2 and 4 STROKE DESIGNS

[TartanMac]

Well I made a thread that asked about engine design for books and info but would also like if people could tell me about designs of engines I have. Eventually I want to attempt to make my own engine 2 and 4 stoke engines. Rather than look for performance I would much rather base it on character traits and just make an engine that is a joy to operate. I have to say I am more of a fan of 2 stroke glow engines than any other. When you get a good one they are just awesome. So I would like to put up photos and see what I get back for information on the engines design to pick up any little bits of information that can help me understand the very basics.

I have read David Vizards book about 10 years ago on the A series Mini engine and that was an eye opener and have watched the videos of him online giving a seminar to engine tuners in the USA. I have read a couple of University books also but they were a little too simple and not on 2 strokes either. I am not really looking for building up a brief, description or specification at this time for the engines I would like to build just looking for any info on designs and what they do and give to the engine. I will post a bunch of pics of different engines in pieces and any feedback would be great.

[PatMc]

You might some useful info in this book . It's the 1968 edition so won't contain anything about schnuerle porting.

[J D 8]

Harry Ricardo was very much the father of modern engine design,his story will be of interest to you,also look up the Rolls Royce Crecy a V12 two stroke.About the pinnacle of piston power in development at the end of WW2 but eclipsed by the jet engine.

[bert baker]

Plans are available for both two and four stroke home build engines.

David Parker did a plan for a Vega twin four stroke

Plans are avalible for a Matador single four stroke and a extra plan is avalible to make it into a boxer twin.

Wasn't that long ago there was a two stroke build in rcme

There is a plan for a Maltese boxer

[TartanMac]

Thanks for the replies and I will download that book looks like a great read.

This engine is very interesting to me I like the character traits of this engine a great deal. Maybe not up to peoples expectations today but a great engine that is unbelievably stable under very high loads. It stays very cool and steady even at low running speeds and seems to be able to fuel itself under high loads very accurately. When I say high load I mean 13x5 and 12x6 nylon props. When I say steady what I mean is there is no nah nah nah noise it is constant even at very low rpms like 3.5K. Most engines at below 8K start to loose that constant smooth hum. But at the core the noise level is notably quieter as I ran this engine next to an Irvine MKII 40 sport with the same case and the same std muffler not the Q silencer and I was shocked at how much quieter it is and would love for someone to explain how Irvine achieved this with the liner design I put a picture up and the port at the bottom is also what I would like to know about is it there to cool the piston ? I do know that this engine was designed to be quiet and that is what the Q stood for but I would have thought that the hp would have suffered more than it did a very interesting piece of engineering.

[TartanMac]

Well here is another engine but I have not yet run this one so do not have practical experience with it. But this engine is probably the engine with the most amount of work that has been done by the factory that I have and it is machined like no other engine I have ever seen.

[TartanMac]

Novarossi claim 3.4hp @15,500 rpm I don't believe that it can make that without a pipe but I do think it can make 3.4 with a pipe. I have a Novarossi car engine and the crank looks identical just smaller even the cut outs are in the same place and look at the same angle. I know it creates swirl and I'm guessing that the dimple is to balance the crank. I'm not sure why they put a hole in it other than maybe for lubing the bearings ? I would like to know why they opted to go for an 8 port liner ? and also when I look at the bowl in the head it looks deeper than normal. I should say that finish is not polished it is actually machined it is that fine. I think the cooling head is cast I read that cast material is better at getting rid of heat but I also read 6061 is the best heat sink material. I have heard 7 and 9 port cars they are way smoother and very high revving and compared to 3,4 and even 5 port engines but low end torque suffers. What I would love to know is does the 8 ports give a nature of smoothness ?

[TartanMac]

I also noticed that the case at the top where the cylinder fits is the same shape as my West 52V1 engine so I am guessing that the square cylinder gives stiffness but at the top you want a round shape nearer the head for cooling evenly around the hottest part. Any info on design features on this engine would be very welcome.

