|This article is about building a Honda CB/CL 160 Vintage RoadRacer. It will be a work in progress for a while so please bear with me. For most of you this will probably be more detail than you need, but feel free to email with questions if you need to.|
Michael's CB160 racer on the workbench at the Bateman Racing Skunkwerks
Tim Fowler and John Bundy have been building and racing Honda 160s in the Northwest for quite a few years. They've settled on a formula for building an inexpensive and reliable 160 vintage roadracer. That's what we'll be talking about in this article. This bike won't build killer horsepower, but then again no 160 does. This is the "budget" level of race preparation, and the lowest level of preparation we recommend. You can (and some people do) get away with even less preparation work, but we think it's generally false economy. However, if it's the only way you can get to the track then perhaps you should go for it. Just don't skimp on the safety aspect - none of us out there want you on an unsafe bike, mostly because we don't want to see you crash and possibly get hurt, but also because we don't want you to crash into us!
Additional speed modifications will be appearing in later articles. We refer to this basic level of modification as the "Fowler Formula" after Tim and John's method of building a vintage roadracer. I've added some pictures to the article to make things clearer. Let me know if you think I should add pictures of anything else. When I get into the engine I'll take some more and include them here.
There is a complete page of suppliers on the website here - everyone I mention as having parts available or recommend service by them is listed on the suppliers page.
Dan Hill in Bremerton has built a nice 160 for racing this year. I've included a few photos of his progress here. He informs me that this page may not be as informative as it could be as to how much time is required. "It sounds quick and easy by the website, but it's not so in real life!" or words to that effect. Well Dan - here it is in print - this will for sure take you much longer than it sounds like and longer than you'd think. But - stick with it - it'll come out fine in the end. There's always snags along the way - recalcitrant bolts, things that don't quite line up, things that warp, etc etc.
|Start by finding a Honda CB or CL 160. You can also start from a 175 and have a few advantages such as greater displacement and a five speed transmission. Here we'll concentrate on the 160. Starting from a "runner" is best as you know it's all working, but even a rusty hulk with a frozen engine will work fine. It'll be a bit more work for you, but then again it'll probably be very cheap. Like free, or close to it. If you do start from a 175 you'll want to find the earlier model with the "sloper" motor if you can as opposed to the later model with vertical cylinders. If you are stuck with a later model pay attention to the year of the bike. Most vintage classes have a cutoff year and for small Honda twins it's generally about 1972. Anything newer than that is usually not eligible to race in vintage. Of course it's probably fine anyway as the design wasn't changed, and I'm sure if you need to use a 175 built after '72 it can be accomodated.|
The essence of the Fowler Formula is to keep the motor fairly stock so that it's inexpensive to build and run, and is reliable so that it keeps running. Let's start with the motor.
You'll want to clean up the bores to whatever oversize they need. New matching pistons and rings should be used. If the engine is currently running or the bores are in still in good shape it is possible to race on whatever pistons you have in the bike (probably stock bore) by cleaning up and deglazing the bores and using new rings, but you'll be better off with new pistons. If you do re-use your existing pistons be sure to measure them (or have them measured) to make sure they're still in spec. Generally look over the engine and replace the stuff that needs to be replaced to keep it from breaking. Send the head out to someone like Phil at MSI or Craig Hanson at Hanson Racing Technology, or Les Barker at The Vintage Advantage/Little Engine Service for a valve job, light porting and general cleanup. Take a close look at the cam chain and tension roller as both can be pretty badly worn. We usually go through the stack of bits from torn down engines and use the best ones. You can also buy new ones from Honda, but they're spendy. David Silver Spares in England usually has them in stock, or Les Barker can build you a new racing tensioner from your core for a good price. Les is an excellent source for many fine racing parts for your 160.
