Does a glow engine get tighter as it gets run in? i have a .28 dynamite engine in my savage and it never had alot of pinch, if i was to take the head off i could spin it over by hand with my wand starter . after letting it idle through most of a tank today. the engine got way tight and now if i take the head off and try turning it it pushes the sleeve a quarter of the way out of the engine. i figured the pinch would lessen the more it was run.

Idling is not good for a ABC type engine. The sleeve contracts because the engine is not up to operating temperature.

The piston may be galled now?

Galled? how long should it be able to idle? i can just let it sit there and it would idle all night if i wanted it to? is that a sign of it being tuned wrong? it would stay at about 215 degrees at idle

You may be seeing a lot of carbon buildup on the piston that would normally not be there during high rpms. I would give it a good close inspection and take it for a test run if it looks OK.

the sleeve looks more chromelike that it did before.

If you remove the piston does it have any scratches in it?

nope
its pretty clean inside

Can you look in the exhaust at the piston wall?

Or the sleeve could have become warped and is no longer round.

Aluminium pistons don't permanently 'grow' as meehanite (B grade cast-iron) ones do, from heat treating.

...Neither can brass sleeves shrink.


Becoming 'out of round' is the only 'wrong' dimensional change that can occur; beside galling.

no offense, but i think you should stop taking your engine apart so often.....just break it in according to the manual and enjoy it

That's what I think too Dar. Ask anyone who has overheated a Chevy Vega Four (oval) cylinder. My guess it's just the manufacturing "luck of the draw".

Bill

Why would you idle a tank of fuel through an engine - is this a car thing? I'd never do that to an ABC aircraft engine - what is the point of doing so?

MJD

What rpm were you idling at?

Yep...some R/C car engine and RTR vehicle manuf. recommend idling a tank or two first for "break-in"...Not recommended in my book, but...

veedub...have you found this forum yet?
http://www.rcuniverse.com/forum/m_5517128/tm.htm

You should find some interesting reading there...good luck[8D]

P.S. it's possable that when you re-torqued the head bolts that either they were torqued unevenly or too much?

Ugh [:'(]. I don't like the sound of that for some reason. If'n I had me a car engine, I'd want to put it on a test stand with a itty-bitty prop and break it in with a few short runs and heat/cool cycles. But I guess that is not really practical, what with no prop driver and all that. So whatcha gonna do?

MJD

Quote:

ORIGINAL: MJD

...If'n I had me a car engine, I'd want to put it on a test stand with a itty-bitty prop and break it in with a few short runs and heat/cool cycles. But I guess that is not really practical, what with no prop driver and all that. So whatcha gonna do?

MJD,


That is not right either. Any cold-cycling is not good for a 'pinchy' ABC engine.

For such an engine, [link=http://www.rcuniverse.com/forum/Tapered%2DBore_Engine_Break%2Din_%2D_Upgraded/m_1850473/tm.htm]THIS[/link] is what you want. You see it right here on RCU.

Actually yeah you are quite right, I went into auto-response mode. If it is that pinchy then for sure some better bedside manner is needed. Mostly I meant to say I'd rather put a prop on it and bench run it WFO.

MJD

double post

Jezz. You guys are really stuck in your ways. Idleing temps are not that far off from full power temps, and the modern ABC engines don't care as much as many posting here do. The only bad thing about breaking in an engine at idle is it takes longer to break in. Most likely, being a car engine it simply injested some dirt. Or with that low oil fuel washed the machine oil off and it just seems tighter because of less lube.

looking in from the exhaust the piston looks like it has some tiny scratches? i thought the sleeve getting chromed out like that meant that the piston was worn in with the sleeve. there isnt any visible scratches on the sleeve itself . has good compression runs good and has had a clean air filter on it . the air here isn't dry and dusty . I did a heat cycle break in on the motor that a postor named fuelman posted in some forum a while back. but decided i would let it idle through a half tank to finish it off. idk im just calling it good. if it makes it through another gallon or two then im happy. lesson learned

Give us a report after then

if the weather is decent tomorrow i will run it and see how it goes. its not getting warmer than 40F here often. Factory settings for this engine's mixture screw are 2 turns out and as of last time i ran it are almost three, im guessing thats normal for winter air? i had some trouble with that at first , the engine would start idleing way up after a few seconds of no throttle. Ill keep you posted.
-Mike

If the idle speeds up on you it is too lean at idle

If the idle slows down on you it is too rich at idle

Running in a car engine is a bit more difficult than a plane engine especially if someone new to engines hasn't yet got an ear for tune. Car engines usually idle somewhere around 6000 so it's not quite like a plane engine in that respect. With a car there's no way to put a load on it unless it's being driven and even then there's not much load so unless you have it tuned quite rich you can't really go full throttle for more than a few seconds. Most car engines can't be fitted with a prop unless you have a lathe although sometimes I've contemplated fitting a couple of props to the axle .

When my son ran in his car engine (and here we go ) he did it using normal 80/20 all castor fuel driving around a grass oval at full throttle but 4 stroking the whole time. That allowed the engine to rev out a bit (I'd guess maybe 20,000) and then slowly leaned it out over 30-40 minutes. We never checked the temperature because that's useless.

As to why the pinch increased in the engine in question (with the head off) I have no idea other than at idle (even at 6000) there's not that much fuel flow which means not much oil flow (especially with car type fuels) so the piston may have overheated.

Well, cautious is certainly right. When you've had the mantra pounded into your head for so long it's hard to change the tune. If it works, hey, it works..! I understand about the practicality of just how you do break in a car engine.

MJD