Need Help With '41 Exhaust Leak

[neil morse]

I recently got a new exhaust system from Waldron's and had it installed by a muffler shop.  After a few weeks, it had developed a leak at the expansion joint in the Y-pipe just under the manifolds.  The joint in question is shown in this pic of the pipe before it was installed.

 

 

I could hear the leak, and could feel it by holding my hand above the upper, front side of the expansion joint.  I took the pipe off and found this damage to the "doughnut" gasket at the joint.

 

 

I put the pipe back on with a new set of gaskets, being careful to follow the procedure in the shop manual on the order in which to tighten up each joint.  However, after a single heat cycle, the pipe is leaking in exactly the same spot.  I made sure the bolts are tight, and they are at their maximum.  Those two plates are absolutely clamped together.

 

I called Waldron's, and the guy I spoke with was friendly but couldn't offer any particular help.  He did say that it might help for the straight pipe to extend further into the lower pipe, and said they would fabricate a longer pipe for me if I couldn't otherwise solve the issue.  He also suggested that a product called "exhaust paste" could help.  I searched the internet and found several suppliers.  This is one:

 

https://www.wurthusa.com/Chemical-Product/Miscellaneous/Exhaust-Assembly-Paste-4-94-Fl-Oz-Tube/p/0890100045

 

I'm going to send for another set of gaskets and give it another try.  Has anyone worked with one of these joints?  Any other suggestions or comments?

 

Thanks in advance,

 

Neil

[Bloo]

I have used a lot of Wurth products when working in European car shops, but have never seen that particular exhaust paste and I am not sure what it is or what it is like.

 

If someone said "exhaust paste" to me, the first thing I would think of is Walker Acousti-Seal. It might or not be similar to stove cement. Acousti-Seal is a black tarry substance that you don't want on your hands because it will never come off until it wears off. It cures with heat and becomes fireproof but brittle. It is most useful for slip joints in exhaust, because it seals them, but what is rarely mentioned is that the joint will seal up with less clamping force, and also that it acts as an INSULATOR. This is a big deal because when it is time to take the slip joint apart, it won't be as warped, and the brittle Acousti-Seal will break up and turn to powder when you twist on it. Better yet, if the slip joint still won't come apart, when you put a torch on the outer pipe it will expand a lot and come off, because the Acousti-Seal acts as an insulator. If the joint were instead allowed to rust together, the torch would heat up both the inner and the outer pipes and both would expand and the joint still wouldn't come apart.

 

Acousti-Seal can be good on flat gaskets on exhaust pipes as well when the flatness of the flanges is questionable. It wouldn't have occurred to me to use it on a donut gasket because they are meant to move a little, but I wouldn't be opposed to trying it.

 

Maybe extending the pipe would help. Some flanges like that do have a little more pipe that extends through the donut. The thing that stands out to me is that the plates were clamped together tightly. Normally I don't think that would be true with that type of donut gasket. Maybe the donut is a little too small and the flanges are bottoming too soon?

 

Edited July 28, 2022 by Bloo (see edit history)

[Matt Harwood]

They make exhaust donuts like the one you've got but with a steel core. It's less flexible but the steel core should fit into the upper and lower pipes and hold the donut in place at the joint. That way the gasket material is just sealing the joint while the steel sleeve is handling the structural integrity. Your auto parts store should have a bunch of them--ask if you can go back there and look at them and see which one will fit best. I used them for a while between my cracked exhaust manifolds and the old Y-pipe and they worked pretty well.

 

It should be something like this, although I've seen them where the steel flange sticks up on both sides of the donut to fit into both sides of the joint and reinforce it:

 

[Bloo]

Isn't there a central pipe sticking down the middle of the upper piece, locating the gasket on the flare? It looks like it in the pictures. Wasn't that what the Waldron rep was potentially going to lengthen?

[EmTee]

Yes, it does look like the doughnut fits onto a stub of pipe.

 

 

Seems like that should slip into the lower pipe if it's really a 'slip joint'.  The way it is looks more like the joint where a manifold mates with a headpipe.

[neil morse]

Thank you all for your helpful responses.  I'm sorry for any confusion about the configuration here -- I posted the only photo of the pipe that I have from before it was first installed, and it's a bit unclear.  Yes, Bloo is correct.  The upper pipe reduces in diameter and then extends through the doughnut and down into the lower pipe.  I can post much better photos of the whole thing once I get it apart again.  The "extension" portion is only about an inch or an inch-and-a-half.  Again, sorry to be so vague but I can't measure things until I get the pipe off again.