If you've got more than one cam to pick from have someone take a look at what you've got and pick the one with the "sweetest numbers," generally the highest lift. Do the same with the points cam looking for the one that is in the best shape. Most of the CB160s out there these days have rusted and pitted points cams from sitting around in the rain. Even those work fine once you clean them up as race distance is short but you'll need to keep a pretty close eye on the point gap and timing between races. If you have the option - use the one that's in the best shape. Some of the bikes have the advance mechanism welded or brazed in the advance position, but they'll start easier if you leave that alone. As long as the advance mechanism works well you should be fine. If you're worried about it go ahead and weld it. You should probably use blue locktite on the bolt that holds the points cam to the cam, I've had that come loose on me before and mine's locktited now. Replace any of the engine seals that need it to keep the oil in. Replace all of them if you can afford it. Check the valve springs carefully. We recommend that you replace them as several of the bikes have had valve spring trouble. I'm now recommending that you buy good valve springs from Les Barker at The Vintage Advantage instead of using Honda springs, even new ones. They will work much better, last longer and help prevent valve float which can be disasterous for your engine's health.
Take a close look at the transmission shift forks and slider gears if you get that deep into the motor as they wear and cause poor shifting. Take a look at the spring on the shift detent as well as the detent roller. The spring is sometimes weak and the roller is often worn out and not rolling. This will cause you to shift 1-1/2 gears at a time putting you into a false neutral if you are too quick with the shifter. Remember, your bike is over 30 years old - flaws like that are called "Character." If it turns out once you get on the track that your bike has this kind of "Character" you'll need to shift more slowly to make sure you get a positive shift into the gear you want. Replacing the shift forks (and sliding gear if necessary) as well as rebuilding the roller, replacing the spring and replacing the bushing locating pins will make a big difference in reducing shifting "Character." The bushing locating pins are often bent and the holes in the bushings ovaled - this is a big source of slop in the transmission and subsequently bad shifting.
You can remove the alternator rotor if you choose since you'll be going constant loss on the ignition, but we generally leave them on to make it easier to time the bikes as the timing marks are on the rotor. The bike should rev faster without the rotor, but it may have a little less "grunt" off the line and out of slow corners. You can also remove the alternator stator if you want. You'll need to plug the hole in the cases where the wiring harness came through and do some work to the sidecover as the alternator cover screws are threaded into the stator, which is bolted to the sidecover. We've just been leaving the stator in the bike and letting the existing grommet plug the hole. Clip the wires off at the grommet and call it good. You have to decide how much work you want to do. We recommend you get your bike running and on the track first, then attend to details like that.
Remove the electric starter and all the starter gear, including the starter clutch stuff on the back of the alternator rotor (if you're keeping the rotor). You'll need to plug the hole in the case left by the removal of the starter. You can
Starter Blockoff Plug - Honda P/N 11921-223-010
Moving on to the rest of the bike you can remove all of the street gear, including most of the wiring harness. You might find it easier to remove the entire wiring harness and start over with a simple ignition circuit. If you do, make sure you have a clearly labeled kill switch in an obvious location, like the left handlebar or the triple clamp. You'll need this to pass tech inspection. On my bike the kill switch is actually a power switch between the battery and the coil. Also - make sure to tape the switch in the Off position when you're transporting the bike to the track. It's easy to bump the switch on and not notice it, meaning you'll have a dead battery when you get to the track. I doubt I need to explain how I know that....
We usually go with stock size batteries. They are bigger and heavier than some alternatives, but they also go a whole weekend without recharging if you're careful, and fit in the stock battery box without having to modify the box. Do make sure to pad the box with old innertubes or something similar to help isolate the battery from vibration.
Leave the fenders - you'll want those. Take off the stock footpegs and bracket and use the passenger pegs and brackets for your rearsets. Remove the rear brake pedal. You'll need to fabricate a new pedal and weld a new brake cable mount on the frame to suit the new footpeg location. Turning a shift lever around backwards works very well if you're comfortable with a GP shift pattern. You can also work up a linkage for a standard shift pattern. You may have to look for a shifter from another bike if the one you have isn't the right length to get the peg/shifter relationship you're looking for (or cut/weld it to the length you want). You may also have to heat and bend the shifter for exhaust pipe clearance depending on what you use for an exhaust pipe. Replace the stock handlebars with clubman bars (or clipons if you want to be trick). Craig Hanson can make clipons, or you can purchase them from Pro-Flo (www.pro-flo.com).
