New (to me) internet myth
 

A customer told me today he heard that the A stamped on top of a Sachs piston means top of the line, a D on top means industrial grade...What a CROCK...Maybe we should start a thread with all these internet MYTHS listed for newbies..We ALL know the old timers don't perpetuate these things, don't we ? :eek:;)

RE: New (to me) internet myth
 

I heard from these old guys that your plane will stall on a down wind turn.

RE: New (to me) internet myth
 

This piston has a "AB" ?

http://img.photobucket.com/albums/v1...g?t=1328638530

RE: New (to me) internet myth
 

Between aircraft grade and blower grade?:D

RE: New (to me) internet myth
 

I have no clue about the Sachs pistons but many (not necessarily 2 stroke) pistons have numbers or letters stamped on them to denote size / bore fit / tolerance, etc. As far as the Sachs piston, if it were true, I would think that industrial grade would be top of the line!

RE: New (to me) internet myth
 

AB means that it can be used in both A and B size cylinders...The differences are in the tenths of thousandths, only shows the attention to detail the chainsaw manufacturers go to....A D piston will fit in an A cylinder, but won't run for long....An A piston in a D cylinder is borderline loose....

RE: New (to me) internet myth
 

OK RC, while talking about engine bores .... do quality cylinders have any bore taper? I have to say I've never measured this on any 2 stroke gasser I ever worked on though I do check ring end gap from top to bottom of stroke. I know some full scale aircraft cylinders have a bit of taper to allow for the top of the cylinder running at a higher temperature than the bottom .... theory being that when up to temperature the bore would be straight. Just curious.

RE: New (to me) internet myth
 

Off to go make some popcorn and grab a soda. Be right back as this is going to be interesting.:D

Industrial grade is just fine by me.

Bliksem

RE: New (to me) internet myth
 

And what is that comment supposed to mean? At least this isn't another stupid oil or ethanol in gas thread. I would like to see more real technical questions and comments on this forum. But no, we'll probably have more of the same old stuff that has been covered dozens of times before.

RE: New (to me) internet myth
 

Yes, in a true high performance engine such as a full sized Aero enigne, the bores do in fact have a taper when at room temperature. This is to allow it to be "round and parallel" when at operating temperature.

Generally on our RC sized Gas engines there will be no engineered taper. The cylinders are too small and the power outputs are too low to require it. Even on the best quality engines, the amount of taper would be very small even if it was intentionally added.

So the bores should not only be parallel but they should also be round. Very few (by numbers sold) actually are

This is because the majority of the engines that are bought nowadays have a very basic manufacturing technique used. Teh cylinders are molded on a mandrel, chemically cleaned, flame plated with Chrome then the final surface finish is achieved with a basic hone unit.

That technique results in bores that are neither parallel nor round. They are however cheap to produce that way and they will allow the engine to run. What they do not allow is good ring sealing so power is lost.

Roundness is difficult to measure due to the open port designs commonly used (another source of power loss).

RE: New (to me) internet myth
 

Thanks, Ssteve, beat me to it, my computer is screwed up again tonight.;)
Hign quality ABC glow engines are tapered at the top, a new one can't be easily rotated...

RE: New (to me) internet myth
 

Thanks, I didn't think our small engines would exhibit much if any taper but thought I would ask.

RE: New (to me) internet myth
 

Yes, regarding taper in the ABC glo engines. I watched years of development and tried every trick I could find during many years of pylon racing. From the early no taper ST designs to some of the highly tapered F-1 ST customs such as Terry Prather put out, etc. For a local Q500 class that required reasonably stock engines, I once crudely honed as much taper into an existing almost straight walled ST cylinder as I could removing all of the chrome from the bottom 1/3 of the bore. Left the pinch area untouched as piston fit was excellent there. Also relieved the bottom 2/3 or so of the piston skirt. Worked great and won many trophies with that engine. I still have it in my collection and it would run as good today as it did back then. Modern ARF buyers and overnight wonders wouldn't understand trying these sorts of things though. But then, you did what you had to do to be competitive. Sorry, not gasser related but I thought it interesting.

