Back firing

[Rick C]

My engine has started to back fire and will not run long. Has caused muffler damage. Compression. 62 - 66 - 38 - 62. Burnt exhaust valve? Rick

[Mitch]

I would do a leak down test next. This will give you an idea of the exact issue.

Welcome to the site Rick

[DaWizard]

Hey Rick C, WELCOME to the VFF!!

Mitch is correct.

[Mitch]

I always refrain from tear down and exploratory surgery. It's best to do some testing before hand. I recently had one that showed a bad valve in one cylinder and excess pressure coming up through the crankcase in another. Here it had a ring issue that i might have missed without the leak down

[George Miller]

I did that one time and had to put it all back together to find the knock.
George

[CM2]

Mitch is talking about a 'wet /dry' compression test..make a set of compression readings,then squirt some oil in the spark plug holes and do it again..if that 38 reading doesn't come up its a valve,if it does,its rings..

[Mitch]

Actually i'm not..

I am talking about a leak down test

[BNCHIEF]

This would be a good explanation for the tech section.

[CM2]

Excuse me...wet/dry is effective for diagnosis of the 38 pound cylinder,odds are the heads coming off

[tbirdtbird]

leak down is the way to go, and this prolly is a good time to put this forth on the VFF. Mitch is the king of leak down
It could be as simple as a valve lash problem

Engine new to you? Been happening long? Been driving it anyway? Work recently done?
Bore scope might let you get a look in there.
But start w/ leak down

One of the problems with the 63# flywheel is that you could have a weak cylinder and you might not know it for a while; that massive flywheel is just gonna keep churning away and glide right past the weak cylinder. Were the FW lighter, you'd be more likely to notice the imbalance, especially in a 4-banger

Keep us posted we'll walk you thru it

[BNCHIEF]

Bore scope is one of the things in my toolbox when I go to check out a car.

[Tom F]

Why doesn't someone explain the leak down test for us that has never done it.

[BNCHIEF]

Here is a good explanation Tom

[Mitch]

Thanks Chief, that gives a good idea of what it's about. I use shop air sometimes using a hollowed out spark plug. It can be regulated by pinching off the air line.
The actual tool is nice though, but rudimentary works

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[BNCHIEF]

I understand Mitch poor guys have poor ways but it spruces it up a little in that cadillac toolbox you have.

[tbirdtbird]

Basically you block the wheels/set the ebrake, bring a cylinder to TDC on compression stroke, apply air, and listen for where the air is leaking out. That is the quick version.

I have several different size plugs that I have busted out the porcelain and welded in an air fitting

[Mitch]

The one i pictured was brazed

[tbirdtbird]

haha you braze, I weld

[Tom F]

Thanks bnchief. Now I understand what their talking about. This is sort of like useing a kuhlman guage to test inside natural gas lines.

[BNCHIEF]

You are most welcome Tom some of us here wrongly assume at times that every one understands what we are talking about. There is a lot of expertise here and Mitch wants what is posted here to be correct and tried and true not just someones theory. With that said thanks for asking that helps some of us understand what others need. Mitch is building a great area to check for help in the different sections he has put together for all to access. There are many here who are in the everyday business and have much to contribute so read some of those sections as well and enjoy the vff great to have you here. Do not be afraid to post something lest you might feel no one will listen, that is important to grow this forum and help others I myself am a newbie to Model A fords and have learned much and enjoyed every minute of it. Have a great day.

[BNCHIEF]

Ok Mitch did you make this for Ed.:rolling:rolling

[Tom Wesenberg]

It's also possible you have two problems going on, so do a simple spark check to make sure that's good.
Hold the coil wire 1/4" from a head nut and check for a hot blue spark.

[CM2]

After you yard off the head and find out why your pulling 38 pounds on that one hole..wet/dry,leakdown,whatever the heads coming off..

[tbirdtbird]

suppose he just has a tight valve

[H. L. Chauvin]

1. First comment was: "My engine has started to back fire and will not run long. Has caused muffler damage. Compression. 62 - 66 - 38 - 62. Burnt exhaust valve? Rick

2. Question A: Was your engine possibly running well before ...... then maybe engine was allowed to sit for a spell without running ...... then when engine started again ..... "my engine has started to backfire and will not run long".? ............ and/or,

3. Question B: What may have possibly happened between the time when your engine was not backfiring ......... and afterwards after your engine started to backfire?