Right footpeg, brake lever and brake cable bracket.
Dan Hill's right footpeg and brake lever.
Left rearset (passenger pegs) and shifter. Also shows expensive custom exhaust...
Dan Hill's nicely done shifter linkage. His rearsets (passenger pegs) are different than the ones on my 160.
Another view of Dan Hill's shifter linkage.
Clubman bars and killswitch. Also shows front number plate mounting.
Remove the airbox, toolbox and related stuff. Some of us use the side covers, some of us don't. They do look nice and give you a place for all those sponsor stickers. They were already removed from this bike (along with the brackets) before I got it so I run without sidecovers. If you don't run the sidecovers you'll probably want to remove the mounting points as they stick out and will catch your leathers. The other option would be to make your seat base wide enough to cover the mounting points. This will be obvious to you when you have the frame in front of you in your shop.
Left side of 160. Note missing sidecovers and Uni sock style air filter. More on that a little further down.
Order Hagon shocks with lightweight springs from Dave Quinn. You can also use Redwing shocks if you can find them, but since Dixie has run out they're getting pretty hard to find. The Hagons work better anyway - the big advantage of the Redwings was that they were cheap. You'll have to sleeve the upper shock mount down if you get Hagons as it's made for a larger mounting pin than the one on the 160. There's a stock steel tubing size that works great. You'll also have to bore out the lower mount on the swingarm to accomodate the larger Hagon mounting bolt. Traditionally the guys have been using 90 pound springs, but in my opinion that's way to stiff. I've got springs on my shocks more like 60 pounds, and probably could go even lighter.
Hagon Shocks mounted on 160.
Change the gearing to something around 18/38, depending on the tracks you'll be running at. Most of the 160s here in the Northwest had been running 17/38 in the past, but we've found that taller gearing works better. I ran 18/38 for a while and I liked it much better. We've been slowly climbing the gearing chart. I ran 18/36 this last season for pretty much the whole year and it worked great for me. Sprocket Specialists makes gearing for the 160, you can get up to a 19 tooth front sprocket, and just about any rear sprocket you could want. I've got 17/18/19 fronts, and 35/36/37/38 rears in my race box when I haven't loaned them all out. That gearing worked great for me at all three local tracks - Seattle, Portland and Spokane.
You can use the stock steel rims and they work fine. Aluminum rims look nice and probably do make a small difference as they should be lighter, but I've ridden bikes with both and didn't notice much if any difference. That said - my racer has D.I.D. shouldered aluminum rims. They're much harder to keep clean than the stock steel rims, but they do look nice. For tires we use Avon Roadrunners. Tim and Frog have been running 80/90 front and 90/90 rear sizes for years. Michael Moore (of eurospares.com) thinks that the bikes don't need the 90/90 on the rear and could easily use 80/90's on both ends. He should know - as that's what he ran on his CR216 racer and it was much faster than these bikes. I ran an 80/90 front and rear all season last year and it worked great. I managed to win the season championship again and set several new 160 lap records, so it works just fine for me. In theory it should be providing lower rolling resistance. Several of the Portland based Flying Circus riders are doing the same and they seem to be going just fine on the smaller tires also. For tire pressures we've traditionally been using between 18 and 22 psi. Other racers are using pressures around 10 psi higher, and in fact according to the chart at http://www.eurospares.com/graphics/avontyre.jpg the recommended pressure is 28-30. I am currently running 26f-27r, and it seems to stick fine. I have been experimenting a bit with higher pressures this year and it seems to be working fine for me. Tim is still using lower pressures but is also climbing up a bit. You'll have to make up your own mind on tire pressures apparently.
Have the drums turned and the brakes relined if you can - it will make a big difference. We use a brake shop in the Seattle area (Metal Friction) that relines the shoes with an industrial truck brake lining which is cheap and works well, turns the drums and radiuses the shoes. I'm sure that real roadrace lining like Ferodo would probably work better, and someone like Michael "Mercury" Morse at www.vintagebrake.com would do a great job for you.
