Topic: Dragging Mac?

[70CB750]

I am the last one you would call daring rider, let's say I don't tilt the bike much, but the mac header is still grinding on the road during a turn every so often.

Is it a matter of all exhaust headers or just Macs?  I have 18" in back and 19" in front, home made straight muffler but the grind is on the spot of 4 - 1, it is not my work that gets eaten by the road.

[Powderman]

Is your bike lowered at all? Not all bikes scrap unless the suspension is weak and you weigh 300lbs.

[70CB750]

Stock height K0 on stock wheels.

[Geeto67]

I had a mac on a 73 cb750K. I bought the bike with lowering blocks in the rear and I couldn't make right turns because the bike would drag the headers for days. I pulled the lowering blocks off it and it only scraped in moderate cornering or cornering at speed. It is just the nature of the pipe to hang low and drag in turns - it's a cheap pipe.

You can take a torch to it, heat up the head pipe, and try to bend the collector closer to the frame but that is a lot of work for maybe an inch of clearance.

[run-tmc]

70CB750, I don't want to hijack your thread, but would you guys say it is normal for the Mac 4-1 to mount so poorly to the exhaust outlets on the head? The pipe diameters appear to be correct, but the mounting bolts are super long due to the flange on the header being so far away from the head. It almost seems like a mismatched product for my K6. Thx guys!


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[Geeto67]

it's normal...it's a cheap pipe designed to fit a bunch of different models within the SOHC line.

Do I even need to discuss the merit of lack of on the finish on these? I would never buy a chrome one again because of the speed at which it rusted. Even if I buy a black one I would paint it because the paint is so thin.

[seanbarney41]

Are we talking 4 into 1 here?  I have never been able to scrape mine on a cb750 despite years of trying...granted roads here in Michigan are generally straight...

[Geeto67]

I thought we were. I have never owned any other Mac pipe.

Here is an old pic of my 73 with the Mac:

[seanbarney41]

looks about the same as mine.  I can see dragging the muffler, but the collector is nearly in the middle of the bike.  I have had problems dragging it on speed bumps...and really not going out of my way to defend MAC's awsome quality lol, just can't see dragging that collector.

[70CB750]

This is how she stands now, the grind comes from the collector.  It was second hand Mac, the bike came with 4-2 chopper and leaking pipes.

it could be just my fat butt that makes her do it.

[Geeto67]

The collector is the lowest point on the pipe. So it is what drags, the actually muffler is much higher so it doesn't.

Something that did help a little was moving the muffler mounting tab to the backside of the footpeg mount. It shifted the pipe inward a little bit which helped when leaned over but it put the pipe in a little bit of tension which might cause cracking later on down the road.

to be fair 70cb750 I get the feeling you and I are bigger guys and probably give the suspension a little bit more of a workout than some of these lightweights. I hated riding 2 up on that bike because it dragged that pipe everywhere.