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-   -   Stank Idle (https://vansairforce.net/community/showthread.php?t=184493)

biscuit112 07-09-2020 08:39 PM

Stank Idle
 
I have been working on my IO-320's idle and cooling for almost a year now. I am a mechanic and pilot but 99% of my PIC time is in gliders... The engine is in a Sam James plenum and cowl. Dear internet come and collect my soul with the judgements of the divine aviation elders (know it alls). Can someone tell me if this idle is to be expected from a bendix FI in a james cowl and plenum. I moved my boost pump from the firewall to the cabin(previous owner's goof). The lines from the servo to the flow divider are as short as I can get them to be on a backdraft intake. The fuel lines out of the flow divider are wrapped elevated as high as possible. .022 restrictors in the injectors. I have a lightweight wooden prop. My idle starts out perfect until 170-200 degrees oil temp comes around. The CHTs and EGTs are uniform and never too hot for all cylinders. The boost pump doesn't change anything. 1300 to max RPM feels stable and clean. I am actually all out of things to do to it and I feel like its the equivalent of race car parts on race car, it just will not idle without lumping. Here is a video. https://www.youtube.com/watch?v=TgzAeOGVeV0

Kyle Boatright 07-09-2020 08:45 PM

Have you checked for induction leaks?

biscuit112 07-09-2020 08:51 PM

Yes I have, all new gaskets. Wouldn't an induction leak show up at all operating temperatures as well? Can they just show up when hot?

scsmith 07-09-2020 11:45 PM

Quote:

Originally Posted by biscuit112 (Post 1445158)
Yes I have, all new gaskets. Wouldn't an induction leak show up at all operating temperatures as well? Can they just show up when hot?

Perhaps, from thermal expansion. To truly eliminate any induction leaks, use Ross Farnham's SDS induction seals. Heaven.

It may also be that with a light prop, it just will never idle very smoothly.

Have you tried leaning it to within an inch of its life when it is warmed up?

rv8ch 07-10-2020 12:17 AM

Ignition?
 
What kind of ignition are you running? Any recent changes or overhauls to any parts the ignition system? Wires? Plugs? Everything connected perfectly? Any change if you switch ignitions L/R?

RV Jerry 07-10-2020 08:48 AM

Something you might check is if you have a primer make sure it?s not leaking

lr172 07-10-2020 08:58 AM

Doesn't look like a classic rough idle due to hot/boiling fuel. Looks more like a miss. Have you checked your plugs, including a resistance check? How long has it been since your mags were serviced (if the egap is not adjusted, the spark gets weaker and weaker over time and if you have your idle mixture adjusted incorrectly, it can be hard to light with a weak spark). Notice that 80% of the time it is running smooth, then it hiccups and recovers. That is not a classic rough idle.

I have a rough idle on my 6 when it is hot, due to injectors in the top ports. It is consistently rough and not intermittent like yours.

biscuit112 07-10-2020 12:45 PM

Hello everyone and thank you for your responses. I have thought about the thermal expansion thing. There is ONE gasket I have not replaced I will try it. I have leaned the pooh out of it when it starts to lump. It just ends up making it to the Idle Cutoff. The engine itself has 30+ hours on it the magnetos were rebuild in 2010-13 or so. Again 30 hours. I have drooled over the very logical and proven design of those SDS seals. (mmmmm tasty) I did end up working on a flange to a inlet tube, but even after that I cant say the hot engine performance changed. Lr172, I'm glad to see you chimed up. I read some of your posts and complaints with the hot idle dysfunction. My injectors are on the top ports. Thank you for saying it's not normal because I have no experience or reference for what is.

pjc 07-10-2020 09:16 PM

FWIW: I have a carbureted O-320 E2D with a wood prop and slick mags that idles much more smoothly (and happily at 750 rpm when warmed up) than your video.

If you are getting ~50 rpm rise on shutdown the idle mixture should be ok, so I too would be looking at ignition items (fouled plugs, bad harness, worn mag cam affecting dwell, etc). If none of those I’d start to worry about cam/lifters/valves but have no idea why these would be masked at low engine temps.

