Indeed technology is better today than it was 30 years ago but some manufacturers still set their engines up very tight. Get your hands on a Jett engine once. They're so tight you need heat before firing the engine up for the first time because otherwise a starter will never turn them over to get them started. You're gonna be hard pressed to hand start a new Jett. I know Jett uses state of the art machines to make their engines; example: their BSE line. All barstock engines made on CNC equipment.

All tapered bore engines that I know of sell piston and liners as matched sets.

Yes they do. I will correct myself some here. The machines with a talented operator could machine the liners to very strict tolerances but was not cost effective to do so. This is really what led to the whole large lot size/matched set deal. Saw it first hand when I toured the K&B plant in the mid "80s

I don't think that's the reason...

I think they simply had too many complaints from people who didn't know how to treat these engines properly, plus the ABN engines are more sencitive, so they make them looser for "simplicity" for the user. They are already broken in, or worn out, depending on how you see it. A well used, proper ABC engine, will still have more pinch than a brand new ABN/ABL engine has...

Now that I could buy into. I worked at one of the largest hobby shops in Cali in the 80's and we would always steer the beginners to a ringed engine. We also had a policy that we would fire up any engine for the first time for free. that saved us lots of headaches. I have however been involved in manufacturing in one form or another in the past 25 years and have seen the improvements in machining.

That matching may just be a grab a piston, grab a liner, and toss into bag.

I really can't say about the modern ABL engines but when I was Q500 racing in the '80s I would order up 6 engines at the beginning of the season. When they came in I would take all 6 and dis assemble them and start measuring with a pair of calipers. I recall that there was a .002 to .003 difference in bore at the top of the liner. I would usually grab the piston and liner that gave the tightest fit. Not sure if that gave me any advantage or not but I think hand selecting the crankshaft did. I would pick the one with the longest timing duraration. My buddies could never figure out why my engines typically ran about 500 rpm more then theirs. When I came back to racing 4 years ago I choose to run Rossi 3+2 pattern engines. Still ABC and very tight up top. Most times I think we have gone backwards with our model 2 strokes. That Rossi Pattern engine put out even more then A Jett LX 61 would have.

No that is tolerance, repeatability is not quite the same. Repeatability is doing it the same way every time, not necessarily more accurate. Also the same for each machine. With out CNC the tolerance is also dependant on the skill of the machinest. So one machinest may be doing a better job than others. Repeatablility is much broader than just tolerance. Put it another way as to the accuracy only, they could machine to the same tolerances and easily make parts meeting the same tolerances. But they would have more rejected parts due to repeatablility.

Actually it was cost effective to do so. But that is why the first ABC engines had a premium cost.

The rejected parts usually become spare parts. I think about this fact when looking at a new engine. I look at piston, liner, and crankshaft costs. If the piston and liner set costs almost as much as a new engine, why buy one in the first place considering the market glut of good engines?

Speedracer is right about the serious competitor buying a bunch of engines and hand fitting the parts to get one or two good ones.

Wouldn't a serious competitor be buying from a high quality engine manufacturer in the first place? I mean, reputable engine producers of high quality performance/racing engines will have a much higher control over quality (and subsequently better fits/tighter tolerances) over the cheapie competition (Chinese/Taiwanese clones and wannabe's)? I understand no two can be exactly alike with today's machines and technologies, but has anyone seen that much variance in tolerance to where it would really benefit to buy a handful of engines and piece together the best possible set of parts? I have a hard time believing that that would be necessary, but what do I know? I'm just an armchair engineer running his mouth off.. (LoL)

Sporto, your just not making much sense here. How is a higher rejection rate cost effective? I would have been smarter to just do matched sets. Model airplanes have always been a low profit margin business, you normally would not find top notch machinists working for a model engine company. Defense budget was huge back then and that's where all the top level machinists wanted to be. How does cost effective and premium cost mean the same thing?

Tim,

A lot of the cost of the old OS Hanno Specials was for the time spent on the line hand fitting parts. I wasn't talking about Jetts or Nelson earlier. I would bet that the serious guys probably still buy batches and hand fit parts like speedracer did. They would sell off the rest unless they kept them for spares.

