Author Topic: Bench breakin a myth? (Read 2636 times)

frank mccune · « **on:** April 14, 2014, 06:47:10 AM »

Hi:

All my life I adhered to the idea that one should "breakin" a new engine on a bench before flying it. I recently met a chap who never does this as he sets his engines in the breakin mode and flies them. No bench running! He has been doing this for about 50 years and claims that he has never had any bad results by doing this. It seems to make sense to me.

Is this prolonged breakin method ever been tested? If so where may I read the results? Many times, unfounded traditions,"myths", are very difficult to challange. Have any readers done any tests to support this tradition? Do you remember the MAN Engine Reviews of the 50's where the engines would be run for about an hour before the test being done? Some for more than an hour! That seeemed to be excessive in those days. The fits must have really been bad.

I recently took a new engine and carefully broke it in to obtain the "perfect" P&C fit. I flew it in a rich 4 cycle with 30% castor oil fuel for a few slights and all should have been good!. Alas alack,when attempting to restart this engine, it had very little compression and could not be restarted. There was very little to no compression. No, the engine had not been run lean or overproped! This was a domestic engine not known for being a great engine with good materials and fits.

Any thoughts or studies done concerning engine breakin?

Tia,

Frank

Dick Pacini · « **Reply #1 on:** April 14, 2014, 08:01:41 AM »

Brodak engines, for example, require a number of short bench runs/cool down cycles to establish a proper fit. I would follow the manufacturer's instructions for break-in procedures, especially using the correct fuel.

I believe the Evo engines are pretty much out of the box ready to go. Not sure about LA engines. I have a bunch of each stacked up still in the boxes but haven't put them in service yet, nor read the manuals.

Tim Wescott · « **Reply #2 on:** April 14, 2014, 08:42:05 AM »

The idea of breaking an engine in in the air is great, until you get a booger in the tank and get ten minutes of hot lean run when you're supposed to be gently breaking in an engine.

Different engines must be broken in differently. You want to read the instructions, but my understanding is that you want short runs with periods of cool-down (because before its broken in it'll run hotter), and that ABC engines want to be run at normal speed (and therefore temperature) while steel/iron engines want to be run rich (and therefor cooler).

Somehow nearly all of my engines have come to me used (!), so I've never had to break one in! So take my comments for what they're obviously worth.

FLOYD CARTER · « **Reply #3 on:** April 14, 2014, 12:43:04 PM »

One prominent engine maker actually says to run a gallon of fuel on the bench! Just to be different, I ran 3 tanks of 4 oz. each (that's 12 oz.) I then put it in a plane and went flying. It has been perfect ever since.

(names removed to protect the innocent)

Floyd

Brett Buck · « **Reply #4 on:** April 14, 2014, 01:58:50 PM »

Quote from: frank mccune on April 14, 2014, 06:47:10 AM

Hi:

All my life I adhered to the idea that one should "breakin" a new engine on a bench before flying it. I recently met a chap who never does this as he sets his engines in the breakin mode and flies them. No bench running! He has been doing this for about 50 years and claims that he has never had any bad results by doing this. It seems to make sense to me.

Is this prolonged breakin method ever been tested? If so where may I read the results? Many times, unfounded traditions,"myths", are very difficult to challange. Have any readers done any tests to support this tradition? Do you remember the MAN Engine Reviews of the 50's where the engines would be run for about an hour before the test being done? Some for more than an hour! That seeemed to be excessive in those days. The fits must have really been bad.

I recently took a new engine and carefully broke it in to obtain the "perfect" P&C fit. I flew it in a rich 4 cycle with 30% castor oil fuel for a few slights and all should have been good!. Alas alack,when attempting to restart this engine, it had very little compression and could not be restarted. There was very little to no compression. No, the engine had not been run lean or overproped! This was a domestic engine not known for being a great engine with good materials and fits.

Any thoughts or studies done concerning engine breakin?

The need to break engines in is a fundamental defect. However, in most practical cases, you can't avoid some changes early in life.

Whether ground running is necessary or not depends entirely on the engine and how it is made, and how well it is made. Some engines can be easily damaged by running them in the air, having a lean run, and then the cylinder/piston fit is ruined forever. Others are safe to "fly" into condition. But they will definitely change over time.

There's probably no harm to breaking it in, in the air, if you are absolutely sure you will never have a lean run. No one is absolutely sure, so you should run it on the ground long enough to be able to tolerate a missed needle or some other problem. This might be nearly 0 time to several hours, depending on the engine.

No matter what you do on the ground, it still takes some actual flights to get them running right, even PA/RO-Jetts. 40-50 flights in some cases.