Good luck!
Peter

lr172 07-10-2020 10:39 PM

Quote:

Originally Posted by biscuit112 (Post 1445295)
Hello everyone and thank you for your responses. I have thought about the thermal expansion thing. There is ONE gasket I have not replaced I will try it. I have leaned the pooh out of it when it starts to lump. It just ends up making it to the Idle Cutoff. The engine itself has 30+ hours on it the magnetos were rebuild in 2010-13 or so. Again 30 hours. I have drooled over the very logical and proven design of those SDS seals. (mmmmm tasty) I did end up working on a flange to a inlet tube, but even after that I cant say the hot engine performance changed. Lr172, I'm glad to see you chimed up. I read some of your posts and complaints with the hot idle dysfunction. My injectors are on the top ports. Thank you for saying it's not normal because I have no experience or reference for what is.

I recommend the 4 psi spring for your spider. It makes a noticeable difference idling in hot weather. You can get them from Don at AFP. I also put reflective tape on the injector lines.

Final fix was to more actively use a fuel return circuit starting at th servo. This was for side port injectors which are much worse than top injectors

Goof luck,

Larry

lr172 07-10-2020 10:41 PM

Quote:

Originally Posted by pjc (Post 1445377)
FWIW: I have a carbureted O-320 E2D with a wood prop and slick mags that idles much more smoothly (and happily at 750 rpm when warmed up) than your video.

If you are getting ~50 rpm rise on shutdown the idle mixture should be ok, so I too would be looking at ignition items (fouled plugs, bad harness, worn mag cam affecting dwell, etc). If none of those I’d start to worry about cam/lifters/valves but have no idea why these would be masked at low engine temps.

Good luck!
Peter

Check the plugs. Ineffectiveness of leaning can point to both ignition and boiling fuel in the injector lines. Your engine doesn’t sound like mine does when hot. My ear still hears a miss. Mine does much better at 1000 rpm. At 750, it is pretty consistently rough when the cowl is heat soaked . Yours runs nicely but occasionally falls off then re recovers. A pretty classic misfire scenario.

If it is boiling fuel, iwould expect it to be happening before the servo, based upon your symptoms.

biscuit112 07-10-2020 11:36 PM

It's getting test flown this morning. I have directed cooling air from an extra NACA duct to the fuel servo. i will talk to don about a 4lb spring next week. i stuck a thermocouple into my cowl yesterday and it read 140degress after 5 minutes of idle. When i would raise the idle to 1100+ you could see the temperature drop. The exhaust flows right next to the fuel servos since this is a IO-320-B1A from a twin Comanche. I will say its less than ideal.

Capflyer 07-11-2020 04:35 AM

Magnetos
 
You mentioned your magnetos were rebuilt in the 2010-2013 time period. Slicks? There was a an issue with the distributor gears and Champion issued a SB and they need to be replaced. The contact on it would bend causing the timing to be way off. This happened to us and resulted in a rough idling and running engine. It's pretty obvious when you look at it, the brass contact will be bent over to one side. Since yours were rebuilt you will need to open them up and do a visual, magneto serial number probably will not be an indicator.

Link to the SB https://www.championaerospace.com/as...A_20181112.pdf

lr172 07-11-2020 07:54 AM

Quote:

Originally Posted by biscuit112 (Post 1445388)
The exhaust flows right next to the fuel servos since this is a IO-320-B1A from a twin Comanche. I will say its less than ideal.

Definitely address that. I had a similar issue on my 320-B1A and made simple aluminum heat shields that clamp on to the exh pipe. In my case, exh was too close to the fuel line for comfort.

Larry

esco 07-11-2020 09:38 AM

Plug check complete?
 
How do all your plugs look?

One of the easiest checks to make, needs few tools, minimally invasive...
and you also confirm that every plug wire is securely affixed...

snopercod 07-12-2020 08:34 AM

Quote:

Originally Posted by scsmith (Post 1445174)
It may also be that with a light prop, it just will never idle very smoothly.

Nah. My O-290-D2 with a wooden prop will idle smoothly down to 500 RPM. I did have a rough running problem on hot days, though. It turned out to be the hot oil in the sump was heat soaking the carburetor bolted onto the bottom. Apparently, the heat was boiling the fuel in the bowl and causing the engine to run rich to the point where it would actually die on me. I solved that problem by adding a 1/16" phenolic gasket as a thermal break between the sump and the carb. I don't think this fix would apply to an injected engine.

lr172 07-12-2020 09:03 AM

Quote:

Originally Posted by snopercod (Post 1445542)
Nah. My O-290-D2 with a wooden prop will idle smoothly down to 500 RPM. I did have a rough running problem on hot days, though. It turned out to be the hot oil in the sump was heat soaking the carburetor bolted onto the bottom. Apparently, the heat was boiling the fuel in the bowl and causing the engine to run rich to the point where it would actually die on me. I solved that problem by adding a 1/16" phenolic gasket as a thermal break between the sump and the carb. I don't think this fix would apply to an injected engine.