[Tim Flyer]

The best book I found on two stroke engines is the Jennings’ Two stroke tuners handbook . It was written by ex Yamaha development engineers I believe. Maybe too much detail for your needs but interesting to me. Properly explains gas flow and pipes etc. The link is from Prestwich models boat site which is run by a guy called Dave Marles who is an ex World Champion model power boater. The page link I attach has lots of other engine information too. **LINK**

[Tim Flyer]

I like your Rex Rossi above . I also have a beautiful 9 port Novarossi top 28 in my hydroplane . It’s supposed to top out at 34,000rpm ....very fast !

Edited By Timothy Harris 1 on 30/10/2017 08:37:40

[TartanMac]

Posted by Timothy Harris 1 on 30/10/2017 08:36:20:

I like your Rex Rossi above . I also have a beautiful 9 port Novarossi top 28 in my hydroplane . It’s supposed to top out at 34,000rpm ....very fast !

Edited By Timothy Harris 1 on 30/10/2017 08:37:40

I saw this engine half price in the USA and had to get it at that time the pound was giving 1.6 dollars so I got it for around £240-£260 all in after postage and her majesty taking her cut on delivery. I got the last one then the pound went down and they restocked with Italian stock that was not moving and the price is much higher now so I got lucky. It was the only true high rpm .91 2 stroke I could find.

That 28 sounds like a great engine I wanted one for my 1/8 Race Truck but I think I will sell up the car stuff, too much servicing and setup sensitive. Seen a few Hydroplanes on YT and they look really fast.

I have the .21 P5XL and a nice JP2 pipe also an 053 HN pipe. That 28 probably has the same HP as my 91.

[Geoff S]

I have a couple of Irvine Q40s. I bought one new and ran it in several models before putting it away. IIRC it suffered a bit in a crash of an own design model which had a few design issues (mainly the designer!). I managed to acquire a new crankcase casting and repaired it. The second I bought on eBay a very long time ago and it looks to have had almost no running at all. I can't remember if I ever either ran it or let alone fitted in a model. I think I bought it because I liked Q40s which were both quiet and torquey (as was the design intention) and would spin large props for a 40 size engine (12x6 IIRC).

I know it was too powerful for the Precedent Funfly I built and I changed it for Super Tigre 34. That combination got me through my 'A' cert.

They are very good engines - as is the ST34 which I also still have. None have been run for ages as I'm just about 100% electric these days.

I don't what sort of engine you intend to make but I was very impressed with a 1/3 scale Gypsy Major engine I saw at the LMA static show on Sunday. A 4 cylinder in-line 4 stroke petrol engine is quite some home build/design project.

Geoff

[TartanMac]

Geoff I will have to go to shows like that and meet some people who have built engines some time. I have never built an engine and am not capable of even coming up with a design at the moment. I was advised to start by modifying engines and making parts to start with which is good advise I think and my Q40 will be the first engineering project I will undertake as it needs the big end re-bushing on the rod. After that I might make a new oversized piston ring for my Enya 41 4C.

For my first engine I would love to stroke a 90 2 stroke as far as possible to see what it would run like and how low an idle I could get but still fly an aeroplane with it. I have an MVVS 90 and a WEBRA 91 P5 but these are built for a market and require throttle response and a competitive total hp out put for aeroplanes popular in the market place. So even though they are torquey engines and longer stroked than others they are still 2,200 rpm idle with very high response. The 90 I would like to build would be more like the Q40 when on a 13x5 very slow pick up but very smooth precise fuelling and cool running with linear throttling (very broad power band)

I talked to a family member and he said the Q40 was basically designed around the idea of manipulating the pressure wave. He explained it a bit more than this but he mentioned that the idea of piston speed being lower makes it quieter like a bullet out of a gun if it is slower it is quieter also if it is larger in diameter it is generally quieter too also the longer stroke makes less of a bang as the pressure wave is reduced. I cannot remember it all precisely but that was the gist and I think the port at the bottom cools the piston as when you make power at lower rpm the engine can build heat quicker and create more heat than with higher rpm as there are less intake charges to cool the piston within a space of time due to lower revs. I think it is easy to criticise an engine when you have info on it and you have the engine running in front of you (as I have) but starting with a blank sheet I think it will be a lot of work even for a 2 stroke single.