Brett

Dennis Toth · « **Reply #5 on:** April 14, 2014, 02:10:43 PM »

Frank,
It sounds like you tried this on a Fox 35. The old iron piston/sleeve engines are a little different then the current ABC/ABN/AAC setups. It sounds like you may have a couple of loose head bolts or loose plug or leaking seal on the plug. If its not one of those you should send the engine back to the factory. Running an engine in a plane with a small prop, high oil, rich isn't much different then on the bench. It likely runs cooler.

For myself and my Fox 35's I like to lap them to a dry fit that has the piston stop with the baffle just at the top of the sleeve. Clean them good, oil run one rich run on the ground then fly rich for a couple more flight and it is good to go.

Best, DennisT

Jim Thomerson · « **Reply #6 on:** April 14, 2014, 04:02:17 PM »

On the bench you have the engine under control. In the air you may or may not. I do Fox 35s similar to what Dennis said. I like to use a 9 x 4 for several rich on the bench runs. I like the engine to be able to run out a 4 oz tank at a rich two cycle (like I would fly it) before I put it in an airplane. I think George Aldrich advocated a partial in the air break in, running rich and flying lazy 8s to subject the engine to varying load.

Bill Little · « **Reply #7 on:** April 14, 2014, 04:25:06 PM »

I have run a good amount of ringed engines, but have almost no experience wit breaking them in. I just am "guessing" if the ring has "seated". What is/area common sign of the ring having seated?

Thanks!

BIG Bear
RNMM/AMM

Mark Scarborough · « **Reply #8 on:** April 14, 2014, 05:14:08 PM »

Quote from: frank mccune on April 14, 2014, 06:47:10 AM

Hi:

I recently took a new engine and carefully broke it in to obtain the "perfect" P&C fit. I flew it in a rich 4 cycle with 30% castor oil fuel for a few slights and all should have been good!. Alas alack,when attempting to restart this engine, it had very little compression and could not be restarted. There was very little to no compression. No, the engine had not been run lean or overproped! This was a domestic engine not known for being a great engine with good materials and fits.

Tia,

Frank

well you could correct me,, but modern engines require heat for the piston and liner to fit properly,, otherwise if to cold they will potentially ruin the fit as well,,

Tim Wescott · « **Reply #9 on:** April 14, 2014, 06:02:28 PM »

Quote from: Mark Scarborough on April 14, 2014, 05:14:08 PM

well you could correct me,, but modern engines require heat for the piston and liner to fit properly,, otherwise if to cold they will potentially ruin the fit as well,,

If it's an ABC or ABN engine then the materials chosen for the piston and liner (hypereutictic aluminum and brass, respectively) are such that the liner grows more than the piston with heat. So if you break it in cold, you lose your "pinch" and it never works right after that.

ABC engine break in and steel-iron engine break in are different.

RandySmith · « **Reply #10 on:** April 14, 2014, 07:45:54 PM »

" There's probably no harm to breaking it in, in the air, if you are absolutely sure you will never have a lean run. No one is absolutely sure, so you should run it on the ground long enough to be able to tolerate a missed needle or some other problem. This might be nearly 0 time to several hours, depending on the engine.

No matter what you do on the ground, it still takes some actual flights to get them running right, even PA/RO-Jetts. 40-50 flights in some cases.

Brett "

Exactly, however there are other factors that come into play, not only lean runs can damage engines, if you try to breakin a tight fitted AAC or ABC engine and it goes rich, you can destroy a ROD, spin bearings, or damage the piston/sleeve in the process, This is one of the big advantages of using ground runs for breakin

Randy

Dave_Trible · « **Reply #11 on:** April 14, 2014, 08:00:14 PM »

This never seems an exact science and a good end result obviously happens a lot despite ourselves but I have a few rules I go by and follow an instinct as to whether an engine is ready to go in the airplane. I do also think an engine isn't entirely broken in until it has some air time, loading, unloading, heating up and cooling down.
I put at least 30 minutes on everything on the test stand. Sometimes it takes two or three times that on some engines. This will be in about 10 minute runs. I start with a small light prop then work up in steps to the actual flight prop. If the engine will hold a very consistent setting for the whole run (save the very bottom of the tank) and I put my finger in the backplate while running and it feels cool, that tells me the shaft and bearing aren't still tight, then I'll move it into the airplane for a few slightly rich runs. If it hold the setting pretty well then it's ready to go but still should gain some power over the next 30 runs. Two like engines can require different amounts of time to break in due to manufacturing tolerances. Usually the engine that seems to take more time ends up being the better engine due to closer fits.

