Break-in in tapered bore engines
 

Most engines that have a ringless high silicon aluminum piston, running in a plated cylinder sleeve, have a conically tapered bore.

This would mean the bore is tighter at the top of the sleeve than at the bottom.

The purpose of this smaller internal diameter upper cylinder, is to cater for the differential heating (and expension) of the cylinder, when the engine attains its normal operating temperatures.

The upper part of the sleeve, near the head and the combustion chamber, is much hotter than the lower part of the sleeve. Therefore it expands more and when at operating temperature, the part of the sleeve, in which the piston reciprocates is nearly cylindrical.

The piston in these engines is made of a low expansion, high silicon content, aluminium alloy (hypereutectic?), so it expands no more than the brass (or aluminium in AAC), base sleeve material, when heated.

All these engine's pistons have an interference fit at the top of the bore, so the engine "squeaks" or even seizes when turned over, especially when new.

Because of this fit, these engines need special break-in procedures. David Gierke, Clarence Lee (of RCM) and Dub Jett (http://www.jettengineering.com, read about break-in) wrote about these principles and they work.

If such an engine is broken-in sloberingly rich and four cycling, like you would normally do with with a ringed engine, it could be run-out, or broken, in stead of being run-in.

If the sleeve is allowed to remain tapered, the interference fit at top stroke would get the piston and the plating scuffed, especially in the inferior ABN engines. Lower cost is the only reason some engine manufacturers prefer nickel plating to hard chrome... The plating can easily be damaged in these engines.

Also, in every non-firing revolution the piston is pushed, into the seize at the top of the bore and then pulled back down, out of the seize, by the conrod. These repeated compression-tension cycles can ultimately cause the conrod to fail, due to metal fatigue (this was common in some older K&B ABC QM engines).

This type of engine must be broken-in in a somewhat rich two-stroke mode, beyond the point it starts to two-cycle, but not too lean.
It must be run with the throttle wide open and shouldn't be idled during the break-in.

It must not be allowed to run for any length of time in four-stroke mode, during the break-in. After the break-in is completed, there is no problem with four-cycling because the interference is minimized and is no longer an issue, even when the engine is run lukewarm.

Use a prop with the same pitch, but with one inch less diameter, than the prop you would normally use. This, to lessen load on the engine without compromising cooling.

In addition, to heat treat the piston (for size stability), the first 20 runs, or so, must be short; starting from 10 seconds and gradually getting longer, to about 1 minute.
The engine must be allowed to cool down completely between these runs.
Harry Higley of MAN (and Harry Higley model products) developed this method years ago and it works.

After that, allow the engine to run for 10-15 minutes, still in a somewhat rich two-stroke mode.

After that the engine should be leaned gradually for short periods and then richened back (still two-cycle) to cool.
After about 10 minute doing that, try to lean the engine carefully to maximum RPM. If it can hold this RPM without sagging, for 60 seconds straight, you have completed the break-in.
If it sags richen it immediately, to prevent damage, repeat the first part of this paragraph for 10 more minutes and then try again.

I have had ample experience with breaking-in ABC engines made by Rossi and MVVS, as well as ABN engines made by OS and Webra.

The only non-success was with an OS40FP, before I adopted this break-in technique. It peeled the nickel off about 25% of the bore.
It still ran for years afterwards, though, until it broke in a bad crash.

good stuff!
 

great advice that simply cannot be repeated enough times, most people learn these things AFTER they toast a few engines.

the cost difference between chrome and nickel depends on where the engine is manufactured, chrome is a heavy metal that is harmful to the environment and many countries require special waste disposale procedures be followed when it is used in plating.

dave

Break-in in tapered bore engines
 

The repeated cool down's accomplish nothing. I have alway's simply ran a tank or two at a rich two stroke. The cool down cycling is a holdover from the first ABC engines which needed anealing, though this didn't do much for that either. The taper remains after the breakin , its just that you have worn off the top of the piston to fit the taper at the top of the cylinder.

Though your break in procedure will do no harm. Just makes it more complicated.

Break-in in tapered bore engines
 

Actually the heat cycling is a hang over from the cast iron pistons and was absolutely necessary if you wanted a good engine. I believe some of the smaller Enyas still use a cast iron piston so be aware of this if you buy one.

Another point of interest is that over time the brass liner will develop a bell mouth at the top because when hot the expanding cylinder head strains the brass a little at a time. This doesn't happen with an AAC though. This was something that George Aldrich discovered.

Break-in
 

DownUnder, SportPilot,

I don't know about the cooling period between short runs. Maybe it is a carryover from times gone by. As far as I know, annealing does stabilize the size of a hypereutectic piston. Maybe it is to a much lesser extent than with a meehanite piston, but I still do it.

