1973 Honda CB500K2 OEM-Spec Four-into-Four Exhaust: Review

1973 Honda CB500K2 right front view: Gettin' that old-time feeling with that original look.
Gettin' that old-time feeling with that original look.

Way back in July 2014, we told you about the original equipment manufacturer’s (OEM) specification replacement four-into-four exhaust system available from David Silver Spares for the 1974 Honda CB350F.

Not only did that system look and sound superb, far better, in my opinion, than many of the after-market systems currently available for that bike, but it also restored the bike to its classic form. The look and sound of the four separate pipes are just impossible to beat.

Now, more than six years later, we can also report that the system on the CB350F is still free of corrosion, chrome discoloration, blistering, or any evidence of internal disintegration—even after being used in land speed racing competition at the Bonneville Salt Flats.

1973 Honda CB500K2 OEM-Spec Four-into-Four Exhaust: Review
BEFORE: The 1973 CB500K2 in November 2018 as it appeared with an aftermarket four-into-two exhaust system.

According to anecdotal information from original owners of these old model Hondas that I’ve talked to, some of the original equipment exhaust systems were rusting through in as little as three years. So, by that standard, the OEM-spec replacement systems available from David Silver Spares may indeed be made with materials superior to the pipes these 1970s-vintage Hondas came with originally.

In the case of that bike, exact compliance with original equipment dimensional specifications was essential because the goal was to qualify the bike for competition in the American Motorcyclist Association (AMA) Land speed Grand Championship at the Bonneville Motorcycle Speed Trials http://bonnevillemst.com/ near Wendover, UT. It did qualify, and I rode it to set the AMA National Speed Record in the 350cc P/PC (Production Classic) class in 2014—and that record still stands.

In 2018, I decided to make a run for the 500cc P/PC class record, which has essentially the same “as produced” requirements for competition as applied to the 350cc bike. After a long search, I finally found a 1973 Honda CB500K2 in basically complete, original condition—with the same exception as that 1974 Honda CB350F—the original exhaust system had long ago rotted out and been replaced with an after-market four-into-two system.

Ironically, after searching for my home region in person and the nation on the Internet, where did the right bike turn up? Only about 20 miles from where I grew up in northern Wisconsin! It was a one-owner bike having been purchased new in 1973 from the same Honda dealer in Hurley, WI, where I bought my first new Honda motorcycle in 1974.

1973 Honda CB500K2 new pipes rt side: AFTER: November 2020 with the new OEM-spec four-into-four pipes
AFTER: November 2020 with the new OEM-spec four-into-four pipes

Almost as soon as I bought the CB500 in November 2018, I got in touch with David Silver Spares about getting the OEM-spec set of pipes. They were not in stock at that time, but in 2018, there was no such thing as COVID-19 and I wanted to confirm the bike would indeed run OK and had no major engine issues before I spent the money for the system, so I didn’t place an advance order.

By the time I confirmed the bike ran well, had good compression, cleaned the fuel system and did other odds and ends, and was ready to order, it was early 2020 and COVID-19 had shut down the factory where the pipes are made, so they were not in stock again until the summer of 2020. Then I got my order in.

The product arrived very well packaged and protected. The quality of the chrome plating is absolutely superb; based on both sets of pipes, compared to the original equipment pipes that were still on the CB350, the quality of the chrome finish on the new pipes is even better than it was on the originals.

In addition, I have since learned that both sets of new pipes are made by the same company that was Honda’s vendor for the original pipes back in the day, so they are made exactly to original equipment dimensional specifications.

Unlike the CB350 order, which still had its original rotted exhaust pipes on it when I got it at an auction and, so also had all the mounting hardware, the CB500K2 had a four-into-two non-OEM after-market exhaust system, so most of the original mounting hardware was gone and had to be replaced.