Clean up the fork tubes and put new seals in them if necessary. If you started from a rusty hulk you may need to look around for fork tubes that aren't so pitted that they kill the seals the first time out. You should also check the tubes for straighness. Anything short of severely bent can probably be straightened - I can do that for you if you find tubes that are otherwise in great shape. There are also many alternatives to the stock CB forks - I'll deal with that in a later article, but anything you find that works would probably be better. For example - Rich Levert has CB360 forks on his 175 racer. Both the CB steel slider forks and the CL aluminum slider forks work fine. Seals are still available for the CL style forks - my understanding is that seals are hard to find for the CB style. Brian Halbert of www.motogizmo.com has apparently found a source of seals for the CB steel slider forks. If you need seals for them it's probably worth shooting him an email to find out what he knows about it. Some claim that new fork oil is cheating - "What! You want Damping!? Next you'll probably want Brakes!" I find that oil in the forks does help some. :-) It will likely chatter the front end no matter what with the stock bits if you're going hard. I chatter a bit in most corners. I've been using 15 to 20wt fork oil and it seems fine. John Munns reports that he bought some special fork oil from Hoyt McKagen and he isn't getting any chatter to speak of. You can also adjust the tire pressure in 1lb increments and it may help, but you probably can't get it to go away completely without actually working on the forks. Maybe not even then. It tells you when you're going hard.....
You've already ditched the stock airbox/filter assembly. We recommend using air filters. You might build a bit more horsepower without filters, but if you crash you'll also suck in lots of dirt and rocks and need to rebuild the engine. These bikes run fine on their sides, starving for oil and eating rocks and dirt. I use foam Uni brand filters (see photo above). You can either get Uni, K&N or similar filters that will clamp on the stock carb bell, or do what I do and use velocity stacks with foam filters over them. Craig Hanson makes really trick carbon fiber velocity stacks that work very well, and that's what I've been using. One of the fellows from Portland last year was running velocity stacks made from bathroom sink drain plumbing. They actually look pretty good. I have no idea how well they work though. Tim likes to leave the stock side panels on. My bike doesn't have them. As I mentioned earlier, they do look nice and give you a place to put stickers, but the bikes without them look a bit more like traditional racers. That could be good or bad depending on your preference.... I don't have a choice as "Kid Bundy" cut off the mounting tabs for the sidecovers on the bike I'm racing. If you use velocity stacks and open the carbs (see below) you'll probably need to re-jet a bit. I had mine running 98 mains, but a run on the dyno showed that it was way too rich. I've got 92s in it now, and might be going back to the stock 90s at the next race. most of the bikes running stock carburetors are running on the stock 90 main jets and seem to run just fine that way. The needles generally are at the center clip position or one either side. I'm right at center right now. If you do experiment you should only change one thing at a time so you know what's working and what's not. Everybody I know runs the 38 pilot jet. You should rebuild the carbs regardless - or at least take them apart and clean everything. They usually need new float bowl gaskets and float needles at least. If you can find float needles with rubber tips use them. Otherwise, make sure you shut off the gas when you stop as the brass tipped ones usually leak and flood the bike when it's not running. You should check the float height while you're at it - it should be 19.5 mm from the surface of the carb body (not the gasket surface) to the top of the float. This is pretty clearly shown in the Clymer manual. Watch out for cheap float bowl gaskets that aren't quite the right size - they can pinch in on the sides and interfere with the float making the carbs overflow. It'll drive you nuts until you figure it out.
Right carburetor. These are the trick Craig Hanson velocity stacks and the machined clamp ring I made to clamp them to the carbs. Uni foam sock air filter clamps over machined ring, fitting completely over velocity stack. The ring outer diameter is 2.5", a stock Uni filter size and just a bit larger than the bell of the velocity stack.
