Survivor Chop: Repairs and upgrades everywhere

 

After a weekend trip to Gettysburg with a couple friends, I found a few things on this bike that could use some love.  On top of that, some of the equipment is just old and could use replacement so I don't have to deal with issues roadside.  This includes some electrical repairs, exhaust repairs, new oil and vent lines, new wheel bearings, new front rotor, and a tighter rear suspension. 

The last one in the list above was a bit of a surprise to me after I loaded the bike up with my gear for the weekend.  I went over a bridge and heard a screeching sound like the wheel locking up.  It turns out that the rear wheel was rubbing the fender... a lot.  To remedy this, I asked John to whip up some spacers out of scrap to preload the rear springs a bit more. I measured the spring rate to be about 185 lbs/in, so we went with 1/4" spacers to add about 90 lbs more preload (46.25 lbs on each side).  This helped quite a bit, but it still rubs slightly over heavy bumps.

I slapped some black paint on the underside of the fender to cover the raw metal from the tire rubbing over the years.  This also gives the tire a fresh canvas to scuff up later.  Overall, the bike rides about the same, but the tire scuffing is only slight.  John made up a second set of spacers to add which are 1/8".  I may add those and see if I can avoid tire contact with the fender altogether.

I hope to use this bike as my touring ride for a long time to come.  With that in mind, I want it to be as reliable as possible.  And while the original regulator and rectifier on the CB750's is quite reliable, it is already 49 years old.  So out with the old and in with the new.  A new regulator rectifier combo from Rick's Motorsports (model 27-10100).  This reg/rect combo is plug and play with the factory wiring harness, which surprisingly, this chop has.  Removing the old parts and installing the new combo unit was a huge pain only because the main wiring fixture from the original CB750 was mounted under the oil tank, making it impossible to remove the original regulator and rectifier without removing the rear fender.  This was one big reason why I did this upgrade. I would not have been able to replace the original parts roadside.

I also replaced the glass tube fuse holder with a more modern blade type fuse.  While this bike retains the factory harness, someone consolidated the fuses to just a single 20 amp fuse.  I would prefer separate fuses, but I've owned and built many bikes with just one main fuse without any trouble.

The exhaust repairs included replacing the no. 10 bolts on the exhaust sleeves at the tube joint near the footpegs with 1/4-20 bolts.  The right side exhaust came loose while up in Gettysburg and I had to use bailing wire to strap it to the frame.  I don't like the fact that the sleeves are a tad small and simply black pipe, but they will work for now. I also sealed some leaks at the spigots with aluminum borrowed from an Arizona Green Tea can.  Nothing but the finest material.

The new oil and vent lines were brought to you by Home Depot.  Reinforced clear vinyl tube for the oil lines and clear non-reinforced vinyl tube for the vent lines.  I like that the oil flow is visible.  This material gets soft as the are heated, so be sure to use reinforced tube for the oil lines.  

I have run many bikes on the original wheel bearings for years without noticing any issues, until I actually replaced a full set on a bike.  The ride was significantly smoother and handling in corners was notably better.  The bearings on this bike had their time in the spotlight and exhibited some rough spots. And while I would have just run these in the past (and did for a while this past year), bearings are cheap, replacing them is good insurance, and the difference is quite noticeable.  

The bearings for the hallcraft front hub were conversion bearings to adapt the wheel to the 5/8" axle.  The part number from NSK is 6203-625VVC3.  Simply drive the old ones out carefully with a punch, clean all the surfaces, inspect the inner sleeve for damage, and install the new bearings.  Be sure not to compress the bearings in so tight that they bind from compressing the inner sleeve.  Press the bearings in until the inner sleeve is in contact with the inner race of each bearing, but both bearings spin easily.  This goes for the rear hub too.

While doing the bearings, I cleaned and polished everything along the way.  It's easy to get to those small spots now, and not so much later.  

The rear wheel has three bearings, two in the hub, and one in the sprocket carrier.  All Balls sells a great kit that I have used many times.  The part number is 25-1362 for the CB750 rear wheel.  It comes with all three bearings and a new shaft seal for the sprocket carrier.  This shaft seal was important for the factory bearings, which were not sealed.  However, the All Balls kit comes with sealed bearings.  

The sprocket carrier has a bearing retainer on it.  When I cant find my retainer tool, I just use a set of hex keys or punches that are close to the diameter of the holes and rotate them with a pry bar.  To prevent the aluminum threads from galling, clean the retainer and spray the threads with penetrant.  Leave the sprocket carrier in the wheel while working on the retainer as it will help hold the piece steady.

Once the retainer is removed, drive the bearing out from the other side and remove the shaft seal.  Clean all the surfaces and install the new bearing and shaft seal.  When installing the new bearing, you can use the old bearing as an intermediate surface to bash on.  It's the same size as the new bearing and will distribute the force evenly. One other tip: If the shaft seal is being a pain to remove, heat the retainer with a torch and melt/soften the rubber shaft seal.  It will pull out easily.

The rear hub also has a bearing retainer and I use a similar method as above.  Instead of hex keys though, I use flathead screwdrivers to engage more of the surface of the retainer. Use penetrant to minimize/prevent thread galling.

