Kitfox 4 + HKS, the saga continues

**rwaltman** · 07-30-2012, 06:05 AM

Originally Posted by tommg13780

Have you considered putting a little more time into problem solving ...

No, but I think is a great idea! Added it to my to-do list, item #2643

More seriously, I'm getting the process rolling. The more I learn, (and I know very little,) the more I'll be able to do on my own.
The plane had to go to an A&P for an annual anyhow, asking him to do these repairs instead of doing them myself before the annual was an attempt to get back to flying in a reasonably short time, while I learn what I don't know, buy the tools that I don't have, etc.
One other option, with which all of us are familiar, is a project progressing steadily but slooooowly, ending in estate sale.

And I'm not typing, I'm venting.

Roberto.

**Mnflyer** · 07-30-2012, 10:30 AM

Roberto, the HKS will never run smooth at 1600 R's with the carbs synd and after it completely warmed up it will run smooth at 1700, but on warm up from cold 2000 is the number to shoot for, the HKS with the oil cooler mounted were yours is (same set up as mine) will take a min. of 5 to 7 minutes to warm up and that will be an oil temp of approx 110*F the erratic instrument reads could be do to a poor ground.

**rwaltman** · 08-05-2012, 05:47 PM

Carbmate finally arrived, torque wrench and digital angle meter ready, but not my other tools.
The type of tools I use in my hobbies are not really suitable for maintaining an airplane. (Soldering iron, wire cutters, multimeter)
So, to complement them, I got a Craftsman box full with some 200-plus shiny metallic objects. (They are really cute. No colored glass beads, unfortunately).
Complemented it with a few more metric sockets and wrenches for the HKS and off we went to the airport, to sync the carbs.

The HKS docs say the carburetors can be balanced without a prop installed, so I decide to remove it.
Mainly for safety, in a compact engine like the HKS the propeller is not too far away from the carbs, I would be working alone, hot and muggy day, etc.
But also I wanted to get a feeling for how much of the vibration I observed was due to the engine 2 opposite cylinders configuration and how much was due to the props torque reaction.

Before removing the prop I verified the blades pitch and tracking, to see if they were contributing to the problem. They were not.

Pitch: Measured with a digital meter, all three blades were between 1/2 a degree of each other. That speaks volumes for the mechanical steel-pin and feeler method that Powerfin used.

Tracking: It was perfect. Put a laser pointer on the ground aiming up, moved it until the dot was just on the edge of blade #1. It stayed there when I rotated blades #2 & #3

Then, off with his prop! Hooked up the Carbmate, started the engine.
With the throttle all out it idled at over 2000, and the vacuum balance was way off. (Shaking, of course.)
After adjusting both carbs back and forth for a few minutes I got the RPM down to just under 1700, (Mnflyer: right on the mark!), with the Carbmate showing balance. HKS docs say 1400 RPM, 1450 without prop. Doubt I could go that low.

Two unexpected problems showed up.

(1) Without the prop to circulate some air through the oil cooler, the oil temp was climbing fast and was already around 190 when I finished the idle setup. I don't think I can run it at 3000 RPM without overheating. (I heard a few hissing noises when I stopped the engine that I never heard before.)

(2) At this low RPM the generator was not properly charging he battery, and the Carbmate (hooked to the plane's battery) begun showing a low-voltage warning.
This is easy to fix. Just ignore it or use a 2nd small battery for the Carbmate only.

#1 is more complicated. I don't want to reinstall the prop to continue. It is really really close to the carbs. Was thinking of getting some kind of fan to force air through the oil cooler.
Was still thinking when it begun to rain. I have a 1/2-T hangar, which forces me to work outside. If it rains hard, work stops.
Barely finished folding the wings and pushing the plane, pulling the plane, pushing the plane, until it was at just the right angle to fit in the available space, when the rain became torrential.
Closed the hangar door and spent some time marking the wheels position on the ground with duct tape, to know where to aim next time.
Tomorrow's forecast is rain. Tuesday looks good, could put 1 and 1/2 hour after work, so I have two days to think about the oil temp problem.

Any suggestions?

Roberto.

PS: I just noticed the date stamp in the camera is one month off.

**SkySteve** · 08-05-2012, 07:40 PM

Roberto,
Thanks for the pics showing your use of the handy "guage clamps". You just solved my problem of holding my digital gauge solid and the same in each blade when I set mine. Ta-da!!

**rwaltman** · 08-05-2012, 07:47 PM

Thanks, but not my idea.
See http://powerfin.com/instructions.html

My only contribution was to use the bubble level on the blade's edge, instead of just "putting the blade in the same position."
I also used the level to make sure the meter was vertical when measuring the hub's slope, otherwise small errors will be introduced.