It does. I feel that the servo is a very good source of picking up heat from the sump and transferring it ti the fuel. I can hear the fuel boiling down by the servo after shut down in the summerin my 6. Don’t hear it in the 10, where I have a phenolic spacer.. the lower the fuel flow, the more heat it picks up.

biscuit112 07-12-2020 11:09 PM

Where does one acquire these spacers? Did you make them yourself LR172?

lr172 07-13-2020 07:38 AM

Quote:

Originally Posted by biscuit112 (Post 1445785)
Where does one acquire these spacers? Did you make them yourself LR172?

Yes. I got the material from mcmaster carr. I forget which material I used. They have a variety of fabric reinforced materials. Just get one with the lowest heat transfer rate and with a >= 200* temp limit. It is not difficult to cut them to fit. You can use a spare gasket as a template.

I would not go any thicker than 1/8 or 3/16, as you will be moving the FAB down and will have alignment issues with the cowl. If you plan to cut and re-glass the FAB, I would go with a 1/4" You will need two gaskets to reinstall; one on each side of the spacer. Even a thin one will make a difference, as you break the metal on metal conduction (aluminum is very efficient at heat tansfer).

Larry

biscuit112 07-22-2020 09:08 PM

UPDATE
 
Soo. I installed a spacer from my rsa5 to the intake/oil sump that seemed to delay when the lumpy idle would occur. I also installed a mechanical fuel pump cooling shroud that didn't appear to make any difference at all. It would still reach a point to where the idle would bungle about. Seemed to be at about 180 instead of 160-170. THE FIX WAS, a 4 psi spring in the flow divider. The Bendix flow divider has either a 2 psi spring or a 4 psi spring. The spring effectively raises the boiling point of the fuel in the stainless lines to the injectors. There is also a lycoming service instruction for rough idles when hot. Instruction 1489C can be found here. https://www.lycoming.com/sites/defau...%20%281%29.pdf The spring part number is Precision P/N 2577011. For grins if anyone wants the phenolic spacer, it is Superior part # 73161. I have been battling this issue for what seems like a year. The battle has been won. I am finally comfortable with my plane.

lr172 07-23-2020 08:26 AM

Quote:

Originally Posted by biscuit112 (Post 1448549)
The spring effectively raises the boiling point of the fuel in the stainless lines to the injectors. .

Actually, it raises the pressure, and therefore increases the boiling point, in the line between the servo and the spider. I does not increase pressure in the SS lines after the spider (injectors are too big to create backpressure at idle level fuel flows, which is the reason for the plumbing inside the spider). That -4 hose absorbs more heat than most think it does.

Larry

rv8ch 07-23-2020 11:51 AM

Quote:

Originally Posted by lr172 (Post 1448629)
Actually, it raises the pressure, and therefore increases the boiling point, in the line between the servo and the spider. I does not increase pressure in the SS lines after the spider (injectors are too big to create backpressure at idle level fuel flows, which is the reason for the plumbing inside the spider). That -4 hose absorbs more heat than most think it does.

Larry

Thanks Larry for your diagnosis. I had no idea this would even be something to consider - the back pressure spring.

I watched a Mike Busch webinar yesterday where someone recommended creating an AI to diagnose engine problems - I think he needs you on his team!

biscuit112 07-23-2020 04:38 PM

Quote:

Originally Posted by lr172 (Post 1448629)
Actually, it raises the pressure, and therefore increases the boiling point, in the line between the servo and the spider. I does not increase pressure in the SS lines after the spider (injectors are too big to create backpressure at idle level fuel flows, which is the reason for the plumbing inside the spider). That -4 hose absorbs more heat than most think it does.

Larry

What he said

ltn6a 10-04-2020 02:49 AM

Rough idle
 
Hi All

Just came across this , I have the almost same issue. Io-320-b1a
The engine ideas fine when cold but once hot the rpm hunts with the occasional misfire.
I have had the mags tested and they tested fine , the injector servo ,distributor valve and lines all bench tested where they did replace an injector nozzle but it made no change..
All lines to and from the servo up to the distributor are fire sleeved .
I will look at the spring pressure in the distributor valve and a look at a non metallic spacer. .
Before coming across this thread the only thing left was an induction leak but we have new seals at the heads the sleeves to the sum all look good .
I have also seen mention of the Savvy induction test but Iím not aware of what this is ?
Any further help would be appreciated

Mark

DanH 10-04-2020 07:01 AM

1 Attachment(s)
Replacing a 2 lb divider spring with a 4 lb spring only raises the boiling point by four, maybe five degrees F. It is a relatively ineffective crutch.

