I just put new stainless bearings in a TT .46 Pro. weren't damaged or anything except for a little wear and rusty. First flew engine in 2004 and used HARD until 2009 when it seemed to be losing power (had it inverted in a Sig Rascal 40). Have always been careful not to run too lean but watched the rich side too since I've heard an ABN will wear quickly if too rich. Put the new bearings in, a new OS3 plug started right up on the test stand, did the pinch test to assure not too lean, probably gained 300/500 rpm, and ran slow, mid, and balls to the wall for 9 oz. Omega 15 % fuel with 4 oz. caster oil mixed in one gallon. Ran great, I'm happy, decided to try again, wouldn't start (by hand, don't have, don't want, electric starter, if I can't start by hand I don't want it). Checked the plug, NO glow, replaced the plug with another, (out of A3's, don't know for sure what it was) wouldn't start and I noticed it had way less compression. After it sat for 10 minutes pressure back up, flipped once and it started. Soooo, I'm guessing the cyl/piston aren't exactly in the best shape, both LOOKED fine ie: no real scratches etc.) when I had it apart for the bearing replacement but due to the fact it lost compression when hot, I assume that's the problem. Sound even close to being right to you guys ?????????????

Thanks in advance for any insight.
Dan

It is hard to tell the compression soon after an engine is shut off after running. The piston and liner expand at a different rate . If you want me to look at it you have but to ask.

Hi Jeff,
Maybe it was those new Boca bearings "wink-wink" I'm going to check a bit farther after the weather warms things up a bit and see what happens, thanks for the come back. I don't normally land, refuel and go right back up, so maybe it's not a big issue. Time will tell. It's kind of an "extra engine" anyway.
Dan

Anything Ican do for you just let me know.

I have had "no compression" with an OS .46AX right after running. Then after a while it comes back. No clue why, but as long as it comes back and does not dead stick in the air I wll use it. I am curious just why this happens after running and not during. You would think the outside and cylinder gets cooler sooner after running and causes differences in the piston and cylinder expansion, but I would think that would make the fit tighter, not looser?????????

I do taxi back to the pit area after landing so maybe I will try shutting the engine down just after landing to see if I get the same condition of no compression.

Regards, Richard

The piston gets all that cool methanol splashed all over it taking away the heat. The liner is made from very dense brass and holds a lot of heat compared to lightweight aluminum, ever touch aluminum foil that just came out of the oven?

A loss of compression is not uncommon after a hard run like that, 9 oz of fuel at full bore on a stand is a little harder than I like to run my engines, but still should not really hurt it if the oil and tune is correct. Which from the sounds of things it was.
I have noticed several times right after a landing the comp is down, but 5 mins later it's back up where it needs to be.
I wouldn't worry about it and fly it, sounds very normal to me.

Hi!
Some missunderstandings here! Rich running will not destroy and engine, be it ABC,ABN or any other combination of materials in the cylinder/piston, on the contrary Lean running will certainly destroy all engines.
Second ,using an A3 OS plug is way to hot a plug to use when running 15% nitro! Better use an OS 8, or even better, a Rossi , or Nova -Rossi 4 or 5 plug.

The A3 is probably too hot for a TT 46 Pro as Jan mentioned but that's not a hard and fast fact as I have an older Tower Hobbies 46 that won't run on anything colder than an OS A3 and 15%. It's an awesome running piece, it just has to have it's A3 and 15%. We have some folks at our field with Evolution engines that won't run right without an A3 in them either. Go figure.

May be the wrong place to ask; but what is the physical difference between hot an cool plugs?   Longer filiaments?  More or less Platinum on the Filiament?  Depth of the Filiament in the sump hole? Thanks Jim

yes

Thanks to all for the info, sounds like a cooler plug, land, taxi back to the pits, shut 'er off, have 2 ice cold beers, and she's ready to go again !!! I like it ! Of course after the 3rd flight I'll probably carry a bag made of Monocoat filled with balsa home.
Dan

If that don't work I'll drive 20 miles and see Jeff.

Iwas being silly earlier about the plug heat range.
Aplugs heat range is affected by several factors , filament diameter composition etc, the size of the hole the filament is in and probably a lot of other things that escape me at the moment. Aldon Kelly of Merlin Glow Plugs is a great resource for plug info.

Yes,..

More turns of filament give more hotter and vice verca
The size of hole in glowplug body is important too: Bigger hole size give more hotter and vice versa.
Thickness of filament is measured by length and voltage: to keep same voltage at 1,5 volt: Longer filament, more thinner filament and vice versa.

The source of information about glowplug and making own glowplug: the book about Model aero engines by Oleg K. Gaevskiy

Thanks for the tip on the book Jens.

"Model aero engines by Oleg K. Gaevskiy"

Is it in English?

Doesn't come up with Google