Roberto.

**rwaltman** · 08-12-2012, 06:31 AM

Yesterday caught a window between the passing thunderstorms and gave the Carbmate a second chance to prove itself.

Set up the plane as usual, still sans propeller, but this time with a couple fans in front of the cylinders and oil cooler, to be able to run for longer times without concerns about heating.

Was able to set the balance correctly at a lower idle, ~1600 RPM, and balanced again at ~3000 RPM. Oil temp reached around ~170
No noteworthy shaking or vibrations.

Before mounting back the propeller checked its balance. (Pitch and tracking verified earlier.) The only thing I could use as an axis was a wooden rod with a somehow rough finish, that didn't really allow the prop to rotate freely, so small imbalances may go unnoticed. But after several cycles of rotating the prop some 30 degrees and nudging it both ways I was satisfied it was OK.

Propeller back on, engine on, shaking and vibration are back. Maybe less than before, but far, far away from running smoothly. Before, I could smooth it out by pushing above 2400 RPM, now there is a band where it shakes badly above the 2400 mark.

I'm wondering if the engine/prop/mount combination is making the whole structure vibrate at some natural resonance frequencies. If that is happening, I doubt there is anything I can do, other that learn what RPM bands cause it and avoid them.

The Carbmate shows good balance up to ~3300 RPM. Trying to throttle it up above ~3500 RPM causes the following: (a) shakes really, really bad. (b) Carbmate shows vacuum going out of balance. (c) One of the EGT readings goes down (a lot!).
Fuel flow problems in one the carburators?

I am officially out of my depth. Suggestions?

Roberto.

**GDN** · 08-12-2012, 09:00 AM

Yes make a dynamic balancing

**Mnflyer** · 08-12-2012, 09:40 AM

Hi Roberto, I see you have a Lost Hills engine mount, check the torque on the bolts going thur the rubber biskets to the engine, do not torque more than 10 ft lbs mine are between 6 and 10" lbs. make sure they are safety wired at those low torques they will back out.
You will also need to syn the carbs at 5000 to 5400 R's when I do mine I secure the plane by tying the tail down with a cable to my truck trailer hitch than sit in the plane with the carbmate with you (prop on).

**Dave F** · 08-12-2012, 11:05 AM

I have zero HKS experience but I will say that you might be expecting more than acceptable. I have no problem with a 503/582 idling at 2000 to 2300 rpm with a 2.58 or a 3 to 1 gear box.
So a HKS with 3.47 gear box idle at 2000 would be acceptable in my opinion.

Also I wold not accept 1/2 degree variance in pitch amongst the 3 blades -- 1/4 Degree MAX. This is not likely your culprit for shaking. Might just the nature of the beast plus a fw more contributing factors?
Engine mounts too tight ?
Wrong stiffness - measure with a durometer.

Here is an article on HKS http://www.lightsportaircraft.ca/exc...rformance.html
And states my thoughts as well .........

The Rotax 503 and 582 will idle comfortably at 2,000 to 2250 rpm while the HKS depending on prop will come in between 1750 and 2000 rpm. The standard prop is a two blade ground adjustable 68 inch, my preference for a 582 is a three blade 66 inch and for a 503 a three blade 64 inch.

Hope this helps - more fun flyign that fixing EH !

**rwaltman** · 08-12-2012, 08:06 PM

Thanks for the replies.

Originally Posted by GDN

Yes make a dynamic balancing

I plan to do it, but as a "final polish". There seem to be some fundamental problems I need to solve first.

Originally Posted by Mnflyer

check the torque on the bolts going thur the rubber biskets to the engine

Good point, will do.

Originally Posted by Mnflyer

syn the carbs at 5000 to 5400 R's when I do mine I secure the plane by tying the tail down with a cable to my truck trailer hitch than sit in the plane with the carbmate with you (prop on).

OK, I can see the logic on this. If there is a small balance error at 3000 RPM it will be "amplified" at higher RPM settings. Conversely, any remaining error at high RPM should be smaller at lower RPM's (I think.)
One problem now is, (I did not write this clearly,) that the engine will no go above 3400-3500 RPM, one cylinder "faints". (I assume the one cylinder loosing power causes the shaking, and not the other way around.)
I'm not sure I want to do the sync at high power if I am alone, and I can not recruit any help were the plane is now. We'll see ...
Using the car as a tie-down is a good tip. Solves one problem: I was planning to do high-power runups tying the plane to posts set up to protect the hangar's electric meters from cars. That is almost on an active taxiway between the hangars. Can take car and plane to the end of the hangar road away from everything.