Sunday, July 27, 2014

CL450 Racer - Installing the Steering Damper (Video Post)

This is my second attempt at a video blog post. I've substituted a better camera, took more footage, and have been learning some more functions in the video editing software. It's still rubbish, but it's slightly better rubbish!

Video blog #2 is presented with better resolution, actual dialog, and 100% more Beach Boys: 

Monday, July 21, 2014

CB350 Cam Chain Tensioner Rebuild

(Brought to you by guest contributor Dan Falkenstrom)

Anyone familiar with early 70’s Honda engines is no doubt familiar with their rubber wheeled cam chain tensioners. Often they are the first component of an engine to fail, putting slack in cam chains and little bits of rubber in oil filters. This is exactly what happened to my little 1971 CB350.   

Due to the surge in popularity of these bikes, replacement OEM parts are all but impossible to find. Once in a while a NOS set can be found on eBay, but the quality of the rubber is suspect due to its age. Except for 100% historically accurate rebuilds, most would avoid putting these in their engines for fear of enduring a premature rebuild in the not-so-distant future.

A rare example of a new OEM replacement for the CB350 cam chain tensioner. The large wheel that attches at the other end is still available from some parts suppliers; this small wheel with steel support arm, however, not so much.

A comparison of small wheels: left is brand new, right is well-worn.
Two very worn large wheels. 
The popular option has been to upgrade to a tensioner system that does away with rubber altogether, using instead Nylon 6/6 (or similar polymer structures). Nylon is becoming more common throughout the automotive industry as polymer technology evolves, offering lighter weight and excellent resistance to wear. In this case, nylon will wear before the cam chain does (which is good), and will last much longer and fail less dramatically than rubber (which is also good). 

The only reliable commercial option has been the custom tensioner available from Bore Tech Engineering. This product has been a preferred upgrade for race engine builders for years, and it has more than proven itself on the track. But at $130, for those building a bike to cruise towards a buck-twenty cup of coffee instead of a buck-twenty speed at the drag strip, it can be an excessive upgrade. Every once in a while an entrepreneurial soul will manufacture a small batch of nylon roller wheels similar in size and design to the OEM ones, offering them for sale through message boards or eBay. Unfortunately, these folks are typically hobbyists with other full-time commitments, and they cannot cater to mass market desires for high-volume and fast shipping (at least, not for very long).

For the rest of us, we are left with no choice but to manufacture our own. My weekend jaunts between the hubs of New York’s Capital District demand little of my CB350’s performance curves, so I opted to rebuild my cam chain tensioner with wheels made of Nylon 6/6, retaining the original design dimensions and steel bushings. The nylon was purchased at $25/foot, and a replacement needle bearing for the small wheel (Torrington B-78-OH) at $15. A few afternoons on the lathe, and I had myself a small nylon wheel, an aluminum retaining pin for the small wheel bushing, and a nylon large wheel, all for a reasonable cost. We shall see how long they last. 

A side note on turning nylon; unlike metals, with high heat it begins to melt, making tolerance parts a challenge. Slow speeds, consistent fluid, and frequent breaks while turning help improve surface finish. 

A breakdown of the components in the CB350 cam chain tensioner system. The stamped-steel bracket and three steel bushings are original. The needle bearing was puchased new. The nylon wheels and aluminum retaining pin for the small wheel were made on the lathe.
A comparison between the OEM rubber wheel and the self-made Nylon wheel replacements.
Large wheel close up.

Small wheel close up, with aluminum retaining pin/rivet.

UPDATE 8/25/14:
After some tea and discussion, I decided to add a brass bushing between the large nylon wheel and original steel bushing. Since the steel bushing was some oddball size, I turned down the ID of a commonly available 0.75" OD/0.5" ID bushing. It press-fit nicely into the nylon wheel, and resulted in noticeably smoother rotation. 


Saturday, July 19, 2014

CL450 Racer - Building the Steering Damper (First Video Post!)

And now for something completely different.

I set up a video camera while I was making the parts for the CL450's steering damper, and then edited the footage into a quick montage.

(bear with me people, this is the first time I have EVER used video editing software)

So presented here, for your derision, is my very first video post!

I was able to find an original triple tree with the steering damper lugs, and a set of NOS friction and steel plates. I had to make an adjustment rod and custom triple tree cap, so I modified a stock cap from my stash and purchased a threaded rod and aluminum knob from McMaster-Carr.

Modifying the CL77 plates to fit the CL450 triple tree

The knob and rod were cross-drilled and pinned together

I modified the cap by drilling through it and pressing a flanged bronze bushing into the hole.

Thursday, July 3, 2014

CL450 Racer - Engineering Failure Analysis and Improvement

With all the news lately about the GM ignition switch recall, I wanted to illustrate an example of how a component failure should be addressed and improved upon by a responsible company.

I have worked as a test and r&d engineer for 4 years, and have developed an eye for spotting the warning signs and causes of part failure. Some are blatantly obvious, while others are only noticeable after they have already broken. In this case, I found a component in my Honda CL450 racer that was under-designed and made from a sub-par metal, but which had not yet failed. 

The part above is the brake actuation cam for the rear wheel drum brake. While disassembling the wheel to replace the brake pads, I found that the rod which spins the cam had twisted from the torque of applying the brakes. This was clearly indicated by the twisted splines at the end of the rod. The splines are keyed to the brake actuation lever to prevent it from slipping.

The part on the left is the original part, and it appears to be made from either a casting or a forging. This can be determined by the grainy surface of the metal and the lack of machine tool marks on many of the features. The cam on the right is from a later model, and demonstrates how Honda recognized the failure and improved the design to compensate. Based on the surface finish, this later part was made from a higher grade of steel. It lacks the grainy surface of the earlier part (large grain size is an indication of a weak material). It also has a noticeably darker color, which may be indicative of higher carbon content or a hardened outer surface. Finally, there are numerous machine tool marks all over its surface, which means this part was machined from a blank piece of material.

I have since replaced the original with the sturdier part. This cam is an excellent example of a part revision that has eliminated a potentially dangerous flaw.