1Qwk. In those days we were running OS, followed by Rossi and then Webra engines. All quality manufacturers. Here is the short version. Any engine manufacturer has competition, he has to meet a market price point. This will determine how much labor he can spend on each engine. That labor is the key. Back in the 80's a good machinist ( expensive ) could make a perfect liner in lets say 2 hours. A fair machinist ( much cheaper ) can make 1 acceptable liner in 1 hour. Then it gets sent out for plating and there would be another tolerance. So you can see how in dollars and cents it would be better to establish a wide tolerance and do matching. Moving forward to CNC machines allows for a more accurate part, fewer rejects, fewer operators, less matching of parts, better engine. Notice how stable prices have been for your staple engines ( .40 to .60 2 strokes ) over the past couple decades? Not a huge price difference whereas gasoline has gone up 300%. This is because with CNC equipment and updated designs they can produce an engine with less labor and materials costs then they were able to do with manual machines.

I never said it was. I was refering to machining by had VS CNC and that the hand machined ABC (before there was a lot of CNC) was cost effective because they could demand a higher premium. Not because it was cheaper to make.

Now the price for ABN is about the same as for ringed. ABC is no longer cost effective for sport engines, so you will find it only on a Jett or higher priced models.

To the best of my knowledge maybe excluding Meccoa with the older K&B stuff and a couple of the Rossi Brothers. I can't think of any airplane engine manufacturer currently using ABC construction. I know that Jett uses and Nelson used AAC

Nelson no longer uses AAC either. Nor any other method. They are no longer making engines.

The HP from Meccoa is a ringed ABC, I don't think there is any taper in the bore. I don't think Meccoa is currently making any engines, just assembling spare parts from time to time.

Fox may have a few ABC engines left. I don't think they plan on making new ABC engines but may have a few ceramic models.

Enya may have a few models.

In the earlier days of making "production" ABC engines, they were still finding out (sometimes the hard way) which alloy(s) of Brass and Aluminum worked better with each other, and which ones didn't...

The taper ratio from top to bottom of the cylinder...single taper...double taper, etc...Silicon content of the Aluminum piston, and the expension rates of the piston vs. the Brass sleeve, and so on...

The alloys used can effect the choices the manuf. make as far as "tightness" of the fit...(just another tidbit for consideration)

Higher Silicon content in the piston makes for a harder piston that doesn't expand quite as much...allows for closer tolerance control (when cold and when running) between piston / sleeve...etc. etc. etc.(I don't know exactly which alloy O.S. uses for their ABN pistons, but I know it's pretty dang hard...)

All duly noted. Thanks for the insight gentlemen. I always appreciate learning something.

I'll add this: nearly ALL RC car engines are true ABC. Very few are ABN for good reason too. I have an engine made by Fuji (I believe) for HPI. No pinch, plated inside and out (the liner) and it has the transfer ports machined into the piston. An oddball for sure in the car realm.

Actually, Nelson q40 and q500 engines are still being built,
maybe better than ever. Aero precision in Julian n.c.

Do you have a update for us as of yet?
When you took off the vent line from muffler you may have noticed that the engine may have wanted a little bit more high speed needle setting to keep running or it may have not, at any rate if you had a better transition when the vent line removed from the muffler that tells me that either you have a blockage or a pinched line or the clunk line is not set up properly. How much running time do you have on the motor as of now? I guess I need a few more bits of information before I can offer a few more suggestions so until I hear from you ill be waiting.

Use a Fox long plug with idle bar. The problem you are describing sounds alot like the problem I had with a new OS 95AX. The Fox plug with idle bar solved the problem.

That's poor advice IMO. Idle bar plugs were originally designed for crossflow/baffle piston engines in an effort to keep the element lit when the intake port opened. The fuel mixture hits the baffle on the piston and goes right into the glow plug. Idle bar plugs in Schnuerle ported engines is either a band-aid for poor tuning or a band-aid for a worn out engine. Maybe I was doing something wrong, but I've never gotten a Schnuerle 2-stroke to run on one without glow support except at WOT. So If you're having problems with an OS engine that isn't remedied with an OS 8 or OS F glow plug, you're doing something wrong. Bad fuel, bad tuning, wrong prop, etc. Moreover, the 95AX is ringed and the 46AX is ABN tapered bore. Totally different methods to run the engine in.

Nothing personal.

Hi!
Your right!
An idle bar plug is no good compared to an Enya 3 or OS 8-
It's all about setting the low speed needle right!