Author Topic: Poor engine run -- looking for suggestions (Read 3834 times)

Tim Wescott · « **on:** April 03, 2014, 02:14:06 PM »

My #2 plane had been hanging in my shop for about six months. A week or so ago I took it out and flew it -- and had a crappy engine run!

Whatever changed in the plane was just a result of hanging in the shop -- I haven't done anything. Where before I would launch at 9750 RPM and get a decent run on 6% nitro, now I can't get more than 9400 RPM, and that's with about 15% nitro.

It has good compression, it makes no funny noises, I changed the glow plug, checked that the head bolts were tight, and made sure that a mud dauber hadn't built a nest in the muffler.

It doesn't seem to be a fuel flow problem -- I can easily open up the needle valve to get a 4-stroke. It just doesn't seem to want to run fast any more.

To whatever degree it matters, it was given to me as a well-broken in engine, and reported as having been modified by Tom Dixon.

So I'm kinda stumped about what to try next. Suggestions are welcome.

Bill Morell · « **Reply #1 on:** April 03, 2014, 02:31:07 PM »

Your tank might need flushing? Maybe the feed line is gummed up from hanging around for 6 months.

Tim Wescott · « **Reply #2 on:** April 03, 2014, 02:51:03 PM »

Correct me if I'm wrong, but wouldn't that prevent it from ever richening up? This engine will go all the way into a deep 4-stroke, but never attain much RPM even when it's dying from being leaned out.

Dave_Trible · « **Reply #3 on:** April 03, 2014, 03:40:32 PM »

Tim did you change prop? That would make a difference. Moisture in the fuel? Or just going over the hill. That's a tell tale sign she could be about done. Might see if the wrist pin is stuck in the rod.

Dave

bob whitney · « **Reply #4 on:** April 03, 2014, 03:50:13 PM »

what engine are we talking about

Larry Fernandez · « **Reply #5 on:** April 03, 2014, 04:10:48 PM »

Quote from: Tim Wescott on April 03, 2014, 02:14:06 PM

My #2 plane had been hanging in my shop for about six months. A week or so ago I took it out and flew it -- and had a crappy engine run!

reported as having been modified by Tom Dixon.

That might explain it.

Larry, Buttafucco Stunt Team

Dennis Toth · « **Reply #6 on:** April 03, 2014, 04:15:06 PM »

Tim,
Sounds like something is tightening up. Take the plug out and pull the prop slowly through. Feel for tightness. If it is an ABC there should be a little pinch at the top but should not be so tight that it makes it hard to pull through. If you feel tightness take a heat gun and heat the head and upper part of the cylinder, get it good and hot then pull it though and see if it gets smoother. If so pull the head and check for varnish. Sometime when they sit if there was some varnish, it hardens causing tightness of the fit and needs to be removes.

For me I have used scotch brite green pad to remove it from the upper part of the cylinder and around the piston sides. If you do this go slow and keep test fitting the piston to see when it feels right.

Best, DennisT

Richard Koehler · « **Reply #7 on:** April 03, 2014, 04:45:09 PM »

Have had this same problem, and after several poor runs the problem just went away by itself. I assume it was a trace of crud somewhere that either dissolved or flowed out.

Steve Helmick · « **Reply #8 on:** April 03, 2014, 04:51:00 PM »

Tim, I had the same problem with the (stock!) Magnum XLS .36 I gave you. But it had been working fine, and this was at a Eugene NW CL Regionals. It wouldn't rev up as fast as it should, and I could make it run slower by either richening or leaning the mixture. Sounded like a problem with the spraybar, eh? I think what I did (during the round) was replace the fuel filter with a new one, fire the engine, open the NV as much as possible for awhile (battery still on), and then readjust to correct launch rpm. One or the other fixed it; I really don't know which. But it does sound a lot like the problem you're having.

Steve

Eric Viglione · « **Reply #9 on:** April 03, 2014, 05:53:44 PM »

Change the plug. Then, on the ground where you can monitor it and needle back from any run away, run a full tank of straight synthetic fuel through it in a wet two. Then recheck status. Might take two tanks.
Has worked for me in the past in similar situation.

