But larger bore engines have a larger piston diameter and therefore area and therefore greater force on the conrod for a given cylinder pressure. Three dimensions control displacement and therefore the mass of fuel/air charge in the cylinder, breathing parameters otherwise the same that is. For a given displacement, if you increase stroke by x percent, you've reduced cylinder cross-sectional area by the same ratio to maintain displacement, so how does the proportionally reduced piston force counteract the same proportion of increase in leverage?

Large bore short stroke engines are good at reducing piston speed, I think that is a key claim to fame with regards their use in high rpm applications. Certainly in F1 (auto) engines where they are at the practical limit of piston speed all the time, whereas surprisingly with our small high rpm engines we rarely get anywhere near as close.

I'm not actually arguing you about the point, but I am curious what other advantage longer stroke and smaller bore actually offer (but better put that on another thread!). Other, that is, when it is incrementally changed by the manufacturer for one reason or another and they can advertise the new engine as "long stroke" or "short stroke" compared to the last version, as if that is the only change that matters.

MJD

It's all good Marty. Thing is, when others have or witness a negative experience with the same engine, you're gonna get arguments. This is on topic so forgive me for mentioning another engine her for a minute, but I recently helped a guy with a GMS .32. The carb is a piece of crap - the through hole to the spraybar from the fuel inlet is mis-indexed, and prevents adeuate fuel flow at WOT. Piss poor quality control. Yet apparently some of them work "fine" - on another thread about multi engine models, someone was asking for opinions about engine choices. A fellow chimed in raving about what a value the GMS .32 was and how great it runs. So, hearing that, suppose the guy with the 4 engine jobbie bought 4 of them, and got three duds? You sure as heck would not call the advice to use them good advice.

So many times in this hobby, someone gets a good deal on something and it works, so they wax eloquent about the product - naturally. But because of the inconstencies with many of these engines, there is a crowd of skeptics out there, and for good reason.

Reporting on your observations and fixes or techniques is a good thing and useful to anyone considering or owning the same engine - no question there. But I would not be surprised to find out that some of the nay-sayers have had legitimate poor experiences with the engine. IMHO, as a sport engine, making it too tight for the average low-engine time sport modeller to deal with is bad design or manufacturing as the case may be, and there is no excuse for that with all the good examples on the market and the decades of knowledge base on the subject. $49.99 sport engines are not supposed to require cylinder heating and super-careful break-in to use. That's for the smaller percentage of modellers with the knowledge or willingness to fiddle.

MJD

I'm up to a gallon and a half through the engine now. I changed the prop from 10 X 7 to 10 X 8 apc and it proved to be too much. I do not find this engine to be any different from any other typical sport .46 in terms of torque. Its a nice, typical .46 2 stroke glow engine.

On one particular point I have to whole heartedly agree. The less expensive engines require the user to be more informed and spend more time getting it right than do the more expensive types so yes I do recommend the beginner buy the highest quality engine they can possibly afford to help eliminate any obstacles to their training.
However if you have a sincere passion for the sport and need to save every penny (so you can afford that new plane or whatever) then the less expensive engines have a place. I could buy a brand new OS 46AX for $130.00 or I could buy a new Aviastar .46 engine ,,,and a plane to boot.
I may need to use more of my engine savvy to get it to run properly in comparison to the OS engine but that for me is half the fun.

OK, you're right and all the others (myself included) are wrong.... happy now?

Jeesh, give it a rest... what happened to;

???

We get it - you were one of the lucky ones who got a $50 engine that you didn't have to fiddle with to overcome problems that both the manufacturer and distributor admit to.

Hurray for you.

ProBroJoe, I posted more in this thread because there was more to share. This isnt gloating or bragging nor is it necessaarily even good news. Jeff had me hoping I might be able to run a 10 X 8 since he found that he seemed to be able to swing larger than average props or more pitch than one typically could with a .46. I was reporting that I didnt find that to be the case for me. Since you are not flying one of these engines and seem to resent good news about this engine, why not just stop reading this thread?

Says who? I have one on my .40 size Kaos, remember? FWIW, it turns a 10 x 8 APC just fine... oh wait, I'm being repetitive...

Nope, I don't remember you ever saying you had one flying. Why so down on the engine then? As for the 10 X 8, that hasn't worked out on my Bobcat but it's nearly 8# with fuel so I assume its that I need the 10 X 7 to plow that big airframe through the sky. They might look like jets but they are draggy airframes.

Page 2 of this thread, post #31.... and you even PM'ed me on November 25th asking if I even owned one, to which I answered; "yes, I'm flying one on my Kaos"... or something to that effect. (Not to mention that I've shared my experiences and what I'm flying the engine on in the other AV .46 threads.)

Because I had to work at it to get a runner, either that, or send it back for warranty work. Even though the engine runs nicely now, and makes good power, the whole ordeal left a bad taste in my mouth. Then you come along in your own personally moderated thread, denounce everyone's bad experiences with them, and blatantly reject our opinions.

Well there ya go...

I found your PM. You said....

