Re: #3 header visibly vibrating

Posted by rrgunslinger on Jun 05, 2012; 6:20pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/3-header-visibly-vibrating-Fixed-tp4022310p4022311.html

Did you remove the muffler before trying to tighten the exhaust?  If not I would.  They should be tightened with no other pressure on them. 

On Tue, Jun 5, 2012 at 1:38 PM, seestheday [via Honda CB750'S] <[hidden email]> wrote:

I just noticed something weird on my 1981 CB750K.

This weekend I took off my headers to address an issue of the #3 one not seating correctly.  I could feel exhaust puffs when I put my hand near it, so I know that it wasn't sealed correctly.

So I took them off, and used a fair amount of high temp gasket sealer following all of the instructions before putting it back together (waited 24 hours before running etc).  The bike ran amazingly well afterwards (I also fixed a jetting issue, ensured that the cam chain tension was adjusted and made sure that the carbs were still in sync).

With the new jets, the exhaust note is lower, and I like it a lot more.  The puffs also went away completely.

I took it out for a highway spin last night and noticed a little more engine noise was starting again.  

When I started it up this morning I noticed that the #3 was visibly vibrating and rattling.  If I push on the exhaust with my foot causing the headers to flex just a bit the rattle goes away completely and it sounds like the engine is running perfectly.  The exhaust puffs are also back, as I imagine the gasket sealer has been perforated.  The aluminum flanges with the heat sink fins built in are definitely tightened all the way down and the copper crush washers are installed (along with lots of high temp gasket sealer).

I haven't noticed the header vibrate before, but it might be because the exhaust note is now lower, which would change the resonant frequency, coupled with the fact that I can now get a steady idle at 1100 rpm's when before the rejetting I had to keep it up around 1500 or it would stall too easily.

The headers are no name/uinknown 4-1's and the exhaust is a no name/unknown slip on.  Note that I said they're 4-1 headers and not 4-2-1 headers.

Has anyone run into this sort of thing before?  Is there an easy fix?  Do I need to figure out how to bend the header pipe so it will fit better?  

1981 CB750K

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