But breaking-in a tapered bore engine very rich and four cycling, as you would with a hardened steel sleeve and a ringed piston, can and will potentially harm an ABC, AAC, or ABN engine.
I don't think you would argue with that.

Breaking-in is NOT supposed to remove the taper in the bore.
It isn't meant to "taper" the piston to fit either.
If this upper stroke "squeak" is completely lost, the engine may be easy to start when cold, but its power will no longer be up to par. All my MVVS ABC engines still have slight interference when cold, despite quite a bit of running time on all of them.

Re: Break-in
 

Actually the control line folks run their ABC engines at a four stroke. One of their favorite engines is the LA 46. They run it at a full four stroke. But they break it in at a two stroke. They use George Aldrich's hot method. Then they start richining it up a little each run until it four cycles at level flight, then breaks into a two cycle when it pitch's up.

If you look at an engine with enough time to have some varnish build up you will notice that there will be no varnish at the top of the piston, this is the part that interfers with the cylinder. And yes during break in some of that piston wears off, that is why you find a lot of black oil on the first few runs.

Running-in
 

Sport_Pilot,

I meant this "four cycle forbiding" only about the break-in period (although R/Ciers do tend to forget other fields of aeromodeling...).
I corrected it both in the original article and in my reply to you.

Thanks for the comment.

And yes, break-in does remove some material from the piston crown. But as long as some interference can be detected when the engine is cold, the clearence is small enough not to allow varnish build up, even in normal running temperature.

This method will give you the best results, engine life, reliability, easy starting...

Sincerely,

Tapered bore
 

This is a quote from the "Break-in with synthetic oils??" thread.

Input by Fancman:

THIS IS FROM K&B

ABC type engines, like the K&B 48, are manufactured with tapered cylinders so a bind is normally felt while turning the engine over top deaad center when cold. As the engine obtains operating temperature, the cylinder becomes straight and the clearances between the piston and cylinder become correct. The straightening is due to the top of the cylinder running at a higher temperature than the bottom, thus the top expands more.



It is also normal for compression to sometimes feel poor when the engine is stopped and turned over while still hot. This is due to the piston cooling faster than the cylinder. If the engine temperature is allowed to stabilize, the compression will return to normal.

RUNNING THE ENGINE TOO RICH WILL RUIN THE FIT as the operating temperature is not reached and piston is prematurely work from lack of clearance. You do not want to "break-in" an ABC engine at a very rich setting. Just a slightly rich setting for the first 30 to 45 minutes of running is adequate.


K&B Homepage • Modelengine.com

Proof of genuinity for the contents of this thread. By an engine manufacturer...

Sincerely,

Break-in in tapered bore engines
 

Uaed to work for an engine rebuilder back in the 60s. Aero engine cyls had to be bored with a 001 to 002 thou taper for the same reason. At operating temp the cyl was straight.

Break-in in tapered bore engines
 

Dear Jaka/DarZeelon & all

I deeply thanks you'll for all the expertise & learnt various reason to RUN IN a new engine that too ABC engine.

One more question ,should I use a spinner while breaking inn ?

Spinner
 

Peter,

Using a spinner (providing it is not a 5 inch, or larger size...) should not affect break-in. You can use it safely and it will ease the use of an electric starter.

Take the utmost care not to get your fingers in the spinning prop.

Sincerely,

Yep!
 

I had helped someone with a troublesome new engine this past weekend. It was a Magnum 61 2 stroke with a 12x6 prop. I couldn't get this thing running right at full throttle and finally broke down and asked the owner about his break in.

He bragged about his meticulous break in running his engine extremely rich, 4 stroking it for about 5 tanks.

The result is that his engine can only propel a 12x6 prop 8500 rpm.

Since he was much more experienced in this hobby (years wise), I wasn't about to tell him his break in probably damaged his engine. Some people don't take advice to well....

Break-in of ABC engines
 

Homebrewer,

Although I started this thread, about 10 years ago I would have probably done the same; rich, cold, slow, four-cycle.

Only after reading stuff written by George Aldrich, Clarence Lee, David Gierke, Dub Jett, Harry Higley and others, did I begin to understand that trying to be "gentle" to a new, tapered bore engine, using rich mixtures, low temperatures, low RPM, will make your engine BREAK DOWN, instead of BREAK-IN.

The problem is that most engine manufacturers, don't bother to tell the new owner of their masterpiece, how to do it right.

Maybe they want to sell more parts....

What looks to some of us like rough handling, engine life threatening, vandalism, is to the engine; a long lease on life.

Although I wrote an article that was published in a local (Israeli) R/C site (http://www.2fly.co.il - If you can read Hebrew...), about breaking engines in, I have a lot of trouble convincing the site owner about the tapered bore engine break-in technique.

He keeps on doing what this friend of yours did...
I personally saw him cause a new Webra .50 to seize due to liner peeling (thankfully, it was replaced under warranty...).

