Hey All,

Recently installed my V&H Big Shots on my '15 Street Bob this past weekend. I made a thread about it and got some help throughout out the process. One thing that came up was whether or not the flanges need to fit flush and tight to the actual engine. I have about an 1/8" gap in between the flange and the engine at the exhaust port. I was told its normal with a good explanation, but after doing research on this site it seems there are varying opinions on the subject.

So which is it, do the flanges need to be snug and flush up against the engine, or is a small gap OK? Does it vary on pipes, gaskets, etc?

 

No the flanges should not be flush. If they were flush, there would be no crush factor or tension keeping the headers sealed to the crushable gaskets.

 

I have seen them both ways. Most of it will depend on the gasket you use, ie. the stock conical gasket or the SE flat gasket, or even say a James copper clad gasket. Some folks will stack 2 of the SE flat gaskets to get a seal. My preference would be to have a little gap between the flange and head with the nuts torqued properly. This way you should have a good seal with a little room to retorque after a couple of heat cycles. With the flange up against the head you may not get a good seal, or in fact the nuts may have been over tightened. Just my .02.

 

You shouldn't be drawing the flange up flush with the head. You would be far over the recommended torque on the nuts before you got there. I'd be interesting in seeing the posts that said the flanges should be flush with the head. Link?

 

Have to agree with above responders. Although after-market pipe designs will vary, mounting procedure pretty much as OEM ~ slight gap between flange and head after proper torque. Can't tell in my pic, but there is actually about the same 1/8" space between flange and head on my FB pipes as your Big Shots.





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Here is the link... scroll down someone has thunderheaders with the flange completely flush.

https://www.hdforums.com/forum/dyna-...ic-inside.html

Good to know its not really supposed to be flush and that it varies. I used the gaskets that came with the pipes. They are not the larger OEM ones though.

 

I'd say mine have a little larger gap, but maybe i just can't tell from your photo. Mine are probably 1/8-1/4". But even all around.

 

If you don't have an exhaust leak don't worry about the gap. As long as the flange is tightened to where it is even, snug, & not bent you are good to go.

 

Thanks. I don't think I have a leak. I heard it's obvious if you do...

 

Invest in a HD Service Manual if you plan on doing your own work. There is a sequence to install & torque down the head pipe.