 

The thing that jumps out at me so far is what Bloo said about the size of the doughnut.  It just doesn't make sense to me that those two plates are in contact.  It seems like the doughnut should be a bit bigger so that it is still under tension forcing the inside diameter to seal against the upper pipe.  But I'm thinking these doughnuts must be standard items?  Matt's post makes me think that maybe I can find a doughnut that's a bit fatter.  The first doughnut (installed by the muffler shop) was provided by Waldron.  The second one (which looked pretty much the same) was one I got from Bob's.  I will look around at some local shops, as suggested by Matt.

 

I will report back after I disassemble it again and can post better pics of the upper pipe.

 

 

[Wayne R]

Neil,  in case this helps---when you rea tach   make sure the  connection is  dead parallel  to each other,.

and when you connect   move the  attachment  plates around  to another position then you  did  at the  first time.

 

Here in my opinion is the best paste on the market---CRC  Maniseal.

[Wayne R]

Sorry   did not realize  its made in Ausy  and NZ---may not be available in  USA---not sure.

[Den41Buick]

I don't know if this will help you but I had the same issue. My solution was to reuse the old doughnut. 

[neil morse]

1 hour ago, Den41Buick said:

I don't know if this will help you but I had the same issue. My solution was to reuse the old doughnut. 

Please tell me more.  Was the old doughnut "fatter?"  That seems to be the problem I'm having.  I haven't had time to do anything about this since I posted a few days ago, but I'm going to start next week searching locally to see what I can find.  From what Matt Harwood said earlier, it looks like all 2" doughnuts are not the same.  If I could find a fatter doughnut, I think the problem would be solved.

[Den41Buick]

From what I can remember I installed the new doughnut and the leak continued. I swapped it out for the doughnut that was already there which was different in shape. I cannot recall if it was fatter or not.  With two 41's it sometimes gets blurred. I have replaced the y pipe in both of them. 

Good luck Neil.

[neil morse]

I have gotten a new doughnut that's a bit thicker and I'm ready to give it another try.  The Walker Acousti-Seal recommended by @Bloo sounds like a good idea, but it seems to be unobtanium.  I haven't spent a whole lot of time searching the Internet, but everywhere I have found it so far it is "out of stock" or "unavailable."  Any other ideas on where to get the Walker's or for an alternative product that would work?  As always, thanks in advance for your help.

[Bloo]

That is odd. I know of no other product like it. There could be others, but I have not seen any. Someone told me it is like "stove cement" as used on wood stoves and flues(?). That is completely unverified. I just looked around and you are right, everyone is out. I did see that Autozone was willing to "ship to home", estimated delivery Aug. 5 (to central WA) so they must have a little left in a warehouse somewhere. Now that you bring it up, I think the last time I tried to buy some I couldn't get it on the shelf locally and had to go to Amazon or something (they are out of stock too right now).

[neil morse]

2 hours ago, Bloo said:

I did see that Autozone was willing to "ship to home", estimated delivery Aug. 5 (to central WA) so they must have a little left in a warehouse somewhere.

Thanks, Bloo!  I missed that in my search.  I just ordered it.

[Lawrence Helfand]

I had sealing issues as well and tried a few seals the best being from looking through the box at my local O Riley's. Still had leakage from both pipes and ended up using a muffler paste to seal every crevice. As its water based you can gob it on  and clean up with a sponge to keep it neat. Its my nose rather then my ears that tell me I have a problem as engine fumes easily enter the cabin even on the fairly well sealed Buick firewall. 

[neil morse]

Update

 

I took the pipe apart again and found the problem.  First, here's what the upper pipe looks like where it reduces in size from 2.25" to 2" and fits into the doughnut.

 

 

The problem is that the OD of the pipe that fits into the doughnut is too small.  The ID of the doughnut is 2.049".  The OD of the pipe (which is slightly out-of-round) varies from 1.965" to 1.984".  There is just too big a gap for the doughnut to ever seal, even when completely compressed.  This little video shows how loose the fit is.

