M20J GAMI spread issue (flow divider?)

[PT20J]

1 hour ago, N201MKTurbo said:

That is not true. The flow through a pipe will be determined by the sum of all the restrictions. The smallest will be the dominant one, but they all contribute.

In my attempt at brevity, I oversimplified and apologize for creating potential confusion. In a long pipe made up of pipes of varying cross sections, or in a pipe with multiple restrictions, of course all contribute to the flow rate. I was simplifying to the case apropos to the current thread where there are multiple restrictions, but one is considerably smaller than the others.  In this case, the smaller restriction will dominate. 

Precision Airmotive lists the ID for the line to the nozzle as 0.085 to 0.090. The lines are supplied by Lycoming. There are only two part numbers for an IO-360-A3B6(D): LW-12098-0-140 for cylinders 1&3 and LW-12098-0-210 for cylinders 2&4. There are not options for different IDs. Lycoming SI  1275C lists the nozzle flow rate as 32 lb/hr at 12 psi under specified test conditions. From this you should be able to calculate the effect of the lines relative to the nozzles.

[carusoam]

12 minutes ago, m20kmooney said:

The viscosity of Newtonian fluids is constant at a given temperature. Avgas is a Newtonian fluid. A non-newtonian flow model does not apply. 

A test of newtonian vs. non-Newtonian nature, would include its dependence on shear rate... not so much temperature dependence... both are temperature dependent...

If fuel molecules align in the flow channel, like oil does, they would become less resistant to flow...

That would be non-Newtonian. 

Best regards,

-a-

[DonMuncy]

From someone who has very little understanding of the nuances of viscosity, flows, pressures, etc., it seems to me that if you have a proper GAMI spread, all the factors that are taking place in the system have been accounted for. The amounts of fuel getting into each cylinder are (at least very close to) equal. So if a different length or size of tube has been put into the system, you may have to adjust the flow, but that is what GAMIs do. Am I wrong?

[m20kmooney]

5 minutes ago, carusoam said:

If fuel molecules align in the flow channel, like oil does, they would become less resistant to flow...

Avgas is not thixotropic crude oil and is not resistant to flow. Newtonian.

[N201MKTurbo]

11 minutes ago, PT20J said:

In my attempt at brevity, I oversimplified and apologize for creating potential confusion. In a long pipe made up of pipes of varying cross sections, or in a pipe with multiple restrictions, of course all contribute to the flow rate. I was simplifying to the case apropos to the current thread where there are multiple restrictions, but one is considerably smaller than the others.  In this case, the smaller restriction will dominate. 

Precision Airmotive lists the ID for the line to the nozzle as 0.085 to 0.090. The lines are supplied by Lycoming. There are only two part numbers for an IO-360-A3B6(D): LW-12098-0-140 for cylinders 1&3 and LW-12098-0-210 for cylinders 2&4. There are not options for different IDs. Lycoming SI  1275C lists the nozzle flow rate as 32 lb/hr at 12 psi under specified test conditions. From this you should be able to calculate the effect of the lines relative to the nozzles.

No problem, while Lycoming currently lists the two lines, I believe most of us have lines that were of an older obsolete design. I will have to look it up in some of my old parts manuals. I think they changed the design about 20 years ago because the soldered fittings were falling off.

[carusoam]

1 hour ago, m20kmooney said:

Avgas is not thixotropic crude oil and is not resistant to flow. Newtonian.

Lucas you are getting more fun as the days go on...

My favorite fluid flow discussions are related to thixotropic fluids... crude oil is one, but Catsup is the fun one... 

Since our fuel is not loaded with solids, their chance of being thixotropic is pretty small.

For everyone else, thixotropic fluids require a minimum shear to allow the flow to begin... kind of like a mudslide... or avalanche...

This is the reason people bang the catsup jar to get the flow to start....  then the catsup people went with squeeze bottle to make it easy for the user...

 

So we might want to review JK’s progress and next steps... (JK, comment if this is correct)

1) He has four EGTs...

2) Has a FF gauge...

3) can lean until rough...

4) can enrich til smooth...

