Loosed Exhaust Port

If the face that the gasket mates against cleaned up ok, and the bolt torqued down ok I can't see it will have done any harm.... _{(except maybe causing the credit crunch and global warming.)}
Maybe the increased sound level annoyed the neigbours?

Del

In addition to the above, silencer and exhaust systems are usually "tuned" to some extent to the engine. If there is a leak then it may have affected the engine's output performance a little, though how much, and in which direction, is difficult to say. In any case, it probably won't have had as much effect as local variations in barometric pressure and humidity caused by weather patterns locally.

The bolt probably wants replacing and the whole lot torqued up properly. The original equipment manufacturer's manuals will probably state whether it is to be done cold, warm and to what extent, and if it isn't then a telephone call to them will probably suffice.

I like ur replies so far. Thank you guys!

Can a leak in the exhaust system cause an increase in the rate of fuel consumption?

Can it cause the engine to be doing more work than neccessary?

Yes, but only slightly. The reduction of back-pressure will slightly advance the timing causing the fuel to ignite late. The efficiency of the fuel burning process will be slightly decreased.

No. The 'work' depends on the load, however, it will try to compensate for the decrease in fuel efficiency.

Is the engine turbocharged? A small exhaust leak can greatly reduce boost thus reducing the available power output.

An engine that looses the integrity of it's exhaust system that close to the exhaust valve can experience damage to the valve.

Exhaust valves are one of the hottest regions in a Otto Cycle engine. Many an engine has had it's SFC compromised by the need to run mixtures richer than needed, just to keep that valve cool or to prevent pre-ignition.

When the valve opens burned gasses leave a conventional manifold and travel the length of the exhaust system. When they exit the pipe, they leave a low pressure "bubble" behind.

Cool surrounding air rushes into to fill that low pressure area in between power pulses. Because the system has some length to it, the cool air only gets just so far into the exhaust before being pushed back again.

However, if a component in the exhaust path fails close to the valve, the hot spent gases exit at the path of least resistance, which in your case is the burned gasket.

When the cold outside air rushes in, in between power pulses from that cylinder, it doesn't have to travel far to reach that hot valve.

The sudden cool air not only imposes a thermal shock to the valve but the uneven cooling can warp the valve head enough to prevent proper seating on the valve seat. That can be quite serious as the valve depends heavily on metal to metal contact at the seat and via the valve stem to dissipate heat.

Back in the 60's I was part of a research effort to develop tuned exhaust and intake systems for modified engines. The intent was to improve low end torque using those same "bubbles".

I got real good at grinding valve seats and refacing exhaust valves after engines with too short an exhaust warped them when we got overzealous with our tuning of the exhaust. We weren't creating overly lean conditions; we simply had cut things too close when shortening the exhaust pipes.

The worst offender was suddenly closing the throttle after a few minutes in the dyno at WOT.

What I've described is a worst case scenario so the factors influencing your particular situation can be fully appreciated.

There isn't enough info to answer for sure what the consequences may be. A lot depends on factors that are unknown to us.

For example, the end cylinders on an in-line carburetor engine tend to run leaner and therefor hotter than those cylinders closer to the carb. Was that burned gasket at the far end of the manifold where the valves run hotter?

Did damage occur? Can't say for sure but it's certainly possible given my experience.

L. J.

"Did damage occur? Can't say for sure but it's certainly possible given my experience."

Amen to all Laughing Jag just offered!

A leakdown test should answer the damage question in short order.

Now for my $0.02 worth: If a single cylinder engine, i like to (immediately @ shutdown) crank engine to the start of the compression cycle, it allows the poppets a heatsink + mechanical stability; they do seem to warp less.

An 'aviation style' safety wire job, or other positive locking scheme might be in order.

I like to provide a degree of flex in the exhaust system; keep the vibes out of any gasket & stud combo.

I think we all need to keep the engine size in perspective here. This is tiny.

Unless the entire exhaust manifold (pipe) fell off and the exhaust valve was exposed to cool outside air when an acoustic exhaust pulse 'reverses' drawing in that air, there will be very little chance of damage.

If this is a small noisy leak with black soot (smoke; your term 'burned') at the leak place but most of the exhaust still travelled into the exhaust header (your term 'port') you should have no damage at all.

Next time you are in a hardware store ask for 'anti-seize' compound which is a paste with copper or aluminum in the paste and remove your exhaust bolts and place a small amount of anti-seize on the threads. This will make the bolts easy to remove in the future otherwise they tend to become corroded and stuck in the threaded hole and break off during removal. I am a diesel mechanic and this is what we do on all exhaust bolts.

If you are worried you can do a compression check easy if this is a petrol engine with a spark plug. Buy a compression tester for EUR 50 and follow the instructions. Then every 250 hours take another reading. If the reading is consistently getting lower by more than 2-3%, you may have damaged your valve. i.e the damage will slowly get worse with time. The compression number isn't so important as the trending pattern to see if it is staying the same or getting lower with time. Lower is bad.