Drive the bearings out from each side, clean, and replace.  Once again, the old bearings can be used to assist with seating the new bearings.  And once again, make sure to inspect the bearing sleeve that rests between the hub bearings and ensure that it is in contact with the inner races of the bearings and the bearings spin freely.  Reinstall the bearing retainer and you're all done.  This is also a good time to inspect your kush drive rubbers, your rear brake shoes, and your brake liner.  Ohh and clean/polish everything!  One more pro tip:  Matching the bearing seal color to the bike adds 20 horsepower at the wheel. Luckily, the All Balls kit is blue!

Last on the list for this post is the front rotor. The original one was heavily pitted.  They were made by Hurst-Airheart, now known as Airheart Brakes.  You can purchase a rotor that's similar in dimension, but will need some modification to mount to the Hallcraft hub.  The part number for this replacement is 3301-1003 (7.75" diameter, 0.119" thickness, 3.50" bolt circle diameter, 0.194" bolt hole diameter).  The bolt holes need to be counter-sinked and opened up to accept the 1/4-28 bolts that the Hallcraft hub uses.

I didn't purchase a new one and go down the route of modifying it to work because I had a few of these rotors sitting around.  I checked the potential replacement for warping, pitting, and thickness.  Then cleaned, sanded, and painted it to make it look purdy.  I installed with the original bolts because they were in good shape and used blue loctite.

So that wraps up a good bit of work to get this bike, that my friends have named "Blue Waffle", in top shape.  Better electrics, newer bearings, fresher brakes, new lines, tighter suspension.  After this, I'm going to spend some time tweaking the tuning a bit.  I feel that there's plenty of room to improve this bike's performance and reliability.  So next we'll take a look back at the carburetors and the ignition.

Another Late Night: Exhausting Work

Working on a set of "Scrambler" or high pipes for the dual sport, british looking, japanese thing I've been wounding myself with for the past month. I'll get some better pictures up eventually. For now, it's time for coffee!

Ohh and puns are phun!

New Product: The Broiler Exhaust System

We designed this exhaust for those long, cold winter rides. 1,400 F is enough to keep you nice and toasty at speed.

Speed Equipment: Taking a look at the Honda Four's Power Potential

Here is another vintage article from Richard Bean. I got this one from the SOHC4.net site and I do not know where the information originally derives from.

Mr. Beans words.

If the big Harley twins can be likened to the Chrysler engine which has dominated automobile drag racing for a decade, then the Honda 750 engine must represent the Chevy V8 of the motorcycle world. With its ability to rev clear out of sight and stay together, it cannot be overlooked as a potential winner in any form of competition. Its appeal as a street engine is as large as its hold over certain classes in both drag and road racing.

The purpose of this article is not to follow the step-by-step construction of any one engine, but to report on the state of the art and inform the engine builder as to what is available in the way of hop-up parts and techniques.

The basic engine is by itself a fine powerplant, capable of giving a good account of itself on the street. It develops considerable power and, for an engine that needs rpm to produce that power, is fairly tractable on the street even in heavy traffic. In its stock form the Honda 750 is able to turn the quarter mile in the high 12's which definitely puts it in the superbike category.

Several riders have written us complaining of the fact that the Honda is a pipey type of bike which comes on quickly at the upper limits of its rpm range, but we haven't found this to be the case. To be sure, the Honda engine doesn't develop much torque at low rpm's, like the Sportster or 74, but it is mostly a matter of getting used to holding the revs up. Another thing is that the engine exhibits very little flywheel effect and revs fall off quickly in between shifts. Again, this is a matter of getting used to the engine and carrying the shift point a little past the point of maximum torque.

For the rider who wants to get additional power out of the engine, two things are immediately apparent. One is that the stock carburetion isn't worth a damn for real high performance operation, the other is that the engine can really benefit from better exhaust.

The 28mm Keihin carb used on the stock Honda 750 is a good, reliable carburetor for a stock engine, but if internal changes are made to the engine to increase the power, the restricted airflow through the carb just about cancel out any gain. In the December issue of HOT BIKE, we ran a story about porting the head on the Honda 750. In the story we pointed out how flow bench testing showed that the stock Keihin restricted the airflow through the intake port to the point where installing a better cam or modifying the port would be almost useless. Honda Four owners are lucky, however, because there are a number of different carburetion setups which can solve the problem.

Probably the best from the standpoint of cost and ease of installation is the Mikuni. In addition to being a better flowing carburetor, the Mikuni offers a substantial number of jets, airbleed correctors, and other tuning parts to get maximum performance. The testing we did on the Honda head used four 32mm units and we feel they are about the right size for racing use, with the smaller 30mm size for street operation. Another good setup which we have seen on several bikes is the constant velocity carbs from the late Honda 450. These can often be found in wrecking yards and will do a good job. These are also a 32mm unit and need little modification to fit.