5) Baby bottle test, with injectors the last time, roughly showed some variations in fuel distribution...

 

6) Were you able to run a Gami spread test?  Leaning slowly enough to allow each cylinder to peak, recording the FF as each cylinder peaks...?

7) were you able to swap the highest FF FI with the lowest FF FI?

 

If re-running the tests...

1) use uniform tall thin glasses... soda bottles add additional variation to the project...

2) put marks on the glasses based on the same volume. Ounces probably works...

3) Doing the gami spread test is probably going to point towards a FI that is blocking more fuel...

4) oddities of FI mounting have been found by finding blue stains on the vent hole of injectors.  Locating the hole properly seems to be the solution... follow the instructions for that...

5) if unable to run a gami spread... we should focus on that some...

These are the normal psychology issues covered often on MS...

I am only a PP, not a mechanic...

Best regards,

-a-

[jkarch]

1 hour ago, N201MKTurbo said:

No problem, while Lycoming currently lists the two lines, I believe most of us have lines that were of an older obsolete design. I will have to look it up in some of my old parts manuals. I think they changed the design about 20 years ago because the soldered fittings were falling off.

I think that’s the issue I am having, half are old original lines and half are the Lw12098-0-140 and 210 parts. These parts are thicker and have uniform soldering to the fitting, whereas the thinner tubes  have a beveled solder joint. Those tubes look tired and old. I did not get an ID measurement yet but after I fly back west will replace all four tubes and clamps with new parts, then rerun the GAMI test.  The old lines may have been 61581 (.0605) as opposed to .0865 with the LW12098-0-xx parts.  I will measure the old parts upon removal.

Carusoam, I will rerun GAMI once I replace the tubes. The baby bottle test however is interesting because it can’t be run at 10GPH, and the increased flow would eccentuate the uneven distribution.  I would use glass tubes however if I rerun.

 

 

 

Edited January 1, 2019 by jkarch

[jkarch]

2 hours ago, DonMuncy said:

From someone who has very little understanding of the nuances of viscosity, flows, pressures, etc., it seems to me that if you have a proper GAMI spread, all the factors that are taking place in the system have been accounted for. The amounts of fuel getting into each cylinder are (at least very close to) equal. So if a different length or size of tube has been put into the system, you may have to adjust the flow, but that is what GAMIs do. Am I wrong?

Basically if your GAMI spread is good it takes account for air, fuel, and ignition all working properly. In my case I am attacking fuel delivery as I believe spark and induction(no leaks) are both working fine. If that doesn’t work, then the backup answer for a strange spread between 1&2 and 3&4 is camshaft wear, which is bad. I’ll post GAMI numbers as I fly across country.

[carusoam]

Signs of cam lobe wear include...

• measuring the lift of the valve stem? (Procedure for that)
• metal analysis of the engine oil.
• parts of metal collecting on oil filters and/or screens.
• taking a cylinder off to visually inspect a few lobes the cam...
• large Gami spread...

The hardened layer of the lobes is very thin.  Once removed, the wear increases rapidly...

 

Other things to look at when valves are concerned...   get pics using a dental cam through the spark plug holes.... the normal pizza look vs hot spots on the edge....

Visually inspecting all the cam lobes is a challenge.  It doesn’t seem to be a good idea to remove more than one cylinder at a time... so your mechanic has to be very familiar with the procedure...

What was the reason for FF not going above 10gph? Just max FF with the electric pump on?

balancing FF and air flow to each cylinder is done for cruising conditions... under T/O and climb, ROP is used with enough excess fuel the balance can be a bit off without much of an issue...  100% power on a 200hp engine is using near 20gph, approximately double the cruise number...

PP thoughts only, not a mechanic....

Best regards,

-a-

[jkarch]

1 hour ago, carusoam said:

Signs of cam lobe wear include...

• measuring the lift of the valve stem? (Procedure for that)
• metal analysis of the engine oil.
• parts of metal collecting on oil filters and/or screens.
• taking a cylinder off to visually inspect a few lobes the cam...

