maintenance tips 101

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BLUEPRINTING IS A time-honoredmethod of achieving morepower from a production

engine. Although the term is oftenassociated with racing, the techniquesare equally applicable to the street-bikes that you and I own.

Remember that production engines,perhaps aside from the best superbikemotors, are not built using the greatestcare or very best machining practices,but are objects of mass production,subject to all manner of cost controlsand variable production tolerances.

This fact gives a careful mechanic theopportunity to improve power signif-icantly with relatively small expense.

The term blueprinting means tobring all the dimensions to the idealnumbers called out in the engine’sblueprints, but it can also mean opti-mizing the range of allowable varia-tions to achieve precisely those thatwill deliver the best power.

We’ll confine our series to the topend, and our current Project Bike,Suzuki’s DR650SE, will be themodel, but the techniques shown

apply to virtually any engine.

The Camshaft The business of the camshaft is to

coordinate the openings and closings of the valves on our four-stroke engines, sothat on every second revolution, combus-tion occurs, creating the power thatdrives our motorcycles forward.

The chant “Intake, Compression,Power, Exhaust” that every shop studentlearns by heart on the first day of classwould make you imagine that each phaseof the process takes precisely half a turn of the crankshaft, but that’s not true. In fact,the Intake stroke steals time from theCompression stroke and the Exhauststroke steals time from the Power stroke.

The intake valve opens just before thepiston starts the downward Intake stroke,and the exhaust valve’s closing is typicallydelayed by a similar amount, to takeadvantage of the gas flow inertia at work as the engine runs. By leaving both valvesopen for a moment as the piston reachestop dead center (TDC) at the end of theExhaust stroke, the out-rushing exhaust

gases will tend to create a suction effect onthe intake side, initiating fuel/air flowbefore the piston’s descent works to create

its own pull. This phase, when both valvesare open, is called Overlap. Engines tunedfor a broad torque range and good low-speed power, like our dual-sport, will usea brief overlap period of perhaps 20°,while engines designed for high-rpmpower will use from 50°–75°.

Long overlap is reserved for high-rpmmotors because at lower revs a delayedexhaust closing will tend to backflow intothe cylinder, and hot exhaust gas will takeup significant space, making filling thecylinder with fresh air and fuel impossibleto accomplish.

The other valve timing events are sim-ilarly adjusted to make the most efficientuse of these inertial flow effects. Theintake valve won’t close at the bottom of the piston’s Intake stroke, which wouldseemingly give the rising piston its max-imum possible compression. Instead, theengine designer will leave the valve openmuch longer, abbreviating the Compres-

sion stroke, utilizing the inertia of theintake flow to continue filling the cylinderas the piston rises for a significant portion

of its travel. An engine designed forstrong low rpm running will have theintake valves close about 45°–50°of crankshaft movement after bottomdead center (ABDC) on the Com-pression stroke, while a high-rpmracing engine may keep the intakevalves open until 100° ABDC ormore. Incidentally, a high staticcompression ratio is required whenthe compression stroke is shortenedthis way, and compression ratios arealways figured as if the intakevalve(s) close at BDC.

Of course, the same backflow sit-uation will happen with late intakeclosings at low rpm, only this timethe intake charge will reverse direc-tion and push back out through thecarb or throttle body, reducing vol-umetric efficiency. This quantity of regurgitated fuel/air mixture willtypically be contained in the airboxso it doesn’t escape entirely, but itwill then be treated to a second shotof fuel as it is drawn back in onthe next intake cycle, ruining itsmixture accuracy.

Exhaust timing is adjusted so thatvalves will open well before the pis-ton’s downward Power stoke endsat bottom dead center (BDC). Again,

the engine’s intended use will determinewhen, and tends to range from 45°–50°before bottom to as much as 75° or more.This early-opening scenario is called“blow down” and is done in order to aid inemptying the burnt contents of the cylin-der after the combustion pressure has donethe majority of its work and before the ris-ing piston expels the remainder. Remem-ber that the volume of the combustionchamber rapidly expands as the pistondescends, reducing the effective workingpressure on the crankshaft.