For the rider interested in maximum performance without worrying too much about the cost, Russ Collins at R.C. Competition Engineering has started production of a manifold which adapts a pair of DCOE -40 Webers to the 750. Russ also has a single Weber manifold for the Honda which is a log type in the works and we should be hearing more about it before too long. Jerry Magnuson, who designed one of the best manifolds on the market for the Weber to Sportster conversion is rumored to be working on a manifold for the Honda, so there is no scarcity of carburetion for the 750. For the all out racing effort, Yoshimura Competition in Waterford, California, sells matched sets of the 31mm GP carbs used on the Honda road racers, and Fuel Injection Engineering is putting the Hilborn injector designed for the Honda LSR bike (see page 52 of this issue), on the market for the drag racer.

Another place where the Honda has a lot going for it is in the area of exhaust systems. A number of manufacturers jumped on the bandwagon early in the game, and there are several good systems available over the counter. Because the Honda 750 is a four cylinder engine, a lot of hard earned design work done by the automotive exhaust system builders can be applied to the Honda in the form of collectors. Basically, the collector uses the pulse from an adjacent cylinder to lower the pressure in side the exhaust, creating a slight scavenging effect. By arranging the exhaust pipes inside the collector, additional effectiveness is gained at certain rpm levels.

The two companies which have the most experience with the collector header on the Honda 750 are Action 4's in Santa Ana, California and R.C. Engineering in Torrance. Both of these companies are active in competition at the dragstrip (against each other), and make a variety of custom exhausts for the 750. Action 4's newest collector header for the Four is a 180-degree tuned system which is just becoming available. Another recent entry into the Honda header market is Jardine Headers, well known for automotive competition exhausts.

In the non-collector field these same companies market make a variety of special exhaust systems for the Honda Four, drag pipes with and without megaphones, and street systems. Yoshimura Competition also offers racing headers with megs for road racing. These pipes tuck in under the engine for maximum cornering ability.

Next, in order of importance, is better internal breathing for the engine. If you add better carburetion and exhaust, probably the first thing that occurs to most builders is to install a better cam. This can be a losing battle in the unmodified Honda engine, because of the fact that the stock head suffers from restricted breathing. Most high performance cams rely on increased lift to get more air/fuel mixture into the cylinders, and this is something that the Honda engine can't make good use of until it has been modified. Our testing on the Honda head pointed out the fact that airflow through the intake reaches a peak at about the .300 lift point, and further increases in lift do not help. If you intend to install a hotter cam in the otherwise stock engine, get a cam which uses somewhat more duration and lifts to only about .350-inch. This is easier on the valve train, as forces increase dramatically with increased lift, and reliability will be increased.

Currently the best cam for competition seems to be the Kenny Harman F grind. This is an all out racing cam and several alterations to the engine, including cutting deeper valve pockets in the pistons are necessary with this cam. Action 4's offers this cam as part of their line and their custom racing pistons are clearanced to handle the extra lift.

If the head is ported and polished, lifts of .400 and above can be used. Valve shape on the Four is excellent and no modifications are necessary. In addition to opening and reshaping the intake port, the engine will gain considerable power by grinding away much of the shrouding around the spark plug tip in the combustion chamber. When finished, it gives the Honda a hemi-like look and really adds to the engine's horsepower. One word of advice that we should offer is don't do the job yourself unless you have quite a bit of experience in porting. This is one job that's best left to the shops that are equipped to handle it.

Increasing the displacement of the Honda is a sure route to more power. There are several kits on the market to enlarge the cylinders of the Four to as large as 915cc's! The popular sizes are 785cc, 811cc, and 836cc. These big bore kits are not too expensive and require only a minor amount of machining to install. Th two major suppliers of the big bore kits for the Honda 750 are Action 4's and Powroll, who supply all sizes and have a complete line of custom made and modified parts to equip the kits.

Several of the speed equipment suppliers are working on the problem of providing better rods for the 750 and we hear rumors that an entirely new forged rod may be available this year from a southern California designer. At the moment, Action 4's offers a carefully lightened and polished rod as part of their engine packages, and Russ Collins at R.C. Competition Engineering sells a heat treated and shot peened version.

Electrical systems for the Honda are limited to two magneto units, one by R.C. Competition, the other by Yoshimura. Later this year we expect the Joe Hunt Magneto for the 750 to become available. For most street applications, the stock ignition system works well, the magneto being necessary only for competition.

The Honda 750 represents a real challenge to the rest of the big engine field in motorcycle drag racing. It is tough, makes a lot of power for its size, and has the added advantage of having more speed equipment available for it than any other engine except the big Harleys. We've included a list of the major speed equipment suppliers for the Honda to assist you in getting the parts you need to turn your Honda Four into a real screamer.

Action 4's	2621 S. Main Street	Santa Ana, California 92707
Yoshimura Competition	P.O. Box 267	Waterford, California 95836
Powroll Performance	P.O. Box 926	Bend, Oregon 97701
R.C. Competition Engineering	2920 Sepulveda Blvd.	Torrance, California 90505
Branch Flowmetrics	1637 E. Burnett	Long Beach, California
Hunt Magnetos	2600 W. Vernon Avenue	Los Angeles, California
Mikuni K. American Corp.	7923 Gloria Avenue	Van Nuys, California 91406
K-H Cams	2163 S. Hathaway Street	Santa Ana, California 91705