The hard layer of the lobes is very thin.  Once removed, the wear increases rapidly...

 

Other things to look at when valves are concerned...   get pics using a dental cam through the spark plug holes.... the normal pizza look vs hot spots on the edge....

Visually inspecting all the cam lobes is a challenge.  It doesn’t seem to be a good idea to remove more than one cylinder at a time... so your mechanic has to be very familiar with the procedure...

What was the reason for FF not going above 10gph? Just max FF with the electric pump on?

balancing FF and air flow to each cylinder is done for cruising conditions... under T/O and climb, ROP is used with enough excess fuel the balance can be a bit off without much of an issue...  100% power on a 200hp engine is using near 20gph, approximately double the cruise number...

PP thoughts only, not a mechanic....

Best regards,

-a-

Outside of oil analysis, everything else is very invasive. Pulling a jug on an engine which otherwise works (even if not optimally) is risky. Oil analysis did show slight increased iron at 28 (averages 24) for 30 hours but all other wear metals are actually lower than universal averages. Silicon was elevated (Ram Air?) . All compressions in mid 70s. Valve lift test involves collapsing lifters so it’s an  involved process beyond valve cover removal. If tubes don’t fix the issue I will wait and see how performance trends. So far the spread is stable(has been so for >200 hrs) and engine is smooth. Fuel economy is excellent. I flew from Seattle to Rapid City in 5 hours (with TW at 13000 ft) and had over 20 gallons left and only added 2qts for the flight across America.

Edited January 1, 2019 by jkarch
Clarified qts added

[carusoam]

JK,

2qts of oil in 5hours?

Something to keep an eye on... at least know where it is going... 

1qt per near 10hours is more normal for Lycomings.

T/O and high powered climbs are a part of the oil usage.... in a five hour flight, you didn’t have many T/Os and climbs...

Of course, filling the case over 6qts causes an increase of oil thrown out the case vent during the climb.

It takes a few details to get the oil usage measuring technique stabilized... practice, practice, practice...

How is the OAT in Rapid City?

Best regards,

-a-

[jkarch]

It’s actually about 1 qt in 7 on average and has been the same since I bought it.  I started my trip with 7.5 qts(added two for the trip) and 14 hours later (New Jersey) I am just under 6. And yes, most of it is out the belly!  I probably added too much but wanted to keep the engine cool for the trip. Tomorrow I will add 1qt before heading towards Chicago. At 13000 ft it was kind of warm, around 20F! Tomorrow I’m trying for 8k

Edited January 1, 2019 by jkarch

[ArtVandelay]

Signs of cam lobe wear include...

• measuring the lift of the valve stem? (Procedure for that)
• metal analysis of the engine oil.
• parts of metal collecting on oil filters and/or screens.
• taking a cylinder off to visually inspect a few lobes the cam...

The hard layer of the lobes is very thin.  Once removed, the wear increases rapidly...

Oil analysis and checking of oil filters for metal gave no indication of my cam wear. But my JPI did. FWIW.


Tom

[jkarch]

Tom, What were the differences in CHT and EGT peak temperatures and spreads(not just GAMI spread) that gave you indications  about Cam wear? For example if you were at the peaks on the good cylinders for EGT, how far down were the bad peaks and what made you decide to pull a jug to inspect?

1 minute ago, ArtVandelay said:

Oil analysis and checking of oil filters for metal gave no indication of my cam wear. But my JPI did. FWIW.


Tom

 

[ArtVandelay]

Tom, What were the differences in CHT and EGT peak temperatures and spreads(not just GAMI spread) that gave you indications  about Cam wear? For example if you were at the peaks on the good cylinders for EGT, how far down were the bad peaks and what made you decide to pull a jug to inspect?
 

EGTs were off by ~80°, spread was ~1.0gph, cylinder temps were normal. I lost a cylinder in flight, didn’t bother with pulling it, with 2200+ hours and the associated problems I decided to just overhaul.