Mark Scarborough · « **Reply #10 on:** April 03, 2014, 07:30:36 PM »

Quote from: Eric Viglione on April 03, 2014, 05:53:44 PM

Change the plug. Then, on the ground where you can monitor it and needle back from any run away, run a full tank of straight synthetic fuel through it in a wet two. Then recheck status. Might take two tanks.
Has worked for me in the past in similar situation.

thats what i was goimg to suggest

Brett Buck · « **Reply #11 on:** April 03, 2014, 07:38:25 PM »

Quote from: Larry Fernandez on April 03, 2014, 04:10:48 PM

Quote from: Tim Wescott on April 03, 2014, 02:14:06 PM
My #2 plane had been hanging in my shop for about six months. A week or so ago I took it out and flew it -- and had a crappy engine run!

reported as having been modified by Tom Dixon.

That might explain it.

Larry, Buttafucco Stunt Team

Oh, dear!

Brett

Randy Cuberly · « **Reply #12 on:** April 03, 2014, 07:48:23 PM »

I agree with Dennis Toth. The most likely reason for this to happen is varnish hardening in the sleeve and causing a loss of seal...and NO that probably wouldn't affect the 4 cycle because combustion pressure is much higher at a higher RPM and is more critical.

Clean the sleeve and piston...NOT with abrasive...or try the synthetic oil running suggested above...Klotz has serious cleaning agents in it!

Incidentally...You do of course use after run oil...YES? It should help avoid this situation.

Randy Cuberly

Brett Buck · « **Reply #13 on:** April 03, 2014, 07:53:38 PM »

Quote from: Randy Cuberly on April 03, 2014, 07:48:23 PM

I agree with Dennis Toth. The most likely reason for this to happen is varnish hardening in the sleeve and causing a loss of seal...and NO that probably wouldn't affect the 4 cycle because combustion pressure is much higher at a higher RPM and is more critical.

Clean the sleeve and piston...NOT with abrasive...or try the synthetic oil running suggested above...Klotz has serious cleaning agents in it!

Crock pot! Works great to devarnish pistons/cylinders, if you take it apart.

Brett

bob whitney · « **Reply #14 on:** April 03, 2014, 10:02:29 PM »

would still like to know what engine we are talking about?

??

Tim Wescott · « **Reply #15 on:** April 03, 2014, 10:13:09 PM »

Quote from: bob whitney on April 03, 2014, 10:02:29 PM

would still like to know what engine we are talking about???

Oh good lord -- I was going to point out the line in my original post with ever so pointed politeness, and what do you know, it's not there!

It's an LA 40.

Dennis Toth · « **Reply #16 on:** April 04, 2014, 07:38:26 AM »

Tim,
With the LA 40 I would try the 100% synthetic fuel for a couple tanks rich and pinch the line as it goes to pick up the rpm and get some heat then release and let the oil work on the crude. If after say 3 tanks there is no improvement then open her up and manually clean.

Best, DennisT

Gerald Arana · « **Reply #17 on:** April 04, 2014, 08:55:53 AM »

Tim,

Don't screw around with it, just do as Brett says.

The LA engines are very simple to work on and the crock pot is a Godsend!

It only takes a few minutes (Less than on tank of fuel) to take it apart and throw it in a crock pot.

Good luck, Jerry

PS: I do all my dirty engines this way and I use after run oil.

Tim Wescott · « **Reply #18 on:** April 04, 2014, 08:59:37 AM »

Into the crock pot it goes. I'm sure that running it with pure synthetic would to the trick, but I'd have to buy or borrow some fuel, while I have a crock pot standing by.

Russell Shaffer · « **Reply #19 on:** April 04, 2014, 12:52:40 PM »

Take the head off and see if all of the cylinder liner plating is still there.

Tim Wescott · « **Reply #20 on:** April 04, 2014, 01:15:05 PM »

Quote from: Russell Shaffer on April 04, 2014, 12:52:40 PM

Take the head off and see if all of the cylinder liner plating is still there.

That was going to be part of chucking it into the crock pot.