The fundamental problem is fuel heating. It would be more effective to slow the rate of heat transfer.

The OP has a rear inlet sump and a top-mounted divider, so (1) the servo is probably exposed to radiant heating from the exhaust, and (2) the long line from servo to divider offers plenty of transfer time at low fuel flow (idle).

The typical aluminum or stainless "heat shield" clamped to a hot exhaust is really a very poor performer. Radiant heat energy strikes the side facing the hot exhaust. Some is reflected and some is absorbed. The absorbed energy spreads through the shield material by conduction. It then leaves the heat shield material by convection (via all surfaces) and re-radiation (surface opposite from the heated side). The re-radiated energy heats the object we wished keep keep cool. Not good.

So, the goal is to slow the rate of re-radiation. The easy way is to slow conduction from the hot side. Simply add an insulator layer to the shield, which can be any material with a low rate of conduction. Again, in our world, good 'ole fiberfrax felt works fine. Cut a patch the size of the shield. Hold in place and tape over it with metallic aluminum duct tape. Now energy transfer from the hot side to the cool side is much slower.

Note the principle, a reflector (here the hot side of the shield) backed by an insulator. The same principle can be applied to the fuel line running from the servo to the divider. Silicone faced firesleeve already provides an insulator, the fiberglass liner. Simply add a reflector to the outside of the sleeve.
For a short length, wrap it with aluminum tape. For a longer length, slip it inside a reflector sleeve, available from lots of sources. Here's an example: http://www.americanfiresleeve.com/hi...rotection.html

Even with a 4 psi spring, I'd still take steps reduce heat transfer. It can only increase the margins.
.

lr172 10-04-2020 07:18 AM

Quote:

Originally Posted by DanH (Post 1467010)
Even with a 4 psi spring, I'd still take steps reduce heat transfer. It can only increase the margins.
.

+1

For my 320, in addition to the spring, I did all of the things mentioned by Dan above to get the hot idle issue under control, except insulating the heat shield, which is a great idea that I will implement next time the cowl is off. Reflective material on the -4 line made a big difference, as did the reflector shields on the exhaust. The vetterman exh on a 320 gets pretty close to the servo and the fuel feed line. I cannot fully address my issue, as my SS injector lines run through the baffling to the hot side (using primer ports)

Oddly, I made no remediation steps on the 10 and see no hot idle issues. I think a lot has to do with the exh so close to the servo and fuel feed line on the 320.

Larry

airguy 10-04-2020 09:05 AM

Quote:

Originally Posted by DanH (Post 1467010)
Replacing a 2 lb divider spring with a 4 lb spring only raises the boiling point by four, maybe five degrees F. It is a relatively ineffective crutch.

Before I installed the SDS system in my airplane, I did LOTS of things to reduce the vapor issue while using 91E10 fuel. I tried the 4# spring in the divider and discovered exactly what Dan says - it only delayed the onset of trouble, and did nothing to really stop it. I ended up later removing it and reinstalling the original stock spring. Don Rivera at Airflow Performance told me I was chasing a losing proposition by doing that, but I had to try it myself to make sure.

What did work, and worked well, was to replace the OEM injector orifices with smaller ones - that presents more backpressure between the injector and the divider in the spider lines, and upstream of there in the divider all the way back to the servo. I got down to a .022 orifice from the original .028, and this effectively cured my loping hot idle on 91E10. The drawback to this plan is also the attractiveness of it - higher pressure drop across the smaller orifice requires a much higher fuel pressure available at the servo to be able to move enough fuel for full takeoff power. I had already installed dual electric pumps and had an adjustable fuel pressure regulator on them, so that was easy to do - I raised my fuel pressure up to 40psig and then it was happy. I could move enough fuel for full power, and still had enough back pressure to avoid boiling the fuel in the lines at hot idle.

I also double-firesleeved all my FWF fuel lines for insulation, and had removed my engine-driven fuel pump (primary fuel heater) when I installed the dual electrics.

I flew that setup for about 550 hours with excellent results - and then I upgraded to the SDS which is even better!


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