Damage from holes in muffler???

[Dmace]

the O2 migration is burning valves when you shut the cylinders off.

There is a little truth to the problems of back pressure building up from the exhaust "when you shut the cylinders off". That is the big difference, when you have an exhaust big enough for a huge V8 big block and only have 4 cylinders pumping out exhuast. The O2 sensor ONLY messures the proportion of oxygen (O2) in the exhuast. Also, you will only burn up the valves if you are running real lean which can happen with an exaust leak before the O2 sensor that causes the computer to get a false reading. There is no worries about this on a tractor. A new Corvette yes, tractor not so much.

There is no harm in having a hole in a muffler except for a slight loss in engine power and the biggest thing I would be worried about is water getting into the cylinder from these holes. Is it a vertical muffler or horizontal? Vertical - I would worry about the water problem, Horizontal-not so much.

 

[zzvyb6]

see

(WO/1980/000167) EXHAUST SYSTEM

and many, many others. Pay attention to claim F:

When you get an anti-node at the end gap you get the negative pressure wave component. Not confined to Big block. All piston engines running at a small rpm band need to deal with this. F1, Indy car, Mack truck and John Deere. Jet engine same deal when supersonic flow because it is not sequenced by a piston/exhaust valve pulse but by speed of sound.

 

[aczlan]

I am probably just feeding the troll here, but here it goes:

Well, for example, in case you are wondering why the new Corvettes don't yet have Active Fuel Management, its because the exhaust is tuned for a flow so free that the O2 migration is burning valves when you shut the cylinders off.

if that is the case why does GM offer AFM on Avalanche, Impala, Silverado, Suburban, Tahoe and Trailblazer??? (Source) and why havent there been problems with this???

That's one of the things an O2 sensor in the downstream exhaust of your minivan is measuring, Frank.

no offense but you are greatly mistaken, the O2 sensor is measuring the amount of O2 LEAVING the engine via the exhaust so that the computer can tell if the Fuel/Air mix is too rich (too little O2 in exhaust) or too lean (too much O2 in the exhaust) for more info I suggest going to wikipedia

also, what exactly would a sensor be able to do to prevent "oxygen migration"??? it is a sensor, not a valve.

while we are on the subject of "oxygen migration" I am join the others in calling it BS unless you can cite some sources, O2 will not go against the flow of the exhaust gases unless it is propelled by a greater force. if you had a greater force the engine would not be able to push the gases out the tailpipe (try stuffing a potato up someones tailpipe and holding it in, the car will stall)

some Catalytic Converters have O2 INJECTION, ie: they pump O2 into the cat, this is to help the reactions in the cat along, but the O2 is put in under pressure, it does not "migrate" all by itself.

Just my $0.02 (or more)

Aaron Z

 

[alchemysa]

Exhaust flow consists of standing waves. Surfers are in a hurry and their waves travel. Ever play with a vibratory conveyer (used for runing pills, parts, rocks, gravel)? Modern exhausts are tuned to make sure this never happens. Google for pix of an engine running on dyno showing header output. You will be able to see the pulse train. Often seen in jet engine exhaust plumes, too. Watch a carrier night launch. Same deal.

Being washed out to sea is every ocean bather's nightmare....

You are confusing waves with current. You are trying to say that fresh air is flowing back up the exhaust pipe against the flow of the exhaust gases. It doesn't happen.

 

[alchemysa]

see

(WO/1980/000167) EXHAUST SYSTEM

and many, many others. Pay attention to claim F:

When you get an anti-node at the end gap you get the negative pressure wave component. Not confined to Big block. All piston engines running at a small rpm band need to deal with this. F1, Indy car, Mack truck and John Deere. Jet engine same deal when supersonic flow because it is not sequenced by a piston/exhaust valve pulse but by speed of sound.

(A) Thats not proof of anything. Its just someone's sales pitch about a type of tuned system. And (B) It doesn't say air can flow backwards up an exhaust pipe anyway. (Because of course, it can't)

As I said before, you are confusing waves with currents (or air flow).

 

[john_bud]

I'm going to state for the record that I don't have enough background to call BS or to support the claims.

I will state that water supply pipes have back flow arrestors to keep contaminated post faucet water from getting back into the supply. So there is some anecdotal support.

I also know that an exhaust on a car with a burnt valve can suck a dollar bill into the pipe. Done that! So a malfunctioning engine can suck from the exhaust side.

Can enough O2 get from the ambient to the valve to do damage to the back side of the valve? Don't know, I sure wouldn't think that it could. But folks used to think the earth was flat and the sun circled the earth...

I do know that there are both moving pressure pulses and standing waves in an exhaust system. But the waves only stand at constant RPM's (but maybe that is showing my ignorance>?)

I would however be comfortable stating that I wouldn't worry about buying a diesel tractor with a rotted muffler. After all, if worse came to worst, I know how to grind valves....


By the way, one of my current diesel tractors has 2 holes in the muffler and they were there for years before I rebuilt the engine. Valves were good.

jb

 

[alchemysa]

I also know that an exhaust on a car with a burnt valve can suck a dollar bill into the pipe. Done that!
jb

Hey, maybe we could perfect and patent that system. Absolutely no exhaust emissions at all if we get the balance right!


(But I'm guessing it blew it back out again a split second later.)

 

[Mundy]

Thanks for the feedback guys.
The muffler is horizontal and the holes are in the side so any water should have draine out the hole before it built up and went into the cylinder.

I am going to start haggleing with the fella this weekend. He wants a little more than I want to pay but I think we can work something out.
I would guess even if the holes have been there for several years it has only been ran 10 to 15 hours in that time so I am no longer concerned about the holes.
I think sitting unused like may have been worse for it than running with the holes.

 

[slowzuki]

A standing pressure wave can in fact slightly stuff exhaust gases back into an engine. In two strokes this is an extremely important design function.

HOWEVER! In a diesel this small and untuned, you will not damage it. It is not close to the ragged edge. It runs at excess air/part load for almost its entire operating life.

Also, the pressure ratio in diesels is such that the exhaust scavenging is so strongly positive, it would be one heck of a pressure wave to overcome it.

 

[sandman2234]

The inrush of air thru a too short exhaust is not an old wifes tale, as that is one of the things I learned from auto tech shop at the local college, 30 years ago. Probability might be the thing to consider, but if you haven't purchased the tractor yet, do a quick search for a replacement muffler and you will see why it hasn't been replaced. The one for my Ford 1100 was $500, which is why you will see it at it's new owners house with a slightly different muffler and mounted via a muffler bearing adapter that I built. (mounting plate adapter). I used one from a Ford 1200 and adapted the bolt pattern to fit. The actual cost of your muffler could be the negotiating leverage you need...
David from jax