Aside from the timing of the valveevents, which are carved into a fixedarrangement by the hardened steel shapesof the cam lobes, valve lift is the other keyto camshaft performance. To see withyour own eyes how small a distance thevalve actually moves away from its seat isto appreciate the potential for flowincrease with higher lifts. (See image)

This is a fundamentally different prob-

lem than cam timing and duration. Wewould prefer to open the valves instantlyto the full height that will eliminate flow

30 FEBRUARY 2011 G MOTORCYCLE CONSUMER NEWS

Technical

Engine Blueprinting 101 - Part One Measuring Cam Timing & Lift by Dave Searle



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restriction between the valve and its seat,but we can’t. The lift necessary to elimi-nate any restriction is possible to achieve,but not instantly by any current means, sothe accelerations induced in the valve trainmust be carefully calculated. The valves,springs, retainers and keepers plus shims,rocker arms, clearance adjusters, pushrodsand lifters, if the engine has them, all have

their own inertial weight and some areeven slightly flexible in addition. Thequicker we move the valves, the strongerthe valve springs must be to control them,and the highest rpm the engine will attaindetermines the required spring pressure.This spring force should not be takenlightly when considering a change of camshafts, as even in the best of circum-stances, it causes friction and wearbetween the lobes and lifters, whichalready constitute one of the mostdifficult lubrication jobs in the motor.Only the desmodromic system used byDucati escapes this conundrum.

Tools A factory shop manual is essential. It

will not only contain nearly all the speci-fications you’ll need, but it will alsoillustrate the correct routing of all thehoses and wiring you’ll disturb as youdisassemble the machine.

Once again, the DR650’s big single-cylinder engine makes disassembly easyand simplifies many subsequent opera-tions. We found the entire top-end job can

be done without removing the motor fromthe frame. And, it’s always important tobegin with a clean bike, especially under

the gastank, to ensure that no dirt fallsinside the motor when the covers havebeen removed. Make sure that any pas-sageway into the motor is plugged withclean rags or paper towels as you proceed.There’s nothing worse than multiplyingyour efforts just to retrieve a clip orwasher that’s fallen into the bottom of themotor when it didn’t have to happen.

On the DR, it doesn’t take much morethan an hour to disconnect everythingattached to the top of the motor: airboxboot, carburetor, exhaust pipe, oil cooler,sparkplugs, etc. If you carefully put thevarious bolts in egg cartons from left toright and top to bottom, you’ll find it easyto reverse the sequence when it’s time toput it all back together. Take pictures of the various hose routings with your

digital camera to serve as maps if yourservice manual doesn’t detail these ade-quately. Use masking tape tags to note

which hose goes where. Rather than justdive in, a little time spent on these detailswill remove a lot of potential stress later.It’s possible the motor will be apart forweeks if you only have time to work on itnights and weekends, like we did, andit’s easy to forget details that seemedinsignificant at the time.

The DR’s cam timing is not given in

the factory service manual, but even if itwere, we’d need to verify it. Lift, overlap,opening and closing times and lobecenters are all important information thatprovide reference points when appraisingthe degree of tuning from the factory orchoosing an appropriate aftermarket cam.Then, if you download the figures for thepossible aftermarket cams available,you’ll be able to see how they compare toyour stocker.

Cam timing that’s off by just 2° at thecrankshaft due to manufacturing toler-ances will change valve events by twicethat amount, which is very significant tohow well your motor runs. Adjustablecam sprockets or modifications to yourstock sprockets will allow you to corrector alter timing without buying a new cam,but even a new cam needs to be checkedand will probably also require adjustmentto achieve the intended timing.

A minimum of special tools are neces-sary. You’ll need a large degree wheelthat will be attached to the end of thecrankshaft, a piston stop, a dial indicatorand a holding fixture to secure the indica-

tor in position over the valve springretainers to measure movement withcrankshaft rotation.

