Exhaust flange thread sealant?

[Randy and Mary Davison]

Ron, Stu or others,

My riser started moving again when gripped at the top end of the blue hump hose.  This means the riser is moving slightly in the exhaust flange again.  I've tried two different types of muffler paste but it still coming loose.  I've examined the threads in the flange and on the riser and they appear to be in good shape.  The hump hose end moves about a sixteenth or so so the motion at the threads is pretty small.  There doesn't appear to be any unusual vibration, nor is the riser up against anything that would induce a side load.

I remember Ron saying he used a high temp RTV.  Do you remember what you used?  Any other suggestions for something that will really cement the riser in the flange?

Thanks,

Randy

[Stu Jackson]

Randy, the only one I could find on short notice was one that you participated in:  http://c34.org/bbs/index.php?topic=3644.0

The RTV, when I bought it at a car store, had many different varieties.  I haven't tried it yet, given the recent post with photos about exhaust gases out of the flange, I should.  (I did a search on " "exhaust riser" " by Stu Jackson and came upon a few.  I assume you've tried a search on RTV.   Ron Hill mentioned muffler patch paste in his old "List" that I included in a recent response to a question.  No one has mentioned a specific RTV with a name and model number as far as I can recall.

OTOH, if it moves a bit, that may be OK, the larger issue is does it leak exhaust gas at the engine end by the manifold and flange? 

[Jeff Kaplan]

randy,rtv products are made by many companies,and come in several colors, each color for a specific use. crc and permatex are top products. if you use one of these, both available at auto and truck parts stores, use only the red or black.the red is for high temp applications, low oror and non-corrosive. the black is for high pressure, non-corrosive. i'd use the red. both seal, bond and are waterproof...jeff

[Kyle Ewing]

Randy,

I have the same problem.  I used red RTV silicone (don't remember the part number).  After several hours on the engine I have a slight smell of exhaust and the riser wobbles slightly at the threads. 

All, is it possible that years of engine vibration has worn the riser or flange threads or otherwise caused the riser to not fit snug in the exhaust flange?  I plan to replace the exhaust riser this winter.  Is a slight wobble normal?  When the riser is tight on the flange it is about 90 degrees from where it needs to be.

Kyle

[Stu Jackson]

Kyle, the only input I can offer is reply #2 at:  http://c34.org/bbs/index.php?topic=3945.0  About halfway down that long thread is Ron Hill's instructions, although he does mention muffler patch paste, which Randy says didn't work for him.  The idea, as I understand it, is to "pre-test" the lineup of the flange and the riser itself first before adding the RTV or paste to the threads. 

I've had that wobble for quite some time, but not when the new riser was originally installed back in 2003.  It's only shown up in the last nine months.  I would think, however, that even if the riser wobbled a bit in the threads, if they were set deep enough, gases shouldn't get by, but that's why they use that thin white Teflon tape on regular plumbing fittings, right?  Perhaps it's an "unforeseen consequence" of the hump hose?  Unusual though that it hasn't popped up as an issue before this, since the hump hose has been around for at least ten years.

Steve M's photos on that thread are great.  I don't know where the "blow-by" is coming from, as we have the same issue, but I've been busy rewiring the start button to the starter solenoid with new wiring and a new fuse holder (second time in 21 years, not bad, last in 2004 - I gotta get better than the factory! )

Two of our Fleet 1 members recently did this work (themselves) and I just emailed them to see what sealant they used.  I'll let you know.

[Randy and Mary Davison]

Thanks all for the replies so far.  Stu, I'll see what you find out and then take another shot at it.  There is a very minor amount of carbon deposited on the heat exchanger so there is a litttle blow-by. 

I suppose the good news is that I'm getting really good at getting the riser in and out quickly....  I'd like not to do it too many more times as the fresh water hoses to the water heater and many other projects await!

Randy

[Stu Jackson]

Bingo, Randy, the soot on the HX is exactly what I have been experiencing!  I'll let U know asap.

[Stu Jackson]

Here's the first reply.  Thanks to Bill Eddy, all around great guy and a sparkplug for C34 Fleet 1 in San Francisco for many many years.  I get to conitnually kid him because his boat is soooo old (#214 - we have #224!!!)

