Franklin Partial Engine Failure- Loose Intake Manifold

[blimpy]

Inflight Partial Engine Failure Franklin 150 14-13-2 Jan 13, 2014

Reason: Fuel Starvation Due to Loose Intake Manifold ( 4 of six cylinder head bolts missing !)

Presumed Causes: A. Improperly Installed Replacement Cylinder (s) -
B. Failure to Check Manifold Bolts Per Franklin Operating Manual 25 hour list ( implied)
C. Intake Manifold Security not on Pre-Flight Check List.

Note Well : Franklin OH/Service Manual spells out sequence for cylinder installation :
1. Install Cylinders with base nuts "snugged up" only this means able to be moved !
2. Install Intake Manifold to obtain proper cylinder alignment
3. Finally, Torque Cylinder Base Nuts

-->>> Failure to do it in this order leads to loose or lost intake manifold to cylinder head bolts, sometimes to cracked
or broken intake manifolds <<<---

A partial engine failure due to a loose intake manifold Monday found me using my emergency landing
check list and procedures yesterday in what was Not a drill.

Engine began running roughly 15 nm from my destination, requiring full carb heat and tolerating no leaning
to yield only 2000 rpm at full throttle at 4500 feet approx 15C/59F. Any thing else and it simply would not run.

All gauges reading normal.. oil press/temp, CHT, Fuel Pressure.
Alternate tanks.. no change. Differential mags.. no change.

Since I was able to maintain altitude and reasonable flying speed, I opted to continue 15 nm to my destination
where I knew the field and many usable off field landing sites.

Circled field paying out altitude after warnings and position reports on the CTAF. Landed without incident,and was able to taxi to the shop.

In other circumstances this well could have resulted in a forced landing in whatever place was available.

---

In the shop we spent some hours inspecting the fuel system, flushing, collecting, and testing.
Found nothing.

Plug Checks and Compression Tests - also nothing.

Off came the prop and cowl to look at all the induction system seals.. and bingo... the missing cylinder head bolts
couldn't hide anymore.. and guess what ? You could rock the left intake manifold like it was on hinges !

Not nice. Makes me feel stupid, because even though I routinely check the Exhaust Manifolds and Mufflers for security
I never once thought about grabbing the Intake Manifolds and giving them a tug ! :mrgreen:

Nor in my occaisional tours around the engine with a wrench checking for loose bolts on the pan or engine cover did I ever check my manifold bolts.

Moral : Don't assume that this got done at the annual no matter how few hours you've flown since then !!!
Don't

 

[blimpy]

Intake Leak Warnings I Missed:

Warnings I misunderstood ! Last two or three cold starts ( 40-70 degrees F) .

The Following were unusual.
I mistook these Warning Signs of Lean Mixture :

A. Popping on Start Up - thought it was due to over priming/ flooding when I wobble pumped with throttle open by mistake
B. Rough Running on Start Up - thought it was carburetor Ice
C. Rough Running on Start Up - thought it was plug fouling

D. required more than 1. starting attempt each with a cycle of 3-4 throttle pumps to prime. Normally starts on 1 try.
B. Required full carb heat to run when cold. I mean just to run at all.
C. Required 2-3 minutes of high idle with full carb heat to run smooth. Usually runs smooth and idles low right away.

All The Above were actually due to lean mixture caused by loose manifold.

A 6 cyl EGT would have shown a developing problem right away !


On the last flight I had to run full carb heat during taxi to run up.. which together with extended idle time
before taxi added up to almost 5 minutes. That's an almost implausible amount of Carburetor Ice . Almost.
.
This was all very unusual, as the engine generally starts first try, and I adjust revs to 900 quickly while
I am watching oil pressure and fuel pressure come up.

After rough engine taxi... engine smoothed out, ran up normally with mag checks at 1700 and "full" static run-up
to 2500 rpm for 30-45 seconds with no problems.

Take off and climb out was "normal" although only 700 fpm indicated when I expected initial 1000 fpm on cold day.
Climbed to 4500 feet and cruised ok for 15 miles.. then crapped out.

Wishful thinking does not = adequate pre-flight or adequate maintenance !

Being in a hurry- lazy- too embarrassed/cheap to call a mechanic or failing to investigate small problems
can put you down in a field, golf course, or shopping center and ruin everything except your funeral.
:roll:

 

[kitepilot]

Imagine that...
We also found several missing bolts (both, manifold intake and exhaust) when we inspected my engine for the annual. I did also notice 'differences' in start-up and idle since I got the bird, which I didn't really thought of too much!

My wrench guy told me that Franklin(s) were notorious for popping those bolts missing, which stroke my odd because the guy was unfamiliar with Franklin(s) until he came across my 14-13. Obviously the guy has been doing his homework.
I didn't ask him to elaborate.
Now I will...

 

[blimpy]

Kite.. go to FranklinParts.com Susan Prall has a page describing how and why these
intake manifold bolts go missing, and about intake leaks in general.

It is all about that torque sequence.

First.. manifolds to cyl heads that establishes the proper alignment of the manifolds to the intake ports on the heads

Second.. only after that has been done, can you torque down the cylinder base nuts.

Susan supplies new bolts with "shake proof" washers, new gaskets, new flanges ( if you need them) new flange packings
( you need those ! ) and new tube that connects the balance tube at the front of the engine.


...

 

[blimpy]

Most mechanics - except older ones - don't know about franklins.

So, you have to educate yourself, lest you be led astray ( making multiple stops at your ATM).

The Franklin Overhaul and Service manual isn't long or hard to read.
But all the most important stuff is in there.

Being familiar with it can prevent something stupid happening.
Look at how the engine pan and the accessory case mate up, and how those bolts get tightened
or the cylinder installation sequence.

small stuff, but important.

I didn't understand how important until yesterday

 

[SoCalPlaneDoc]

Franks have a 1 piece manifold runner that doesn't tolerate misalignment - it hurts that the engine cylinder alignment changes with temp changes too..

that bit about tightening the intake manifolds *before* tightening the cylinder base nuts is critical. I also used a tall bronze nut with a bronze palnut on each stud.

rough running at idle but not off-idle is a dead giveaway of intake manifold leak on carb engines. watch for seals between the manifold sections too...

 

[blimpy]

good tips. Mechanics are installing a complete new set of intake system seals and balance tube seals.

I'm afraid intake leaks were never on my radar - ever.