Improving The Honda 160 Vintage RoadRacer-
Cam Degreeing
Last modified 2/24/2008

 

 

Cam Degreeing

So - you've read here that degreeing your cam is important and will make a big difference in how your bike performs.   Or perhaps you've been racing with someone who recently had his cam degreed and all of a sudden you're not keeping up like you used to. Either way, you want to know more about this mystical art that is cam degreeing.   Well - I'm here to tell you that it will make a big difference, and to my mind is just as important as checking and adjusting your ignition timing.   It is also not particularly difficult.   It does take a reasonable block of time, and also takes some careful work.   If you have someone experienced you can work along side of that's a bonus, but don't be afraid of jumping in yourself.   It's really not particularly difficult, and I'll walk you through it here.   I plan on about two hours assuming everything goes reasonably well and I don't find anything else wrong.   If it's your first time doing it you should plan on at least a full day, perhaps a full weekend if you need to collect or make some of your tools.

It probably also wouldn't hurt for you to go googling about the net for articles on cam degreeing before you get started here - there are several other articles on the web about this and if you see it more than once it'll probably make more sense.

 

Tools

There are some semi-specialized tools you will need that the average racer might not have yet in his shop.   You will need a degree wheel, a 1" or 2" travel dial indicator, a base for the dial indicator, a hydraulic press (I'd suggest 12 ton minimum if possible), and a piston stop.   You can buy most of the tools, but the piston stop you'll probably have to make yourself.   When you buy a degree you don't need to buy one large enough for a semi's diesel engine - mine is about 8" in diameter and it's just fine.   Larger is more accurate of course, but can be more of a pain to deal with.

The piston stop will be used to calibrate the degree wheel to exact Top Dead Center (TDC).   The easiest way to make a TDC pin is to file, grind or machine the rolled lip from the top of the metal part of a spark plug so that the insulator can be knocked out.   Remove the ground electrode while you're at it.   Now weld or braze a bolt in where the insulator used to be, so that it sticks out around 3/4" or so. It's best if you can turn it down a bit in a lathe also where it sticks in the engine - so you can be sure it doesn't hit the valves.   The reason for this will become self-evident later on.

I now make and/or stock many of these tools - check www.batemanracing.com parts and services for details and to see what I've got in stock right now.


The tool on the right is the TDC stop pin.   The tool on the left is a Motion Pro valve adjusting tool - completely worth the price at just under $50 for a set that includes 8, 9 and 10mm wrenches, and adjusters for small square, large square and slotted adjuster screws.   The tool in the center is also very handy - .003" feeler on one side, .002" feeler on the other side and small enough to fit in the 160 adjusting ports easily.   That's also a Motion Pro tool, comes in a set with a few other sizes.   I can order either or both tools for you if you want, see www.batemanracing.com

 

Install the degree wheel

Find a way to mount the degree wheel on the crankshaft.   On a 160 you can remove the bolt holding on the flywheel on the left side of the engine, use a stack of washers to space the wheel out from the engine cases, and use a bolt the same size and pitch (8mm x 1.00mm for a 160) to bolt the wheel to the crankshaft.   You will also need to fabricate a pointer - I use a piece of 1/16" brazing rod bolted to the engine case where the countershaft cover normally bolts.   Sharpen it to a point with a file, and bend it so that it points to the edge of the degree wheel.   I've made a custom adaptor for my degree wheel that really makes it easy to mount the wheel on the crank and to turn the crank without loosening the set screw.   Note that I now make and stock the special tools for this - you can see them at www.batemanracing.com parts/services.   If your degree wheel is precariously mounted on a stack of washers you should probably turn the crank using the castle nut on the other side of the crank that holds the oil filter on.


Here's the degree wheel and pointer set up on the engine waiting for calibration.   The dial indicator base is also mounted to the engine case with a handy-dandy spring clamp.

 

Adjust cam chain tension

You'll want the cam chain properly tensioned for this, so bring the crank forward a bit to put some tension on the chain, loosen the 9mm locknut and the 9mm clamp bolt on the front of the head, let the spring tension the chain and tighten both back up.   It probably should be mentioned too that you'll want the head to be properly torqued or the stack height of head/cylinder won't be correct and none of your cam timing numbers will be correct.   This can be either with the valve cover in place or with some handy dandy little spools made for that purpose.   These spools allow you to remove/install the cam without having to remove the valve cover and retorque on reassembly.   Especially handy if you've got my adjustable cam gear and can adjust the timing without removing the cam.