Hi Stu:   I think we both used the same stuff from the outboard motor shop in Oakland.  It was an Evinrude/Johnson product made for outboard motor head gaskets that is supposed to take high heat and stay flexible.  Gasket sealing compound was its exact name.  The can says that it never hardens or dries out, withstands heat and pressure and prevents corrosion of bolt and fitting threads.  Tech data is available on http://www.evinrude.com/.  Best personal regards, Bill


Oddly enough, I remember buying a tube of that when I went into that same store to ask.  Now all I have to do is find it on the boat!

[Ron Hill]

Guys : The RTV sealant that I've found (red color made by Permitex) is only good to about 400+ degrees (as I recall).  I believe that the exhaust temperature at the flang-to-riser connection is much higher than that!!

What you have to do is to thighten your flang into the riser in a vice.  Then check the orientation in the boat between the engine and the muffler.  When you are satisfied with that orientation, then take it apart, apply muffler paste and screw it back together the same number of turns back to that correct orientation. 
Like any plumbing job, only tighten - do not turn back - only tighten!   

[lazybone]

Mark the orientation then weld it.

[Stu Jackson]

Ron's right, and if you look at the orientation of the riser to the flange, if the riser end under the head sink DROPS that means it is UN-screwing at the flange, if it is rising, like say to stick in the hump hose, then it is screwing at and into the flange.

That's why Ron's instructions say use two people so you don't chance being in a position of unscrewing at the flange when installing.

If you deliberately set the under-the-head end of the riser position LOW, attach the flange to the manifold, then you have to be very careful not to raise it too much to "slip" the hose onto the muffler.  It could be done, but even the hump hose is pretty solid and doesn't bend, so somewhere in the process you're gonna end up doing a little UN-screwing.  Think about, especially if you're single handed.

I don't know if the material that Bill Eddy suggested would survive an UN-screw of a small amount as compared to the muffler paste.  

I think what my problem is is that the guy who installed my riser (only time I'm ever gonna let anybody on my boat to "fix" something ever again) put a loop hose in which I had to replace with the hump hose because the loop was rubbing itself to death.  Moving the riser was convenient, but didn't help the seal at the flange.

I wonder how many of you who are mentioning the blow-by have fussed around under the head recently?

[Stu Jackson]

WELD it?  How ya gonna replace it?  Oh, I see, buy another flange very five years or so when you replace your riser.  That's doable.  What do the rest of you think? 

Of course, welding is not something that everyone has access to, while a can of high temp / high pressure gasket material is pretty readily available.

Anybody welded one yet?

[lazybone]

The weld can be ground off if the riser has to be replaced so the the flange can be reused.  Any decent muffler shop could weld a bead for you. The weld dosen't need deep penetration.

[Randy and Mary Davison]

OK.  I'm going to try the gasket sealer and see how it works.  I'll also use a helper to be sure I don't unscrew the threads when I put on the hump hose.  I don't think I moved it much last time and the paste was still malleable but who knows?

Stu, your thought about plumbing tape is an interesting one.  I wonder if there is a high temp tape-like material that would perform the same function as plumbing tape?  If the gasket sealer doesn't do it, I'm going to see if I can find a tape material to try.  Welding might be fine but somehow I don't find it attractive.  Probably just a comfort zone issue.  I've been bitten way too many times by the law of unintended consequences - a law that makes Murphy's law look weak!

Thanks all - Randy

[Ron Hill]

Randy : I said to put it in a vice and screw it (flange to riser) together as tight as you can get it to about the correct orientation!!!  Then check the orientation and then unscrew or tighten more (you'll need the vice again)!!  I'm talking about 5 to 8 complete turns TIGHT TIGHT !! The paste acts mainly as a lube and then as a sealant so you can TIGHTEN it down again.  Like the muffler system on an auto you don't want any exhaust gasses escaping thru a connection.  In your boat you don't want CO to be escaping into the cabin!!  Welding is NOT necessary!  Muffler sealant is only necessary on the riser/flange threads.  The factory gasket seals the flange to engine joint.

In no way should attaching the hump hose loosen that joint!!  I'll guess that the temperature of those exhaust gases exceed 1000+ F.  I wouldn't recommend touching that exhaust flange after the engine has been running for over 15 minutes.  OUCH!!!