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IO-360 M1B Intake Tube Seals - Backfiring

mfleming

mfleming

Well Known Member
Patron
Two things.

First question. Does anyone have advice or a written procedure for replacing the intake tube seals on the sump end of the tube? Photos below.

I have gotten some great advice from a respected member of VAF about trouble shooting my problem but just casting a wider net.

Second question. Can an intake leak on the intake tube cause a massive backfire? The backfires during hot starts have blown out the air filter several times. Always on a hot start. It happens whether I start on the left impulse Slick, right P-Mag or both. It happens when the mixture is being pushed in as it's trying to start.

I've had experienced mechanics and pilots watch me hot start and find nothing wrong with my technique (I've tried every technique I can think of.

intake-tube1.jpg intake-tube2.jpg intake-tube3.jpg
 
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Not sure why you thing intake seals are the root issue.

As far as backfire, before doing anything else I’d check ignition timing. Remember for this engine the:
- Mag is 25 degrees BTDC
- pMag is also 25 degrees, but to set this timing you move the crank to TDC, then blown into the pMag manifold pressure tube to tell the pMag to set the timing. Do not make the common mistake of setting the pMag timing when the crank is at 25 degree BTDC. If you forget to do this, the pMag will actually be at 50 degrees BTDC.

Carl
 
To install. It's Just a big orange silicon O-ring . Be careful not to cut the o-ring on the sharp edge of the tube o-ring keeper. Any intake leak lowers the demand of fuel from a mass flow sensor. Meaning less fuel to the engine at all times.
 
Carl Froehlich said:
Not sure why you thing intake seals are the root issue.

As far as backfire, before doing anything else I’d check ignition timing. Remember for this engine the:
- Mag is 25 degrees BTDC
- pMag is also 25 degrees, but to set this timing you move the crank to TDC, then blown into the pMag manifold pressure tube to tell the pMag to set the timing. Do not make the common mistake of setting the pMag timing when the crank is at 25 degree BTDC. If you forget to do this, the pMag will actually be at 50 degrees BTDC.

Carl
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I don't know what the root cause is. This intake leak is the only thing I've found out of order so far.
Timing - Been there, done that. Any other suggestions? This darn engine has 160 hrs on it and it's been backfiring on start up since new.
As stated in the OP, the backfire can happen with any combination of ignition being on or off.
 
Full Throttle said:
If your able to crank the engine over a few times before turning on the mag or EI, it clears the engine of residual fuel and should help to not backfire.
Click to expand...
I have thought of that and it might help...but why my engine and not others??
 
mfleming said:
I don't know what the root cause is. This intake leak is the only thing I've found out of order so far.
Timing - Been there, done that. Any other suggestions? This darn engine has 160 hrs on it and it's been backfiring on start up since new.
As stated in the OP, the backfire can happen with any combination of ignition being on or off.
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I do not see how an intake leak can cause this problem. For that matter how do you know you have an intake leak?

Not trying to piss you off, but after many hot starts I finally gave into following the guidance on how to do hot starts. Even so I can advance the mixture too soon and end up with an engine with fuel/air too rich to run. The cure is always to open the thottle, mixture at cut out, and crank. In a few blades the engine purges the excess fuel and runs. At that point an easy advance of the mixture and we are off.

Carl
 
Carl Froehlich said:
I do not see how an intake leak can cause this problem. For that matter how do you know you have an intake leak?

Not trying to piss you off, but after many hot starts I finally gave into following the guidance on how to do hot starts. Even so I can advance the mixture too soon and end up with an engine with fuel/air too rich to run. The cure is always to open the thottle, mixture at cut out, and crank. In a few blades the engine purges the excess fuel and runs. At that point an easy advance of the mixture and we are off.

Carl
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No worries...I'm all ears for fixes...either mechanical or how to operate. Everyone who's been around this engine thinks there's something wrong with how it starts...just trying to get good input.

EDIT: I do like the idea of allowing a few blades to rotate before easing the mixture in. I tend to start pushing the mixture in as soon as the engine starts turning over.
Leak - There is oil dripping from two of the intake tubes at the sump with slight blue stain.
 