1973 Honda CB500K2 pre-assembly: Step one is to make sure all the parts are there, if you need to order all the mounting hardware. The parts list and diagram help visualize how it all fits together.
Step one is to make sure all the parts are there, if you need to order all the mounting hardware. The parts list and diagram help visualize how it all fits together.

So, one of the first steps of installation was to inventory the entire shipment. David Silver Spares provided a complete parts list, an exploded assembly view illustration, but no step-by-step installation instructions.

In the case of the 350F, I had the entire original assembly to go by, so written instructions weren’t as big a deal, though some installation hints would have been welcome. I also have the Honda shop manual for the CB500K2, but that doesn’t have much information on the exhaust system installation.

Here’s where my mistake number one took place that added some time and aggravation to the installation. In checking off item-by-item through the packing list, I found everything there as shown in the list, but I failed to note that the four brackets that were shipped are labeled “L” and “R” in the item descriptions. In looking at them, I assumed they were the same left to right—they are not.

When I tried to install the first two pipes, starting on the right side of the bike, I had loosely attached the brackets on the pipes and found the bolt holes did not line up with the bolt hole for the passenger footpeg, where the brackets are to be secured to the frame using the footpeg bolt (in my installation, the footpegs were not installed because they must be removed from the bike for competition). I took them off, flipped them around thinking that was the problem, but that didn’t work, either. Turns out, I had both of the left-side brackets, which will not work on the right. Lesson learned.

1973 Honda CB500K2 OEM-Spec Four-into-Four Exhaust- Review 2

In the event that you are considering spending the rather substantial sum required to restore your 1970s-vintage SOHC Honda four to its four-into-four former glory, I thought it may be very helpful to provide some step-by-step instructions to help make the installation a little smoother since none come with the pipes.

If you haven’t already removed the passenger footpegs together with whatever exhaust system you are replacing, do that now. You will need the 17mm footpeg bolts for the installation and new bolts are not included in the mounting hardware kit. Also, the exhaust pipe ring clamps (the ones with cooling fins that secure the pipes to the head on two studs) are not included in the mounting hardware, so keep all those. If they are as corroded as mine were, now is a good time to soak them overnight in rust remover to have them back to looking almost as good as new.

You may have your own approaches to any or all of the steps required to complete the installation—these are the methods I’ve found work for me having done this type of exhaust system installation twice. That doesn’t make me an expert, but I hope these ideas will help if you haven’t done this before. Cloth gloves are a good idea to keep hand grime and oils from getting all over the chrome plate and also to give your hands a little skinned knuckle protection. Here we go!

1973 Honda CB500K2 bracket, bumper and jumper tube: Pre-assemble the brackets (loosely), center stand bumper and jumper tube prior to installation.
Pre-assemble the brackets (loosely), center stand bumper and jumper tube prior to installation.

1—Unpack and inspect the pipes for damage and to make sure you received all four correct pipes.

2—If you had to order the complete mounting hardware, take the packing list and check off each item as you locate it. Be sure to note the right and left side bracket part numbers and part description, which includes the “R” and “L” letter and use them with the pipes for the correct side. In my case, everything on the parts list was there and nothing that I needed to complete the installation was missing or incorrect.

3—Install the copper exhaust pipe gasket in each exhaust port as you go. It looks like a copper O-ring. I have found that putting a couple dollops of grease or petroleum jelly on the gasket helps hold it in place until you can attempt to place the pipe.

4—Slip the external ring clamp onto the pipe—remember to have the cooling fins facing away from the end of the pipe that goes into the head.

1973 Honda CB500K2 exhaust ring clamps: These exhaust joint ring clamps are not included in the hardware pack. I soaked these original clamps overnight in rust remover.
These exhaust joint ring clamps are not included in the hardware pack. I soaked these original clamps overnight in rust remover.

5—Assemble the exhaust joint collar halves onto the pipe. To make it easier to get them to stay in place for insertion of the pipe into the head, I learned to do a single wrap of cellophane tape around the two halves when I put them on the end of the header pipe. Be sure to assemble them with the straight edge toward the head and the flange toward the header pipe.

