Author Topic: Gaskets required for heat riser on stock exhaust manifold  (Read 214 times)

Offline 75gmck25

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Gaskets required for heat riser on stock exhaust manifold
« on: July 12, 2018, 11:28:10 AM »
I installed a new set of heads, and now I have an exhaust leak on the passenger side where the heat riser is installed on the stock manifold.  Clearance is tight around the flange, but I think I got it tight.

When I pulled off the manifold there was no gasket between the heat riser and the flange above, only the round gasket where the header pipe connects.  However, I've looked online and there are three-bolt gaskets that look they would fit between the heat riser and the flange.  This is the type of gasket I mean https://www.rockauto.com/en/moreinfo.php?pk=2589708&cc=1159073&jsn=525.

The header pipe seals into the heat riser using the standard round gasket, so it seems like there may be somthing needed on top of the heat riser.  Maybe I was just lucky enough before to get it to seal without a gasket.

Should there be a gasket between the heat riser and the flange above it?

Bruce

Offline bd

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Re: Gaskets required for heat riser on stock exhaust manifold
« Reply #1 on: July 12, 2018, 01:50:16 PM »
IIRC, the heat riser to manifold connection was metal-to-metal.  Gaskets were an aftermarket remedy.  I never cared for the gaskets because it seemed they were a marginal and temporary solution.  When you remove the heat riser to reseal it, check the sealing flange for distortion.  It may need to be resurfaced.  Whether or not you install a gasket, apply some Ultra Copper or similar high-temperature silicone sealer to the joint.
Rich
It's difficult to know just how much you don't know, until you know it....
In other words... if people learn by making mistakes, by now I should know just about everything!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline 75gmck25

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Re: Gaskets required for heat riser on stock exhaust manifold
« Reply #2 on: July 12, 2018, 09:29:21 PM »
I checked it out further today, and  found that the heat riser was not pulled up evenly by the flange, so there was a gap between it and the exhaust manifold.  A gasket might have helped, but wouldn't be needed if it had been fully in place.

The other question I now have is whether I can install it without the heat riser, and will the header pipe seal directly to the exhaust manifold?    My new heads don't have a heat crossover, so I can't get any manifold heat anyway.  I already have it all taken apart, and leaving out the heat riser would be just one fewer part to get lined up and sealed.

Bruce

Offline bd

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Re: Gaskets required for heat riser on stock exhaust manifold
« Reply #3 on: July 12, 2018, 10:02:11 PM »
You need to determine whether the manifold has a tapered seat for the doughnut.  In addition, the Y-pipe (if you are not running true duals) probably won't be long enough to reach w/o compromising the seal to the left manifold.  You could always gut the heat riser and use it as a spacer, or just install SS headers.   :)
Rich
It's difficult to know just how much you don't know, until you know it....
In other words... if people learn by making mistakes, by now I should know just about everything!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Henry

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Re: Gaskets required for heat riser on stock exhaust manifold
« Reply #4 on: July 13, 2018, 12:44:43 PM »
Hi 75gmck25:
Many years ago the heat riser on my 76 got rusted into the open position so I decided to replace it. I experienced the same leaking problem you have when re-assembling it all and it was probably because the aftermarket exhaust system was not as straight and aligned to the exhaust manifold flange as OEM y-pipe. It just took a bunch of tweaking (wood blocks and prybar) of the exhaust pipe while tightening the bolts to get it aligned and sealed. I ended up using a gasket that you found on the internet between the riser and exh manifold...it is probably not OEM as bd has mentioned but I got it in there for whatever reason...it has been in there for over 15 years now. I have bronze nuts holding the whole arrangement together but I do remember using steel nuts during the initial tightening and tweaking process because the bronze nut threads were not strong enough to take the force required to get it all together...also a lot of anti-sieze. I then replaced the nuts one by one with bronze nuts. The downside of your riser should have a countersink surface for a donut gasket to go between the downpipe and riser.
Regards,
Henry

Offline 75gmck25

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Re: Gaskets required for heat riser on stock exhaust manifold
« Reply #5 on: July 14, 2018, 05:39:56 AM »
I took it all apart yesterday, including cutting the exhaust pipe just after it went over the crossmember, so that I wasn't fighting with the entire exhaust pipe on that side to get it all lined up.

I found that you do need the heat riser in place, since the manifold does not have a recess for the header pipe.  I reinstalled the header pipe with a flat gasket between the heat riser and the manifold, and also put a new doughnut gasket between the head pipe and the heat riser.  I was able to move the head pipe around and make sure it seated completely and all three bolts pulled the flange into place and sealed. I then lined it up with the rest of the exhaust and reconnected the pipe running back to the muffler.  I had to loosen all the other exhaust hangers to get enough movement to reconnect the rear pipes, but won the fight with rusty bolts. 

Thanks,

Bruce

Offline Patman

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Re: Gaskets required for heat riser on stock exhaust manifold
« Reply #6 on: July 19, 2018, 11:30:15 AM »
I am having the same issue! Thanks for the great info!
85 K10 350, 700R4, NP208, Quadrajet, Long Bed w/ 33ís
All stock except for the motor, used to be a 305.