My first wankel engine 'bits'!

[RotarySMP]

Here is the tanslation of the instructions I promised:

The first bit is just Blah Blah. There is a reference to FMT magazine edition 97, which likely has some Wankel information.

The SW92 was designed in 1960 – 1962 by Dipl Ing Julian Faleki of Poland, and has the following specs:

Swept volume……………………………......9.2 CC
Compression ……………………………….......7.4:1
Max Power output……………..………......1.5 HP
Power at 12000rpm…………….………....……1HP
Fuel…………………………….........Methylalchohol
Lubricant……………………....10-20% Caster oil
Glow Plugs…………………………......…Start 1.5V
Weight………………………………......….900-930g
Eccentricity…………………………......…….3.5mm
Major Radius…………………………......…….28mm
Rotor thickness………………………....…….18mm
Apex seal replacement interval……….….30 H

Building Instructions.

[ 1 ] Rotor Housing.
Study the plans carefully for the location of the housing screw holes. The sharp edges of the rotor housing are manufactured by first machining the housing 1-2mm wider than plan then, after chroming, they are ground to dimension.
The inlet and exhaust are radiused to exactly 0.5mm. It is important that the M4 holes are carefully drilled with equal spacing, especially in the area of cut B-B. The countersink diameter should not exceed 5mm. Accuracy is extremely important, otherwise sealing and compression will suffer.

[ 2 ] Rotor
The seal slots must be symmetrical to ensure good sealing. The given angles must be maintained, and the axis of symmetry must cross the centre line. Through lapping of the sides of the rotor, using lapping paste on a surface plate, you are aiming for the following tolerance: The middle of the rotor should be 4 to 5 microns wider that the corners.

[ 3 /4 ] Front and Rear Housing

Here it is important to follow the correct order of set ups. First you turn a ring of OD ~110mm ID 90 (–0.02mm) about 30mm wide. This ring is the assembly jig. Press the phasing gear [8] in the rear housing, and then insert the bearing. Install the needles [16], the rotor [2] with tensioners [11], springs [10] and apex seals [10] ontothe E-shaft [5]. The rotating assy is inserted into the rotor housing, and the end housings fitted. Slip the assembly jig ring over the housings, then rotate the rear housing until the E shaft turns freely in both directions without any binding. Now the 4mm holes are bored in the end housings with the jig ring in place. After disassembly, the holes are enlarged to 4.2mm and the R45 finished.



Some Assembly Hints.
Before assembly, the entire rotating assembly should be statically balanced. This is performed on pair of knife edges.
The rotor and needles are installed on the E-shaft with plenty of grease. The forward counterweight [6] with it’s key [18] and rear counterweight [7] with it’s pins [20]. The Phasing gear [8] is secured with 4 screws. It has teeth. The mounting holes are not symmetrical. These bolts should be safetied by peening . The bearing [35] is fitted to the rear housing, with sealing rings [15] on each side, and secured with the nut [13]. The front main bearing [36] with it’s seals [19] is fitted to the forward housing, secured by a nut [12], which must be safetied with a split pin.

Both bearings should be lubricated with caster oil. The exhaust [33] and intake [27] are secured with set screws [34]. The spray bar needle [30] is soldered into the knurled thumbscrew [29], such that the 0.9mm hole in the spray bar can be completely closed.

The main housing screws [24] and mount screw [25] are torqued evenly in a cross pattern. If your work is of sufficient quality, no gaskets or sealant will be necessary.

Starting.
First check that the engine turns over without binding. The compression is checked once the glow plug is installed. The resistance to rotation should be less than equivalent piston engine. For the first runs, choose a prop of around 250m diameter. The fuel tank must be above the level of the spray bar. During running in, a fuel of three parts methylalchohol to one part caster oil by volume is appropriate. You will need a conventional starter giving 3000 – 4000 rpm, although a bend grinder can also be modified for this purpose.

Troubleshooting.
If the motor requires greater starter speed to start than mentioned above, then the rotor to side housing clearance is too loose. On the other hand, if the rotor to side housing clearance is too tight, it can miss, or nip up in service. These symptoms can also occur due to excessively lean mixture, or a propeller of insufficient mass. With insufficient cooling, the motor will tend to miss. If the rotor to side housing clearance is correct, then the motor will run in relatively quickly. It is considered run in when it runs without hesitation to 12000 rpm. The fuel-oil mixture can then be altered to 10-15% caster oil, whereby the higher the percentage of oil, the easier the engine is to start, at lower starter RPM.

[itsme]

Hi Mark,

Thanks for the translation - it should be a great help.

I tried the grinder out yesterday on a piece of cast iron. I dressed the wheel as you suggested and it definitely needed it - it was like an eccentric shaft! At first I was getting a fairly poor finish. It was all 'stripey' and if you ran your finger nail across it, it was quite rough. I then moved onto a bigger diameter wheel that was finer and it sorted the problems. I think the finish is suitable for a running engine. Life is easy with CNC...

Thanks again
Warren

[RotarySMP]

I'm glad you could get a set up with your grinder which gives good results.

Considering the plans call for the medium carbon steel apex seals to run on chromed steel surface, it will be interesting to see your results with a Cast-iron surface.