Sincerely,

Break-in in tapered bore engines
 

Silly question, but why doesn't everyone simply follow the instructions in the manual that came with their engine?

That way, if something goes wrong, you can blame it on the manufacturer, and get it serviced under warranty?

I'm not ridiculing anyone here, I am just confused, being new to the hobby.

Break-in of ABC engines
 

MN_Moose,

Quote:
--------------------------------------------------------------------------------
The problem is that most engine manufacturers, don't bother to tell the new owner of their masterpiece, how to do it right.
--------------------------------------------------------------------------------

Then you get a new set, and another, and another....

They are all for free, but don't you just want one that works?

Do it right in the first place.

Sincerely,

Break-in in tapered bore engines
 

Interesting thread -- I "broke in" an ABC engine (TT46ABC) last year before reading the published material on special approaches for tapered cyclinder engines. Slow and rich for long periods...result is an engine that runs, but will never be a "screamer".
The instructions that came with it didn't provide the kind of info that the "experts" recommend. Go figure...
pj

Break-in in tapered bore engines
 

The instructions that came with it didn't provide the kind of info that the "experts" recommend. Go figure

Why is it my TT 46 had the correct procedure?

Break-in in tapered bore engines
 

I read a while ago that ABC engines were originally designed for one speed: FULL THROTTLE for racing applications and that extended operation at low or partial throttle was also damaging to engine longevity.

Break-in in tapered bore engines
 

Those of us who were boating the late 70's and early 80's were using ABC OPS aero engines converted to marine use. One of the things a guy named Bill Trammel here in the Tulsa area did was "lap" his piston to the sleeve. It was done with 1000grit wet dry sand paper, and a lubricant, ie wd 40. When he finished the pop at the top was still there, but the feel of the compression was reduced a tad and a very smooth transition at the top was accomplished. He also did it to allow quicker breakin and use higher nito. I have done that some over the years with engines in fact just finished it on an MDS 40. Makes for a great feel at the top and the motors run like nothing else. It is a feel you get with time and experience. Mike the piston, cylinder first if it is REALLY tight, take your time, get the fit and believe me it will make a difference. Rpms will pick up too, and pipe response is better.

An old boater
Curt

Break-in in tapered bore engines
 

ABC was first introduced by Super Tigre for their 2.5cc (.15) engine used in FAI control line speed. Before then all engines of that size used a cast iron piston which was prone to seizing if the mixture wasn't exactly correct through the entire flight. A bonus was that the lighter piston allowed better balancing.

Break-in in tapered bore engines
 

Maybe because the instructions which came with BOTH my 40 LA and 46 FX are wrong? :mad: They state that you should switch from 4-stroke to 2-stroke every 10 seconds for some time during the initial break-in. Well, silly me, I followed directions. Fortunately, the engines don't seem to have suffered much.

4cycle-2cycle
 

BGI,

You are lucky.
Many others wound up with peeled cylinder liners.

It was blamed on QC and fixed by the new two stage, Copper-Nickel process. It lessens the chance of peeling, but it is still wrong. It was a break-in technique problem.

Instead of changing their break-in instructions, OS made the sleeve more tolerant to the wrong (or should I write; prescribed) technique... Beating around the bush, I would say.

Sincerely,

Re: 4cycle-2cycle
 

OS should have addressed both issues: instructions and peeling. It makes sense to address the manufacturing process because most modellers won't read directions and the old-timers are familiar with the old ringed break-in process. So if they had ONLY fixed the directions, they would still have an image issue to deal with. The really strange thing is that the instructions are still wrong!

Which leads me to question my faith in manufacturer's directions, as you did, in the other TT 91 FS thread. ;)

TT .91
 

BGI,

Nice of you to notice and to respond.

Manufacturers who are somewhat responsible do tend to be overanxious. Running the TT .91 through three litres of fuel, at 4K-5K RPM, will not cause the engine any damage whatsoever. It will only be a waste of fuel, which could have been used for flying.

During this type of break-in, the engine is making about 1/8-1/12 of its intended maximum horsepower. Most non-glider models will not take-off with such low power.

1-1.5 litres (or quarts...) and 65-75% of the intended maximum RPM should do the job just as well. With temperatures a glow engine experiences, the cylinder will not be glazed with oil residue either.

While OS tell us how to perform break-down on the engine, TT only runs us through a more tedious, over-careful break-in.

Sincerely,

Break-in in tapered bore engines
 

This may sound totally stupid to most of you but can you please explain the term "four-cycling" when used to describe a 2 stroke engine. If I'm reading all of this right, "four-cycling" would be low RPM and very rich needle setting, right? Wrong? I'm confused...not the first time but I want to make sure I break in my new Irvine for the best performance and not the "OS" way...I must admit, after reading this, I broke my first OS in wrong...Thanks!!

Humbly,
Mike