Tech Tips Camshafts

A Good Start
At max lift, top retainer to valve guide seal should .030 minimum.
At max lift, minimum of .015 between three coils for a total clearance of .045 of clearance. (Springs)
With both valves open, minimum of .040 clearance is needed.
Piston to cylinder head clearance (with head gasket) should be .030. (Steel rods)
Piston to intake and exhaust valve clearance should be .050 intake and .080 exhaust. (Checked at various degrees)

Why do cam manufactures say "must be used with 12.1 or more compression pistons"?
When looking at the power output of a engine, the mass or volume of the trapped charge is the important thing.
With a static (not running) look, flow dynamics are not present. But once the engine starts turning or running, everything changes.
At low RPM or cranking speed with a later closing intake valve with performance camshafts the cylinder fill is reduced.
When the engine starts its combustion cycle, RPM and exhaust pulses are introduced to the game, things greatly change.
Closing the intake valve later with performance cam shafts at higher RPM will allow more flow inertia resulting in more cylinder fill.
Because a later closing intake valve with performance camshafts and the cylinder fill reduced at lower RPM the term corrected compression ratios is often mentioned.

Hence: The statement use 12 or more compression pistons are needed.
We have our favorite ways to increase or correct compression ratios on Honda CB750 engines. A look at the piston section might be advised.

But, in the mean time, Here is a "quick reference" of some off-the-shelf piston and recommended camshaft choices.

Stock domed and those inexpensive eBay 836cc similar domed pistons will be limited to our CX-1 or KHD CX-1 camshaft because of the valve pockets.

10.25 to 1 compression ratio pistons like Wiseco and others have the compression ratios and valve pockets to use CX-1, CX-2, KHD CX-1 or CX-3 camshafts.

12.5 to 1 compression ratio pistons like Wiseco and others have the compression ratios and valve pockets to use CX-3, CX-4 and CX-7 camshafts.

Interesting? Maybe!
Note: You will notice some of the manufactures do not state where these numbers were measured from.

Grind Number	Cam Part Number	Timing	Valve Clearance	Valve Lift	Duration	General Characteristics
RB282	1000	I.O. 37 I.C. 65 E.O. 65 E.C. 37	.004" .004"	.375" .375"	282° 282°	The ultimate street and touring cam for the 750. Provides increased performance from idle through top R.P.M. Easy starting and smooth idle. Clears stock pistons, no machine work required for installation.
*SS288	1001	I.O. 40 I.C. 68 E.O. 68 E.C. 40	.004" .004"	.395" .395"	288° 288°	Street, touring, drag strip, cafe racer. Increased performance from 3500 R.P.M. up. Slightly higher idle speed, but smooth. Valve to piston clearance must be checked.
*SS298	1002	I.O. 45 I.C. 73 E.O. 73 E.C. 45	.004" .004"	.420" .420"	298° 298°	Strong mid range and top end cam for the hot street and strip machine. Big power increase from 5000 R.P.M. up. Must have added valve to piston clearance.
*SS310	1003	I.O. 51 I.C. 79 E.O. 79 E.C. 51	.004" .004"	.400" .400"	310° 310°	Upper mid range and top end cam. Drag strip, road racing, all out road burner. Needs improved exhaust and proper gearing for best results. Great in bored and stroked engines. Runs hard!
*DS324	1004	I.O. 54 I.C. 90 E.O. 90 E.C. 54	.004" .004"	.425" .425"	324° 324°	Drag strip, time trails, road racing, etc. Top end power cam, pulls hard from 7500 R.P.M. up. Well suited to large displacement engines. Needs good exhaust system.

H750 valve spring kit is recommended with all cams for best results.

Titanium retainers are only recommended for all out racing applications where high R.P.M will be maintained.

*These cams must be carefully checked for valve to piston clearance. Most high performance pistons have adequate clearance but must be checked during assembly. Factory pistons may be machined for added clearance. Valve to valve interference should be checked with cams over 310° duration.

None of the listed cams will work in the 1977 750 F2 model Honda as valve to valve interference will occur due to the larger diameter valve fitted. For the 1977 750 F2 engine, only one cam will work. Grind number RB278SPC, Part #1005.

POWROLL

High Performance Billet Cams

These totally new cams, precision-machined from billet steel, eliminate the need for an "exchange" with your present stock cam. High-lift lobes are of the required contour without hardwelding or regrinding. Choose from two different profiles engineered specifically for Honda 750s.

FOR STOCK OR BIG BORE displacements, this grind aids performance throughout the power range. Although compatible with stock springs, we recommend the use of our special valve springs.

12661	Valve Opens	Valve Closes	Valve Lifts	Running Clearance
Intake	19° BTDC	46° ABDC	.333 in.	.004 in.
Exhaust	48° BBDC	19° ATDC	.325 in.	.004 in.