Once you have the rotor finished and need to grind the sides smooth and provide the 4-5micron clearance at the tips you might want to consider making an arbor to hold it in the chuck and press it onto a peice of very fine sand paper, sitting on balsa wood. I have used this method to polish rivet snaps which have a slight crown. The internal roller bearing surface is to be case hardened to HRC 58 for a depth of around 1mm. The sides of the rotor are chromed.

note from the RH side of the plans that the E shaft bearing surface is to be case hardened to HRC 58 to a depth of about 1mm.

The Apex seal is nominally 1mm thick, and there should be a 0.01 - 0.03 clearance between seal and slot. The length os the apex seal should be 0.03 - 0.05 shorter than the rotor housing width.

[itsme]

Hi there,

This weekend I've been working on the housing for my engine and it is just about finished. With the CNC running, it was quicker than I thought it would be.

I started with with a lump of 105mm diameter cast iron and turned it down on the lathe to 95mm. I then cut the fins 8mm deep using a parting-off tool. Unlike the drawings, I decided to keep the fins and the 'inner part' of the housing concentric (it is much easier this way). Once this was done, I moved onto the mill, where I cut out the epitrochoid using a 6mm endmill. Whilst the housing was still setup on the mill, I also ground it and drilled all the holes so that they are all in the correct position relative to the centre of the epitrochoid. I then set the housing up vertically to machine the ports and the glow plug hole.

There are still a few things that I need to do to finish the housing off. The 0.5mm radius hasn't been added to the ports yet (where they enter the housing), the holes for the intake and exhaust tube retaining screws/pins haven't been drilled and the sides need to be lapped. I think I'm going to find a piece of fairly thick glass to finish off the side surfaces (using abrasives).

I will probably start on the rotor next. I'm going to have a look to see if I can find a standard needle roller bearing to fit it, otherwise I'll just make my own. If I can find one to fit, it'll save me trying to harden the rotor. I'm also trying to decide what material I should make the apex seals out of. I would like to use something that is fairly soft. Any suggestions?

Regards
Warren

[itsme]

Mark,

I've just seen that it is possible to get a needle roller bearing that has an OD of 28mm, ID of 22mm and width of 12mm.

I've had a quick look at the plans and I think it would be possible to fit this into the rotor. The needles would still run on the eccentric shaft (so it would need to be hardened), but I think the diameter of the eccentric 'lobe' could be reduced from 24mm to 22mm without having to adjust the rest of the shaft. What do you think?

[CJL5585]

Itsme
------------------

Your project is looking good. I am following your progress. So far, it is looking like you are going to have a WINNER.

Jerry

[RotarySMP]

We're not worthy...
We're not worthy..

Fantastic progress you are making here Warren. Great to see someone who has the time doing something interesting with it.

From the photos you sent, that grinder looks like it gives a pretty nice finish.

I am not so sure you want something soft fo the seals. One classic pair is chrome and cast iron. I wonder if you can find some 1mm chromed steel? Cast iron piston rings are also used in cast iron bores, although the apex seals would be extremely fragile made of C.I.

You may find that that the cast iron Trochoid surface is too soft, only time will tell. I'd just use medium carbon steel and see what wears out first. Material compatiblity was THE devil in the details of early wankel development. Accept you are taking some shortcuts, and will likely have to redo some bits in service.

The main thing is you are making huge progress.

That bearing sounds like it is worth the try. I have some 2.5mm silver steel, and had a bit of a play with turning up some needles this weekend, but the steel measured 2.47mm, does not have a perfect polished finish (good but probably not good enough for 12000rpm), and is soft. Hardening and polishing 33 little needles seems like a mugs game.

It is a lot easier to make one perfect bearing surface and harden the e-shaft, than to try and make a perfect fitting e-shaft, and 33 neddles, and that recessed ID. Do you have an model engineering club or school machine shop where you live. It shouldn't be too hard to find someone who can case harden your e shaft for you.

A better option for you next engine will be a pressure lubrication system and plain bearings. (the two rotor and liquid cooled, and ....)

[LongRat]

Just like to add that I am following this progress intently too. This recent progress is very exciting, well done! I'm very impressed with the finish that the grinder gives, better than I expected.

[rboeser]

Add me to the list of people impressed. Very nice work indeed, It's good to see a project like this move forward. Great job!

[devincox]

Firstly, Thanks for posting your work Warren.

Does anyone have an example of the parametric equation, to plot out the epitrochoid, as it would be used in excel. I have found the equation:

x = (a + b)cos(t) + h cos((a/b + 1)t)
y = (a + b)sin(t) + h sin((a/b + 1)t)

online but do not know but do not know which values to plug in for a,b,t.
I assume a is the radius from the large circle and b is the radius from the small circle and h is the height between some point and the center of the small circle, but what is t? Tangent?

I have a 4 axis CNC sherline mill and 2 axis cnc sherline lathe and would love to be able to start cutting on a project like this.

Thanks for your help,
Devin

[ViperTX]

and this is an equation for what??....fist I thought it was for an ellipse....anyway t is an angle, h generally is the height of something, and a and b are generally major and minor axis lengths.....

[devincox]

ViperTx, the equation is to plot out an epitrochoid in excel so I can generate the gcode for my cnc machine.

Devin