Tom

[Shadrach]

8 hours ago, jkarch said:

Outside of oil analysis, everything else is very invasive. Pulling a jug on an engine which otherwise works (even if not optimally) is risky. Oil analysis did show slight increased iron at 28 (averages 24) for 30 hours but all other wear metals are actually lower than universal averages. Silicon was elevated (Ram Air?) . All compressions in mid 70s. Valve lift test involves collapsing lifters so it’s an  involved process beyond valve cover removal. If tubes don’t fix the issue I will wait and see how performance trends. So far the spread is stable(has been so for >200 hrs) and engine is smooth. Fuel economy is excellent. I flew from Seattle to Rapid City in 5 hours (with TW at 13000 ft) and had over 20 gallons left and only added 2qts for the flight across America.

It’s not an involved process. Lifters collapse without oil pressure. While they are called lifters, they do not actually provide lift (though many falsely believe that they do). Have your mechanic measure the cam lift.

Edited January 2, 2019 by Shadrach

[Guest]

If you’re replacing the four fuel lines, make sure that they are all from the same manufacturer.  I’ve seen a line made by Superior mess up the performance of a Bravo engine.  Installed a Lycoming line and things went back to normal.

Clarence

[jkarch]

Just now, M20Doc said:

If you’re replacing the four fuel lines, make sure that they are all from the same manufacturer.  I’ve seen a line made by Superior mess up the performance of a Bravo engine.  Installed a Lycoming line and things went back to normal.

Clarence

Clarence,  they're all original lycoming parts.  I don't know who manufactured the thinner lines in the rear, but I will install 4 fresh lines and make sure there aren't too many bends along the way, besides bending enough to comply with the clamp AD.

[wpbarnar]

 

Engine runs smooth, fuel economy is good, oil analysis is good.  Oil consumption not great but acceptable.  You are apparently not afraid of flying it long distance cross country.

@jkarch What is the problem you are trying to solve?  

After digesting the thread, I personally think you are in search of a problem that may not exist.

In several of your early post, you commented on the difficulty of obtaining information from the engine monitor,  large changes in fuel flow with small vernier moments, age of the engine monitor etc....   don’t think I would spend money chasing a problem until I could completely trust the data. 

Bill

[jkarch]

1 hour ago, wpbarnar said:

 

Engine runs smooth, fuel economy is good, oil analysis is good.  Oil consumption not great but acceptable.  You are apparently not afraid of flying it long distance cross country.

@jkarch What is the problem you are trying to solve?  

After digesting the thread, I personally think you are in search of a problem that may not exist.

In several of your early post, you commented on the difficulty of obtaining information from the engine monitor,  large changes in fuel flow with small vernier moments, age of the engine monitor etc....   don’t think I would spend money chasing a problem until I could completely trust the data. 

Bill

Bill, the pilot in me has no qualms about flying the plane, but the engineer in me wants to understand how everything fits together and interacts. The end result of this really is splitting hairs, as the engine is well tuned it seems, outside of potential gauge indications and perceptible differences in fuel tube diameters. But true, most people (including different mechanics over the past few years) just say fly it and call it a day, so that’s what I am going to do.

[wpbarnar]

9 hours ago, jkarch said:

Bill, the pilot in me has no qualms about flying the plane, but the engineer in me wants to understand how everything fits together and interacts. The end result of this really is splitting hairs, as the engine is well tuned it seems, outside of potential gauge indications and perceptible differences in fuel tube diameters. But true, most people (including different mechanics over the past few years) just say fly it and call it a day, so that’s what I am going to do.

I throughly understand the engineer’s mentality and wanting to understand.  In your Dec 3 post you mentioned several issues with your engine monitor and I read into it that you may not trust the data.    

I always believe that first you need a good data set that you can trust before analyzing a problem.    What I intended to convey, is you may not have a problem because you are being mislead by your data.    The injection lines and talk of cam wear could be red herrings.

Bill

 

[Shadrach]

9 hours ago, jkarch said:

Bill, the pilot in me has no qualms about flying the plane, but the engineer in me wants to understand how everything fits together and interacts. The end result of this really is splitting hairs, as the engine is well tuned it seems, outside of potential gauge indications and perceptible differences in fuel tube diameters. But true, most people (including different mechanics over the past few years) just say fly it and call it a day, so that’s what I am going to do.