I would like a small V twin engine also but I will post that later when I get to it.

I had a small 34 ST also it was pretty powerful had a unique sound to it also, quite a nice engine. 1/3 Gypsy that would be really nice that would be way beyond me right now.

[Tim Flyer]

I think it would be great in a race truck. There are quite a few Novarossi dealers on the continent too . I Bought mine from a German dealer. Prestwich Models also do Rossi and lots of engine work and tuning . With model power boating it’s almost “all about the engine” so there is s massive wealth of information there on that Prestwich link I put above. Apart from Pylon racers few flyers seem that interested in tuning etc. I realise why as obviously reliability and throttling are the main needs of an aero engine. CMB 2stroke engines also dominate boating . They are also super high rpm racing 2 /strokes with very high top end power for racing. The pistons on many of these are barrelled ABC so they are very tight when cold and need a nice swift warm up and not over rich running in. The guys that make them are ultra skilled.

[Kim Taylor]

Back in the day when we were racing karts, I had a book called, I think, Two Stroke Tuning In Theory and Practice.

It was a Haynes publication and it was very thorough. I used it only to calculate the length of the primary runner for the tuned exhausts we were using, which differed track to track.

Kim

[TartanMac]

Timothy 8 pages in on that book and it is great not too much detail at all. I already knew most of what I have read but only generally this is more focused with some formulas I did not know I'm sure I will learn a lot from the rest. I am sure I downloaded a similar covered book about piston rings great link thank you.

I searched the book you gave Kim I think I will get it looks good also.

[TartanMac]

Well a little change I was looking at 4 stroke engines and thought I wonder what combustion chamber shape the O.S 56 Alpha I have has so I took the engine apart.

My O.S is new and never run. I only bought it as I had the chance to get it for £100. I thought what a great deal. This has sat in its box for around 2 years and I never took it apart. I was amazed at how well made this engine is. I would say in terms of CNC cutting quality this is probably the same as my Novarossi possibly better in some areas. Everything just fits so well and everything has a smooth finnish. The liner came out nice and smooth. What else is amazing to me is the quality of the castings. I think this is the best casting I have seen there are no flaws anywhere. It has no pin holes anywhere on the machined surfaces. My Enya's and my Saito's both have pin holes here and there but this is immaculate. I know that does not mean it gives the strongest and stiffest to weight ratio but still very nice.

This is the engine with the controversial oil circulating system. Me personally I cannot comment if it affects the running or not as I have not run it yet. However I think I would prefer a vent line to put oil into on initial start up of the day and also when I choke a four stroke engine sometimes and quite often I can feel I have flooded it so I usually rock the piston over TDC to get the fuel past the ring then get rid of it out the vent by flipping it over. I'm not sure how this is going to work on this setup.

What really bothers me about this engine is the liner. I don't really trust the durability of the O.S liners they are a weird colour and from what I have seen still have failures. My old FP that was new had a ruined liner after 10 tanks. I have run in plenty engines and not even my MDS engines had the coating peel off. And from what I have read in general it is O.S engines weak spot pretty major weak spot I would say. It must be how they are applying the coating maybe they are using high voltage or current to plate it faster I don't know.

A real shame as the rest of this engine is really amazing in terms of quality.

The combustion chamber seems to be what I think is a bathtub design which seems to be all about turbulence. Maybe that is why it is a great idling engine at low rpm. This is an interesting engine to me but only because of the combustion chamber in terms of design. The reason why is because it seems Enya decided to drop the design in favour of the wedge shape which I read is the most efficient shape in David Vizards book if I remember right. Maybe this engine depends on the nitro to perform It is interesting that O.S stuck with it and managed to get 1hp out of this engine which is very good. However it does have valves tailored for exhaust and intake individually as you can see they are not the same and are vertically mounted. I do know that the Enya 1.20 just cannot breath and is very sensitive to its nitro and load but I was sure that this combustion chamber cannot decompress the cylinder as quickly as the wedge shape and same for intake it does not flow as straight with the port like the wedge shape I would love to hear what others think about this engines design also as when an engine brand like Enya drop a design I would think it was a big deal or maybe it was a mistake ?

