Fricken engine!

1345 Views 9 Replies 5 Participants Last post by tpstorey, Sep 9, 2004

xjet

Discussion Starter · Sep 8, 2004

Okay bros, here's one for ya...

I've just run in a Thunder Tiger GP42 (okay, so it's not in a profile but cut me some slack here :- ) and it's acting really strange.

I put a tank of fuel through it on the ground with a nice rich two-stroke setting and I used a 10.5x5 prop to keep it lightly loaded.

The next time I started it, it wouldn't run for more than 3-4 seconds after the glowplug clip was removed -- so I changed the plug and everything was sweet so we threw it into the air (attached to an airframe of course) and it flew just dandy.

The next day we put a couple more flights on it and it was running really sweet with a gentle purr of an idle, good transition and a surprising amount of top-end power for a plain-bearing 40.

Today I fired it up and once again it refused to run after the plug clip was pulled. No matter what the throttle setting was, within 3-4 seconds of pulling the clip it would stop abruptly.

So, once again I stuck a new plug in and all was sweet again. However, after a long flight the engine died on the landing approach (it was at a high-idle at the time) and now it's back to stopping a couple of seconds after the lead is pulled.

The same fuel (about 25% castor/synth blend oil, 70% methanol, 5% oil) has been used all along and so far I've used one no-name plug and two OS ones, all with the same effect.

I'm quite used to ABC/ABN/AAN engines throwing a small amount of aluminum onto the plug element during the break-in period and this contamination of the filiament almost always produces the symptoms I'm encountering here.

However, I've never had one do this after 30-40 minutes of accumulated running time -- and the exhaust residue is nice and clear -- indicating no sign of excessive wear in the engine that might be contributing to the problem.

With cheap plugs costing nearly $10 and OS#8 plugs costing $13-$15 here in NZ I'm reluctant to just keep feeding this thing new plugs until it decides to settle down so I'm wondering if anyone's got any ideas here.

I will mix up a new batch of new fuel tomorrow with 20% oil, 70% methanol and 10% nitromethane just to make sure this isn't a problem -- but it *does* run like a dream on this fuel so long as the plug is fresh so I'm not confident that this will be the answer.

The fuel system is free of leaks and blockages and when the engine cuts it's obviously getting adequate fuel -- it's just as if someone turns out the light with a switch.

Okay bros -- lend me your wisdom and experience here.

See less See more

Save

1 - 10 of 10 Posts

Scat-r-d

· #2 · Sep 8, 2004

If it was mine I'd tear it down to find out just what the hell is going on inside. If your getting shrapnel taking out plugs like that you should be able to see it in the oil residue or on the bottom of the plug.
I'd open 'er up and inspect for what's going on.
While you've got it open give it a good bath to wash out any that might still be in there.

Save

tpstorey

· #3 · Sep 8, 2004

What do the plugs look like when they are no longer working?

Save

xjet

Discussion Starter · #4 · Sep 8, 2004

tpstorey said:
What do the plugs look like when they are no longer working?

They've lost a bit of their shine and have a slightly granulated surface.

Save

RSands

· #5 · Sep 8, 2004

Well this is a long shot, but worth a look. YOu might have some crap in the low speed needle adjustment? The bottom end on these are an air bleed adjsutment. If it's dying when you pull the glow ignitor, it's rich. A blocked air passage on the low speed adjustment would do this. That the plane burns a plug out after a run may be that you're compensating for it by over leaning the top end. It's a long shot, but makes sense in theory.

Save

tpstorey

· #6 · Sep 9, 2004

xjet said:
They've lost a bit of their shine and have a slightly granulated surface.

If the plug is not frosty looking then it should still be okay unless it's gotten coated with something. I would try the "used" plug with different fuel and in another engine to see if it works. I had these same symptoms with a bad batch (I think water-logged) fuel.

I had a GP .42 that took a long time to break in, but is working well after that.

Save

Gordo

· #7 · Sep 9, 2004

Kinda high oil content? We had a guy with a fox motor he couldn't keep running, and he had lots of oil. Took him 3 trips to the field, wouldn't listen. But he finally tried normal fuel, and VIOLA ran great. Just a thought.

Save

xjet

Discussion Starter · #8 · Sep 9, 2004

Gordo said:
Kinda high oil content? We had a guy with a fox motor he couldn't keep running, and he had lots of oil. Took him 3 trips to the field, wouldn't listen. But he finally tried normal fuel, and VIOLA ran great. Just a thought.

The user-manual says to use 25% (castor) oil for break-in and then 20% (preferably castor) for normal running. It is a plain-bushed motor so 20% isn't unreasonable.

However, today I changed the plug (again) and closed the needle 1/4 turn and it's running fine. Even after several flights it's running like a dream so it seems that (touch wood) the problem has resolved itself.

It's not as if the engine was too rich though -- it was still a good half-turn away from 4-stroking.

It may have been helped a little by the fact that I flew the snot out of it at full throttle for a couple of flights -- even though it nearly pulled the wings off the club trainer. I'm thinking that trying to run it-in at the 1/3-1/2 throttle needed to power the trainer may have contributed to the problem.

I'm thinking that maybe the engine is finally broken in now and has knocked all the high-spots off, and that leaning it up just tad has made it run a bit hotter so the piston-bore clearance is now a little looser.

I am impressed with the amount of power this thing spits out though -- for a plain-bearing 40 anyway. It hauls the club's 5.5lb trainer up like a rocket, sustaining a 75-degree climb for as long as you like.

Now I just have to finish my Burrito and run in my TT46pro. Does anyone bother running a tank-load of fuel through on the ground?

And isn't it bad for an ABC/ABN engine to run it in at the kind of low-throttle settings that it takes to keep a profile in the air -- because it won't reach an appropriate operating temperature to get decent expansion of the liner/piston?

As I suggested earlier, I'm thinking that the reason the TT42GP was giving me problems was that it was in a ARF trainer and I was seriously worried about pulling the wings off it at full-throttle so I was spending most of the time at around 1/2 power.

See less See more

Save

tpstorey

· #9 · Sep 9, 2004

xjet said:
Now I just have to finish my Burrito and run in my TT46pro. Does anyone bother running a tank-load of fuel through on the ground?

Yep, I break it in on the ground if it's in a 3D plane, because you don't spend enough time at full throttle when flying 3D.

Save

tpstorey

· #10 · Sep 9, 2004

xjet said:
And isn't it bad for an ABC/ABN engine to run it in at the kind of low-throttle settings that it takes to keep a profile in the air -- because it won't reach an appropriate operating temperature to get decent expansion of the liner/piston?

Yes, I agree with the above statement.

(I should have read further before I posted the one before this.)

Save

1 - 10 of 10 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month