TOYAN RS-S100 Rotary Engine Real Review by Customer Steven | Stirlingkit - Stirlingkit
TOYAN RS-S100 Rotary Engine Real Review by Customer Steven | Stirlingkit

TOYAN RS-S100 Rotary Engine Real Review by Customer Steven | Stirlingkit

I just received a notification that my little Wankel has been delivered Time to make the short journey to my mailbox and collect the little gem.

To be very far to how I would score it there needs to be different categories. Shipping Speed- 8
Appearance- 10
Packaging- 4
Price- 5
Value- 2
Accessories- 2
Assembly- 8
Running- (unknown)
Parts Support-(unknown)
Documentation- 3

Here’s a quick view containing a ruler for a reference. The shiny surface of the ruler makes reading the markings difficult. Max length, carb inlet to opposing mounting ear is 85mm.

that pumped carb needs a good pressure pulse to get the diaphragm moving. What’s the source of the pressure pulse? A small enough carb bore will allow proper fuel draw. My operable OS 4.9PI has a Perry carb that was intended for a .15 two stroke. The power is excellent as well as fuel draw. It sucks down 2oz of 30% nitro per minute.

let’s see where the carb pump pulse passageway leads. I’m expecting it to be a drilling straight into the center of the rotor chamber. But maybe it’s a port drilled to communicate with the exhaust port. Will look and see.

Here’s a quick view containing a ruler for a reference. The shiny surface of the ruler makes reading the markings difficult. Max length, carb inlet to opposing mounting ear is 85mm.

Clearly Toyan didn’t have the enthusiasm needed to generate a new foam insert to properly fit this engine. The little rotary was loosely shaking all aboutwhen I picked up and wiggled the box.

Overall the construction is very clean and worthy of display. But turning the flywheel gives on the impression that breaking-in will take a long, long time. She’s tight, too tight to run as received. I have no choice but to open up the housing and see how the fits are influencing the tight operation.

I thought some spare ‘shims’ of some sort were included with this engine. I removed all the packing … Ooops, found them hiding in the folded instructions And they are stainless as predicted and creased too. the damage is almost a crease, could be difficult for the case bolts to flatten it completely. We shall


Careful when opening you’re box as there are hidden extra metal thin gaskets that they don’t mention are included within the paper manual. I found them.I thought I saw someone else retrieving a clear poly envelope containing the shims, gaskets or whatever from one side wall or under the box foam. I then thought to open the ‘instructions’ and whoopie, Found’m! Some predisassembly pix: The carburetor has no auxiliary pump pressure port. It’s using intake vacuum pulses to drive the diaphragm. I wonder how effective that will be?

The silencer/muffler is very small. Has a real gasket for sealing.

The mounting flange was sorta ground a little lop-sided..

Flywheel nut is double-secured.

It’s a “belt and suspenders” sort of thing. The nut has serrations to allow it to dig into the flywheel surface and threadlock to hold it there too.

the flywheel isn’t difficult to remove - leave the nut on the shaft one or two turns and press on the nut with your thumb while supporting the flywheel rim with your fingers. Slides off easy. The flywheel is keyed to the shaft and for a very important reason. There has to be a mass counterweight to offset the rotor going around its orbit. The flywheel has material removed to help with this balance. I’m expecting to see a second counterbalance within the cover on the opposite end of the shaft. This means adding a propeller would need some sort of adapter that either bolts to the face of the flywheel (and retains unwanted weight) or a special light-weight prop adapter with an integrated weigh be made.

I’d expect that can work as long as the pulse is strong enough. Many two strokes are still using pistonport intake timing rather than reed and rotary valves.This gives a sharpnegative pulse when the piston skirt uncovers the passage to the carb.

This little Wankel - eh, can’t imagine the pulse having much effect. That diaphragm better be super supple to react properly.

All fittings need a 5mm open end wrench.

Glow plug side. What are the threaded bosses for I wonder?

The plenum that the carb is connected to. This may act as a heat block as it will be cooled by the air/fuel charge passing through. Note the grey depositon the gasket. It’s directly in line with the intake port. Why is that deposit there?

This engine was ‘motored’ with a starter motor in an attempt to free it up a little. If spun in reverse the fine metal particles from the combustion chamber would be blown at that gasket.

You see how the exhaust port and intake ports are identical? If it wasn’t for this bump on the end of that plenum you could swap the carb and muffler locations and reverse the engine. It’s so close to have that capability.I wouldn’t assume that. When I show the coolant passages you’ll see why. And the surface area made available could have been much larger for greater thermal contact if that was the intent. Maybe one day Miss Mona will pass along that secret to us. Anyway, now that my phone is charged I can upload the rest of my photos.

So where was I?

The intake (top) and exhaust port (bottom) are identical. If the carburetor plenum was a little smaller the engine could be made to run in reverse by simply moving the carb to the lower port.

Under this cover I expect to find a second balance weight, same as the O.S. Wankels use

Well what do you know? I guessed correctly

A little closeup shot showing a pin that locks the weight in the correct orientation in relation to the eccentric lobe on the shaft.

Here’s the output end of the eccentric shaft and the support bearing. Why there’s a gasket between the retaining ring and case is beyond me. There’s nothing in that location that requires sealing.

Peek-a-boo! There are two of the stainless shims (that I’ll now refer to as “wear plates”) stacked together at the front and back of the combustion chamber housing.

Notice that rough finish on the outside edge of the housing. I believe it’s a result of using a machining technique known as Wire EDM (Electro-Discharge Machining). It can be much smoother than that and can cleanly cut through extremely hard metals.

A little look at the cuts in the right side of the front plate where coolant passes through. Those passages are only around the glow plug and symmetrical before and after the plug hole.

