exhaust leak?

[mikeyo]

hey that noise in my engine couldn't be an exhaust leak, could it? that's the latest opinion i've been given. the mechanic's son said he was sure of it. but then another friend of mine said if it were an exhaust leak (from the manifold) it would make that rattling noise constantly, and not just atcertain rpms or mph. any way to find out?

[Conrad]

Your description - "rattling noise" - doesn't fit my expierience for an exhaust leak.  Does the rattling noise have a mettalic sound to it?  if so, i doubt it is an exhause leak.  You can try to feel the exhaust leak around the exhaust manifold with your fingers, just be carefule of the heat!  The leak will pulse in time with the piston exhaust cycle.  Or get an inspection mirror and check around the gaskets where it mates to the head.  Black carbon build up will be evidence of a leak.

Try a rubber hose (vacuum, fuel, etc) and use it as a stethescope.

Play doctor with your girl!

[Andy Illes]

Agree with Conrad... that's not what a manifold leak sounds like, I've had 'em.  The most common spot for leaks is in the middle two, which are siamese, and sounds like "pfft, pfft, pfft" at first... increasing to fairly loud clearl exhaust sounds as the hole grows.  Those sounds are also constantly present, increasing with engine rpms.

For what you're describing, you might wanna get under there (cool engine/exhaust) and wiggle the exhaust pipe at various points front to back.... sounds more like that might be hitting something at certain vibration points.  Another intermittent "rattling" sound could be the fan blades striking something... check that too... particularly when you rev the engine, and have weak engine mounts.

Good luck, Andy

[Andy Illes]

PS.... to check engine (transmission) mounts, just try prying the engine on both sides.  Good mounts will allow only minimal rocking and feel stiff.... shot ones, depending on how bad, will at least feel "mushy" and allow anywhere from a lot of engine movement to actually visually lifting apart.

You can do that with the engine running, in which case, you can also listen for the fan blades hitting anything,  ditto the exhaust system.

[susan-y]

So on the subject of exhaust leaks.  I am pretty sure I have one (after my engine rebuilt). Sounds like it is on the drivers side.  The mech who works on my rig says he can't hear it. My nephew said he could "barely" hear it and they are just a nuisance.. not worth the time to track them down and fix.  Is there a test, other than hearing?  I assume that it will be warranty if/when I can get them to work on it.  Sue

[Rodney]

So on the subject of exhaust leaks.  I am pretty sure I have one (after my engine rebuilt). Sounds like it is on the drivers side.  The mech who works on my rig says he can't hear it. My nephew said he could "barely" hear it and they are just a nuisance.. not worth the time to track them down and fix.  Is there a test, other than hearing?  I assume that it will be warranty if/when I can get them to work on it.  Sue

If the leak is close to the head you may be able to see evidence of leaking between the gasket and head  or manifold. if your engine has recently been repaired and new gaskets were installed they should be checked and retightened. you might try at night in the dark to start the engine and rev and let up on the throttle {have someone do this for you} while looking for the leak area you might be able to see some fire if the leak is close to the head. The hose {I have used a couple feet of 3/4 in. of garden hose} to the ear and poke it around the leaking area has worked best for me. I have found that a leak may be worse when the engine is cold and as heat build and the cast iron expands the noise gets less.  
Rodney

[Andy Illes]

All 3 times I've replaced manifold gaskets, they were burned right by the siamese middle two, and looking at it, IMHO, it's just a poor bolt placement that allows the manifold to warp right there, so the bolts can't clinch that area tight.

I put in another post that the list time, I smeared both sides of the new gaskets with "furnace cement" I got at Home Depot and although I still have a very faint "pfft pfft pfft" on the driver's side, it's a LOT better.  I'm thinking of getting TWO sets of gaskets, smearing 'em all with the goop.  Seems to me that way, I could get enough gasket compression at that spot to take care of it once and for all.

As to a test, yeah... the hose works, except it's nearly impossible to get under the manifold at the center (where the leaks usually are) cuz of the design.  Rodney's idea about watching it at night also sounds good.   one idea I haven't tried is it seems there'd be stuff you could spray/pour into the carb to make an UNHOLY amount of smoke you might be able to see leaking out too, though you'd have to shield the area from the fan... anybody try that?

[Rodney]

Ya got to be careful when using two gaskets!! with that much material between the manifold and head you can crack or break the manifold. if you have the manifold off the engine lay a stright edge across the surface in question and see just how bad it is. if it needs resurfaced have that done. but be aware that some machine shops use a table belt sander affair for this and it's not a good fix IMHO. the manifold needs to be set up on a mill and made perfictly flat. or replace the manifold with a new one of better yet a set of Doug Thorley headers.
you can trickle ATF down the carb if you want to set up a smoke screen and kill all of the mosquitos for miles around. Marvel mistry oil would work to it you want to go that route :?: there are some good hi temp gasket sealers at your local parts store. just let it dry before you start the engine.
Rodney