4. One or more sticky valves in a Model A can make a Model A engine sound like a 30 caliber machine gun firing in a 55 gallon drum ..... a sticky valve can remain slightly open & can also render low compression reading.

5. If it is a simple sticky valve ...... it would be a very simple vintage quick fix to remedy without unscrewing bolts and studs.

[CM2]

simple perhaps..for a farmer fix,but to actually repair you need to see the root cause and examine all potential issues arising from it.

[Rick C]

I am listening ! Rick C

[DaWizard]

I wonder if there has been any use of MMO, and if not, why not? Granted, you do need to find the cause of the low cylinder, but if it just started like it sounds, I'd say something has collapsed.

Was there any note before this started, maybe like running rough, or starving for power, or falling flat on it's face? Say the intake manifold has a leak causing one jug to run lean, that would burn an intake valve.

Looks like Henry and I were typing at the same time.....a simple check would be to pull the intake/exhaust manifold. 4 nuts and washers, to look into the valves and determine if one is hanging open in that jug. It cost a whole gasket.

[Tom Wesenberg]

A slow to close valve could cause a low compression reading. I'd do the leak down check to see if you hear air leaking out the intake, exhaust, or oil fill pipe. If the leak down checks OK, then I'd suspect a slow to close valve, and I'd put a can of Sea Foam in the oil, and another can in the gas, to see if that clears the problem.

[tbirdtbird]

all of the above.

we can advise better once the leakdown is completed

[H. L. Chauvin]

Relaying Problems to Mechanics and Doctors:

I went to one of these after hours doctors last year and told him I had just visited my druggist and my druggist said none of his "over the counter" medicines could cure what I had ....... and my druggist said after hearing my symptoms, I needed to visit a doctor to get some doctor prescribed antibiotic medicine.

This senior doctor replied that from his many past experiences, druggist are always 100% correct in diagnosing patients.

I asked this doctor why was this?

He responded that when we visit a druggist we go into minute details, relating the before and after conditions, tell the druggist absolutley "everything".

But this doctor added that when we visit a doctor, we tell him "very little" or "almost nothing" ..... because we have a profound fear that the doctor will put us in the hospital.

Appears describing Model A mechanical problems, and asking Model A Forum mechanical questions on Model A Forums, some questions are somewhat similar.

Like, "Hey, my Model A won't start ..... what's wrong?"

Maybe at times, we all need to be reminded that Model A Forums do not operate hospitals! LOL

[Mike V. Florida]

Welcome Rick C.

[BNCHIEF]

Wonder if my doctor can prescribe new parts for my model A and if my medicare will pay for them, Mind altering comes to mind it puts me in a good mood.

[DaWizard]

X10!!

[CM2]

The only way to correctly fix an issue is to put your finger,and eye, on the root cause. I'm all for getting lucky with snake oil or whacking it with a hammer and calling it good,if its an 'ice cream runner' Id try it too..but there is only one way to do it right,

[Chevmn56]

X2

[H. L. Chauvin]

Something tells me Mr. Rick C. already suspects that the 38 low reading indicates a possible combustion chamber leak through a non-sealing accompanying valve.

In lieu of internal combustion of a fuel mixture occurring with less noise inside an enclosed, sealed combustion chamber ......ignited fuel, i.e., combustion is also occurring much louder outside of the combustion chamber ...... and raw non-ignited fuel was pumped inside the muffler such that afterwards, combustion within the muffler caused enough force to damage the muffler.

Backfiring suspects could be: Possible burnt valve leaking, possible sticky valve leaking, possible damaged valve spring causing valve leaks, ignition misfires, improper ignition of fuel timing, or something similar.

Usually sticky valves occur after engine is not operated for some time.

When engine was last operated, and engine cut off, over time, this sticky valve remained open to outside air through the tail pipe; hence, valve stem rust can occur with ambient heat and cold condensation causing rust; and/or volatile petroleum molecules evaporating into outside air and causing sticky varnish on valve stems and valve guides.

Maybe because of our high humidity in our coastal area, valve relatedbackfiring is most often caused by engines not operating for a spell associated with easy to fix sticky valves.

[Mitch]

A little MMO will fix it

[Rick C]

Thanks. Best way to determine stuck valve and remedy

[Tom Wesenberg]

OK, now for part two of the problem. Why does it not run long?

[DaWizard]

Oh, now THAT is the easiest to answer. The gas cap vent is clogged! Duh!