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(Small) Induction leaks can easily cause loud popping in the exhaust as a result of combustion instability(s); typically a very lean local condition. It is not a "backfire" or after-fire but the terms are often mistakingly interchanged. Harder to detect than to fix. Keep us informed.
 
mfleming said:
There is oil dripping from two of the intake tubes at the sump with slight blue stain.
Click to expand...
Just for data point, I also have the same M1B at about 72 hours but I don't have the leak like you have. I have some very minor oil leaks but not around the intake tubes
 
mfleming said:
Two things.

First question. Does anyone have advice or a written procedure for replacing the intake tube seals on the sump end of the tube? Photos below.

I have gotten some great advice from a respected member of VAF about trouble shooting my problem but just casting a wider net.

Second question. Can an intake leak on the intake tube cause a massive backfire? The backfires during hot starts have blown out the air filter several times. Always on a hot start. It happens whether I start on the left impulse Slick, right P-Mag or both. It happens when the mixture is being used in as it's trying to start.

I've had experienced mechanics and pilots watch me hot start and find nothing wrong with my technique (I've tried every technique I can think of.

View attachment 68232 View attachment 68233 View attachment 68234
Click to expand...
Sent you a PM (conversation)
 
Michael,
I also had an air-filter blew out on a hot start-up. IO-390, no purge valve or return line.
Technique: no boost pump, WOT, ICO.
Engaged starter and within one or two blades, a bang and a white puff of smoke in front of the cowl. (Have not yet even moved the mix forward for starting.)

Spoke to Don at Airflow Performance about this.
His suggestion for a hot start was to pull the prop through, before starting up, in order to clear the cylinders of residual vapour.

Now for a different scenario: Shut-down.
Was advised not to kill the engine with the P mags (instead of the usual "pull the mix"), as it can reset the timing. Accurate or true?

Back to start-up: Safe to clear, using the starter, while P mags off ?
 
Michael - do you have a sniffle valve fitted ?
GOFF - inaccurate re the shift in P- Mag timing shift as that only applied to earlier software versions.
 
bjdecker said:
…Stuck sniffle valve…
Click to expand...
Damn, that was on my list to check…. I’ll check in the morning. Is the stuck sniffle vale the culprit due to sticking open?
I have a small amount of liquid in the sump…doesn’t seem bad.
IMG_5620.jpeg
 
mfleming said:
Damn, that was on my list to check…. I’ll check in the morning. Is the stuck sniffle vale the culprit due to sticking open?
I have a small amount of liquid in the sump…doesn’t seem bad.
View attachment 68253
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If the sniffle valve is stuck closed, then fuel can pool in the sump. Open will cause a very very slight intake leak, no fuel pooling.

What FI system do you have, and how do you shut down? Best way to do this is to let the engine run to about 800-1000 RPM for a second or so, cut the mixture, pull the purge value (if you have one), let the engine stop, then cut the ignitions.

I had a backfire once, and it's because I tried to start with my ignitions off. Next start it backfired. The engine ignited the fuel that had been sucked in during the first attempt.
 
mfleming said:
Two things.

First question. Does anyone have advice or a written procedure for replacing the intake tube seals on the sump end of the tube? Photos below.

I have gotten some great advice from a respected member of VAF about trouble shooting my problem but just casting a wider net.

Second question. Can an intake leak on the intake tube cause a massive backfire? The backfires during hot starts have blown out the air filter several times. Always on a hot start. It happens whether I start on the left impulse Slick, right P-Mag or both. It happens when the mixture is being used in as it's trying to start.

I've had experienced mechanics and pilots watch me hot start and find nothing wrong with my technique (I've tried every technique I can think of.

View attachment 68232 View attachment 68233 View attachment 68234
Click to expand...
Yes on the intake sump seal! Yes. This very scenario happened to me on the angle-valve IO-360 on my Aviat Husky. Especially when taxiing in after flight when things were hot. More often in the Summer. Also during hot starts. It was backfiring. Blowing out & charring both a Bracket and Donaldson air filters. I replaced the fuel injection servo. I had the injector lines and injectors bench flowed and tested with the fuel servo. I changed the sump fuel drain valve (sniffle?). I replaced fuel lines from the gascolator to servo and servo to spider. I tried optimizing the idle mixture setting. I had excess fuel pooling in my sump, mainly towards the back probably exasperated by being in a 3-point attitude on the ground. I was pulling my hair out. Finally after months of trouble shooting I pulled the intake tubes out of the sump and found one of the orange sump O-ring seals that was pinched, cut and "rolled" on installation. I had had a commercial shop change out all gaskets the year before and the technician who installed the rubber sump O-ring seals at the sump had rolled one on installation. Replace with new paying attention to not let the ring "roll" as the tube was inserted. So as is common with airplane stuff, it was one cheap thing that made the difference after spending a lot of time and money on more expensive stuff.