Intake Overlap phase beginsbefore TDC on the Exhauststroke, so that negative pres-

sure in the exhaust pipe willinitiate intake flow before thepiston’s descent creates itsown suction effect.

Compression is cut short byextending the intake cycle totake advantage of inertial

ramming. The compressionratio is raised to compensatefor the degree of reducedpiston travel before closing.

Power stroke is cut short byearly opening of the exhaustvalve, after combustion pres-

sure has done the majority ofits work. This is called “blowdown” and helps to evacuatethe cylinder of burnt gases.

Exhaust starts early and lastspast TDC to aid intake flowduring overlap.Too much

overlap can cause backflowinto the cylinder at lower rpm,hurting the engine’s ability todraw in fresh air/fuel.

The DR’s intake valve at full lift. The temp-

tation to increase lift for more flow is great,but stronger springs may be required,increasing friction, wear and parts expense.



You can make a piston stop from an oldsparkplug held in a vise. Breaking off the

top and pounding on the center electrodewith a drift will drive the porcelainthrough the middle so a length of threadedrod can then be epoxied inside. Be carefulnot to allow interference between the stopand the valve heads or you could bend avalve. Because the DR has a pair of spark-plug holes, we used the outermost hole tokeep a safe distance away from the valves.The length of the stop can be estimatedwith a thin screwdriver inserted in the plughole with the engine 10°–15° from TDC.Degree wheels are available from all thecamshaft manufacturers and dial indica-

tors and holding fixtures are offered onthe internet; $100 can buy all three.

Set-Up The first step is to locate Top Dead

Center. Of course, you’ll find TDCmarked on your ignition rotor, to be linedup with a corresponding point on theengine case, but it can’t be trusted.Manufacturing tolerances allow all sortsof misalignments.

Make a sturdy pointer to serve as yourdegree wheel’s reference point. We madeone from the steel rod in a pants hanger,sharpening the end on the bench grinder.Secure the degree wheel so that theengine’s marked TDC corresponds to thepointer. The piston stop is next. This willprevent the piston from reaching the top of the stroke so that by carefully rotating theengine back and forth to reach the stop,the degree wheel will show if the factorymark is perfectly aligned. Any discrep-ancy will give a different number of degrees BTDC (Before Top Dead Center)and ATDC (After). Move the degreewheel to split the difference and you’ve

located the true TDC point. Make sure thedegree wheel is then well tightened so thatit cannot be shifted accidentally.

From that point on, rotate the motor byturning the rotor and not the degree wheel

to avoid possible misalignment. Don’t besurprised if this is more difficult than youimagined. Even with the sparkplugs out,the rotor’s magnets and especially thevalve springs create significant resistance.This can be minimized on four-valveengines by measuring while only a singlevalve operates on each side. With theengine at TDC on the combustion stroke

(both valves fully closed) eliminate thevalve lash on the most accessible intakeand exhaust valves (left side on the DR).

This is easy with the DR’s screw andlocknut adjusters. Very carefully turn theadjuster screw by hand until it just stopsand then carefully snug the locknut with-out moving the adjuster any further. Onthe second intake valve, unscrew theadjuster as much as possible without let-ting it fall out; this way it won’t compressthe valve, saving the extra effort to com-press its springs. Do the same on the

exhaust side. Shim-adjusted valves in aDOHC engine will require thicker shimsto be fitted in order to exactly zero the

lash. Pro engine builders will leave noth-ing to chance and measure the timing of

every single valve, to make sure that alllobes are matched for duration, lobecenter and lift.

Position your dial indicator’s tip on thetop of the spring retainer on the valve youare measuring, with the gauge compressedfar enough that full compression of thevalve is within its range, then rotate theindicator’s bezel to align the zero mark with the pointer on its face. Because arocker arm moves across the valve as itcompresses, you’ll find it difficult toensure that the rocker arm and dial indica-tor don’t interfere at full lift. Don’t force

anything, which could spoil the measure-ments and possibly damage the expensiveindicator, and check to make sure every-thing is good before proceeding with themeasurements. Always turn the crank inthe direction of engine rotation. If youexceed your mark, back up a short distanceand turn forward again carefully; we don’twant cam chain slack to alter our readings.