If you want to open up the carbs a bit take a good look down the carb throat. You'll see that it's sort of figure eight shaped instead of round. At the middle of the eight the carb throat is only about 18mm wide. As the carb slides are 20mm wide you can open the carbs up to much closer to round. You can remove quite a bit of material from the left and right sides of the carb throat. Just make sure that you don't take out so much material that you uncover the slide. Also make sure you don't damage the needle jet - it's probably a good idea to take it out before working on the carbs. Once you take out the emulsion tube (the brass piece that threads into the carb body and has the main jet threaded into it) the needle jet can be pushed out the bottom of the carb with a small blunt drift. It shouldn't take very much force, just a few light taps of a mallet on the drift. You could use a rat tail or half-round file and several beers sitting in front of the TV along with some patience to modify the carbs. I use a metal cutting burr on a dremel tool to do the bulk of the metal removal, and a half-round file for finer work and smoothing. This will cause you to need to mess around further with the jetting. I'd start with a 92 or 95 main and center clip on the needle. You'll have to experiment from there yourself - you may find yourself back at stock 90 jets, but it's good to be conservative to begin with. You can also do some smoothing on the carb bell by filling in some with epoxy and grinding down casting bumps. More on this in a future article.
Right carburetor. You can see a bit of the carb smoothing in this picture. You'd probably have to have a stock carb in your hand to see the difference.
Go to straight pipes. A 2 into 1 should work better, and in fact I have a 2 into 1 kit from Craig Hanson that I'll be putting together eventually. Most of the bikes we're running have little shortie mufflers on the pipes, but they're not particularly effective and mostly for looks. Mine currently has 2 into 2 straight pipes I made from muffler shop scrap clamped onto the stock headpipes and it's no louder than the rest of them. They cost me $3, as the muffler guy felt he had to charge me something for having him put a couple of bends in one of the pipes. I had him put two 45 degree bends in a piece of straight pipe, then I cut it apart at an angle through the bends and straight halfway between the bends. Those are my fancy "slash cuts" that direct the exhaust away from the rear tire. Mig weld the whole thing together and weld a clamp on the one pipe. Use the stock head pipes. Tim and Simon-Pierre have 2 into 2 megaphones made by Aircone and they seem to work fine. Theoretically the 2 into 2 would work better with a 180 degree crank, and the 2 into 1 should work better with the 360 degree crank of the 160. Frog has a 2 into 1 that seems to work fine. The Flying Circus bikes from Portland have a wide variety of pipes on their bikes, and they all seem to work just fine.
160 right side showing custom $3 exhaust system.
Take off the seat and associated hardware and make yourself a racing seat. I've got a tasteful bumstop style fiberglass seat that was on the bike when I got it. You can use an upholstered piece of plywood for a seat and half a salad bowl from the thrift store for a bumstop, or you can go fancy and make a nice seat yourself, or order one from someone like Craig Hanson. He has nice aerodynamic ones available that are vintage legal. Dan Hill's bumstop looks super trick and was fabricated from a thrift store teapot.   Glass from the Past makes some really nice bodywork for vintage racing motorcycles, as does Airtech.
We use the stock fuel tanks. There are other bikes out there with nice looking fuel tanks that fit - Frog has one from a Honda 350, Dan Hill is using a nice looking tank from a Ducati, Tom Deem has a nice looking tank from another Honda, and Eirik has fabricated his own fiberglass tank. Regardless, make sure you clean it well, using a sealer like "Kreem" or "POR-15" (which has a better reputation than Kreem) if necessary. Also make sure to really clean the petcock well and blow out the screen with compressed air. You should probably do this several times a year, as a clogged screen will cause lean symptoms due to the reduced fuel flow that will be hard to track down. You can also add in filters to the fuel lines, but be careful of the filter bore size and flow capacity as the fuel flow capabilities of the setup isn't great to begin with.
Left rear numberplate and seat. The rear fender is almost visible in this shot.
Take off the kick starter and push start the bike. They push start very easy, and most racing organizations will make you take the kick starter off to race anyway. You can also remove the entire kick starter mechanism if you choose. You'll need to plug the resultant hole in the right case cover if you do. However, we recommend that you don't do that as we find it very handy to be able to use the kick starter if we choose, like on the work table or in the pits when you want to time the bike. Put the kick starter in the bottom of your toolbox and it comes in handy. Speaking of adjusting the timing - you'll probably want to get an extra sidecover for the left side and cut a piece out of it where the timing marks are. This keeps the oil in the bike and still lets you see the timing marks with the bike running. We use sidecovers from crashed bikes that would probably leak if used on the track. Waste not want not you know.
