D

Darren S

Well Known Member
I fly an RV7 with a Superior IO-360, Hartzell prop. I recently had the 500 hour mag rebuild done. I have dual Slicks. 1700 rpm mag drop is 100 and 90. Everything seems great at takeoff and cruise. The issue is on downwind. I pull power back slowly otherwise the engine wants to pop and backfire.

After the mag rebuild the engine doesn't "pop" as much but at 12 MP and . the engine runs noticeably rough. Even when the power is pulled back completely and the prop is driving the engine ie. on final, the engine is still running rough.

I have had the prop balanced.

It's got to be a timing issue right? Would leaning on down wind help? Currently the mixture is out about 1 cm. Is it too lean?

Should I get the mechanic to put in a lightspeed ?

Help please

Darren
 
"Induction leak". Please expand. Where are you thinking? Around the air filter? From my air filter there is a big fiberglass tunnel to the fuel injection throttle body. This area wasn't messed with at the shop, as far as I know.

Thanks for the reply
 
Darren S said:
"Induction leak". Please expand...
Click to expand...

While you don't say if you have the tuned induction tubes of the 200 HP or the more typical rubber boots of the 180, the place to look for leaks is around there. I pulled the throttle to idle in the pattern once and it began to run extremely rough. On the ground, an inspection of one of the induction tubes showed that the bushing holding the O ring seal (normally silver soldered to the tube) had broken and was drawn down the tube to the inside the plenum. This created a huge vacuum leak. It's unlikely that you have a leak this big as indicated by continued flight, but it might be creeping up on you.

Check your induction tubes (from one end to the other) and your servo for security.

To the question about leaning... Make sure that you have your idle mixture set properly, then don't worry about leaning too much in the pattern at sea level airports.
 
Last edited:
Thanks for the help. I have the 180 hp engine. I will check out the induction boots that you have suggested.

The problem is easy to replicate. Fly at 70-75 knots. MP is about 10, prop is about 2200 and the nose is high. She runs rough at this setting.

Ok off to church then the hanger. Thanks again

Darren
 
Any induction leak.......the rubber tubes, and in my experience it was the gasket from the tube to the head.

We had 5 out of six gaskets broken after about 230 hours from a factory new installation.

You may see fuel stains around the flanges.....you may not.

Its quite likely all the problem is, but you will not know until you take a look....and a very close one.
 
Forgive me if you already know this and ruled this out, but you do know that most RV's with 360's pop when you pull the power back in the pattern, right? Are you experiencing more than is usual? We actually had a crop-duster crew stop us at Fort Scott )KS) a couple of weeks ago when we stopped for gas, and they asked if our engine was alright - they heard it "missing" when we were in the pattern. It was actually just a more aggressive than usual power-back when trying to go down and slow down at the same time.

Paul
 
Check the timing. Wasn't the last thing you did to the plane was reinstall the rebuilt mags?

If that is all you did, it's the most obvious.
 
I called the fella who rebuilt the mags and he said an induction leak was unlikely and that an induction leak is less likely to cause roughness on a fuel injected engine vs. a carb. engine. I'm not sure, I just have to take his word for it as I'm not really sure where to look.

If you have a picture that you can share that would be great.

I know that most RV's "pop" when the power is pulled back. Mine does too. After the mags were redone it was noticeably less but still there. I pull power slowly. My mechanic said my timing was very retarded prior to the rebuild. He said a slightly advanced timing helps a bit.

He said that if the timing was off it would be more noticeable on full power and cruise power situations. Those situations are fine. It is the low power, 70 - 80 knot cruise , flying final situations that the shake is evident.

He suggested that the prop hub grease needed time to even out. I had the 100 hour greasing done. Perhaps slightly more is in one side? Also I'm going to check that the spinner was put back on correctly

I did find one slightly loose plug wire but I haven't flown the plane yet to see if that has anything to do with it.

Thanks to all for the input. I'll report back


Darren
 
Last edited:
Darren

Your mate might be right.......but ponder this thought for a moment.

If you are at circuit height and pull back the power, what happens to the MP? Now when you consider the MP pressure gauge is measuring a atmospheric pressure from inside the induction section of the engine and its now at a low pressure, with pistons racing up and down trying to suck air in, and there is all this higher pressure air under your cowling (say29") as the piston sucks against the throttle plate, air is going to be sucked in through the path of least resistance.

Trust me, on an IO 540 we chased this for a while along with another unrelated bug. It does happen, 5 out of 6 of them!

Examine all things. Set the timing accurately, check all plugs are gapped between 16-18 thou, with one of these http://www.aircraftspruce.com/catalog/topages/ATSgap.php and check all your leads are secure etc.

Be interested to see what you find in the end. :)

DB:cool:
 
Ok an update. Took the plane back into the shop.

Cold start today was noticeably rougher than before, idle power is fine but a slight bit of power would elicit the same annoying roughness as before. Even when warm. This was on the ground, in air same thing......low power there is a shake that wasn't there before.

I had the good fortune of RV guru Troy Branch stop by my hanger yesterday and confirm that I didn't have an induction leak. Thanks again Troy.

Did a ground and in air mag check. All is fine. Watched Mike Busch's videos to make sure that I knew what to look for. So I guess ignition system is fine.

So here's what I've been told. The engine could be over fueling and causing the roughness. The fuel system was set up to work with the old ignition timing....now that the timing has been set to the factory settings, the fuel system needs to be adjusted.