So by all means you are likely on the right path. Probably on #3 due to the fuel staining but you should be able to check all 4 positions. I would remove all 4 positions. Why not put all new intake seals, 4 flat gaskets at the cylinder and the 4 O-rings at the sump. Your time is more valuable than the cost of 8 new gaskets.

Meanwhile as to your first question, here is how Lycoming describes the proper O-ring seal installation procedure:

Intake Pipe Installation
NOTICE: Make sure the intake pipe of the correct part number is installed for the respective
engine cylinder. Refer to the IO-360-M1B Illustrated Parts Catalog.
(1) Apply a coating of clean engine oil to a new ring seal.
(2) Install a new ring seal in the groove in the oil sump (Figure 1 Below).
(3) Push the intake pipe into the oil sump until it seats.
(4) Attach the corresponding intake pipe to the correct engine cylinder flange with a new
gasket, two bolts, two new lock washers, and two washers. Torque the two bolts to 96 to
108 in.-lb. (11 to 12 Nm).


Intake Sump.jpg

P.S. We have a couple of Fire Boss amphibious air tankers working just South of your area scooping out of the Snake river, when they're not grounded by IMC smoke conditions.
 
jliltd said:
Intake Pipe Installation
NOTICE: Make sure the intake pipe of the correct part number is installed for the respective
engine cylinder. Refer to the IO-360-M1B Illustrated Parts Catalog.
(1) Apply a coating of clean engine oil to a new ring seal.
(2) Install a new ring seal in the groove in the oil sump (Figure 1 Below).
(3) Push the intake pipe into the oil sump until it seats.
Click to expand...

Curiousity question...

Step (2) above caught my eye. I've not personally R&R'd an M1B tube, but for other models with a horizontal intake sump, the o-ring is installed on the tube, between two flanges, then the assembly is pushed into the sump. And note the drawing below, from the M1B parts catalog. The M1B does not have the two flanges shown in the parts drawing?

M1B Intake Tube.jpg
 
jliltd said:
Yes on the intake sump seal! Yes. This very scenario happened to me on the angle-valve IO-360 on my Aviat Husky. Especially when taxiing in after flight when things were hot. More often in the Summer. Also during hot starts. It was backfiring. Blowing out & charring both a Bracket and Donaldson air filters. I replaced the fuel injection servo. I had the injector lines and injectors bench flowed and tested with the fuel servo. I changed the sump fuel drain valve (sniffle?). I replaced fuel lines from the gascolator to servo and servo to spider. I tried optimizing the idle mixture setting. I had excess fuel pooling in my sump, mainly towards the back probably exasperated by being in a 3-point attitude on the ground. I was pulling my hair out. Finally after months of trouble shooting I pulled the intake tubes out of the sump and found one of the orange sump O-ring seals that was pinched, cut and "rolled" on installation. I had had a commercial shop change out all gaskets the year before and the technician who installed the rubber sump O-ring seals at the sump had rolled one on installation. Replace with new paying attention to not let the ring "roll" as the tube was inserted. So as is common with airplane stuff, it was one cheap thing that made the difference after spending a lot of time and money on more expensive stuff.

So by all means you are likely on the right path. Probably on #3 due to the fuel staining but you should be able to check all 4 positions. I would remove all 4 positions. Why not put all new intake seals, 4 flat gaskets at the cylinder and the 4 O-rings at the sump. Your time is more valuable than the cost of 8 new gaskets.