Perhaps I've missed something with regard to engine data.  Looking at your richest cylinder's data, at what mixture setting does the engine begin to get rough?

[Andy95W]

10 hours ago, jkarch said:

Bill, the pilot in me has no qualms about flying the plane, but the engineer in me wants to understand how everything fits together and interacts. The end result of this really is splitting hairs, as the engine is well tuned it seems, outside of potential gauge indications and perceptible differences in fuel tube diameters. But true, most people (including different mechanics over the past few years) just say fly it and call it a day, so that’s what I am going to do.

Evidently these are the perils of flying behind 1940's technology in the modern, digital age...

[jkarch]

So an update.  I flew across the country,  the engine flew great.  18 hours of fun.    I have the tubes ready to install, but instead I pause.  I have a question about overhauls.  I now understand the talk about cams.  It's a common problem, and 1&2 intake lobe is the victim.  My engine has 1200 hours on it, 800 from me in 8 years and 400 from the previous owner in six.  The plane did sit in the bay area for about 5 months and 7 hours on it and once it appears went through 100 hours without an oil change before I took possession.   Let's say it's the cam.  It seems even if I don't plan on selling the plane, that an overhaul is worth the 10K plus over IRAN, especially because of the "ok" (1 qt in 6-7 hrs) oil consumption (compressions above 74 however), and the 0 SMOH value increase of $12,500 over a 1200 SMOH engine.    So pretending I go with an overhaul, any thoughts about DLC lifters and their potential to solve the Cam Lobe Wear problem, and also Zephyr and Jewell for overhaul shops?  Anyone think it's worth the 10-15k premium for Lycoming exchange for roller tappets and removal of the "D" mags?    Zephyr seems to suggest the complete overhaul solution, while Jewell is a la cart.  My Mags only have 200 hours since overhaul and seem great.  Any reason to overhaul them?  It seems like roller tappets and "D" mag removal makes the engine smoother but also not quite as powerful.      Thoughts?  -J

[jaylw314]

48 minutes ago, jkarch said:

So an update.  I flew across the country,  the engine flew great.  18 hours of fun.    I have the tubes ready to install, but instead I pause.  I have a question about overhauls.  I now understand the talk about cams.  It's a common problem, and 1&2 intake lobe is the victim.  My engine has 1200 hours on it, 800 from me in 8 years and 400 from the previous owner in six.  The plane did sit in the bay area for about 5 months and 7 hours on it and once it appears went through 100 hours without an oil change before I took possession.   Let's say it's the cam.  It seems even if I don't plan on selling the plane, that an overhaul is worth the 10K plus over IRAN, especially because of the "ok" (1 qt in 6-7 hrs) oil consumption (compressions above 74 however), and the 0 SMOH value increase of $12,500 over a 1200 SMOH engine.    So pretending I go with an overhaul, any thoughts about DLC lifters and their potential to solve the Cam Lobe Wear problem, and also Zephyr and Jewell for overhaul shops?  Anyone think it's worth the 10-15k premium for Lycoming exchange for roller tappets and removal of the "D" mags?    Zephyr seems to suggest the complete overhaul solution, while Jewell is a la cart.  My Mags only have 200 hours since overhaul and seem great.  Any reason to overhaul them?  It seems like roller tappets and "D" mag removal makes the engine smoother but also not quite as powerful.      Thoughts?  -J

You'll almost never recoup the cost of the overhaul if you sell the plane, especially if it is running fine now.  If you're going to overhaul, do so for your own peace of mind or because the engine needs it--it's not a financial investment for later

I've never heard of the A3B6 motor running smoother because of the roller tappets?  The A3B6 should make the same power at 25^o, but many are retimed to the optional 20^o, which makes them less powerful but run cooler.  The Bendix mag can only be set to 25^o. (I hope I have that right, I seem to get that backwards a lot!)

FWIW I have the roller tappet A3B6 and it doesn't stop me from worrying about the camshaft, so I didn't buy myself peace of mind