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post #1 of (permalink) Old 12-25-2000, 08:32 PM Thread Starter
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Cleaning Combustion Chambers....


This sounds like another one of those Urban Legends.....

Pouring 'Oil' (ATF, Brake Fluid, Antifreeze, Rubbing Alcohol, Beer or anything else nasty) down the intake...

But I've seen people do this with my own eyes.
Bad medicine....

Let me categorically state for the record,
1. I have personally worked on 10's of thousands of engines.
2. I have probably seen every ailment that can befall a gasoline engine.
3. I have worked on hundreds of engines that 'Ran On' after you turned the key off.
4. NOT ONCE, in the twenty five years I've been doing this for a living, have I EVER seen an engine actually run backwards.

I've hear about it from every tobacco juice dribbling old timer I've ever ran into,
And every 'Other Side Of The Tracks' "Mechanic" (I use the term loosely) has his favorite 'run backwards' story to tell, but I have never actually SEEN an engine turn backwards...

If your 'Mechanic' mentions 'Run Backwards', RUN LIKE HELL!!
Find someone that can diagnose the real problem, instead of trying to fix an imaginary problem, and doing more damage....

Most likely what is happening is what is more correctly referred to as 'Dieseling'.
It's actually a form of detonation in most cases.

The engine CAN NOT run backwards.
Simple physics won't allow it.
Even if you could stop the engine, and crank it backwards in the split second after you turn the key off, which you can not, it would not fire.
No fuel supply in the exhaust tract to make it run.
The few unburned vapors in your exhaust do not supply the oxygen it would take for the combustion process.

The engine is actually running forward, or clockwise if you are standing in front of it looking at it.
The 'Rattle' or 'Knocking' you hear is similar to a diesel truck because essentially the same thing is happening in the chamber as a diesel engine.

Only one problem with that, Gasoline engines are dainty, fragile things compared to a diesel engine, and the pre-ignition or compression combustion that is happening is damaging your engine.

Here are the basic ways to 'Diesel' a gasoline engine...

The piston is not close enough to the top of the cylinder to have proper combustion in the chamber when an ignition source ignites the fuel mixture, and tries to force the piston back down the way it came, instead of letting it roll ahead over...
That is where the big 'KNOCK' comes from, the piston getting hit with a combustion 'Hammer'.
There is enough momentum in the rotating assembly to have the piston go ahead over, but the burn happened too early, and there is just enough force to get the crank to roll the next cylinder over.... Ect. Ect. Ect.....

The source of the ignition could be anything from a piece of a broken ring or spark plug stuck in the head of a piston, or a spark plug of too hot of a heat range, or a metal burr from a degrading head gasket or bad machine job of the block or head, or just plain old carbon buildup raising the cylinder compression so high the fuel and air mixture compression combust or detonate, or ridges of soft suit in the chamber that still glow....
(Compression combustion isn't unusual the case in pre-ignition)

Then there are the other ways to 'Diesel' a gasoline engine...
This consists of the combustion being too late, about the time the piston reaches the top of the cylinder. This type of 'Dieseling' is very destructive. It's also called 'Detonation Run'....
The piston reaches Top Dead Center, and the cylinder is full of charge (Gasoline vapor and air),
Then something sets the mixture off...

1. Bleed through of electrical current to the ignition. Just because you turned the key off doesn't mean you have taken all of the power from the ignition. (this is an incomplete, or weak burn, and carbons the crap out of the combustion chamber and plugs up catalytic converters)
2. Red hot suit from a too rich fuel mixture. Lots of ways to have fuel mix too hot.
3. Red hot hard 'carbon' from too rich of a fuel mixture, or incombustible materials in the fuel.
This carbon can build up in the chamber and cause compression fire, see next line.
4. Too low of a flash point of cheap fuel. Simple compression can fire some gasolines.
That's why gasoline engines are about limited to 10:1 mechanical compression, and some diesels have compression ratings of 50:1 or more.
5. Too hot of heat range plugs. Plugs are glowing after you turn the engine off.
6. Debris glowing in the chamber, like broken rings, broken spark plug electrodes, ect.
Those things make nice ignition sources.
7. Bad machine work on the block or heads. Sharp edges will glow red hot, and become an ignition source (like the edge of a knife in a fire, the edge will glow first).
8. Cam timing problems.
Usually flat lobes not letting enough charge in the chamber for complete combustion, and flat lobes will allow charge to 'settle out', meaning that the fuel and air in the intake runner are not used, so they have time to separate, and then you get raw, liquid fuel turning into carbon in the chamber.
With the engines equipped with alloy cam chain gears, or nylon cam gear teeth, the timing chain can slip, or a timing chain with 100K on it, will allow the can timing to be off sufficiently to cause problems with combustion...

