Topic: CB750 exhaust question

[callbr549]

I bought a new 4 into 2 exhaust from Mac to install on my 1972 CB750. Has anyone here installed this system? If so, could you post pictures? I'm not sure I have the mufflers on the correct sides and attached to the passenger pegs correctly. The centerstand now stops on the new mufflers, is this OK?

Of more concern, on one of the exhaust clamps (#4) I tighten the clamp as tight as I can, it looks there is no room for it to tighten anymore, but I can still turn the clamp. Its snug, but the others don't budge when I try to turn them. Will this be a problem, and if so, what should I do.

Thanks again. I'm always amazed at what good answers I've gotten here and how fast they come.

Rob

[KB02]

I should probably refrain from answering due to my clear bias against Mac, BUT...

The 4 into 2 has turn out, right? They should turn out to the outside.

As for the loose header, is there a chance you could post a picture? Sounbds like you've gt some kind of issue going on there. Do you have the copper crush washer/gasket in place on that port?

[callbr549]

The mufflers are the  megaphone style, so no turnout.  I used new copper crush gaskets in all 4 and did get the old ones out first. I'm not sure of the terminology for the components. When I look at the parts fiche on cmnsl.com the part that crushes the gasket is the "exhaust frange" (I'm assuming that should be flange?) and the part that clamps the pipe onto the exhaust flange is called an "exhaust joint".  The frange is tight into the cylinder, I don't think theres a problem there. Its the exhaust joint (the star looking thing) that won't tighten on the exhaust pipe, and the two halves of the joint look like they've met so can't get any tighter.

I'll try to get a camera working today so I can post pictures.

If not Mac, where would you go for exhaust, for futre reference? I looked at original style replacements on ebay and elsewhere, but they cost almost as much as I paid for the motorcycle. For my first bike I didn't want to put that much cash into it.

Thanks,
Rob

[PJ]

I have a Mac 4 into 2 but mine uses the origional head pipes. They were cut at a measurement specific to this system and I just had to buy the mufflers. I think Mac still offers this setup, I like it because you get the look of the old school head pipes. Not sure the pic will help much but if you would like a close up of something I can get some.

[andy750]

Ive used Mac 4-2 before - a couple of sets in fact and both fitted fine. The second set were a tad loud for my tastes and I sold them and bought a second hand set of HM300s (original 4-4 pipes for $300). Anyway to answer your question....make sure you have the the tab on the muffler fitting to to the correct side of the passenger foot peg  - see photo of my former setup below...










In this last pic you can see the spacer under the muffler where the rubber stopper should go...




 Since the mufflers slip off the headers then Id fit the headers first and then make sure they are tight before slipping on the muffler and aligning that with the rear foot peg. You have done the right thing in using 4 new exhaust gaskets - otherwise air leaks would occur!

With the Mac 4-2 the sidestand will hit the exhaust  -this is NOT good and so you should fab up a stopper to prevent that happening. I think on the underside of the exhaust there is a spacer where a rubber stopper can be placed - check this. If so find something that will fit on here.

Thats all I can think of for the moment. Photos of your setup would help.

cheers
Andy

[bwaller]

On your exhaust clamp you can take a grinder with a thin cutting blade or even a hacksaw and remove some material off the inside of the split opposite the threaded portion so it will clamp tight again.

[callbr549]

Here's what I've got for the right side,you can see the center stand pushing up on the muffler:


The left side:


The clamp that won't tighten:

[callbr549]

I finally got this to work. I had the mufflers on the wrong sides. Once I switched and then put the hangers on the inside of the frame, everything seemed to jive right.  The square bracket thingy that hangs off the bottom of one muffler now is the contact point for the centerstand. I bought a rubber stopper, cut it in half, drilled a hole through it and a matching hole in the bracket, so now the centerstand rests on a rubber bumper.  Thanks for your photos Andy, they were helpful.