Meanwhile as to your first question, here is how Lycoming describes the proper O-ring seal installation procedure:

Intake Pipe Installation
NOTICE: Make sure the intake pipe of the correct part number is installed for the respective
engine cylinder. Refer to the IO-360-M1B Illustrated Parts Catalog.
(1) Apply a coating of clean engine oil to a new ring seal.
(2) Install a new ring seal in the groove in the oil sump (Figure 1 Below).
(3) Push the intake pipe into the oil sump until it seats.
(4) Attach the corresponding intake pipe to the correct engine cylinder flange with a new
gasket, two bolts, two new lock washers, and two washers. Torque the two bolts to 96 to
108 in.-lb. (11 to 12 Nm).


View attachment 68255

P.S. We have a couple of Fire Boss amphibious air tankers working just South of your area scooping out of the Snake river, when they're not grounded by IMC smoke conditions.
Click to expand...
Thanks for the story and written installation instructions. Hopefully my O rings and new intake gaskets will be here in a couple days. Gives me more hope that I’m onto a fix.
Which manual is the installation instructions from?

I’ve seen the Fire Boss tankers on adsb working that fire. We had a couple scooping water out of Wallowa lake a couple weeks ago. They were departing right over my house.
 
DanH said:
Curiousity question...

Step (2) above caught my eye. I've not personally R&R'd an M1B tube, but for other models with a horizontal intake sump, the o-ring is installed on the tube, between two flanges, then the assembly is pushed into the sump. And note the drawing below, from the M1B parts catalog. The M1B does not have the two flanges shown in the parts drawing?

View attachment 68262
Click to expand...

The O-ring fits in a groove in the collar shown that is part of the tube. you do have to be careful not to push the tube into engine too far. It will go all the way into the plenum and you will damage the O-ring trying to pull it back out.
 
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DanH said:
Curiousity question...

Step (2) above caught my eye. I've not personally R&R'd an M1B tube, but for other models with a horizontal intake sump, the o-ring is installed on the tube, between two flanges, then the assembly is pushed into the sump. And note the drawing below, from the M1B parts catalog. The M1B does not have the two flanges shown in the parts drawing?

View attachment 68262
Click to expand...
Dan. Come to think about it I do remember the O-ring flange on the tube and installing the ring on the tube first. Then inserting the tube into the sump. So maybe Lycoming has two different designs. Mine is not an M model.
 
My IO-360 hot start procedure is fuel pump on, mixture in cut off, throttle pushed in about an inch and crank until engine fires up and then push mixture in. Works good every time and no backfires or flooded starts
 
I used to pop the intake on the RV-8 from time to time on hot start and the “fix” was a less aggressive throttle opening. Not sure how wide you are going with your technique, but mine was WOT. I reduced that to 25% max and never popped again. Start cranking with throttle closed and open to 25% max, it it hasn’t started by the time you have reached that point, just keep cranking…. 1/4 throttle is plenty of airflow to clear the cylinders.
 
rv8ch said:
If the sniffle valve is stuck closed, then fuel can pool in the sump. Open will cause a very very slight intake leak, no fuel pooling.
Click to expand...
Yep - that will do it.

A functioning sniffle valve will drain a small amount of fuel out of the intake after shutdown. I keep a standard drip pan under the engine for this, the small blue stains provide witness marks.

Is your sniffle valve drawing any fuel after shutdown?

Remember the sniffle valve’s other function is to drain water if you have the plane sitting out in the rain with no cover over the intake.

Carl
 
Toobuilder said:
I used to pop the intake on the RV-8 from time to time on hot start and the “fix” was a less aggressive throttle opening. Not sure how wide you are going with your technique, but mine was WOT. I reduced that to 25% max and never popped again. Start cranking with throttle closed and open to 25% max, it it hasn’t started by the time you have reached that point, just keep cranking…. 1/4 throttle is plenty of airflow to clear the cylinders.
Click to expand...
I use the similar hot start technique. Throttle was about 1/4 forward. My engine cranked over like it's a slightly rich condition and went into high idle (1200-1300 rpm) as the rich condition became leaner. Then I moved the mixture up and slowly pull the throttle back to fast idle (900-1100 rpm) to prevent the engine from stopping.

If the engine died after starting then I used the same technique after running the fuel pump for a couple of seconds.
 
Regarding the sniffle valve: The tail low attitude in conventional geared aircraft allows significant fuel pooling aft of the sniffle due to it not being positioned at the resultant low point of the sump.
A local -7 had the exact issues as the OP.
 