 

Calibrate the degree wheel

Now we'll use your cool TDC pin to calibrate TDC on the degree wheel with actual TDC on the engine. You can get pretty close by lining up the "T" mark on the flywheel with the timing mark, then turning the degree wheel so that your pointer is pointing to "TDC" on the degree wheel and tighten the bolt.   You're close now, but we need it to be exact.   Remove both spark plugs - there's no sense working against more compression than you need to.   Turn the crank so that the engine is away from TDC by 30 degrees or more and completely slack off the valve lifter lash adjusters on the cylinder you're using the piston stop in (otherwise the valves will hit the piston stop, possibly bending them.   Nobody wants that.     Thread your TDC pin into the spark plug hole.   When your first start turning the engine be careful and feel for extra resistance - if the valve is contacting the TDC pin you want to take care of it now before you bend a valve, not after.   Turn the crank forward until the piston hits (lightly!) the TDC pin and write down the number on the degree wheel - it should be something like 30 degrees Before TDC.   Now roll it around backwards until the piston hits the pin again and write that number down.   If you were good at lining it up to begin with the number should be reasonably close to the first number, like say 24 degrees After TDC.   Actual TDC is exactly between these two, so in this case if you move the pointer to 27 degrees ATDC, it should be right on.   You can either move the wheel (loosen it, move it, tighen it again), or just bend the pointer to the right spot.   Roll the crank back and forth until the BTDC number is the same as the ATDC number, and you're right on.   I check it several times before I'm satisfied.   Precision and careful work really matters here - so be patient and take your time.   And - don't bump your pointer.   If you do you'll have to go through this all over again to recalibrate the degree wheel.

 

Degree the cam "as found"

Here we'll find out where the intake lobe is set right now.   We'll be doing an operation similar to using the TDC pin to set the degree wheel to TDC.   We're going to measure the angle at which the cam makes .040" lift on the beginning (intake side) of the ramp, then measure where it makes .040" lift on the closing side of the ramp.   The center of the lobe and the point of highest lift will be halfway between those two numbers.   The stock setting intended by Honda on the 160 is that the intake valve cam lobe center should be at 102.5 degrees BTDC, and the exhaust valve cam lobe center should be at 102.5 degrees ATDC. Vertical 175's are 105 degrees intake and exhaust.   This is called symmetrical or split valve timing.   I've found that either straight up or a little advance on the cam seems to be best for our (racing) purposes, so I've been setting the 160 cams somewhere between 102.5 and 101.5 degrees intake lobe center.   This will make the exhaust lobe center between 102.5 and 103.5 degrees.   Someday I'll do some dyno testing and come up with a better idea of optimum.   Bikes with intake cam lobe centers up to 100 degrees (160 - 102.5 175) intake seem to run pretty well.   I don't think I'd go much beyond that.   It's worth it to check both intake and exhaust valves at least once to make sure you know what cam you have and what split timing would actually be (intake L.C. plus exhaust L.C. divided by two)

Set the intake valve lash somewhere close to the running clearance of .002".   It doesn't have to be exact, but it should be close.   A little on the tight side will make sure that the math will be easy later.   Now set up your dial indicator so that it's roughly in line with the valve axis and reading on the valve spring upper retainer.   Watch out that the lifter doesn't foul the indicator as it describes an arc when the valve is lifted.   Zero it so that it's reading zero lift when the cam is on it's base circle (no lift on the valve).   Turn the crank over several times to make sure that you're reading zero after the valve has been through one lift cycle (being careful to not turn so hard that you loosen the bolt holding on the degree wheel - if you do that you'll have to start over with the TDC pin).   I'm now making a really slick dial indicator holder for this that makes installing the dial indicator a piece of cake, and makes the readings rock steady.   It can be seen at www.batemanracing.com parts and services.

 


Here's the dial indicator set on the valve spring seat, ready to start taking readings.

Now take some readings.   Turn the crank forward until you see .040" lift on the dial indicator and write that number down.   It should be a small number before TDC - something like 5 degrees BTDC.   If it's after TDC write it down as a negative number.   Keep turning the crank forward and write down when the dial indicator reading comes back down to .040" lift - this should be a number ABDC, something like 30 degrees ABDC.   I usually do it twice to make sure that I'm reading everything correctly - one degree of cam movement is a pretty large number, so again careful work is necessary.   If you screw up and go past your number, you'll need to back up quite a bit before you come forward to the reading again - you want all the slack in the camchain taken up.   Also make sure you're reading your indicator correctly - there are generally numbers on there for reading in both positive and negative indicator travel directions.