[john stones 1 - Moderator]

Interesting thread TM, beautiful things engines, even in bits.

[Nigel R]

" I don't really trust the durability of the O.S liners they are a weird colour and from what I have seen still have failures. "

Were the failures not reported on the AAC two strokes, all around the FX series age?

This is a ringed 4 stroke, so a bit different.

Personally I like the OS four strokes especially the Surpass, I have a few of differing sizes, none currently flying though. Always good runners with consistent build quality.

 

"in favour of the wedge shape which I read is the most efficient shape in David Vizards book if I remember right"

I wonder what the current automotive industry are using these days? Their designs are highly advanced now with the current direct injection petrol engines; part throttle combustion is limited to a small area within the combustion chamber which must mean superb control over the gas flow. Our little model engines are like simple copies of 1950s designs, very primitive by comparison.

 

PS £100 for an unrun 56 alpha is a bargain indeed!

Edited By Nigel R on 03/11/2017 10:06:22

[Denis Watkins]

Just look to Formula 1, separate combustion and plug chamber

Initiates a constant burn, and piston push

Lightweight pistons, less contact, less friction

[Robin Colbourne]

Peter Chinn's engine reviews that used to appear in RCM&E and Aeromodeller are well worth reading. Each review included a stripdown and analysis of significant parts. Peter appeared to know his stuff, so it was a very good way of learning about the reasoning behind each facet of the design.

Here's one of my favourite engines, the OS25FSR:

**LINK**

Here is an obituary for Peter Chinn that appeared in Model Engine News:  http://www.modelenginenews.org/ed.2005.05.html

 

Edited By Robin Colbourne on 03/11/2017 10:38:19

[TartanMac]

@ Nigel R. I have heard of 55 AX engines doing the same and I also heard one of these 56 FSA engine ruining its liner after running in. My FP had a brass liner and sure it was ABC. You might be right and these incidents I mentioned might be a lot more rare than in the past as I have not looked at model engines for about 4-5 years with any great detail. But I still would not pay full retail on an O.S if there is something else out there.

Most engines in cars I think use the hemi head but it is not really a fare comparison to draw a conclusion from on what to use in a model engine. I think yeah the 4 valves per cylinder gives more power in a car but I doubt it is worth doing on a model engine as going past 9 to 1 compression on a glow engine does not really seem a good idea without spark ignition. So 2 valves per cylinder is really what I would use and when I look at the hemi head in that context it is not really that attractive and to be honest I don't think there is a need for it unless you are struggling with head space for valves which I don't really think I would. I tested a Saito FA40 and my Enya 41 4C and the Enya with I think a wedge shape head out turned it with an 11x6 Graupner Super Nylon I understand that the Saito has both valves the same so it is not optimised but the Enya is the same and it had no compression at all

Enya 41 4C

11x6 @ 10,500 rpm touched 10,800 at one point

Saito FA40

11x6 @ 10,000 rpm peaked

[TartanMac]

I took a look at the F1 engine you mentioned that is a very cool idea someone had good post denis.. And nice pic similar to the laser piston.

[TartanMac]

@ Robin Coulbourne

Yes I have read a few of his reviews from the sceptreflight website he really did know a lot it seems. I have never run an FSR but I had an SF and on full throttle it is really really smooth. I have an FX but never run it needs a set of bearings. The 25 size is one of my favourites.

[TartanMac]

I'm not sure if this is classed as a wedge shape or not ? Hybrid maybe ? As you can see it is not like the Laser 75 head below

These are heads from O.S 56 FSA (left) Enya 41 4C (mid) and the Saito 40 on the right the colour is not green in person it is just the flash on the camera. As you can see the valves are very similar in size for the 2 forties. And the exhaust valve is not far off the same size on the 56 fsa. I am seriously thinking about making a tailor made head for the Enya 41 and 1.20. The 41 has the 46 head and valves but has a short throw on the crank. The saito is longer stroked I'm sure but have not checked I think it might use a 45 crank.