Back to work: help again with my leak/noise

[drooartz]

After broken ankles, winter, and diversions into MGBs, it's time to get back to work on the Tunebug. Specifically I need to sort out this noise. To recap for those who didn't watch last season, this noise is a ticking under load. My initial feel is that it is an exhaust leak where the header (Maniflow LCB) attached to the head. I did not do anything to the header when I installed it, just bolted it up as it came from the factory, though it is JetHot coated.

So where do I start again? I'm trying to go back to the beginning and work through from the initial diagnosis stages. Where else do I look? I certainly can't guarantee that this is an exhaust leak -- I'm not an experienced enough mechanic to really know, and I don't want to be hung up on any one thing that blinds me to other possible causes.

 

[Trevor Jessie]

Refresh our memory... were you able to create the sound with the bonnet open and the car stationary?

 

[drooartz]

Refresh our memory... were you able to create the sound with the bonnet open and the car stationary?

Not really. I seem to remember that I had some luck revving it in gear with the brakes on and a friend listening at the bonnet. I'll try it this weekend if I can round up a helper.

Noise was not there if revved with no load.

 

[Bayless]

A small exhaust leak could match that sort of sound. Of course, pre-ignition would too, especially with the quality of gas we can get these days.

 

[drooartz]

Of course, pre-ignition would too, especially with the quality of gas we can get these days.

Was wondering about that as well as a source. What's the best way to test for that?

 

[DrEntropy]

What "octane" fuel are you feeding it?

 

[Deleted member 8987]

Had a ccar in the shop once (V-8) everyone was convinced it was an exhaust leak.
Ends up it was a head gasket. To the outside, under the exhaust manifold, only made noise under load.

 

[Mickey Richaud]

Of course, pre-ignition would too, especially with the quality of gas we can get these days.

Was wondering about that as well as a source. What's the best way to test for that?

Retard the timing a bit. If the noise goes away, you've found it.

 

[drooartz]

What "octane" fuel are you feeding it?

90 or 91, the highest grade I can get around here.

Retard the timing a bit. If the noise goes away, you've found it.

I'll have to check the timing again -- it's about 30 (maybe a tad below) at 3500rpm. Hap figures I should be able to be closer to 32. I did try that last time around, but I'm trying to start over from the beginning so I'll give it another go. I want to go about this systematically without any prejudice towards a possible cause.

 

[ChrisS]

What are you running for ignition. i.e. points or aftermarket? I had a Crane xr-700 in one of the cars and the trigger wheel wasn't exactly on center. This meant each cylinder had different timing. I checked timing on #1 and #4 (180' apart but same timing marks) and there was 5' difference in timing.

Can you upload the audio of the squeak again?

 

[drooartz]

I'm running a dizzy rebuilt by Jeff at Advance, along with his points and condenser.

Here's a MP3 of the noise taken last year, sound is noticeable starting around 0:20 or so (also at about 0:30 and 1:00):

https://www.drooartz.com/public/tunebug_noises.mp3

 

[Mickey Richaud]

That's not detonation...

Exhaust leak is what I hear.

 

[14dna]

Drew;
Do you have a header on the tunebug?
I have had headers leak where the pipe is welded to the flange.
Just thinking out loud.

Dave

 

[Deleted member 8987]

We came up with exhaust leak last year, and he does have headers.
But I thought he had it back to the shop and they had sorted it all out.
I was surprised to see this come back up again.
Did they machine the header surface?

 

[Trevor Jessie]

Thinking out loud.... what about partially blocking the exhaust and seeing if you can hear the noise at fast idle? Maybe a little squirt of ATF in the carbs to make it smoke and look for a leak?

 

[drooartz]

We came up with exhaust leak last year, and he does have headers.
But I thought he had it back to the shop and they had sorted it all out.

Shop did not sort it out (though they said they did), was going to bring it back down there last October but my broken ankle, and then winter, prevented it. I lost a few months in there and I'm just getting back into it now.

I'm still guessing that the header surface needs to be machined, but want to make sure I have eliminated all other issues first before trying again.

I'll have the car back over here this weekend, and I've got a bunch of things now to try. It's a chance to further my mechanical education, and I'd really like to fix this myself if I can.

 

[Silverghost]

Restrict the exhaust - the leak won't be able to hide....

 

[texas_bugeye]

Mainflow Header?Check the connection between the header and the tail pipe. make sure there is a good seal Had to scoot my mainflow pipe and header farther togather than i wanted due to the slot cut in it could be from there.

 

[Deleted member 8987]

He went through the exhaust pipe to header connection last time.