Honda CB350F Four-into-Four Replacement Exhaust System
In 1974 Honda was still rocking everybody’s world with their single overhead cam in-line four cylinder superbikes for the street. It all started with the CB750 in 1969 and later a 500 cc version was added and then, in 1972 the small-bore four CB350F.
The littlest in-line four Honda built for export to North America really wasn’t a superbike — but it had the look of a superbike. Mainly, it had that distinctive four-into-four exhaust system that told the world, “yeah—it’s a four!”
Even though it was easy prey for Yamaha’s road rocket RD350, it had something the super-quick Yamaha didn’t — an awesome exhaust note that made the ring-ding of a two-stroke seem as annoying as a mosquito in your ear.
The CB350F was dropped from Honda’s line-up in 1974 without achieving the kind of adoration a piece of engineering like it was should have. Now, forty years later, there aren’t that many of them around and for all but the most recent years, getting exact replica replacement pipes was not possible.
That was a downer because nearly all of the CB350F original exhaust systems that weren’t damaged one way or another, or removed in favor of a four-into-one system rotted out so catastrophically, there was virtually no hope of repairing them. That forced the use of a four-into-one system whether you wanted it or not.
Now, however, it is a new day for anyone lucky enough to have one of these great little bikes that would be so cool again, if only it had those awesome-looking four-into-four pipes. Vintage Honda parts specialty house, David Silver Spares, which has locations in the U.K. and U.S. (David Silver Spares USA) now has original equipment equivalent replica four-into-four pipes available. The part number is HM333 SIL SET.
My 1974 CB350F has only 10,500 original miles on it, but the pipes were all horrifically rotted out. I had improvised repairs as best I could with muffler bond and high-temperature pipe wrap, which worked well enough to allow me to compete in motorcycle speed trials at Bonneville with the bike, but they simply would not last — and they looked pretty bad, as well.
Delivery came in only four days from my order and the pipes were well packed to protect the deep, high-luster chrome finish from header to outlet pipe.
If you have an aftermarket four-into-one system on the bike now, you’ll need to order the brackets, rubber connecting balancer tubes and clamps (one to each side) and rubber stand stopper that will be missing without the OEM pipes in place.
If you have the original pipes, be sure to harvest all these items and all the fasteners if you don’t plan to buy any new hardware, as you’ll need them. The pipes as delivered do not include any hardware.
Tools for the replacement are basic, 14 mm socket and open/box end wrench, 10 mm socket and short extension, 12 mm socket and/or open/box end wrench, Phillips head screwdriver and some thread locker. Some sort of pillow blocks to support the end of the pipes while you’re inserting the header end into the head will be very helpful, as well.\
When removing the old headers, be sure to note which way the flanged shims that go between the header pipe and circular finned ring clamp that attaches the header pipe to the head are arranged.
After you unpack the pipes take the time to loosely lay them out on each side to help visualize how they’ll fit together, then start the assembly. The Honda service manual for the CB350F/CB400F shows the assembly only vaguely, so this pre-assembly planning can save some aggravation, even if you have the manual.
Install the circular finned ring clamp on the header pipe. The inside diameter of these was large enough to easily come off the original pipes, but I found I had to use a hammer to tap them onto three of the four replacement pipes because the flange outside diameter was just a bit bigger. Not a difficult thing, but they were very snug. Be sure to have the cooling fins facing the right way—away from the head when installed.
Install the header flanged shims (two halves) on the header pipe at the header flange. I find it really makes things easy to use a wrap of cellophane tape around them to hold them in place while making the installation.
Lay out the pipes with the mounting stud side facing up, put some thread locker on the studs, if you plan to use it, loosely install the bracket to help maintain placement and install the rubber gasket around the balancer tubes between the muffler bodies. Tighten the bracket nuts up and check to make sure nothing has come loose on the balancer tube.
Using a pillow block under the mufflers makes things a lot easier when first trying to install the pair of pipes because until the header flanges are a way into the exhaust opening on the head, the top hole on the mounting bracket won’t line up with the hole for the bolt that holds the pipes and the passenger footpeg in place on the frame.
Mounting the pipes at the head can be a little tricky, but take your time and get the header pipes aligned with the exhaust outlet and keep working the pipes in and bring the finned ring clamp into place. Tapping the ring with a hammer once it is on the mounting studs will help drive the pipes into place. Take care not to damage the threads on the studs.
Once the studs are exposed enough to start the 10 mm nuts on the studs, you can finish the placement by progressively tightening one side then the other a few turns until the header pipe is seated.
Repeat the assembly process on the other side. The kickstand side will include a bracket on the bottom of the lowest pipe for the rubber kickstand stopper. Installation of the joined pipes on the kickstand side is a little tricky because if you leave the kickstand in place it must be threaded between the pipes.
The process may take a couple hours give or take, but the end result is worth it. That mellow, understated rumble at idle and the Honda howl at high RPM (the CB350F has a 10,000 RPM red line) you may remember from the original four-into-four pipes is back!
One thing that does not appear to be coming back is the blue cast to the chrome after getting the header pipes good and hot. With over 100 miles on the set of pipes since the installation, the chrome headers have no hint of blue or yellow discoloration.
Of course, time will tell if that will eventually develop, but so far so good. The product is not cheap, but for CB350F faithful who plan to keep their bike on the road for years to come, it is well worth the investment.
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