Get out your notebook and record themeasurements. Cam manufacturers willtypically give lifts at either .040" (equiv-alent to 1mm) or .050" (traditional in theUS). Be sure to record both these num-bers, as well as the additional steps at .100,.150", .200", etc. until the cam lift peaks(record this figure, too) and then as itreturns to its seat. We’d suggest yourecord the smaller numbers; the point of initial movement and steps at finer incre-ments like .010", .020" and .030", also.These smaller lifts happen much moregradually and represent the opening andclosing ramps on the cams, designed tosmoothly take up slack before moving thevalve quickly. Double check your mea-surements. Repeatability is your assurance

it’s correct. Keep working until you’veachieved this. A slightly loose holding fix-ture, overtightened adjuster or interfer-

32 FEBRUARY 2011 G MOTORCYCLE CONSUMER NEWS

With the indicator compressed enough torecord full movement and the lifter on thecam’s base circle, zero the bezel.

Precisely set valve lash to zero before-hand in order to read cam timing and getan accurate measurement of lift.

The tip of the indicator must contact thespring retainer without being hit by thelifter over the full range of its travel.

Home-made piston stop: Created from anold sparkplug with a vise, hammer anddrift, with threaded rod epoxied inside.

Technical



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ence in the indicator’s movement willthrow off the measurements.

With this done, several important figureswill be known: Lift, duration and lobe cen-ters. Lift is self-explanatory. Duration isthe time in degrees of crankshaft rotationthat the valves are open (given from eitherthe .040" or .050" lift points). Higher liftand longer duration with different cams arethe time-honored ways to add flow capabil-ity. The “lobe center” numbers are meant tobe an easy way to visualize the alignmentpoint of maximum lift, given in degrees,either BTDC (for exhaust cams) or ATDC(for intake cams). For intake cams, youdivide the duration in half and subtract thenumber of degrees the cam opens beforeTDC during the overlap phase. For exhaustcams, divide duration in half and subtractthe number of degrees the cam is kept openafter TDC during overlap.

With these numbers, it’s easy to com-pare your stock and aftermarket cams. Notethat aftermarket cams do not specify the

opening and closing points butexpect you to determine thesenumbers from the duration and lobecenter figures.

Perhaps the most critical numberis intake closing as this is where truecylinder compression starts. Thelater the intake closes ABDC, thehigher the rpm at which peak torquewill be produced. Figure that thetorque peak rises roughly 100 rpmlater in the power curve for eachdegree of later intake closing. Forinstance: Do you want more low-rpm power than stock? Advance thecam. Do you want the same low rpmtorque as stock? If so, choose a camthat has nearly the same intake clos-ing as stock. Would you like themaximum torque 500 rpm later thanstock? Choose one with the intake

closing roughly 5° later.Lift is obvious. More is typicallybetter, but to get much more, otherchanges will usually need to bemade. The stock valve springs maynot be strong enough to control thevalve accelerations at high speed if the lift is much higher. Your cammaker will usually recommend thenecessary springs. The stock valve-to-piston clearance may also beinadequate if much higher lift isused. The time-honored method of checking this is to “clay” the clear-

ance. You must reassemble the camand top end, placing pieces of mod-eling clay (lightly oiled on bothsides) in the piston’s valve cutouts,turn the engine over, remove thehead, carefully slice through and

remove half the clay and measure thethickness. But if you are careful with a dig-ital caliper, you can check clearance with-out a mock-up assembly and disassembly.A minimum of additional clearance is nec-essary, the precise amount dependent onthe size of the motor and the rpm antici-pated (as much as .080" on big exhaustsand up to .100" inch for big intakes) Nat-urally the costs of special valve springswill need to be calculated (about $200 perfour-valve cylinder) and located as well asthe expense of piston valve pocket machin-ing if you get greedy with lift. But, as ourfocus is optimizing the stock engine, wedon’t have to worry about that.