Cheers

PetroPower wrote: ". . . remove your exhaust bolts and place a small amount of anti-seize on the threads. This will make the bolts easy to remove in the future otherwise they tend to become corroded and stuck in the threaded hole and break off during removal."

That solution is better than none but by far the best method for preventing broken studs or bolts is to replace the bolts with new studs and use brass nuts instead.

No engine size was specified in in the original inquiry. Without that info, I was limited to responding generically with what I knew was a worse case scenario. I believe I identified it as such.

L. J.

My thoughts after reading all post and thinking back on 50 years of exhaust repairs.

Normally ALL engines are designed for and come with high strength studs and nuts on exhaust manifolds.Weed eaters to huge ship propelling diesels use these special fasteners due to the stretching effect when they heat up and then cool when shut down.Also vibration.If a bolt was found,the odds are that it was not original equipment.If the wrong bolt or stud was used,it will stretch,become loose and possibly vibrate out,damaging the threads while it does.Putting the wrong bolt or stud back in will only cause the problem to reoccur in the future.Just to replace a bolt or stud in a exhaust manifold is "Shade tree" with out regard to the future.The average bolt,nut or stud found at most auto parts or hardware stores is not designed nor made for such service and will often fail.They normally stretch and everything become loose.Use a stud and nut designed and made for such.

As for brass.Copper alloys such as the various forms of Brass alloys work hardens and become brittle with vibration along with heating and cooling.It can also soften with heat.Which is the correct brass alloy for any job,is often a big question.It does not normally have the strength or qualities needed for exhaust manifolds.I have not seen a "factory" brass nut on a exhaust system on a weed eater size,US Submarine size to huge ship size engine.I have seen most everything shade treed and used when it was all that was available at the instant needed.

While it use to be common to cut a head and manifold gasket out of copper in the south as sheet copper was readily available and cheap,you usually changed it repeatedly along with your oil.

Any used engine with "bolts" on a exhaust manifold is something to be questioned and checked out to see if it is correct in my belief.

People often use what is readily available with out thought of the future consequences.Next time the surfaces may be cut along with the bolt.

From Nuclear Submarines at sea,to chemical plants.I made my living shade treeing to keep the job going till the correct repairs could be made.This is no substitute for doing the job correctly.A leaking exhaust has killed thousands of people over the years from carbon monoxide to fires.I do not know the situation here,but the correct repair is the right repair to keep it from reoccurring.Alfred

A Good Answer for sure - but voting it as such would be pretty much a waste. Please consider registering as a member here so your efforts can be properly appreciated!

Anonymous wrote: "As for brass.Copper alloys such as the various forms of Brass alloys work hardens and become brittle with vibration along with heating and cooling.It can also soften with heat.Which is the correct brass alloy for any job,is often a big question.It does not normally have the strength or qualities needed for exhaust manifolds.I have not seen a "factory" brass nut on a exhaust system on a weed eater size,US Submarine size to huge ship size engine.I have seen most everything shade treed and used when it was all that was available at the instant needed."As for brass.Copper alloys such as the various forms of Brass alloys work hardens and become brittle with vibration along with heating and cooling.It can also soften with heat.Which is the correct brass alloy for any job,is often a big question.It does not normally have the strength or qualities needed for exhaust manifolds.I have not seen a "factory" brass nut on a exhaust system on a weed eater size,US Submarine size to huge ship size engine.I have seen most everything shade treed and used when it was all that was available at the instant needed?"

I'll be certain to pass along your observations to the Regional Engineering office of the Federal Aviation Administration.

I'll also pass it along to those decision makers at Avco-Lycoming and Teledyne-Continental who have been manufacturing certified aircraft engines for over 75 years under a TSO with brass nuts on exhaust studs.

L. J.

Hi L J. Could be you missed the 7.2 kVA in the opening dialogue, which at 0.8 PF would be 5.76 ekW which would be be about 6 bkW or about 8 bHP. A small riding lawn mower size engine. Unfortunately I am used to 500 kW up to 10 MW size engines so for one reason or another we don't use exhaust manifold studs, and I've never seen brass or bronze nuts anywhere due to strength issues. I think it is a different world of bolt torque and high tech material selections for out exhaust fasteners. But one thing is sure, all of us use ant-seize on the threads if we want it to ever come off a few years from now. I'll try the brass nuts on my small stuff at home though and see if it helps (6 hp log splitter with studs). Thanks for the idea.

Despite our Laughing cat's worst-case scenario, you mentioned "some hours" of run time, not "some days", so I'll vote with the "other" cat (Del) that annoyed neighbors, _{(the credit crunch, and global warming)} are the most likely to have been negatively impacted by this. Presuming, of course, your information was correct, and the exhaust leak was recent, not just un-noticed over a longer time. That might give away the biscuits...