Engine sag during break-in

Last weekend between monsoons I was breaking in (on the ground) a new Thunder Tiger .25 GP at a medium-fast 4-cycle, and found that when I disconnected the battery, the engine would sag a few hundred rpm (dead battery in tach = no reading). I have always understood that sagging means a bad plug. I was using a plug of unknown provenance which had worked very nicely in my now worn-out .20 FP. I replaced it with a new OS #8, same results. I tried a Fox, a McCoy, and got sagging to one degree or another with them all. Doesn't seem the bad plug idea works here. Could it be, tight new engine, too cold plug, unlucky alignment of the planets . . . ?

APC cut to 8x4, 10/25 all-castor, stock muffler, suction (but will be uniflo/muffler pressure in the air), sprinkler venturi, OS NVA, black spinner nut, white tube socks . . .

Thanks,
Kim Mortimore

Kim, I wonder if it wasn't too rich. The ABC motors have to be run-in leaner than the iron piston pieces. The trick to ABC is that the brass sleeve heats up and expands faster than the aluminum piston. If a new ABC engine is run too rich, it can bind up because the sleeve doesn't get hot enough to expand properly.
Kelvin

True about ABC, ABN and AAC's. Note, however, that TT's are generally ABN, not ABC, even though the box says ABC. I gotta talk to Mitch about a class action lawsuit against Thunder Tiger.

Does Mr. Thunder Tiger mandate all castor fuel for break-in? Magnum does, and I tend to like this thinking, but I wonder if that isn't what's doing it. You might try a Thunderbolt, Zinger or K&B 4 stroke glowplug, I would. How much time/fuel qty. have you run it? Anyway, the book says to run a rich 2 cycle, not a 4 stroking run for break-in. Steve

Just out of curiosity, Steve, what is this Avatar of yours? I was thinking of doing a contest to get the best caption for it.

Here's some I thought of

10) It was suddenly discovered that the stunt circle was built on a mound of fire ants.

9) Customers rushing back to McDonalds to get a refund after hearing about "mad cow disease".

8) The contestants just got their score sheets and each one is headed over to have a talk with judge number 3.

7) The sandwitch wagon showed up at the field and a ten minute break has just been declared.

6) After wolfing down their burritos, everyone is heading to the lone porta potty on the field.

5) It is aerobics night at the club, knowing that a long winter of just sitting at the workbench is ahead for most club members.

4) The busload of Democratic candidates just unloaded in Pella, Iowa, and they are all headed over to woo the lone registered Democratic voter.

3) Tower Hobbies just announced that the ARF Noblers will be in stock for the next 3 1/2 hours.

2) The St. Louis Ice-O-Lated contest this year included a dip in the frozen Mississippi.

And number one on the list:

1) It was just announced that after being offline for a couple of days, the Stuka Stunt Forum has just come back on.

leonard i think number 6 should have been in the number 1 spot its the best and funniest caption for it

steve
the superglue kid

>leonard i think number 6 should have been in the number 1 spot its the best and funniest caption for it >
> steve
> the superglue kid

Perhaps number two would be more appropriate.

>Just out of curiosity, Steve, what is this Avatar of yours?
>I was thinking of doing a contest to get the best caption
>for it.
>
Leonard, that there is a gaggle of those "Dancing Smileys". It's for Dan, ya know. I considered others. Steve

I'm thinking about damages..... Hmmm, intentional infliction of emotional distress, perhaps? Loss of enjoyment? Loss of income from the time spent fiddling with said defective engine when plaintiff would have otherwise been working for income? Oh wait. I don't worry about the plaintiffs if it's a Class Action because I'd be the only one to make any money. Plaintiffs would likely get a coupon to save $1 on their next purchase of a TT engine if purchased within next 12 months.

Just great! Then TT's would be just as scarce as EZ-Just handles.

George

Edit: Sorry, Kim - got distracted. If all else fails, try a different can of fuel.

Your engine is attempting to communicate with you. It is saying, "Lean me out, you are wearing out my piston and distorting my liner and I will hate you for the rest of my limited life!" Seriously, an engine running rich will often sag with a good plug; and you are doing your ABwhatever engine no favor running it in a 4-cycle.

Putting a glow driver on a engine and the engine RPM picks up is a normal sign of being rich(or you have a bad glow plug)You already eliminated that.Pinch the fuel line for a second and the same response ,RPM picks up.Like has been mentioned above make sure you are lean enough that you are coming up to a decent operating tempature.
Dennis

Looks like this is another old dog/new trick thing. I broke in quite a few new engines back in the Iron Age, when it was a longer, slower process. I think it's just a matter of getting over "you mean it wants run THAT lean THIS soon?!" Mr. Thunder's instructions don't help, as they emphasize rich and "ample smoke".

Mr. T sez 75/25 straight fuel, either all-castor or a blend, is good for break-in and general flying. 5-15% nitro and not less than 20% oil for more power. No all-synthetic. I've read in SN and elsewhere that engines built for nitroless countries need a compression change to run on fuel with nitro. This is a theoretical thing of course, since we have nitro 'n it works jes fine in all these clones.

The label on the box sez ABC, the instructions say ABN. O.S. tech notes still list the .25LA as ABC.

Is the best Thunderbolt plug for stunt the r/c long, and Hobby People the only source?

Thanks,
Kim

On the glowplug issue, results vary, but the Zinger glowplug appears to be identical in all ways to the Thunderbolts, and may be much easier to get at the LHS. SIG, McCoy and K&B plugs are also good, and the thing they have in common is that they are all made by the Ohlsson & Rice derived company, still operating after all these years. Steve

R/C long for all of these?

Thx,
Kim

Yes, R/C long, or hotter yet would be the 4 stroke plug, which has no idle bar. GMA was high on them. Steve

Many thanks to all for the (as usual) excellent replies. Stuka is ahhsum.

Happy New Year,
Kim

TT Gp 25 only need about ten min of break in. 10/25 , 10/22 fuel works very well. TT are ABN but have a long life if not over leaned. Try a little leaner as JT suggest, above.
I resleeve every year on my high time combat engines. ( 200-300) dirty flights. MM

>The label on the box sez ABC, the instructions say ABN.
>O.S. tech notes still list the .25LA as ABC.

Really not an issue - in fact it's an common red herring in quality complaints. If everything else is right, in stunt, the nickel will last more flights than you will likely ever fly!

>Is the best Thunderbolt plug for stunt the r/c long, and
>Hobby People the only source?
>

R/C or 4-Cycle. I use the 4-cycle. You can get them from most cottage industry suppliers, but Hobby People is a good way to go - 5 minutes of surfing, and they will arrive in few days. If you order now, you will likely get them Tuesday. Excellent service, as long as they are in stock and not back-ordered.

Also, no one mentioned it but a drop in rpm when you remove the battery can be a sign of fuel gone bad.