Yes I am down on this engine, and yes, I currently own one. I've had it since May '08, replaced the carb with one from a Super Tigre, and it's been OK, but still behaves in such a way that it doesn't give a warm and fuzzy feeling when I fly it.

If you don't like it, why not dump it and move on? Life is short and you obviously are not enjoying the hobby with this $50 engine. As for denouncing other people's problems or opinions, I have offered possible explanations for some people's trouble and have passed along my first hand experience. I went on to suggest that if there were problems with this engine, I dont think there are now and that if someone buys one from Sig after the date I bought mine and has trouble that I would encourage them to send it to me. I'm sorry this thread sits so wrong with you. I say again, why not just stop reading it?

Yeesh guys lighten up

And that's just the attitude that doesn't sit well with me. You make it sound like you and your superior tuning skills have proven that this whole carb issue never existed. When, in fact, the manufacturer and distributor have both admitted it.

Because it runs OK for what it is, and it's not the engine that I have a problem with.

Who exactly are you to tell me how I feel?

Because I believe we both live in a country where free speech is still accepted. You have taken it upon yourself to moderate your own thread to ensure that it represents your opinion and your opinion only. It's my job as "the other side" (i.e. the one with verifiable AV .46 issues past or present) to not let that happen.

Why would they do that? Because after one lucky purchase you are an Aviastar .46 expert? Please folks, save yourself the trouble and trust Sig to fix your ailing Aviastar, at least they aren't in denial about it's shortcomings.

Ok, I quit ProBroJoe. I've been just trying to help guys in a positive manner with this engine by sharing my real world experience. This is about the greatest hobby I can think of! I apologize to you for not having problems with the engine. Your negativity wins. I'll spend my time more productively somewhere else.

Geez Joe. Yer so sensitive dont worry , be happy

Well thank-you Dr. Phil...

Thats Doctor Detroit to you mister

Is that 15% Helimix fuel all synthetic? If so your ABC type engine isn't getting much scuff protection. (zero clearance at the top of the stroke) A small amount of castor in the mix would be a good insurance policy for longevity. Just my opinion though....

Thanks for the great updates,

Ernie

Received some great news late last night. Alvin So of Aviatronics is out of the hospital and working at the plant on a limited basis.
Apparetly he has been in and out of the hospital over the last 6 months and at one time spent 22 straight days there.
He has contacted me and we are going to straighten out any issues we can with his engines to ensure they become the premiere model airplane engines that Alvin wants them to be.
Iam wondering if anyone thinks (besides me) that a ringed version of his .46 and .53 would be a good idea? If so Iwill see if we can get it implemented.

So long as the carburetor SNAFU is behind them, I think the best thing that Sig and Aviatech can do is expand the Aviastar engine offerings. Brodak is selling the C/L engines at a pretty high premium; why isn't Sig distributing them? Also, Sig used to carry the Aviastar 1.2 and 1.8 cu in 2-strokes, but dropped them from the lineup last year. Filling in a couple of sizes between .53 and 1.5 might be a good thing.

Sig listed the Aviastar 1.20 at $179.99; I thought that was a pretty attractive engine at that price. Sig might be inclined to offer any smaller Aviastar engines that aren't currently being imported to North America. An Aviastar .25 might be fun to try, for example. I don't know if Aviatronics manufacturers any smaller engines, it's just a thought.

http://www.aviatronics.com/review.htm

One of my trips to the hobby shop many months ago got me looking at the Avia 46's he had (nothing catches your eye like a 49.99 price tag). I didnt pull the trigger that day because I knew nothing about them. Once I got home I got on RCU and started searching and found several posts on the Avia's and noticed the Carb SNAFU's that went along with them, I think it had something to do with the 46's carb spraybar (it was the wrong one) and Sig was repairing the effected units, but that was a good while back from when I was reading it. On my next trip in I couldn't help myself and picked one up, I knew I was taking a chance that it may have problems but I really enjoy tinkering with engines (have been working on/rebuilding ATV and Dirtbike engines since I was around 14). I put the engine on a high wing trainer replacing the Super Tigre 45 that was on it. Sorry but that Super Tigre muffler is absolutely the ugliest piece of engineering I've seen in a while. Super Tigre went back on the Sig 4* it was transplanted from. Which was fine because the 4* balanced perfectly with the Tigre but left the trainer way nose heavy. The Avia is a little lighter and the muffler isn't fugly. Bolted the Avia in the trainer and went to break it in. Engine was tight but it still started very easily. Ran 4 or 5 tanks through it at around 4000rpm with a few short higher RPM blips, then started leaning it a little and increasing the RPMs. This is where I expected my problems to begin but they never did. The engine ran like a screamin demon. The throttle response was great, the transition was great and it would idle for as long as I asked it to without loading up and petering out. I think the transition on the Avia is cleaner than the Super Tigre, the Avia will also idle longer without loading up. Power wise I'd say they are both dead even but I like the Avia better.

Next time I need another .40 sized engine I'm buying another Avia.

Ithink that post will make Alvin feel much better Thanks.