I always hot start with:

1. No fuel pump priming,
2. Throttle barely cracked,
3. Mixture idle cutoff.

Then as I crank and hear the engine make an effort to start I slowly sweep the mixture from ICO in towards rich until the engine starts running. Depending on how it sounds I might increase the throttle another 1/4" and if it seems really grumpy will turn on the boost pump until everything sounds normal and the engine idles smoothly. This works exactly the same for a cold start except for the addition of fuel pump priming with mixture full and a sweep of the throttle in and then back out prior to the start sequence 2 and 3 above.

After the first cold start of the day on a cross-country I only use the fuel pump on takeoff and landing but never again for priming.
 
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I suggested the sniffle valve as the culprit since it was the case when my -7 developed an “after fire” (popping when throttle was closed abruptly).
The little ball in the valve had become stuck due to the fuel/oil mixture pooling in & around the valve seat, baking in the heat of the exhaust cross over tube. Cleaned out the valve with Hoopes #9, Birchwood-Casey Gun scrubber. Added a heat shield on the exhaust cross-over tube in front of the sniffle valve, and it’s been trouble free (pop-free) since.
 
No two ways about it....number one source of back fires (which is a lean event, by definition)...intake leaks.

Fix that.

Easy to find with a little diligence. First find the lean plug, then inspect the intake tubes and almost guarantee you will find poorly seated tube, damaged gasket, damaged tube or face of a tube...anyway...Yes. Leaky intake, farts, stumbles, backfires, pops, even surges.


Steve.
 
Here’s my follow up. Replaced the intake tube O-rings on #1 & 3 cylinders. Both were trashed, looks like were rolled from pushing them in too far and damaging them pulling them back out…chunks missing.
Installed the new O-rings and that richened the idle mixture considerably. Hot starts are easy now but that may be due to starting procedure changes as well as no intake leak.
 
mfleming said:
Here’s my follow up. Replaced the intake tube O-rings on #1 & 3 cylinders. Both were trashed, looks like were rolled from pushing them in too far and damaging them pulling them back out…chunks missing.
Installed the new O-rings and that richened the idle mixture considerably. Hot starts are easy now but that may be due to starting procedure changes as well as no intake leak.
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Exactly my experience based on the same symptoms. The one-piece intake tube design is nice as long as the sump o-ring seals are paid attention to during installation. Glad it worked out.
 
I removed the lower cowl to perform oil change and I took the opportunity to inspect the intake tubes. The #4 tube showed a smudge of oil that was seeping for a while. I'll keep an eye on this to see if more oil was leaking.
 
mfleming said:
Here’s my follow up. Replaced the intake tube O-rings on #1 & 3 cylinders. Both were trashed, looks like were rolled from pushing them in too far and damaging them pulling them back out…chunks missing.
Installed the new O-rings and that richened the idle mixture considerably. Hot starts are easy now but that may be due to starting procedure changes as well as no intake leak.
Click to expand...
Gotta ask - who built your engine?
 
I've come into the discussion a little late however this has been an interesting thread to follow as I recall exactly these kinds of issues years ago when I was working on the HIO-360's in the Hu300's. When fitting the intake tubes we were taught to dip the tube (with the red o-ring installed) into some white spirits and then carefully install the tube onto the engine. You couldn't soak the red o-ring in the white spirits as it tended to swell if left there, but the quick dip was sufficient to give you the lubrication needed to install the tube with ease. As these engines were known to give issues with intake leaks like the OP's example, we would apply high-temp silicon sealant around the base of the tube at the sump end to ensure no intake leaks. It seemed to work well.
 
I took an input tube off to install an inverted oil line. The O-ring on the tube sits close to the inside edge of the hole in the case. The inside edge of the hole is not chamfered like the outside edge and has a small radius edge. It’s very easy to get the tube It in too far as you are connecting the tube to the head. The tube and oil lubricated O-ring slide into the chamfered end easily. Go a 1/4” too far and no amount of lubrication will protect the O-ring as it slides across the edge being pulled back. Fortunately I bought an extra $14 O-ring. If I did it again I would hose clamp a stop to the tube before I removed it to keep it from falling in.
 

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