Building the Honda 160 Vintage RoadRacer

Tim "Fats" Fowler (219), Simon-Pierre Smith (123) and John "Frog" Bundy (157) at PIR, 1998

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 a reliable 160 racer.   That's what we'll be talking about in this article - the building of a basic, reliable vintage 160 roadracer.   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 a later article.   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.

Dan Hill in Bremerton is building 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.

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 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.

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.   Most 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.   Replace any of the engine seals that need it to keep the oil in.   Replace all of them if you can afford it.   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 and replacing the spring will make a big difference in reducing shifting "character."

You can remove the alternator rotor if you choose since you'll be going constant loss on the ignition, but we 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, but 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 buy the plug from Honda (P/N 11921-223-010), make one yourself (It's 67mm in diameter with a groove for an o-ring), have a plate welded to the case, or take apart the starter and make a plug from the end plate of the starter.   Some folks have had good luck with that and JB Weld.   I've not done that myself but it is the cheapest way.

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.   Leave the fenders - you'll want those.   You only need to leave the ignition circuit and a wire for the kill switch.   Take off the stock footpegs and bracket and use the passenger pegs and brackets for your rearsets.   Remove the rear brake pedal.   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), and add a kill switch either to the left handlebar or to the brackets you use for the front number plate.   Make sure to mark the switch for On and Off.   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....

Speaking of batteries - we 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.

Left side of the 160 - showing removed stock footpegs and reversed shifter.   Also note modified drive gear cover.

Left rearset (passenger pegs) and shifter.   Also note 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.

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.

Hagon Shocks mounted on 160.

Change the gearing to something around 17/38, depending on the tracks you'll be running at. Most of the 160s here in the Northwest are running 17/38.   I'm running 18/38 on mine and I like it better.   Tim Fowler recently tried 18/38 at Portland and thought it was better as well.

You can use the stock steel rims and they work fine.   Aluminum rims look nice and probably do make a difference as they should be lighter, but I've ridden bikes with both and didn't notice much of a 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 in 80/90 front and 90/90 rear sizes.   Michael Moore 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 am experimenting this season with rear tire sizes and I'm currently running an 80/90 in the rear.   Several of the Portland based Flying Circus riders are doing the same and they seem to be going fine on the smaller tires.   For tire pressures we've 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 may have to do some tire pressure experimentation this year as well, but the lower pressures have been working very well for us.   You'll have to make up your own mind on that.

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 work better, and someone like Michael "Mercury" Morse at www.vintagebrake.com would do a great job for you.   You'll need to weld a small bracket on the frame to hold the rear brake cable and fabricate a new rear brake pedal.  

Right footpeg, brake lever and brake cable bracket.

Dan Hill's right footpeg and brake lever.

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.   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.   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.   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.   You can adjust the tire pressure in 1lb increments and it will help, but you probably can't get it to go away 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'll build 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 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 need to re-jet a bit.   You'll probably need to go to at least 95 main jets or larger, and mess with the needle position and idle air screw to make the bike run smooth.   Some of the bikes running mostly stock setups are running on the stock 90 main jets.   They could probably stand bigger mains, but that's up to the individual rider to experiment with.   The needles generally are at the center clip position or one either side.   I'm one position rich of center.   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.   Watch out for cheap float bowl gaskets that aren't quite the right size - they can pinch in on the sides and hang the float and it'll drive you nuts until you figure it out.

Right carburetor.   Note 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.   Just make sure that you don't uncover the slide.   You can remove quite a bit of material from the left and right sides of the carb throat.   You could use a rat tail file and several beers sitting in front of the TV along with some patience.   I use a metal cutting burr on a dremel tool to do the bulk of the metal removal.   This will cause you to need to mess around further with the jetting. I'd start with a 95 or 98 main and one clip richer on the needle.   You'll have to experiment from there yourself.   You can also do some smoothing on the carb bell by filling in some with epoxy.   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 would work better, and in fact I have a 2 into 1 kit from Craig Hanson that I'll be putting together this winter.   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, but theoretically the 2 into 2 would work better with a 180 degree crank.   Frog has a 2 into 1 that also seems to work 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.

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.

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.

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 mmoore@eurospares.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.   I've recently found a possible source of cheap tachometers, surplus tachs from boats.   Pacific Industrial in Seattle has 6,000 rpm tachometers that appear to be for 4 cylinder engines, which theoretically should make 12,000 rpm tachs for the 160.   I bought one for $7, and I'll let you all know how it works out.

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 this 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 this last year (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!

Michael