There’s the little rotor! It’s so cute! The wear plate has seen lots of rotations in an attempt to do a preliminary break in and polish the plate surface. More on that later.

This rotor looks to be extremely well made. It’s clearly coated in fine metal particles (black stuff) from rubbing on the plate but a close look reveals a fine surface finish that I’ll talk more about later.

The only moving parts of any significance. Rotor (with internal gear), apex seals w/springs and eccentric shaft.

Just the way O.S. Made their springs, two are used in parallel.

The gear is acting as a retainer for a ball-race bearing that the eccentric rides in. The O.S. Graupner Wankel used a needle roller bearing and the needles rolled directly against the eccentric surface. I’ve seen the rollers start beating into the eccentric’s surface and that’s a bad thing. This ball bearing would be far less expensive to replace than a new shaft.

The rotor has the usual combustion chamber relief milled out of the side to add volume.

Here’s something unexpected and done wrong too. That deep groove thrust bearing has no business being in there. It lives under the aft counterweight. If a propeller, oriented in which to pull the engine axially, was attached to the flywheel-end of the eccentric shaft, there could be some merit in having a thrust bearing but even so, the installation of this bearing was 1: Installed ‘backwards’ and 2: Not going to be able to provide its full benefit. Here’s why; There are two races that are kept separate by the balls that are set in a brass retainer. Per standard thrust bearing design, one race has an I.D. that is larger than the I.D. of the other race. This is because one race is allowed to rotate with the shaft it is installed on and the other race has a gap so it can’t rub on the same shaft causing wear and friction. This thrust bearing was installed wrong race first, the small I.D. race. The first race is supposed to be static and not move while making contact with the case where the radial ball bearing sits. There’s nothing stopping the shaft from rubbing against the bore of the hardened race and causing metal particles to be spread back into the bearing assembly. Also, because the radial bearing inner race can float axially enough, it can move toward the hardened thrust bearing race and grind themselves together, again making extra friction and fine metal particles. The fix is simple: on the plain face of the larger bore race you grind a shallow relief right around the race’s bore. This relief prevents the radial bearing inner race from ever contacting the thrust race. I’ve done it before. The other and easier thing that needs doing is making sure the small bore race is all the way at the end of the shaft directly under the counter weight.

Here we see the only coolant passages in this engine. The in and out coolant fitting screw into the back of the right-hand plate - one fitting at the top of the milled passage and one at the bottom. The coolant moves in a serpentine path from the back cover through the center chamber holes and to the front plate. Then coolant moves along the path, comes back through the second chamber hole and so on. Eventually the hot coolant leaves via the other hose fitting and on to a radiating device. As this engine *must be* liquid cooled it’s odd that there’s no provision for a coolant pump added to the aft-end of the eccentric shaft.

DAMAGE! This aft case was dropped on a corner and damaged. Metal was deformed and forced into one of the wear plates, as seen next…

The dented aluminum case deformed (dented) the edge of the wear plate.


That case half must have bounced because there’s two damaged corners

The inner wall of the combustion chamber looks very nice, for the most part. It’s not perfect though as the next photos will show, see?

One of three…

Two of three…

…and three of three…

These are areas of the combustion chamber sealing area that were cut and then finish-ground to remove the rough-cut area. In this location the rough area was cut oversized and the final grinding passes couldn’t clean up the chamber surface. Not good and will eat up the apex seals as a result. I need a new chamber, are you listening,

I measured the combustion chamber housing thickness and also the thickness of the rotor. The results were interesting and frustrating at the same time. Ideally the rotor should be .0001” thinner than the combustion housing. That would allow complete freedom of motion and a decent gas seal. This one is more, much more. I’m going to stay Imperial measuring system here for consistency, sorry. The combustion housing measured @ 0.3152” all around the complete chamber. I’m impressed! That’s so parallel! There are a few burrs though and that’s where the close-fitting case assembly screws were rubbing in their drilled holes and displaced a little metal. The rotor thickness is ALSO very consistent but thinner @ .3146” or .0006” thinner than the chamber housing. That’s normally far too much clearance but my engine binds anyway. Why is that? How can it possibly bind (the rotor faces are rubbing hard against the wear plates) if there’s so much clearance?

Here’s why: Those wear plates are very flexible. There’s no positive force wanting to naturally keep the plates perfectly parallel with the front and rear case plates. Anything, and I mean ANYTHING, can cause the wear plates to bulge or bow out away from their case surfaces. Just the act of tightening the peripheral case bolts can pinch the edges of the wear plates and make them go not-flat. This is a big problem and the best ‘fix’ is to finish grind or lap the case end surfaces the use a ‘hard anodized’ surface coating treatment. This stainless wear plate system may eventually break in and drop the drag but who wants to wait that long? I have a third option that could be practical and that’s to replace the four stainless shim/wear plates with two hardened and ground (flat) carbon steel plates, each one the equivalent thickness of two stainless plates. They’re more likely to stay flat and not bulge into the center of the chamber.

So, Stirlingkit, Miss Mona, are you willing to get me a replacement combustion housing after seeing the photographs of the poorly-finished areas of my chamber? Thank you

it’s already polished. That’s not going to improve. It will tear up the seals.

The deeper I get into the machining quality the higher my respect for Toyan’s abilities. The tightness I’m experiencing with this engine is due to either a too-thick rotor or the paired shims at each end of the combustion chamber bowing in towards each other caused by their springing action. But anyway, on with the new pix before my phone needs charging again…

I’m not running anything. I’m only dissecting this engine for now. When it comes time to run it I’ll install whatever plug is new and closest to me at the time. All it has to do is not bottom out in the plug chamber before the copper washer can seal.

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