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1931 60 exhaust leak


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I have been driving my 31 a good bit and have managed to develop an exhaust leak. It appears to be coming from one exhaust port gasket- no cracks that I can see. As fragile as these manifolds are I thought I better get some advise here before doing something stupid. Two thoughts come to mind; 1) can I try tightening the nuts holding on the manifold without getting into trouble? If that doesn't work. can the manifolds be loosened and pulled away enough to replace the gasket without removing the exhaust pipe and heat riser?

 

Any other recommendations are welcome, thanks

 

Dave

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Dave,

    It is difficult to answer without more information.  All straight 8 manifolds art attached with heavy convex (spring) washers that compensate for heat expansion and contraction.  The torque specs for these manifolds is not a much as one would think.  Since everything expands when heated, these washers help to maintain the correct pressure to prevent leaks.  Does your car still have the original washers in place?  

    Check out this post too...  

 

 

 

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This is problematic on these early straight 8's.  The exhaust manifold gets as hot as 700 degrees and the cylinder head gets to 250 degrees.  You have almost 3 feet of  one piece cast iron that must be able  to expand and contract without binding.  Cast iron takes compressive force well.  It does not like extension forces that happen at cool down.  You will not save yourself much time by trying to keep the manifold connected to the exhaust pipe.  The intake will come loose with the exhaust.  Plan to remove the additional 2 bolts  at the exhaust diverter valve to remove the exhaust manifold. 

 

Get copper gaskets for the intake / exhaust manifold, not the composite ones.   Olson gaskets has these.Check the manifold for flatness across all ports. and polish the surfaces.  On the opposite side, clean the surfaces where the curved washers make contact.   Don't be tempted to used bellville washers in place of the original thick washers.  Mac Blair has new correct washers.  Make a thick paste of graphite and motor oil.  Apply liberally to both side of the gasket.  After assembly and running, the motor oil will smoke and burn off but leave the graphite  there to aid in the movement of the  manifold.  Tighten  the manifold nuts no tighter than needed to not leak.  I leave then on the loose side and tighten as needed to prevent leaks when hot.  Too tight or binding on the sliding surfaces and you risk cracking the manifold.  

 

Bob Engle

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I agree on the nailheads that the Remflex is a great gasket.  The straight 8's are a different animal.   Especially the early ones that are a one piece manifold.  The amount of movement that occurs through the heat cycle  is double the amount of a V8.  Replacement exhaust manifolds are well over $1,000.  Repair of cracked manifolds is an iffy proposition.  It's best to baby the original manifolds and make sure they slide on the gaskets with minimal fastener torque.

 

Bob Engle

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Also consider purchasing stainless studs and brass nuts.  Use antiseize on both threads of the stud.  If you don't want to pull the studs, at least use brass nuts.  It makes the job a whole lot easier the next time you have to work on the manifold.  

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11 hours ago, Bob Engle said:

You have almost 3 feet of  one piece cast iron that must be able  to expand and contract without binding. 

 

That is *the* issue on any long engine (and good advice on little short v8s too). It moves. If you do anything that stops it, things will not go well.

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While you are that far into the project, I recommend plugging the exhaust directed toward the carb heat riser.  You don'tneed or want any exhaust flowing to the carb.  There are a number of threads dealing with this on this site.

 

Bob Engle

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Bob, I did plug the heat riser tube when I replaced the riser and tubes inside. It made a real difference in the way it runs in this hot weather. It is such a wonderful car to drive I may be running it too much!

 

Hugh, I like the brass nut idea I am not sure on the stainless studs. One stud (the one with a flat washer) has been replaced since it looks like 7/16. The others are 3/8.

It is important to me to have it run good and be dependable but it is an unrestored original 45,000 mile car so I hate to put a lot of shiny new parts on the engine.

 

Thanks again

 

Dave

 

 

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Dave-  I'm following this thread closely because I'm sure when I get to the point of starting and running my 8-66S I will encounter some of the problems you have already dealt with.  I'm still grubbing around with body stuff for now but later this fall I will be starting this car up for the first time for me though I have video clips of it running and driving from the previous owner.   You spoke about blocking off the heat riser tubes to prevent exhaust flow to the riser.  Did you install a flat plate at the exhaust diverter or how did you do that?  You also stated you replaced some tubes, were these the 2 exhaust tubes that connect the heat riser and diverter or are they the throttle butterfly tubes in the riser?  If you replaced the tubes inside the riser what material did you use for the new tubes?  I had a riser re-sleeved on the 90 series car I had when I was a teenager and the machine shop used stainless steel tube.  I didn't keep the car long enough to know how those held up and have been warned that stainless might be a no-no because it may expand faster than the iron riser and cause the riser to crack.   

 

Thanks...

 

Dave 

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I used a core plug (freeze plug) to block off the tube to the heat riser,. The tubes I replaced inside the riser were replaced with McMaster-Carr stainless tubing. It was  slightly too large but the machine shop was not concerned and did a great job in making the swap. No cracks so far, the old heat riser with the factory tubes was cracked extensively so I am not sure on the stainless being a problem. There were several discussions on this topic  on this forum that were helpful.

 

Dave

 

Edited by Dave39MD (see edit history)
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If you block the tubes from the exhaust manifold to the carb heat riser, the only temperature rise you'll see is about what the engine runs. At that temperature, the difference in coefficient of thermal expansion between cast iron and stainless is negligible.

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  • 4 weeks later...

Found the root cause of the leak, the last guy damaged the gasket putting it together. I re-read the advice since I am getting ready to put it back together.

 

The advice on using Olson's gaskets was excellent. They are very knowledgeable and seem to really want to help their customers.

 

Dave

 

 

exh manifold gasket leaking.jpg

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