RE: New (to me) internet myth
 

What I fail to see explained here, Ralph scratched the surface of it, is the system behind the A,B,C.... markings.
To continue from where Aussiesteve left off:
Once in production, after all those many operations, the operator is satisfied with roundness and taper he stops working on the bore. The next station is a hydraulic measuring device that defines the true mean dimension of the bore at height specified in specs. Dependine on that dimension, the cylinder is marked.
Same with piston dimensions. rather than working to the EXACT dimension, which is nearly impossible regarding tool wear and operator intervention, the piston when done is measured. According to measurement it is "classed" to match the class of the cylinder sizes.
There you have it in a nutshell. Minimal production costs, and accuracy that competes with multiple cost production systems.
BTW,
MVVS, my favorite manufacurer, does not use this system. Any Cylinder will fit ANY piston in their gas engines (costly, costly). They have to learn a bit still.

RE: New (to me) internet myth
 

RE: New (to me) internet myth
 

Some numbers from an older Sachs set of pistons, dimensions are in MM
A= XX.919-XX.923
AB= XX.923-XX.933
B= XX.933-XX.937
So for being "just" an dumb ole chainsaw they were petty fussy when they built them.
TKG

RE: New (to me) internet myth
 

You cannot buy a cylinder without a matching piston but you can buy a piston by itself

RE: New (to me) internet myth
 

I didn't have a need to mention the final measurement / acceptance because I was referring to how the majority (by numbers sold) of RC engines are made (In china mostly). - there they set up for an approximate size, then use pretty much everythign that comes off the line.

A REAL cylinder is made slightly differently.

Casting
Rough Machining
Finish Machining (with a different cutting tool to what was used in the Rough Machining)
Inspection for acceptance / rejection
Plating / Coating (Either Electro-plating of multiple metallic layers with a Chrome alloy as the final run - or with a Silicon Alloying coating such as Nikasil)
Inspection for acceptance / rejection
Final Grinding to size
Finish Honing with fixed hone tooling
Final measurement
Acceptance or rejection
Grading.

Pe - the beauty of such manufacturers as MVVS is that the product is consistently great from one engine to the next - it took me a while to really "get" that but once it is experienced, it sure is a nice thing.

RE: New (to me) internet myth
 

:D:D:D

RE: New (to me) internet myth
 

As does Zenoah and DA....:D

RE: New (to me) internet myth
 

I hear newbies insist that a glow engine won't run without nitro methane in the fuel. Tell'em that international FAI competitions use a spec fuel with 0-nitro and they won't believe you.

RE: New (to me) internet myth
 

dont use that piston,,,,they were made for weed wackers only ! the dred ad piston,,,,,,,,,,

RE: New (to me) internet myth
 

The piston in my post is from a current production Husqvarna 346XP 50cc chainsaw. They are one of the hottest stock 50cc saws made and I happen to own one.

RE: New (to me) internet myth
 

You gonna do a conversion on it?
What prop will it spin, how many RPM?
How much will it cost?
Which oil?

:D

RE: New (to me) internet myth
 

I like chainsaws and most of them will remain to be chainsaws. I have a lot of them.

RE: New (to me) internet myth
 

Unfortunately I have a few more than I need too, that just means I have more to experiment with porting on:), Next I am going to make a pop-up piston and see how that works out. Messing with chainsaws is pretty addicting too.

RE: New (to me) internet myth
 

+1

RE: New (to me) internet myth
 

What is it about DA and 3W cylinders that causes them to turn pink if overheated. Is it a coating or something similar. Also, some of the better cylinders seem to be cast from an alloy that is very light in color ... almost approaching white in some cases. I assume it is just the particular alloy but does anybody know what that alloy is? On the other hand, quality cylinders such as Mahle have a darker appearance. I have also noticed the lighter alloy castings on high end racing glo engines such as Nelson and Jett. In most cases, these are not die castings. Just curious what the alloy might be. I'm a curious sort of guy and just need to know more about these things.

RE: New (to me) internet myth
 

I believe the pinking of the cylinders happens when the solvents used are exposed to high temperatures

RE: New (to me) internet myth
 

Look at all the posts that followed yours. Tell me if I was wrong that I predicted this would be interesting?

Good information to be had from the people here that know their business. I might not be a youngster but I appreciate any information about the things we use in our obsession.

Live and learn.

Bliksem

RE: New (to me) internet myth
 

Chain saws = work

But I do love my Lil Husky though:D

RE: New (to me) internet myth
 

Agree with you there Bliksem! No youngster here either and I enjoy real engine info rather than just the plain old stuff over and over again. I questioned you the first time around, but now .....would you please pass the popcorn? :D

RE: New (to me) internet myth
 

Solvents? Where do these solvents exist and where do they come from?

