaft connection impeller. Does someone have more knowledge about mixed flow propellers?

Other

As you can begin this week set up a concept of backside enclosure or cover or also part of crankcase. These would be printed at home of Nylon12 with fiber reinforcement. Support of separate output shaft bearing. Need to make a extra opening or removable plate in the Cover for easy adjustment of oil pump PRV.

Piston

Test milling of Ovality. 0.15mm depth cut. Surface look better with small step over (0.15mm) of 2mm single flute . Maybe better to remove a bit more like other pistons or wider angle instead of 90 degrees theoretical

[AlexS]

Cylinder

Continued with boring and honing cylinder.

10x10 boring tool had to stick 80mm out so was looking for stable rpm and feed rate. hard metal tip could allow more rpm but find a setting for less vibration.

Around 200 rpm and speed up feed 0.065 to 0.1 mm/rev an 0.5 depth cuts.

Surface is after boring is better then previous cylinder.

Only the size is a bit smaller than required. +- 38.90. I only need to enlarge piston ring gaps and would machine outer diameter piston to 39.0 After stone honing I suspect that bore should be enlarge a bit. The honing stones was 240 grid, this was only one could find at automotive shop, it is more a finishing hone. After that let do the brush his job at 20-30 seconds honing for finish.

Surface look fine for model engine. Real life if feels same compared to Asia air cooled cylinder for a moped.

Not sure how long you have to hone with a brush. I think for this engine it is good enough. I saw a honing pattern around 30-45 degrees. Honing speed 800 rpm and 2 strokes each second more than less!

What do you guys think?

[Admiral_dk]

There is a difference between looking at a picture and holding the Cylinder in your hand .... looks like there is enough pattern to hold Oil and that is all I can see ....

Per     

[AlexS]

Thanks Per  Would be good enough for this engine.

Forced Cooling

Continued playing with CAD on designing forced cooling.

Create an impeller. Downloaded a step file of a T5 48 tooth pulley. And tried to create a impeller. With global dimensions of inlet inner diameter 22 to 30 outlet. Inlet outer diameter 60 outlet 65. Angles starting outlet 30 degree shifted at hub, at outer inner diameter inlet 40 to outlet 70 degrees. Thickness blades 2 at hub to 1 mm at outer diameter.

Today played with how to get a 2.5:1 ratio from crank to impeller without having a pulley in front of the inlet.

Idea to increase rpm with 2:1 a between shaft double helical gear. And then a big T5 60 pulley belt drive to the impeller with 48 tooth.

Should be good enough 10.000 rpm impeller speed at top rpm engine 4000 rpm.

Only have to look how to setup a good support of that 60 tooth pulley with double gear connected.

La chouffe is a big support

Work in progress!

[AlexS]

Connecting Rod

Today arrived second batch with the machined connecting rod and piston.

Did not I didn't expect such a neat finish. Big and small end inner surfaces look very smooth I did give roughness of 0.6. But looking at it, I see a thin cross hatch of 45 degrees in inner  surfaces.

I think I leave it like it is, I was planning to do a honing of these bores my self. Because using needle bearings, I suggest now that pin diameter surfaces are more important. Big end.

Not machined raw rod 69 gram. Machined 51 gram.

Piston

I do not have a piston rod to test fitment, but would be fine I guess.

Ready to machine at home to fitment of new cylinder. But first would making cutting tools for compression and oil groove. And would test that on the previous test piston.

Need to adjust compression ring end gap to fit cylinder too.


To be continued

[AlexS]

Piston

Test machining of piston ring grooves.
More difficult than what I suspected. 0.8-0.85 groove width of compression rings. 2mm oil scraper.
1st ring was a bit wider because need to apply other spacer under small tooling when clamping.

Cut the 0.85 mm tool from hss toolbit. But first time forget lubrication so quit heat build up and tools got less wide.

2nd need to modified tool to increase width to 0.8, next time would make it 0.85. because it is difficult to make it wider with same tool because of axial tool bit is not stiff enough.


Test rings and fit in cylinder. Good enough for prepair final piston.