Dave

Mark Scarborough · « **Reply #12 on:** April 14, 2014, 10:09:14 PM »

Quote from: Tim Wescott on April 14, 2014, 06:02:28 PM

If it's an ABC or ABN engine then the materials chosen for the piston and liner (hypereutictic aluminum and brass, respectively) are such that the liner grows more than the piston with heat. So if you break it in cold, you lose your "pinch" and it never works right after that.

ABC engine break in and steel-iron engine break in are different.

Dude,, thats what I said, but with more engineerish words,, sorta,,

Tim Wescott · « **Reply #13 on:** April 15, 2014, 12:09:42 AM »

It bears repeating, in as many different ways as necessary.

Mike Greb · « **Reply #14 on:** April 15, 2014, 04:45:48 AM »

The last stunt engine I broke in i gave it about 6 laps before pulling into a wingover.

frank mccune · « **Reply #15 on:** April 15, 2014, 06:58:42 AM »

Hi Dennis an others:

No, it was not a Fox .35 but a Fox.25 from the 50's. This engine broke my heart as I did spend a long time making sure that it was "broken in" and ready to fly. I had it in a rich 4 cycle at all times with a 9X6 prop. I have also have had this same problem with the old Fox .15 pb engines. This was, a very short prime time life. Yes, they were all broken in and I did not run them hard. I ran the .15's in a fast 4 cycle with an 8X4 prop.

I have had great luck with the Fox Stunt.35 engines and did very well with a coupe in my Foxberg racing days. I have also had great "luck" with O.S., Enya and Super Tigre engines. It seems to me that the old Italian made S.T. engines were very well made with great materials and fits. I found the old G21/.35 and the G20 engines would run forever. Enya engines would last for ever! also! Great sport engines.

Perhaps there is a difference in materials used in the p&c that determine the longivity of an engine.

One thing that I should mention, is a bad run that I did have with the O.S .35 baffle engine. I had a ten minute flight that was very very lean. The plane was going too fast to land it in a controlled crash. I would rather ruin the motor than risk having to build another plane. In any case, the plane finally ran out of fuel and landed. The engine was covered in that dreaded black burned on castor oil finish. After the engine cooled, I checked the compression and it was great! No damage to the p&c! Perhaps it was the 30% castor oil that I had in the fuel. Or, perhaps it was the good materials used in the engine.

Stay well my friends.

Frank

Steve Helmick · « **Reply #16 on:** April 15, 2014, 03:42:05 PM »

Sometimes new engines have stuff inside that's not supposed to be there. When I was a teen, I got a shiny new OS Max III .35 and curiosity got me to take the backplate off. There was a huge steel chip in the crankshaft bore that would have totally trashed the engine on the first run. I've been in favor of taking off the backplate and giving it a good look...easy with OS LA series engines, since I replace the imitation backplate with a real one, made from 'luminum.

Steve

Kim Doherty · « **Reply #17 on:** April 16, 2014, 09:34:00 AM »

Breakin, Shmakein

Assuming one of ABC/ABN/AAC no test stand break in is needed or advised.

Here is Henry Nelson's last step in piston fitting and then break in:

A piston is taken from a tray of several OD's and fit to the liner.

It is given a good Whack!! to set it.

Motor is taken directly to a test stand and a fuel hose attached. Started and then needled without mercy till it is SCREAMING!!. After a minute it is shut down.

So much for gentle breaking in.

Too many myths, to much gibberish.

YMMV

Kim.

Dennis Toth · « **Reply #18 on:** April 19, 2014, 06:01:41 AM »

Frank,
With the steel/iron ps engines there is a heat stabilization that goes on for the first several runs. For you engine I would do a couple checks. First, put a couple drops of fuel in the exhaust and turn it through the compression stroke. If it is bubbling out a lot it indicates a possible fit problem. I would next take the engine and submerge the head/plug and upper cylinder in a container (clear one if you have it) of water and turn it through compression. See if the head is leaking or plug seal or gasket is leaking. If the head or plug is leaking remove and clean the area where the gasket seats and the gasket itself and reinstall being careful to pull down the head in a cross tighten pattern. As you tighten the head check that there are no binds (sometimes the head bolts cause the case to twist and bind the ps).

If it is only the piston fit blowing through compression I would send it back to Fox or if not under warranty (I suspect it isn't) just get a new ps from Fox or ebay.

Best, DennisT

frank mccune · « **Reply #19 on:** April 19, 2014, 07:46:30 AM »

Hi Dennis et.al.:

Thanks for the replies.

I have not done the tests that Dennis sugested as I like many others, have too many hobbies. I will do these tests when I get time.

Stay well my friends,

Frank