6—Loosely fasten the muffler body support brackets to the muffler body with the 8 mm nuts and lock washers and then take the pipe and hold it in place from its correct cylinder exhaust port to roughly check the alignment of the mounting bolt hole with the footpeg bolt hole. A drop of thread locking compound is a good idea for all the fasteners.

7—While it probably doesn’t matter if you install the upper or lower pipe first, I found getting the bottom pipe on first can be helpful in supporting the upper pipe for installation. If you are working alone, having a block of wood, small jack or something similar to place under the muffler body during installation can make things easier. That’s how I worked on the installation, but if you have someone to help support and position the pipe, that’s even better.

1973 Honda CB500K2 collar and ring clamp: Tape the two halves of the collar together and place the ring clamp on the pipe prior to installation.
Tape the two halves of the collar together and place the ring clamp on the pipe prior to installation.

8—Install the header pipe into the exhaust port as snug as you can by hand, support the muffler body while you bring the exhaust joint ring clamp into position, slide it on the head studs until you can start the 6 mm nuts and snug them up until the hold the pipe end in place. For this initial phase, you may have to start them without the lock washers, but after you drive the pipe and ring clamp into place, back the nuts off and reinstall them with the lock washers but don’t drive them all the way down just yet. Leave them slightly slack to allow the mufflers to be repositioned for aligning the mounting brackets.

9—Slide the footpeg bolt into place to hold up the muffler end temporarily. This is a good point to assemble the rubber exhaust jumper tube and its clamp and place it on the nipple for it at the outlet end of the pipe. Doing it now will prevent securing the pipes in final position only to realize it has been overlooked and things have to be undone to install it.

10—Repeat steps 3-9 for the upper pipe, making sure the jumper tube is engaged and then place the footpeg bolt through the frame and both brackets and snug it up, but don’t fully tighten it down.

11—Switch to the opposite side and repeat the steps. On the left side, the kickstand is between the two header pipes, the interior cylinder’s pipe running behind it, the outside cylinder pipe running outside it. One step is unique to the left side—remember to install the rubber center stand bumper block to the bottom of the left lower pipe. It is attached by pushing the rubber button through the hole in the mounting point. I have found that using a small flat-blade screwdriver to push it through works pretty well.

12—Once all is in place, check for extra parts on the bench—if there are any, you may want to double-check the diagram to see if something is missing. If nothing appears amiss after you inspect the overall install, then work from the ring clamp stud nuts back to the rear of the pipes putting the final tightening touches on every fastener. Wipe the chrome down and stand back and admire the finished product.

1973 Honda CB500K2 right rear view: Those four pipe ends say it all.
Those four pipe ends say it all.

When I fired up the 500-four with its gleaming new pipes, the sound was sweet music to my ears. Some may disagree but to me, it was worth every penny to hear those four pipes singing in unison, like the Honda engineers intended back in the day. And, even though I never was particularly taken by the fluted muffler tips, now, looking exactly as they did in 1973 (the year I graduated from Hurley High School), they complete the unique, original look of my 47-year-old CB500K2.

Whether this bike sets a new 500cc P/PC land speed record or not, it is a two-wheeled time machine that takes me back in time as well as down the road.

Here are the details:

Vendor: David Silver Spares, in the UK: www.davidsilverspares.co.uk U.S.: www.davidsilverspares.co.uk/DSS-US-INFO/

Product site: Pipes for the 1973 CB500K2: www.davidsilverspares.co.uk/CB500K2-FOUR-1973-USA/part_273942/

Part number: HM374P SIL SET

MSRP: (prices subject to change—check exchange rates at time of order—best to get a full quote before ordering):

  • $1081.25 (U.S.). £820 (UK) (£984 inc. VAT EU), Approx.
  • Mounting hardware sold separately—(est.): $224
  • Shipping (from U.S. store in the continental US): $20