What We Found As expected, the stock cam is biased

toward the lower end of the rpm range;good for dual-sport and off-road use.

Supermoto applications would suggest anew cam that raises the torque peak maybe 500 rpm; road racing perhaps even

more. Engine tuning is about compro-mise; giving up something to get some-thing more in a different place. Analyzeyour favorite type of riding. What wouldbe ideal?

In fact, we learned our DR’s cam timingis retarded by 4° from the common “split”overlap, the intake lobe center at 111.5°ATDC and the exhaust lobe center at 107°ATDC. Such retarded timing is unusual,and evenly split or advanced timing shouldimprove performance, adding effectivecompression, low-speed power and reduc-ing the tendency for back flow on the intakeand exhaust. Although dyno tuning isrequired to optimize the exact timing fig-ures, we feel comfortable advancing thestock cam timing by 4° to achieve splitoverlap, which we will cover in Part Fourof this series, when we reassemble themotor after verifying and correcting the

actual compression ratio in Part Two andcleaning up the ports and machining thevalve seats in Part Three.

Comparing our stock cam with the mostpopular aftermarket alternative was alsoilluminating. The new cam’s timing wasalmost identical and the new cam’s lift wasactually less. Although we’d really need toknow all the lift/degree figures to beabsolutely sure (which are not normallydivulged by cam manufacturers), the com-parison suggests we’d be wasting ourmoney if we hoped for more power (anddyno tests by other tuners using this cam

back up our numerical analysis).The surprises continue in Part Two, so

stay tuned, we think you’ll enjoy the trip.

R ESOURCES

Reading: Four-Stroke Performance

Tuning by A. Graham Bell. 3rd Editionby Haynes Publishing. Probably thebest single reference book on the sub-ject. Highly recommended. Hardcover$60.98, available from Amazon.com for$23.94, or even less in used condition.

Degree wheel: Competition Cams 7.5"Sportsman wheel, Part # COC-4787.$14.25 from www.888murrays.com

Central Tools 1"-travel dial indicatorwith magnetic holding fixture. Mfg #3D102. Model # 112202, $71.20 fromwww.toolsource.com.

Cam degreeing kit (everything needed)with video. Web Cam # AP-144, $265.

Web is also a good source for instruc-tional info. www.webcamshafts.com

DR650SE

INTAKE EXHAUST

Lift Degrees Lift Degrees.040" 4.5° BTDC .040" 46.4° BBDC.050" 2° BTDC .050" 43° BBDC

.100" 11.5° ATDC .100" 28.5° BBDC

.150" 24° ATDC .150" 11° BBDC

.200" 37° ATDC .200" 3° BBDC

.250" 51° ATDC .250" 11° ABDC

.300" 67.5° ATDC .300" 61.5° ABDC

.350" 85° BBDC .350" 86° ABDC

.361" 73° BBDC .363" 84° BTDC

.350" 51° BBDC .350" 86° BTDC

.300" 24° BBDC .300" 61.5° BTDC

.250" 8.5° BBDC .250" 45° BTDC

.200" 7° ABDC .200" 30.5° BTDC

.150" 19° ABDC .150" 18° BTDC

.100" 31° ABDC .100" 5° BTDC

.050" 45° ABDC .050" 9° ATDC

.040" 48° ABDC .040" 12.5° ATDC

Intake Duration: Exhaust Duration:@ .040" lift = 232.5° @ .040" lift = 239°@ .050" lift = 227° @ .050" lift = 232°Lobe Center = 111.5° Lobe Center = 107°

If stock cam is advanced 4° (@ .040" lift)Intake opens @ 8.5° BTDC, closes @ 44° ABDCExhaust opens @ 44.4° ATDC, closes @ 8.5° ATDC

ATDC (After Top Dead Center)BTDC (Before Top Dead Center)BBDC (Before Bottom Dead Center)ABDC (After Bottom Dead Center)

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