 

 

If I were more experienced, I would have noticed this right away.  I talked to John, the owner of Waldron's, this morning about the problem.  He's going to make me a new upper pipe, and said he thought he could have it done and shipped out by Thursday.  In the meantime, I have gotten some of the sealant that Bloo recommended, and I will use that as well.  So I'm hopeful the problem will be solved.  I will keep you posted.

[EmTee]

I'm glad to hear that you found the problem and Waldron's is standing behind their product.  In the meantime I was going to suggest using a pipe expander to improve the fit.

 

https://www.harborfreight.com/large-exhaust-pipe-expander-57184.html

 

[neil morse]

3 hours ago, EmTee said:

I'm glad to hear that you found the problem and Waldron's is standing behind their product.  In the meantime I was going to suggest using a pipe expander to improve the fit.

That's a great idea, and if Waldron weren't going to send me another pipe, that's exactly what I would do.  John at Waldron's told me that sometimes the tool they use to shrink the pipe down from 2.25" to 2.00" goes overboard and they end up with a pipe (like mine) that's too small.  He said they can then remedy the problem by expanding the pipe back to the correct dimension.  I don't know why they didn't catch the problem with my pipe (and I didn't ask), but it sounds like a QC problem.  In any event, I'm happy that John is willing to make it right.

[Larry Schramm]

John at Waldron's is a good guy.

[neil morse]

13 minutes ago, Larry Schramm said:

John at Waldron's is a good guy.

Yes, for sure.

[neil morse]

Update

 

I'm happy to report that I got the new pipe from John at Waldron's and the new gaskets that he supplied as well.  What a difference!  The OD of the new pipe was 2.009.  And most curiously, the doughnut gasket he supplied had an ID of 2.006.  So a very snug fit indeed.  I guess all 2" doughnut gaskets are not created equal, but that's quite a jump from the 2.049" doughnut that I got from Bob's Automobilia.

 

Here's a shot of the pipe with the doughnut -- quite a difference from the earlier combination.

 

 

I had ordered the Walker sealant recommended by @Bloo, which AutoZone said they had in stock.  Turns out what I got was a "replacement" for the part number for the Walker sealant, something made by Yale Automotive.  

 

 

So I put it all back together today, using a coating of the "Muffler Cement" on the pipe where it fit into the doughnut.  So far, so good.  I can't hear any exhaust leak, but I'm quick to admit that I had trouble hearing the leaks in the first place.  Both Don and Konrad heard them immediately, but I'm just not experienced enough to know what to listen for.  But I can't feel any leaks this time.  And the past leaks were very evident.  In any event, I can't imagine a tighter fit on the doughnut, so I'm hoping this chapter is done!

 

 

[neil morse]

On 7/28/2022 at 4:34 PM, Bloo said:

The thing that stands out to me is that the plates were clamped together tightly. Normally I don't think that would be true with that type of donut gasket. Maybe the donut is a little too small and the flanges are bottoming too soon?

I have revived this thread after a two year break for a further report on the problem I was continuing to have with the slip joint on the downpipe on my '41 Super.  I'm starting off with this quote from @Bloo because, as is often the case, his observation was right on the money!

 

Where we left off, I had gotten a new pipe from Waldron, with a new donut gasket that seemed tighter, and also used an "muffler cement" product.  As I said at the end of my post above, it seemed like it wasn't leaking and I was hoping the problem was solved.  However, I had a nagging feeling that I was just "whistling in the dark" because the two plates holding the donut in place were still clamped together tightly.  I just continued to drive the car and pretended it was okay (but it wasn't). 

 

As I stated above, I don't have enough of an educated ear to hear the leaks, but one clear tip off that I couldn't ignore was after-firing both on a cold start and idling in second gear on a steep downgrade (of which there are many in San Francisco).  This symptom was a clear indication of a leak in this area, and it was getting progressively worse.  So a few weeks ago I finally bit the bullet and forced myself to really look at the situation.  Whatever bond that had temporarily sealed the leak was clearly gone, and I could actually rotate the two plates around the pipe just by hand.  I could also feel the leak, which was occurring all the way around the area where the downpipe inserts into the lower pipe.

 

What I realized is that no matter how "tight" the donut fit around the downpipe, it wasn't going to do its job unless there was actual compression of the donut.  The donuts I was using (both supplied by Bob's Automobilia and by Waldron) were just too thin.  So I set out to try and find a thicker donut.  This wasn't easy because everything nowadays in auto parts marketing is geared to what car a part fits.  I could go online and search for "exhaust donut gasket" and get many results, but only a few of the websites (or Ebay results) actually listed the specifications of the gasket.  But I found a few on Ebay where the i.d. of 2" was specified, and the photo seemed to show something thicker than the donuts I had been using.  They're not expensive, so I just ordered several that looked promising to see what turned up.

