need a good radial guy

[svcta]

I've been sort of unhappy with my regular 'guru' as of late. Can anyone steer me toward a good radial man around Ga. or Al.? R-1340 on a T-6 that finally has me convinced that it needs some attention.

In the last few times that I've flow it I've allowed some less than stellar performance off the ground because of the 3 digit temperatures, but today I noticed in the t/o climb that the RPM had come off about 75 revs. I always verify proper power settings when I push the throttle up on the roll, but as the gear hit the well it was clear that it ain't as happy as I would like it to be.

Anyone got some thoughts?

 

[bugchaser]

How many hrs on the engine? Have you had the valves adjusted at any time? There could be many possible reasons for this. How did the engine sound? Any problems with excessive mag drop at run up? I have sat behind these engines for several thousand hours and have seen most problems. Give me some more specifics and I will see if we can troubleshoot it a little more.

 

[bell47]

Was it making good MAP (36 inches) with still some power left over? I would first do as the other poster said and adjust the valves, I would also remove, clean, gap and test all the plugs, I would also time the mags(internal and to the engine). A compression check wouldn't be a bad Idea. You could also do a crayon check to make sure you don't have a dead cylinder. Just some suggestions. How much time is on the engine and who did the last OH? Do you do oil test to see if it is making metal? Is it an AN-1 1340?

 

[svcta]

Thanks for the replies so far.....the valves were adjusted probably 20 hours ago, the engine has less than 200 hours on it..an Aero Engines overhaul that sat for nearly 15 years until we bought it. It has run flawlessly until now and we've put probably 70 hours on it since October(about a year). It threw a little oil and grease for about 10 hours but it has tightened up wonderfully.

Man. Press. is good, all 36 inches with no problem, I tried to get a good static run up before I put it in the hangar yesterday, but the grass wouldn't keep me in one spot and I didn't have the time left in my day to get to a good paved run up area. As I said, I got 2250 RPM on the take off roll but I noticed a small drop and what felt like a very lack luster climb after I got in the air. I flew around the airport for about 15 minutes and ran some different power settings. It seemed as if I could get full RPM at 36" if I pushed against the forward stop of the Propeller knob. One of the others involved in the airplane has felt for a while now like the carb needed to be overhauled and that's our next step.

We had the mags timed about 20 hours ago....RPM loss on mag checks is about 89-90 RPM left mag, and maybe a shade over 100 on the right, which I know is marginal(tell me if I'm wrong). All of this is on the heels of about a 2 week sit, which is never good for old airplanes, but I think it's a little more than an exercise issue. Compression check next is a great idea, I'm gonna get on that for sure...now, is a crayon check what I think it is?

The guy who did the work on the mags and the valves has a historically good rep with round motors, but I'm beginning to lose faith in his technique a little; his work doesn't seem to be as good as it used to. Therefore, I'd like to find someone else to look at it this time.

Thanks for the insights so far...keep 'em coming!

 

[avbug]

If your engine is pulling boost without issues, your mag checks are in line and no roughness, I don't see an engine issue. I see a propeller issue...especially as you're well into the governing range and seeing engine RPM issues. This speaks to the propeller.

 

[svcta]

I've sort of been waiting to hear from you, bug! I like where you are going with this, well, not in terms of dollars but i digress. Can you elaborate at all? Thanks!

 

[avbug]

Some more information is in order. How about the idle RPM checks, and your high and low RPM checks during the runup? When you do your runup on the ground, you should be cycling the propeller to see where the low RPM limit lies...should be about 1200, and you should be seeing at barometric pressure the same standard RPM you always see. Usually the high and low checks are done at barometric pressure, just shy of governing, rather than at a typical runup RPM of 1700 or so...in other word, the power setting for that check is set by manifold pressure, and hasn't pushed into a governing range.

The reason for doing it this way is because at a typical runup power setting, you're not exploring the full operating static RPM range for the propeller. By continuing to apply power to barometric (about thirty inches at sea level, about 25 inches at five thousand feet, etc), you're seeing the max RPM you're going to get static...taking he propeller as fast as it will go before the governor takes over and starts increasing blade angle or interfering with the propeller.

If the RPM is low at this point, you may have an engine that's producing inadequate power. Accompanying this you may or may not have roughness, depending on why the power loss is occuring. Generally a problem isolated to one or two cylinders will produce roughness and vibration.

If you're pulling manifold pressure in the order of 36", then clearly your engine is producing power, and it's being boosted properly. This isn't to say that it doesn't have problems, but if you're pushing the power above barometric, the problem with low RPM must be governng...something is holding the RPM down, and that can only be the propeller. The propeller is restricted by the governor, and the first thing to determine there is if the governor limits have been changed.

A low RPM could be a linkage issue, restricting the governor limit (working the same as the propeller control being retarded). It could be debris in the pilot valve, sludge in the propeller shaft, a physical restriction to the propeller limits, a counterbalance issue (check for loose or shifted counterbalances), a broken speeder spring, a leaking governor assembly, or possibly other problems. But the first step is to see where it's failng to govern properly. If you're seeing a low RPM during the barometric check, and the engine is at barometric pressure, you have a propeller which isn't reaching it's high RPM pitch stops for some reason or other.

I'd also be for checking the individual blades very carefully as part of the preflight, looking for leakage around the hub and blade shank/hub interface, and any play in the blades themselves. Look for one that's different, rather than both blades having play.

I had a five blade hartzel on a turbine installation this summer that turned out to have a problem...it had a very occasional vibration that came and went so infrequently, and lasted for so short a duration, I thought it was my imagination or perhaps an unusual turbulence. It was found during a preflight inspection, and as manifest as a very slight play in one blade. It was immediately grounded, removed and overhauled.

Let us know what you find.

 

[erj-145mech]

The prop doesn't have a pilot valve, its a Ham Std 12D40, counterweight type.
In this case I would check the counterweight bearings. They are somewhat exposed and if the counterweights are binding up at all, you won't make full blade travel to low pitch (high RPM).
Avbug is right, it sounds like a prop issue vs basic powerplant.

 

[svcta]

Bug,
that's some great info. I'll make this check in the next few days as soon as I can get to the plane. I've noticed no excessive grease on the blades and I always pull a few blades by hand before I crank...I haven't noticed any play, but I'll pay more attention next time.

I will certainly let you all know what I find.

Now, for a very simple question: What kind of mag drop do you look for on a 1340? We typically see 75-100, and I've always accepted that as well within what I would consider to be normal, but what makes me curious is the military maintenance manual.....it calls for 50 RPM.

 

[svcta]

erj-145,
I just posted after you hit the button, it's funny but I was just discussing greasing those bearings with one of the other guys...back to the original Mx manual, it was called for after every flight. So that will be the first thing I do before the next running.