Can a big block run with one broken exhaust valve??????????

If yes......

How long could the engine run for?

What signs could you expect?

Would you hear a loud popping when throttling up, almost like a backfire but then it goes at high RPM's and full throttle?

My new engine now has a broken exhaust valve at 50 hours of run time.

After about 25 hours of running I started to notice a loud popping like a back fire that was occuring only as I increased the throttle. If you tapped on the throttle a little you got through the popping sound and as the RPM's increased the sound went away. At the time the mechanic blamed the issue on the quicksilver throttle and said it sticks a little and should eventually be replaced but it wasn't something to immediately worry about.....25 more running hours from the day the mechanic told me that the boat died in the water and was towed in. Pulled the motor and found a busted exhaust valve. I'm trying to determine if the valve had been broken the whole time during those last 25 hours and was the cause of the popping noise and the mechanic was wrong for thinking it was the throttle and that day the engine finally failed completely because it just had enough...

Re: Can a big block run with one broken exhaust valve??????????

Why was the engine replaced to begin with. it may be that what ever happened to your old engine, is now happening to your new engine as well. Perhaps a lean condition from a faulty fuel system, perhaps a timing/advance problem. All impossible for us to know at this point
We also have no idea what engine you have, Year, make, model, serial number, carbed or EFI, kind of ignition, nothing.
My guess is the throttle lever has nothing to do with the problem, and i doubt your mechanic meant to blame it for engine failure, but mentioned it in passing or something else that needs fixed. I feel we are not getting the full story of what's going on.

Re: Can a big block run with one broken exhaust valve??????????

Well if it's a new engine it should be under warranty..... Take it back

Re: Can a big block run with one broken exhaust valve??????????

My new engine now has a broken exhaust valve at 50 hours of run time.

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Ayuh,... Broken Where,..??

Your just tooo generally speakin' to answer....

Answer Don's questions, 'n We'll see what We can do for ya....

Re: Can a big block run with one broken exhaust valve??????????

It may run till the valve falls down into the combustion chamber then the block and heads are toast too.

Re: Can a big block run with one broken exhaust valve??????????

Don. You wrote

Why was the engine replaced to begin with. it may be that what ever happened to your old engine, is now happening to your new engine as well. Perhaps a lean condition from a faulty fuel system, perhaps a timing/advance problem. All impossible for us to know at this point-------The original engine was replaced due to severe freeze damage. Prior to the freeze damage it was a great running motor. It was replaced with a new drop ready carbed 454. All the bolt on componets and accesories were new including exhaust.

Im not sure the year, I could get the serial number and will have to post later.

My questions are

1) In a carbed 454 BB with through hull exhasut, is it possible for the motor to run for 25 hours with a damaged or non properly seated exhaust valve?

2) If the anwser to the question above is yes, could you expect to hear some popping or noises similar to backfiring at lower RPM's?

3) If a raw water cooled engine shuts off while its running in the river, your towed in and the engine is pulled, what happens to the remaining water that was left in the cooling system? Could it work its way down into the oil pan a couple days later?

Re: Can a big block run with one broken exhaust valve??????????

jan9898 said:

3) If a raw water cooled engine shuts off while its running in the river, your towed in and the engine is pulled, what happens to the remaining water that was left in the cooling system? Could it work its way down into the oil pan a couple days later?

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no
it shouldn't "work it's way" anywhere.
there would have to be a crack or faulty gasket/part somewhere - suspect manifolds, intake, block etc.

depends how the engine was "pulled" though. If someone removed heads, intake manifold etc in the hull, before opening drains, they could spill water into the oil side. You'd almost have to try.

Re: Can a big block run with one broken exhaust valve??????????

My questions are

1) In a carbed 454 BB with through hull exhasut, is it possible for the motor to run for 25 hours with a damaged or non properly seated exhaust valve?

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Yes........and depending on how "bad" (or good) it is, you might not even be able to detect it.....

2) If the anwser to the question above is yes, could you expect to hear some popping or noises similar to backfiring at lower RPM's?

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Maybe and maybe not. It could run like that and not sound bad at all. (until the valve breaks)

3) If a raw water cooled engine shuts off while its running in the river, your towed in and the engine is pulled, what happens to the remaining water that was left in the cooling system? Could it work its way down into the oil pan a couple days later?

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The exhaust manifolds and risers are always FULL of water when the raw water pump is operating.


When the pump stops turning, the remaining water in the risers fairly slowly goes down until most of it drains out depending on how well it leaks past the raw water pump (either engine mounted[Bravo] or in the drive [Alpha])

It doesn't go down immediately.....or at all if the raw water pump "seals" well.............SO if a riser gasket is leaking, water that is in the riser (ABOVE the riser gasket) will be leaking into the exhaust area until the water level in the riser/manifold drains to a level below the riser gasket.

That water (above the leaking gasket) WILL run directly into any cylinder with an open exhaust valve. (you ALWAYS have open exhaust valves when the engine is not turning!)

That water doesn't get in there (with leaking riser gaskets or cracked manifolds/risers) when the engine is running because the exhaust pressures "blow" the water out..........

My previously installed OMG 460 King Cobra did exactly that for an entire summer. It was enough water to cause a "slight" hydro-lock condition EVERY TIME I shut the engine down!

If I tried to restart immediately, it would start right up. I f I tried to start after about 10 minutes, it would act like the battery was dead or the starter was dragging.(hydrolock)

If I waited 45min to an hour, or over night, it would start right up. It was enough water to hydrolock but not enough to produce an excessive amount of water in the pan (the little bit of water eventually leaked past the rings...............But subsequent running of the engine would evaporate all the water out of the oil)


If you're looking to place blame on someone......it's going to be hard unless you can prove that they didn't install the riser gaskets correctly. They should step up though.........

Re: Can a big block run with one broken exhaust valve??????????

1) In a carbed 454 BB with through hull exhasut, is it possible for the motor to run for 25 hours with a damaged or non properly seated exhaust valve?

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Ayuh,... You Still haven't told Us, Exactly what happened to the valve...

There are several definitions of Broken...

Re: Can a big block run with one broken exhaust valve??????????

leak down test, will tell all problems... sounds like you over ignition timing and you burnt a valve, typical on new aftermarket engines, most people know what their doing... but some let the rest of the world down...