 

Here are some photos showing what looked like the most promising candidate compared to one of the type I had been using.

 

 

 

 

The new one had a 2" i.d. giving a tight fit on the pipe, but was both thicker and also had a larger o.d.  It did not have a taper on both sides, which concerned me a bit because the shop manual refers to the fact that the side of the gasket with the "longer taper" should be on the lower side.  But, again, the fact that the ones I had used earlier had a symmetrical taper should have tipped me off that they weren't right to begin with.  Anyhow, I decided to try the new candidate and with the help of my buddy @Konrad , we went ahead and installed it yesterday.

 

Here's what it looks like now:

 

 

So now the two plates are compressing the donut down into the lower pipe the way they should and hopefully accomplishing the intended purpose of sealing the joint tightly enough to stop any leaks but still allowing the upper pipe to slip inside the joint.  This seems so simple now (and unlike the way it was before) that I'm kind of baffled that the muffler shop where I originally took the car to have the Waldron system installed didn't realize right away that they need to use a different gasket.  I'm just a newbie who didn't know better, but these guys are supposed to be pros!  (But I guess on another level I can't complain since they used the gasket that I had provided and could say, "well, this is what the customer wanted us to use.")  Anyhow, I'm hoping I finally got things the way they should be.

 

For anyone confronted by the same problem, here's a link to the supplier of the gasket I ended up using:

 

https://www.adlerspeed.com/products/2-header-manifold-downpipe-exhaust-flange-weld-on-graphite-donut-gasket?_pos=4&_sid=d7576f5eb&_ss=r

 

 

 

 

 

 

 

 

[Matt Harwood]

That's exactly the solution I used on my Limited before I built the header. It would blow out anything else, but once I found those donuts, they worked like a charm. I think I eventually found some with a section of pipe through the middle to provide some strength and bought 4 of them for future use. I was lucky enough that our local auto parts store let me go through their cache of donuts until I found a few that I thought would work.

 

 

Is there anything more annoying than an exhaust leak? And anything more satisfying than fixing it? I bet it feels like a whole new car!

 

 

Edited August 6 by Matt Harwood (see edit history)

[60s GM Fan]

I had a similar issue on my 66.  When the donut was replaced it make it almost whisper quiet except when you stand in the back....then she sounds like a 425 should sound!

[Matt Harwood]

Dang, I didn't realize I made almost the exact same post twice in the same thread. I'm such an idiot. Sorry, Neil.

[neil morse]

Not at all, Matt, please don't apologize and you are not an idiot!  I was actually writing to acknowledge your previous helpful post just now when you posted.  I tried to find something like what you suggested locally, but I wasn't able to find anything.  I went to the only remaining independent auto parts store that I knew of in SF (now closed), but they didn't have anything like it.  And I knew that the people at Auto Zone or O'Reilly weren't going to let me poke around in the back.  I suppose I was fortunate -- ignorance is bliss -- that I wasn't annoyed by the sound because I didn't have the ear for it.  Also, there's something to be said for the "Car Talk" solution to annoying sounds -- just turn up the radio!  Anyhow, you are absolutely right that finally fixing it is very satisfying!

[Eddie-O]

Am I lucky! I had just received my exhaust from Waldrons the other day for my 41 248 with compound carbs. Have it all hung on the car with the exception of locking it all up ( loose). Was reading this post and noticed that I was going to have the same problem since the doughnut looked like it was not going to fill the void when tight. Didn’t even try to lock things down and went and ordered the doughnut (2) from Alders two days ago. I didn’t want to go through the trouble of completing the job with the Waldrons doughnut and have to take things apart the second time so I’m waiting for the Alders doughnut and do it once. I must say this post showed up at just the right time for me. Saved me a lot of headaches! All your efforts didn’t go to waste Neil. You helped another from going crazy. Thank you. BTW, the Waldrons exhaust fit perfect. Should let them know of this issue for the future.  

[EmTee]

Good for you!  Now, please tell Waldrons about this and suggest they supply the better (i.e., correct) doughnut with their compound carb headpipes in the future.