Here's the math you'll use to find the intake lobe center number - first reading + second reading + 180 degrees, divide that number by two, then subtract the first reading.   In this case:

5 + 30 + 180 = 215, 215 / 2 = 107.5, 107.5 - 5 = 102.5 degrees.

That's a good number - the stock setting and it's very unlikely that you'll find that the first time.   So far I've found every engine I've checked to be retarded to at least 104 degrees, and some up to 108 degrees.   That's 5.5 degrees retarded from the stock setting.   Remembering that 1 degree change is a pretty large change - it's not surprising that some bikes are pretty slow compared to a properly set up bike.

If your cam is extremely retarded you may end up with a negative number (After TDC) for the first reading.   Say you ended up with -5 (5 degrees ATDC) and 31 degrees After BDC. The math then works out to:

-5 + 31 + 180 = 206, 206 / 2 = 103, 103 - (-5) = 108 degrees.

That's about where we found Dan's cam.   His cylinders had been machined shorter by the DPO (Dreaded Previous Owner) which had retarded the cam even beyond where it would have been.

Again - f this is the first time you've degreed your cam and you're not 100% certain what cam you have, you should probably degree the exhaust valve cam timing as well to make sure you know what cam you're dealing with.   The order you read the numbers in will be reversed - ie you'll get something like 30 BBDC exhaust valve opening, and 5 ATDC exhaust valve closing.   use the same math, but when subtracting use the second (ATDC) number instead of the first number like in the example above.

Same math: 30 + 5 + 180 = 215, 215/2 = 107.5, 107.5 - 5 = 102.5 degrees

For a stock 160 the cam timing if straight up would work out to 102.5 degrees intake, 102.5 degees exhaust.   As the cam is advanced the intake lobe center (LC) number will go down - ie 100 degrees intake LC is 2.5 degrees advanced.   At the same time the exhaust LC number will go up by the same amount - at 100 degrees intake LC the exhaust will be at 105 degrees LC.   175 cam timing straight up is 105/105 for stock camshafts.

 

Moving the cam gear

Now it's time to move the gear on the cam.   Now is also the time that you're going to get jealous of those guys whos cam gears are bolted onto the cam.   They can slot the holes for the mounting bolts and change the cam timing without disassembling the engine.   You're not so lucky - unless you've had your cam modified by Bateman Racing.   I have developed a modification to the 160/175 camshaft to allow slotted hole cam gear adjustment.   You can check it out in the services section of Bateman Racing.

But - if you haven't you'll have to do it the old fashioned way.   Take the dial indicator off, unbolt the valve cover (don't forget the small 6mm bolt in the center front), remove the valve cover and turn the engine over so that the master link on the cam chain is at the top.   Slack all the valve lash adjusters, remove both right and left side cam bearings, remove all four rocker arm pins, remove all four rocker arms, remove the cam chain master link (being careful to not drop any of the parts into the engine), connect some safety wire to the ends of the cam chain so they don't get lost down in the engine and remove the cam.


Cam chain split and wired back for cam removal.


Both cam bearings and one rocker removed.

You'll need to mark the cam and gear for how much you need to move things.   If you measure the diameter of the bearing surface for the cam gear and do some math, you'll find out that about 0.010" movement where the cam and sprocket meet (for the 160) corresponds to 1 degree of rotation.   The cam moves at half engine speed so 1 degree on the cam is 2 degrees on the crank where our degree wheel is, so a 0.005" movement will equate to about 1 crank degree (which is want we're measuring).   Say you found the cam at 105 degrees, and you want to shoot for 101.5 degrees - that's a change of 3.5 degrees.   3.5 x 0.010" / 2 is 0.018".   Now - that's not much.   Make a scratch with a carbide tip scriber across the cam and gear, them make a scratch on the gear 0.018" forward of that.   Hold the cam next to the engine in the operating position to be sure you're advancing the cam relative to the gear if necessary.  


This photo is pretty blurry - but here's where you'll make your scratch marks for moving the cam.

Now take the cam to your press, press it apart and press it back together on your target mark.   Sounds easy right?   Well - it takes a bit of time to get the feel for it.   At first it took me three or four trys to hit the mark I was shooting for.  


