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Noises for your analysis please!

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Sounds like an exhaust leak to me, especially considering it seems to get louder on the right side where the manifold and exhaust piper are.
 
Scout,

Well, I've just replaced the head gasket. I used a new manifold gasket and I'm pretty confident I done a good job tightening up the nuts evenly. I checked them last night and some were very, very slightly loose, maybe 1/2 turn - re-tightened them down seriously - even the pesky ones underneath, but apparently it did not help.

Replaced the donut down below some time this year, double-nutting, new split washers and lock-tite. Sounds more like from up above though.

I'll pull the carb and see if there is anything obvious - I'm loathe to pull the manifolds off again but...

Oh yeah, I sprayed carb cleaner all along the manifold/head and manifold/carb junctions but no change in engine rpm. Strange.

Thanks for the reply anyhows.

Cheers!
 
I've got a pesky leak right where the exhaust pipe meets the manifold (old style clamp without donut ring). It sounds a bit like that for a few minutes after I start the car, then goes away after warmed up. If I spray a little smoke producing thing, such as carb cleaner, in the carbs, I can see where it is coming from, but it's awkward to get at. I have decided to live with it until the next time I have a reason to pull the carbs.

Bryan
 
scoutll said:
Sounds like an exhaust leak to me, especially considering it seems to get louder on the right side where the manifold and exhaust piper are.
Click to expand...


:iagree:

Might be a gasket or maybe a cracked exhaust manifold. Use a length of rubber hose, one end at your ear and the other end at each exhaust port/manifold junction and any other junctions such as manifold to exhaust pipe. You'll find it for sure.
 
Jim,

Thanks for the tip about the hose. No point tearing stuff apart 'cause I know there's nothing to see.

If the exhaust manifold has a crack in it, that would really tick me off. When I first bought this MG I had to replace the cracked manifold - this was before Ebay and what-not so I payed VB full price for a new one (ha!)- it was like hundreds of dollars.

Back at it tomorrow morning.

Cheers!
 
Still haven't found it.

Tried the hose trick but couldn't tell where it is coming from.
Pulled the carb to have a look round - no obvious manifold cracks.
I'll put the carb back on and try Bryans trick with the carb cleaner to produce smoke if no one has any more suggestions.

Oh yeah, how important is it to have that bolt in place that bolts together the intake and exhaust manifolds?

Cheers
 
I would have liked to hear the sound with the engine reved up. Sounds worse on the exhaust side, but does not sound like an exhaust leak, but more metallic. The slowness of the sound seems like maybe a valve or rocker arm or maybe timing chain. Are you sure the valve clearances are set OK? I would open the oil filler and see if the sound is worse or no change. For the exhaust leak, you can stuff a rag in the tailpipe, and if the manifold leaks, it should be a more obvious sound.
Good luck,
Scott in CA
 
Scott,

Here's another video revving the engine up from 800rpm. Not much to gone on, unfortunately.

https://tinyurl.com/28ocba4

Sound doesn't seem to come from the valve cover or the timing chain cover.

I re-installed the bolt connecting intake to exhaust manifolds but that didn't help.

Cheers!
 
Took another look at it today outside in the fresh air.

I would say it definitely is some kind of leak, rather than mechanical.
Would the intake make that kind of sound? I mean, I just put on a new carb spacer (with gaskets, of course).

Took the valve cover off and ran the engine - definitely not coming from the valves.
 
Exhaust leak, from the connection between the manifold and the exhaust pipe.

Is several bolts, a flange, and a gasket. Might have to pull the carbs to get at it properly but then maybe you have small hands.
 
Jack,

Thanks for the reply.

OK, here's the plan then - I'll remove the (big, home-made) heat shield and re-fit carb. Run the engine off the choke cable. Probably then be able to carefully feel around that connection for leaks. This is the connection between the exhaust manifold and the "down-pipe". I had checked the tightness of those nuts and they are TIGHT, so it not like they have somehow come loose. (There is also the connection between this "down pipe" and the pipe that leads to the muffler - already checked that and it's fine (in fact, recently renewed the do-nut))

Is it possible for a gasket to fail on its own accord? This manifold/"down pipe" gasket was installed about 10 years ago by yours truly when I replaced the (cracked) exhaust manifold.

I've been pondering gaskets lately - specifically the failure of the head gasket on the friend of a friends car. Does the head gasket need an outside influence to fail (eg. engine over-heating) or can it just blow one fine day when it feels like it? For example, over the years, with the engine in constant use, the head studs stretch ever so slightly but just enough to allow the combustion gas to escape and blow the gasket.

Cheers!
 
Surely it could fail all by its self. Best check of sure. Here is how I would do it.

Duct tape, tape it up and see if that solves the prob. Yea I know duct tape burns but you don't have to run it even that long.

Let us know as usual.
 
Tried the duct tape - it's not leaking around the flange between manifold and down pipe - the duct didn't blow out and the noise is still the same.

Tried again with the hose-in-the-ear trick - no luck.

I'll check the valve clearances tomorrow on the cold engine.

Cheers
 
That is not valves.

Check for leak between exhaust manifold and head.

Sure sounds like it must be exhaust system.
 
Just checked the valve clearances - they were fine.

https://tinyurl.com/3yz2njl

Note the built-in tool shelf!

Unless someone has a bright idea, I'll order up a new manifold gasket. PITA to replace but I'm thinking the appearance of the old one will tell us something.

2 days to go before Christmas!

Cheers!

PS. Thanks for confirmation Jack, we kind of overlapped on messages there.
 
You will find some of those bolts a challenge to remove. Be sure and soak them well in your favorite rust busting solution for several days. If you are lucky you've got brass bolts on there which they are supposed top be and they will come off easily. The two inside bolts as I recall are a real challenge. But One Flat at a time...
 
Startech,
I sprayed carb cleaner wherever I could and no change to engine noise. Of course, I can't get under the manifolds to spray.

Jim,
I hear you on those pesky nuts underneath, however, I modified an existing wrench (bottom one) to deal with them. It has to be bent at a different angle as the tightening process procedes and one flat at a time, like you say. (1500 engine, btw)

Wrenches.jpg


One thing I need clarification on: at what stage do you install the bolt that bolts together the two manifolds? (And what is the purpose of bolting them together?)

(I mean, you could install it when both manifolds are bolted to the head, or install it when just the exhaust manifold is bolted to the head, or install it before any of them is bolted to the head.)

Cheers!
 
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