Remedies for the above described problems...

Get your self a windshield washer tank, one of the kind that goes Squirt, Squirt, Squirt....
Mount a nozzle on the air cleaner stem, pointing down the carb throat.
While you are at HIGHWAY SPEED (not idle, like most people say) push the button and add water to the combustion process!
The live steam will scour the inside of your combustion chambers, although it may plug up your catalytic converter and muffler with pieces of hard carbon.
This way is cheap, easy to do, and VERY effective...
Don't stand on the button, just squirt a few times, go down the road a little way, and squirt again.
Do this over three or four days time, or until black water quits running out of the exhaust.
(Black water, not the normal condensation moisture that leaks from cat equipped vehicles)

Moving down the road, at part throttle, the engine and combustion chambers are hot enough to make good use of the water, turning it to steam.
The windshield washer sprayer will keep you from adding too much water and 'hydraulic locking' things up (lots of bent parts when you do that!).
The higher RPM will keep good flow through the engine, and whisk away most of the dislodged carbon and residue from gasoline.

The people behind you won't appreciate the crap that comes out your tailpipe!!
Good remedy for tailgaters!!

Some of the crap will find it's way into your oil (carbon, deposits, acids and moisture), so be sure and change your oil at the end of the week you clean things out.

This includes brake fluid, automatic transmission fluid, ect.
All you will do is add more hard carbon, and plug up the exhaust system, causing MORE problems...
Your exhaust system was designed to handle VAPOR.
Not oil, solids or anything like them....
Also take into consideration that oil does not compress, and the vapor point is much higher than water.

Can you say, BENT RODS? I knew you could.....

The first law of Hydraulics, Liquids do not compress. (but water turns to steam!)
If you pour oil down your intake, even small amounts, you are asking for serious trouble.
I've seen pistons with the entire center top blown into the oil pan.
I've seen connecting rods bent so badly they look like someone screwed the ends together.
I've seen crank and rod bearings compressed completely out of the caps.
Why take the chance?

As far as foreign objects stuck in the top of the piston, or bad machine work, there is nothing you can do, short of re-machining the block and replacing pistons.

Cheap gas, or crap in the gas should be easy to solve, but I'm going to state the obvious...

The same with too hot of heat range spark plugs, GET COOLER PLUGS.

Cam timing problems can cause this problem...
Change your cam, lifters, chain and gears, and check all the rockers, push rods, valve stems, springs.
No excuse for polluting the atmosphere (MY BREATHING AIR !!) and using WAY too much fuel when all of this is pretty easy to check with a compression check, and a leak down test.
Takes maybe an hour and $100 worth of tools...

Well, I've spent an hour writing this, hope it helps someone....

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post #2 of (permalink) Old 12-25-2000, 09:30 PM
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Re: Cleaning Combustion Chambers....

good post.. but could someone tell me a story of an engine running backwards.. this is new to me.. would like to hear it.. and get a laugh..
thanks TR...

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post #3 of (permalink) Old 12-25-2000, 10:18 PM
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Re: Cleaning Combustion Chambers....

My '89 258 used to run-on after I'd kill the ignition. It annoyed the hell out of me so I'd put it in first and pop the clutch. My Wrangler would promptly jump backwards and stall out. Putting it in 4th or 5th would give less of a jolt, but it still jumped back. If I had something close to the rear bumper I'd stick it in reverse, so the Jeep would jump forwards instead. All things being equal I'd have to say the engine was spinning backwards; I'm simply not mechanically inclined enough to figure it any other way.