Cam in the press.


Cam ready for pressing apart.

Now - notice that I'm pressing directly on a pretty small and thin part of the cam here - you really shouldn't do that.   I've got a slug of steel with a hole in the middle just a bit over 11mm that I usually use for pressing the cams apart - I didn't think to put it on for this photo.   Doing it like this I would worry about damaging the nose of the cam.   Sometimes you really need to put a lot of pressure on the cam to get it apart the first time - that gear's been stuck on there for 40 years now and it's not going to want to come off easily.   Once you get it broken free it will press on and off a lot easier.   Heating the gear will also make it come off the cam a lot easier the first time.


Cam being pressed back together.

I've found it to be easiest to hold the cam above the gear with one hand while I operate the press with the other hand.   I don't drop the cam that way, and I preserve the approximate relationship between the cam and the gear as it's pressed apart.   This makes it easier to make a small movement and press the cam back together in about the right spot.  

 

Reassemble

Reassemble the engine and torque everything down properly.   Be careful that the cam chain is on the gear on the crank and not next to it - that's easy to do.   Make sure you remember to tension the cam chain with the tensioner too.   Basically - put the engine together like you're going to run it, but don't put the spark plugs in and don't bother to adjust the lash yet.   Cross your fingers.

 

Degree the cam again

Now - double check the TDC calibration on your degree wheel with the TDC pin (that's why you haven't adjusted the valve lash yet).   Then set the valve lash on the intake valve you're using for checking, set up your dial indicator again and take the readings again. Check your numbers and do your math.   I usually take the readings a second time just to make sure I didn't misread anything.   It's very easy to do - especially since the degree wheel reads both clockwise and counterclockwise from TDC - you have to pay attention to which side of TDC you're on and make sure you're reading the wheel correctly.

If you're lucky and/or talented, you will now have a cam with an intake lobe center set at somewhere between 100 and 102.5 degrees.   We're dealing in such small movements at the cam that we're happy with anything close.   So far I've only hit it on the first shot a few times, although I'm getting better.   If you're out from where you want to be, take everything apart again, press the cam apart and back together again, assemble again and check again.   Sometimes it can take three or four dissassembly/assembly cycles to get a number you're satisfied with.   As I do it more I'm getting a better feeling for it and i t's easier to hit a number I'm looking for on the first shot.

Before you take anything apart, turn the crank around to TDC on the degree wheel and check the "T" mark on your flywheel. If it doesn't agree with the degree wheel either bend/move the pointer so it does or put a new scratch on the flywheel.   When that mark is incorrect you will be setting your ignition timing incorrect and that's no good.   On Dan Hill's bike we found that the pin that indexes the flywheel on the crank was sheared and the flywheel TDC mark was off by 9 degrees.   Subsequently his ignition timing was off by 9 degrees and both of the top piston rings were broken from detonation.   It really pays to check all this stuff!   Also - some model bikes have the keyways in different locations, so vertical 175 crankshafts and 160 flywheels don't mix for instance.

Assemble, adjust and put it back in the frame.   Make sure you remember to double check the cam chain tensioner, and make sure you carefully adjust the valve lash to the correct settings.   We're using .002" intake and .003" exhaust.   The Honda specs for a street 160 is .002" intake and exhaust both.   If you've got an aftermarket cam make sure to follow the manufacturer's recommendations for valve lash.

 

A few final notes

Now - remember that any changes you make to the engine that affects the way the cylinders/head/cam etc stacks up will affect cam timing.   Cam chain stretch, machining the cylinder head, machining the cylinders, etc all shorten the stack and retard the cam.   Even changing the head gasket and base gasket can make a small difference.   Also remember that every engine is different, don't go thinking that a cam degreed to 101 degrees in your engine will end up at 101 degrees in a different engine.   The stack will be completely different and you'll have to degree that cam all over again.  

I have developed an adapter so that we can have bolted on cam gears with slotted holes and adjust our cams easily just like the big boys.   It is a lot of work and subsequently is not very cheap to do.   However - I am doing it in short runs.   Check out Bateman Racing for details and pricing.  

Now go out and enjoy your rediscovered lost horsepower!

Michael


 

Copyright 2002, 2003, 2007 Michael Bateman
Photographs Copyright 2002 Michael Bateman

Email: michael@batemanracing.com