Brett Buck · « **Reply #21 on:** April 04, 2014, 03:54:57 PM »

Quote from: Russell Shaffer on April 04, 2014, 12:52:40 PM

Take the head off and see if all of the cylinder liner plating is still there.

That's of academic interest, but it didn't lose the plating while it was hanging on the wall. And, if it still runs right afterwards...

This is a higher-than-normal chance since grinding on it with a Dremel tool and maybe not being a circumspect as possible about cleaning up the burrs leaves it more vulnerable to liner damage. It would not be the first 40FP I have seen that ate itself up after rework.

Brett

Tim Wescott · « **Reply #22 on:** April 04, 2014, 04:33:17 PM »

Quote from: Brett Buck on April 04, 2014, 03:54:57 PM

This is a higher-than-normal chance since grinding on it with a Dremel tool and maybe not being a circumspect as possible about cleaning up the burrs leaves it more vulnerable to liner damage. It would not be the first 40FP I have seen that ate itself up after rework.

It had a long and happy life after rework, and the guy who did it has a good rep, so I wouldn't expect it to be a workmanship issue.

As much as I know about the history of the motor, it's had enough flights on it that it could be frankly worn out.

Brett Buck · « **Reply #23 on:** April 04, 2014, 05:40:00 PM »

Quote from: Tim Wescott on April 04, 2014, 04:33:17 PM

It had a long and happy life after rework, and the guy who did it has a good rep, so I wouldn't expect it to be a workmanship issue.

Read Larry's post again.

Brett

tom brightbill · « **Reply #24 on:** April 04, 2014, 09:22:00 PM »

Tim, When you get a moment, hook another (known to be good) tank to it and see what it does. You don't even have to take it off the plane. Isolate the possibilities...

Steve Fitton · « **Reply #25 on:** April 05, 2014, 10:02:42 PM »

Is this the silver LA-40?

Steve Fitton · « **Reply #26 on:** April 05, 2014, 10:12:12 PM »

Quote from: Brett Buck on April 04, 2014, 03:54:57 PM

That's of academic interest, but it didn't lose the plating while it was hanging on the wall. And, if it still runs right afterwards...

This is a higher-than-normal chance since grinding on it with a Dremel tool and maybe not being a circumspect as possible about cleaning up the burrs leaves it more vulnerable to liner damage. It would not be the first 40FP I have seen that ate itself up after rework.

Brett

If its the motor I'm thinking of, it didn't self destruct after rework.

I'm betting the fix will be simple. Actually, my number one suspect before even looking at the engine would be the tach.

Now I *have* seen several LA 40/46 motors where the nickel plating just "went away" at the pinch. When examined, the nickel layer was translucent at that spot. Those engines lost some quantifiable level of performance. In some I never saw any issue, in one instance only 130 or so flights, and in my case the liner went away in 350 flights. My engine was stock. One engine we got to go away in two or three flights on a pipe.

When the liner peels, it seemed to be catastrophic. My buddy Jimmy Welch had an LA-65 liner go and the engine instantly stopped.

Steve Fitton · « **Reply #27 on:** April 13, 2014, 07:24:26 PM »

If the engine is still in the crock pot, its probably dissolved by now...!

Tim Wescott · « **Reply #28 on:** April 13, 2014, 09:14:14 PM »

Quote from: Steve Fitton on April 13, 2014, 07:24:26 PM

If the engine is still in the crock pot, its probably dissolved by now...!

The airplane has been repurposed, and the LA 40 set aside for the moment.

It should go into the pot, though (with a reminder not to leave it in forever!)

Timothy Payne · « **Reply #29 on:** April 25, 2014, 12:29:17 AM »

I'd take it out of the plane, strip it and check condition of the liner/piston.

Chellie's (McCoy expert) got some good tips on resizing/lapping pistons etc. She sells McCoy gasket sets on ebay, just buy em and you'll find her instructions very helpful. (Doesn't sound like it needs lapping though! - More like a blockage somewhere.)

After you've stripped rebuilt the engine fix it to a static engine mount, get some fuel into it and fire her up.

Could just need a run, and at least then you'll know it's not your motor thats the problem!

Good luck,

Tim

Ps Failing this, flog it and get a Fox 40 instead! :-)