More $$ I'm sure but if she runs smooth again then I'm cool :)

Will update again
 
Basics first: Is your idle mixture set properly? (see post #4) Do you get a slight RPM rise (~50) when going from full rich to cutoff?
 
Yes and yes. I get the rise with the mixture cutoff and as far as i can tell the idle mixture is set correctly. Personally I think it's something to do with ignition but I'll have to wait and see.

Frustrating !
 
I am glad you had no leaks.....always happy to be wrong like that! :)

Now here is a next question or two!

What mixture position are you using on the ground?

What are you using on approach in the circuit?

If the answer to either of these is full rich........STOP DOING IT!!!!

Once started all ground ops should be done leaned to the point the RPM rises and starts falling again.....not too much further or she will stop! Do not fear you will not forget and take off like that so long as you lean it that far.

On descent from where wever you were, to parking at your hanger should never require more mixture input than maybe a tiny tweak richer if required. Do not use full rich in the circuit (pattern), and only and I mean only if you need to do a GA, then its RED KNOB, BLUE KNOB, BLACK KNOB. If they are levers all together works too!

Lastly did you check all the plugs for gap settings?
 
I will get to the bottom of this. I didn't hear back from the mechanic today so I'm calling in the morning. As promised I will update.

As for leaning; as soon as I start up I lean till the RPM picks up then richen a little bit to taxi. I lean on run up, at 3400 foot elevation field I lean slightly for take off and of course lean for cruise. I just did the plugs and gap 3 weeks ago along with the oil and filter. Gapped all plugs to 22 as per the mechanics suggestion. All plugs were burning nicely, even the bottom ones, with very little lead deposits. I attribute this to leaning properly. None were oily and goopy.

I still think it has something to do with ignition despite a the inflight mag check showing all is ok..... but I have to let my guy do his thing

Thanks for the suggestions.
 
Hi Darren

I have been waiting for a call from you for some time now. Sorry to read about your troubles that you are having. I remember you writing something not to long ago about having low compression on one cylinder. Have you rechecked that cylinder lately. Worth a try maybe. Anyways give me a call, I want to hear how your demonstration went.

L8R

Jarvis
 
Gapped all plugs to 22 as per the mechanics suggestion.
Click to expand...

Probably not your plugs then, however the range you should be setting to is 16-18 though MAX. That way over 50 hours the should not have exceeded 22.

I can tell from my engine monitor when they get past 25.

Have a look at the gapping guage at Aircraft spruce. I assume you are using these not a normal feeler gauge with a flat blade.

Look forward to hearing the answer to this one!
 
Latest word from the shop is that he is going to check each plug to see if they are all working as they should.

They are at least 225 hours old (what i put on last year) and the logbook that I have from 150 hours on, show no plug changes. So they could be original plugs which would put them at 488 hours.

Mechanic says that this "over fueling " issue can cause plugs to foul pretty quick. The saga continues. Hope it's as easy as changing the plugs.

Hey Jarvis I will give you a call soon. I want to hear how your Stab rebuild is coming along.

Thanks to all others who have offered suggestions.

Darren
 
And when he gets the new ones, have a look at the gap, even though they should be checked from new, they are usally spot on in my experience. :)
 
I wanted to update the situation as it seems to have been resolved. I got the RV back yesterday and on the first flight I took it right to the rough spot: 70 - 90 knot slow flight. Very little roughness. Probably like it was before but now that I am hypersensitive to it, it's hard to tell. As it turns out the roughness wasn't just one source.

Much improved though and I can loaf around, nose high, mushy controls etc... and the shake isn't there nearly as much as it was before.

The mechanic ended up changing the plugs and easing up some of the tension on the mag wires. He also said that some wire on the left mag was a little "loose" due to this tension and so he relieved the stress and tightened the wire.

There is still one area to debug and I'm going to start a new thread on this over in the General Discussion area. Throughout all flight parameters the engine is smooth, wonderful, lovely. However upon start up with just a crack of throttle, at say 800 - 900 rpm, there is noticable shake.

It is from my spinner. When the spinner is off, no problem. I don't know how this happened as the spinner has been in operation for almost 500 hours. At idle no shake, rev it up above 1000 RPM, no shake but right in that zone, rough shake. I don't notice it in flight though.

I made some calls and was told that it is a harmonic at that RPM. It wasn't there before and the spinner is the same but for some reason it is the cause, definitely.

Will dig further but this concludes this "rough on downwind" segment.

Thanks to all for the help.

Darren
 
Great news.

I would strongly suggest you dynamically balance your prop/spinner.

Ours was like a turbine after this result :)
balanceprop8-5-11.jpg


And several others like RV6's with fixed props etc.....lots of smooth aircraft over here in my part of the world!
 
I just wanted to put a final update as this situation may help someone in the future. Vibrations are a tricky thing to diagnose sometimes and the cause may be multiple factors.

As it turned out the cause was: possibly a loose wire when the mags were rebuilt, a faulty spark plug and a spinner that went put of balance. How the spinner went out of balance after all these years is a mystery, but was a big factor.

Today I put on a new spinner and the smoothness was restored. I put on a new fiberglass spinner and got rid of the aluminum one. I dialed it to 0.020.

So even the most obscure things can cause problems. How does a spinner go out of balance on its own? who knows

thanks for all the help

Darren
 
You must log in or register to reply here.