Exhaust flange gasket leaking again

[dom14]

Hi guys,
I replaced a leaking flange gasket of my GQ RB30 couple of weeks ago, and it started leaking again yesterday.
I'm guessing,

1) Either a flange surface is warped and pitted badly(not from what I could see though, I saw one end and looked good and shiny, I felt the manifold end and felt smooth and shiny for the most part, warped may be, but I don't think it's badly pitted at all)

or

2) Too much back pressure(I think it started blowing up when I revved above 3k or so.)

I did a Vacuum test. Didn't show up any bad back pressure issues. Muffler appears to be working fine atm.

What else can cause the flange gasket to keep blowing up like this?!?!?

Thanx in advance for any help

[no eye deer]

What gasket sealant are you using? I tried some exhaust silastic, and it blew out the next day. Then used the proper stuff I think its called Mani-seal or something, and followed the directions (that was a first). Hasnt leaked since. Got the gasket from "Best Mufflers" cost was about 4 bucks.

[dom14]

I didn't use any gasket sealant on the above flange, but did use on the ether end of it.

I just had a look and found out all the nuts are loose, and one of them badly loose.
I can confirm that I've tightened them properly last time.
I also found flange gasket has some water in it, probably from leaking exhaust gas.
Just wondering what's causing the nuts to come loose
Vibration obviously.
BTW, there're no washers between flange and the nuts.

May be I should use some spring washers?!!

[mudnut]

Did you test to see
that the protruding
bits of the pipe actually
fit into the manifold?
They tend to catch in
the manifold and
make you think
that you have torqued
the nuts up, but
they're not.

The exhaust mechanic
had to grind them
off level with the
flange on mine.

[dom14]

Did you test to see
that the protruding
bits of the pipe actually
fit into the manifold?
They tend to catch in
the manifold and
make you think
that you have torqued
the nuts up, but
they're not.

The exhaust mechanic
had to grind them
off level with the
flange on mine.

Thanx Craig. I'll be pulling it out tomorrow. I'll pull out the manifold off the head as well, so I can have a good, close inspection.
I just tightened the the three nuts, but still leaking from the flange gasket. It's either as you said the excess bit of the pipe sticking out and getting caught between the two ends,
or plus that problem and the gasket is stuffed now from leaking.


BTW, I just finished the first one of the exhaust gas leak tests that I've been developing.
I'll post the details in our RB30 Facts thread as well as a separate thread.

[Geoff67]

Did you find out what the problem was because i am having the same problem

[dom14]

Did you find out what the problem was because i am having the same problem

Yes, I think it's caused by the excess stick out of the exhaust pipe, which get stuck between the flanges, as Mudnut described above.
I'm planning to grind it off and then use exhaust gasket sealant with a new flange gasket.
Also discovered the manifold gasket has crapped itself as well. So, with two new gaskets combined with gasket sealant should fix the problem for long time.

I did the vacuum tester test properly and there's no excess exhaust back pressure that was causing these leaks. So, it's definitely caused by bad seals.

[threedogs]

What style gasket are you using, perforated silver, or a normal cardboard style gasket

[dom14]

What style gasket are you using, perforated silver, or a normal cardboard style gasket

Perforated silver, of course. :)
I don't think I would have any chance of succeeding with paper gaskets on exhaust flange near the manifold.

BTW, the major reason I think is that the flange on the pipe end(not the manifold end) has a slight curve in the middle.
This must have developed over time and caused a poor seal. Only solution is to use exhaust sealant combined with the gasket.
Excess vibration created by that must have caused the flange nuts to come loose as well. Since, I didn't use any gasket sealant, it was bound to
fail in no time. I also think, using two gaskets combined with gasket sealant can fix the problem for a good long time.

[dom14]

What gasket sealant are you using? I tried some exhaust silastic, and it blew out the next day. Then used the proper stuff I think its called Mani-seal or something, and followed the directions (that was a first). Hasnt leaked since. Got the gasket from "Best Mufflers" cost was about 4 bucks.

Maniseal is a ceramic paste that you apply from outside of the gasket leaks AFAIK.
For gasket leaks, I used,

http://www.ebay.com.au/itm/Permatex-Ultra-Copper-RTV-Silicone-Gasket-Maker-Exhaust-Sealant-Gasket-Silicon-/251349397706?hash=item3a859770ca

I'm yet to put a new gasket and sealant on it. Once I do that, it should work like a charm.

[mudnut]

I tried filing the
flange flat and
then applying
maniseal, but
it only lasted a week.
The new engine
pipe flange is
much thicker steel
and after the excess
pipe was removed
it is still sealed.
Touch wood.

[dom14]

I tried filing the
flange flat and
then applying
maniseal, but
it only lasted a week.
The new engine
pipe flange is
much thicker steel
and after the excess
pipe was removed
it is still sealed.
Touch wood.

I pulled out both the manifold & the pipe and then checked if the excess of pipe goes inside the manifold without any issues.
It appeared to be going ok all the way inside. The excess of the one of the pipes bit bent, but still goes inside all the way.
When I checked the pipe flange I quickly discovered that it's not flat but has about 0.5mm gap in the middle.
I thought about taking the flange out and filing it and then rewelding it. But, it's bit too much fiddling for me.
I reckon two gaskets(instead of one) coupled with generous layer of exhaust gasket sealant should fix the problem for good.

[threedogs]

is there any way you can put a straight edge across the entire manifold to check if its true.
you might be chasing your tail if its not true.

[dom14]

is there any way you can put a straight edge across the entire manifold to check if its true.
you might be chasing your tail if its not true.

That's how I found out the flange is warped in the middle. I used a straight edge steel ruler combined with a feeler gauge.
I didn't do it with the cylinder head end of the manifold. I didn't think it was necessary as the major leak was from the other end.
I will do it anyway. I think it's a very good idea.