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post #4 of (permalink) Old 12-25-2000, 10:49 PM
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Re: Cleaning Combustion Chambers....

Well, not a jeep engine, but I have had a 2 stroke motorcycle engine run backwards. I kick started it like normal, and it was running normally, but when I put it in gear and dumped the clutch to take off, it shoved me into the gas tank (big OUCH!) and the bike and I went over. It was a Yamaha RT360, single cylinder 2 cycle. Like I said, not really relevant, but it was running backwards.

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post #5 of (permalink) Old 12-25-2000, 11:00 PM Thread Starter
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Re: Cleaning Combustion Chambers....

I've heard that before.

Try letting the vehicle idle, and popping the clutch in 1rd gear....
You will get the same effect.
It's gear lash and the recoil from the chassis energy unloading.

You have to figure there is around 25 horsepower stored in the rubber mounts, frame twist, axle mounts and springs, ect.
When you load them by popping the clutch, with a manual trans giving mechanical gear reduction to the energy loaded into the chassis, then the engine stops abruptly, all of that energy that was transferred to the drive train and chassis unloads.

Now, stay with me here, cause this is where it might get confusing....
If you twist something up, like a rubber band, forward, and you let go all at once, it unloads 'backwards', or opposite of the way you loaded it.

The 'backwards' movement is the energy stored in the drive train and the chassis.
It was loaded 'forward' by the engine, and unloads 'backwards' when the engine power is stopped.
Everything from the rubber of the tires, to the twist in the axles, to the twist in the drive shaft, to the energy stored in the rubber mounts and vehicle springs....

Every chassis will absorb anywhere between 25 and 50 horsepower on a clutch 'Pop'....
All of that energy is returned, and unloads very quickly, and can get your attention, just like when you pop the clutch.

Make sense now?

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post #6 of (permalink) Old 12-25-2000, 11:54 PM
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Re: Cleaning Combustion Chambers....

I'm almost afraid ive learned too much today, that whas one heck of an explination and answer hope you arent too upset cause im gonna email you with every question i ever come up with that seem unanswerable!!!!!

if it aint broke, break it so you can learn to fix it
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post #7 of (permalink) Old 12-26-2000, 12:21 AM
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Re: Cleaning Combustion Chambers....

Teamrush. I agree with you on everything you stated about gasoline engines, however, diesel are also very fragile when it comes to detonation problems. Two cycle detroits are fairly sensitive to leaking blower seals, ie when lubricating oil is introduced to the inlet airflow, preignition of the lube oil will cause problems. The connecting rods on trunk pistons will crack through length of the oil galley.
I think that the four cycle diesels would be damaged just as easily, but usually the only source of oil is the turbo, and the turbo that is leaking a sufficient amount of oil to cause a problem will soon enough sieze its bearings, making that a self limiting failure other than a catastophic compressor failure.
And lastly, two cycles run all too well backwards! the air flow through the engine is still the same. As long as the fuel is gravity supplied or the lift pump is nondirectional, fuel will be available. The big problem is the oil supply, not to many oilpumps will supply oil to the bearings when running backwards.


post #8 of (permalink) Old 12-26-2000, 12:54 PM
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Re: Cleaning Combustion Chambers....

can you clean the chambers by having someone run the rpm up or should you use the setup for the road that you talked about so that it would be under load when injecting moisture to the intake.

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post #9 of (permalink) Old 12-26-2000, 01:16 PM
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Re: Cleaning Combustion Chambers....

<font color=blue>Well, I've spent an hour writing this, hope it helps someone....</font color=blue>

Damn right. Thanks for writing it, answered a lot of my questions.

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post #10 of (permalink) Old 12-26-2000, 02:20 PM
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Re: Cleaning Combustion Chambers....

Whatever happened to that stuff that I believe GM marketed back in the 70s. It was a combustion chamber cleaner, you would pour the stuff into your intake. Great gobs of smoke! Haven't seen it in years.

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