RE: New (to me) internet myth
 

The newer DLE cylinders look to have machined bores? There have relatively clean, and what appear to be machined lines between the bore and the port edges. etc. A new ring inserted in the bore appears to fit quite well with very good compression when the engine is first assembled with all new parts. OTOH, I have an older 3MM 53 that I would believe has a bore that was probably plated as cast. There are visible mold marks everywhere and these even extend into the bore in places. I still don't have a lot of time on this engine and though it runs quite well, compression is poor and still improving. It would benefit from softer rings that could conform to the bore.

I'm curious if the DLE bore is indeed machined or just a very good plated as cast example. Can you shed any light on these two examples of cylinders?

RE: New (to me) internet myth
 

I guess by comparison, some would classify me as a "youngster" though I feel a little wiser than others my age (32 next month). I do however value the "veteran" information and experiences that many members here possess. I come from radio control car experience of roughly 15 years now, and in the last few years have slowly gravitated towards r/c aviation. In that time, I've "discussed" with the car guys (young crowd, seemingly "know-it-alls") and the airplane guys (older, wiser, willing to share their experiences, not "what they heard"). I am by no means picking on one group or the other. I am merely sharing my opinion that the older generation of guys around here are far more enjoyable to converse with simply because the information is far more legit and free from "internet expertism".

No matter the subject, if you post your opinion in a car forum, there will be a 12 year old telling you you're wrong because "so-and-so" says so. I've learned more constructive information in the past year than I learned in the first 14 years of running rc cars.

Sorry I was off the subject a bit.. Keep on sharing the good stuff! My brain still has a little room for improvement yet (and I too have a chainsaw or two..).

RE: New (to me) internet myth
 

Solvents used in the manufacturing process

RE: New (to me) internet myth
 

3-W puts something in the metal on purpose thats turns pink so they can tell if the engine has been abused. They can even tell what the temp was by the shade of pink. Stops a lot arguments about "I didn't do anything wrong". Never heard that DA does the same thing. Dennis

RE: New (to me) internet myth
 

I don't have any inside information but that sure sounds like be internet BS to me.

RE: New (to me) internet myth
 

Well, they certainly turn pink if overheated! There is no disputing that. My guess there is some kind of coating on the outside of the cylinder that causes this. What this is or how it works ... I have no clue. In normal operation, there seems to be just a bit of pink near the exhaust port. So far I have avoided the dreaded pink cylinder condition but have certainly seen it on other people's engines. Mostly on engines of people who do extended hovers.

RE: New (to me) internet myth
 

INTERESTING....I "cooked" the cylinders on an old 3W 140 two years ago and did not notice any "pinkening" of the cylinders. I have noticed this on DA's though. My 3W was in a Trueworthy Pitts M12. I'm pretty sure my overheating issues were cooling air related. I continued flying the plane as I tried various baffling/exit air combos. Well...before I got things worked out...the engine quit on a flight and after landing the nose of the crankcase and prop hub were still so hot that it was uncomfortable to touch for long. After cooling...the engine would restart but was WAY DOWN on power at mid to high throttle. When I pulled the jugs off...one had an area roughly the size of a quarter in the exhaust port area of the cyl wall that was missing the plating. The other cyl had a few very small spots where it looked like the plating was just starting to go. I learned on RCU that quite a ways back 3W had some issues with poor plating and/or out of round cyclinders. I'm guessing that since my engine was VERY hot...the damage was caused by that and not faulty cylinders. I'll have to find these cyls and look again at the color...

On a side note...after the above incident I bought a cheap "laser/infared thermometer" and started checking both my own and others engine temps. I know this method of temp checking on engines that have just returned from a flight is not "usefull" to the engine experts but I was just playing around. I was pleased to find that the temps on my other 3W's was very close to the temps on other guys 3W's that I checked. I was usually getting ~250-280 deg in between the top cooling fins on the cyl. I only have one DA right now. Its a well used "older" 100 and the temp on that eng was ~200 deg taken right after landing. I checked a buddies and got about the same so it looks like DA's run cooler?? I know...not the most accurate method to monitor temp and many variables...cooling air, oil, prop loading... Just found it interesting though.

Steve