160 Timing Cover - allows adjusting timing without making a mess.
Improved 160 Timing Cover - leaving the rim and just making a hole where you need it makes the cover work even better.
Use a new chain. Chains for these bikes are cheap, and you'd be surprised how much horsepower can be lost in a worn chain. You haven't got very much horsepower to begin with, and you can't afford to be giving it away to a worn out chain and sprockets. This is also a safety issue - if your chain breaks it will often wrap itself around the swingarm locking the rear tire. Crashes at any speed are bad - crashes in fast corners could easily hurt you (or those around you) pretty bad.
Safety wire the bike. Take a look at your club's rulebook and wire at least what they require, then take a look and think about what else might come loose or fall off. I've got a lot more wired than the club requires, and generally nothing ever falls off my 160. I did lose the swingarm nut this year once, and it's wired now too. Most clubs require .032 stainless safety wire. Everything that's not safety wired should be considered a candidate for blue locktite. Make sure you don't forget the front axle pinch bolts.
Front of engine. Valve cover caps and exhaust clamp nuts are safety wired.
Front brake and fork. The front fender is hanging down in this picture as I'm getting ready to take the front end apart. We use lots of safety wire on the front brake linkage.
Front brake, right side. Note cooling holes - these would be much more effective with some work on the left side to scoop the air in. Note also the safety wired pinch bolts (nuts) and safety wired fork drain plug. The axle nut cotter pin is wired to the bike per WMRRA rules.
That's about the basic formula.
Some guys have gone beyond that with frame bracing, etc. As I mentioned I've opened up my carbs a bit with a file and dremel. Anyone can do that. If you want to go beyond to an actual performance engine I highly recommend that you buy Michael Moore's booklet on 160/175 modifications for racing. Actually - I highly recommend that you buy it if you want to race a 160 even if you want to follow the Fowler formula. The booklet is only 20 bucks including shipping and the information in it is invaluable. You can reach Michael at email@example.com. You could also add nice vintage looking bodywork, especially since it looks like most racing organizations are starting to require bellypans on all bikes. A tachometer can be sourced from a junk bike with an electronic tach like the V35 magna if you want - but so far we've been running our bikes without tachs.
Written out it seems like a lot of work, but it's really not too bad, although Dan Hill might disagree. Once you get the bike built you'll need to do very little to it during the year unless you crash. Even then they crash fairly well, especially if you run filters on the carbs. I was on the ground once last year due to someone in another class running into me and the bike survived fine. Pat Dowd piled the white bike into the tire wall in Turn Seven at SIR in 2001 and the worst of it was a bent handlebar, bent front fender, and a lot of dirt on and in the bike.
With a bike like this you can have one heck of a lot of fun in club vintage roadracing, especially if there are a bunch of other similarly prepared bikes to race with. I won the WMRRA 250 Vintage season championship on just such a bike this year. There is a lot more you can do if you want to - and it's possible to make the bikes much faster and more capable. This will be the subject of some future articles, but don't hold your breath waiting! In the meantime, read your copy of Michael Moore's 160/175 booklet, and check out his Honda CR216 roadracer project on his website www.eurospares.com. The eurospares site has lots and lots of information about vintage racing, frame building, custom race bikes, racing history and all kinds of great stuff. You can spend hours poking around there. Also check out the Moto Zastrow website for more ideas on racing and modifying Honda 160/175/200s. There's a pretty good write-up on the Moto Zastrow site about replacing the points with an electronic hall effect sensor and building a bellypan among other mods. Then think about getting signed up for the Vintage Roadrace List. You can find information on signing up at www.eurospares.com.
Good luck, and we'll see you on the grid!
Copyright © 2001, 2002, 2003 Michael Bateman
Photographs Copyright © 2001, 2002, 2003 Michael Bateman