Note: All timing specs are standardized at .040 in. valve lift and zero clearance.

Powroll Order No. 12661

FOR HIGH-DISPLACEMENT ENGINES only, this cam is inappropriate for the stock 750. Provides maximum engine-breathing capability for displacement over 900cc. Compatible with stock springs, but operated more effectively with Powroll's special valve springs.

12662	Valve Opens	Valve Closes	Valve Lifts	Running Clearance
Intake	23° BTDC	53° ABDC	.373 in.	.004 in.
Exhaust	50° BBDC	19° ATDC	.350 in.	.004 in.

Powroll Order No. 12662

ANDREWS PRODUCTS

Grind Number

Timing

Valve Lift*

Duration**

General Characteristics

STREET / STRIP

20/40

40/20

.350"

.345"

240°

Mild street cam for bolting into stock 750 motors. No modifications or head work required. Stock springs OK. More power thru RPM range; slightly higher idle speed; smoothness unaffected.

DAYTONA +

19/45

45/19

.365"

244°

Daytona; For modified and hotter engines 750/850cc; much more power especially middle and higher RPM ranges. Requires springs, spacing, and head work. Very streetable but slight lope @ idle.

SUPER STREET

35/63

63/35

.375"

.365"

278°

Super Street grind. Best for big inch 750s (over 860 ccs) Strong pull from 5000/9500 RPM. Springs, spacing, and head work required.

DRAGS

32/68

70/30

.400"

280°

Hottest Competition Cam made for 750 engines! On a big inch dragster #4 cam yields more HP and lower ETS than anything else available! Springs and head work required for installation.

*Maximum valve lift @ 0 Lash.

**Durations measured @ .050 valve lift; cam @ 0 Lash.

R.C ENGINEERING PERFORMANCE PRODUCTS

RACING CAMS: HONDA, 1969-78 CB750

RC240 Torque Cam - The only R.C. Honda cam that can be bolted into a stock motor without piston valve pocket machining. No head disassembly necessary. For smaller bore, low compression motors. Good for road racing. (Sold as a regrind only - send us your cam)

RC240 Timing:

Total Duration	Lobe Centers	Lift	Lash
296°	118°	.327" in.; .330" ex.	.004" in.; .004" ex.

RC295 Racer Cam - Smooth, good idle and torque with lots of the top end. Quiet operation. Exceptional for smaller motor. Ideal for 900cc motors.

RC295 Timing:

Total Duration	Lobe Centers	Lift	Lash
306° in./296° ex.	105°	.390" in.; .360" ex.	.004" in.; .006" ex.

RC315 Hot Racer Cam - Strong torque curve from the ground up. Comes on low and never quits. This one makes lots of horsepower. Very good for heavy street and altered race bikes. Our favorite in the Street Class. Has flowed us to many national records. Very tractable. Fair idle - quiet. Ideal for 900cc and larger motors.

RC315 Timing:

Total Duration	Lobe Centers	Lift	Lash
310°	104°	.365" in.; .365" ex.	.012" in.; .012" ex.

RC327 Full Competition Cam - Similar to #315, but with more lift and overlap. Designed with more duration for maximum revs and BHP on all big motors. The best choice for use in 1000cc motors.

RC327 Timing:

Total Duration	Lobe Centers	Lift	Lash
325°	104°	.368" in.; .368" ex.	.012" in.; .012" ex.

ACTION FOURS

We use new, cast billets exclusively. Regrinds are cheaper, but there is not enough material to obtain an efficient profile and adequate base circle dimensions.

Stock pistons cannot be used with any cams we sell. You would not get your money's worth. A proper profile that would give safe valve-to-piston clearance would not increase performance significantly. A cam that would give clearance and increased performance could not have a safe profile. Notching stock pistons is not of much value either, since a hot cammed, low compression motor is a very poor performer.

Lift and duration figures are real. The drawing below shows how "extra" lift and duration may be added to no advantage. Buying the "biggest number" without regard to proven results is a fool's game.

THE "NUMBERS GAME"

Are the cams above the same? They are by the "numbers"!

Cams A, B, and C above all have the same lift (shown at "L") and duration (shown at "D"). Yet, there are obviously very different. If cam B is correct in design, then cam A would give good "low end" but less H.P and float the valves more easily. Cam C would have plenty of "top end", but would exhibit a narrow power band and open the valves too rapidly for good reliability.

No degreeing-in is required if stock components (tensioner, cam chain, etc.) in good condition are used. All our cams are indexed from the sprocket mounting rather than the drive slot. This insures far greater accuracy for "drop in" installation.

Most cams are located for grinding from the keyway as shown at "Y". The same arrangement is used on Kawasaki cam but is removed after grinding. All our cams are located from the mounting bolt holes, as shown at "X". Since the bolt holes determine the cam location, "spot on" results. The keyways becomes your "which tooth" indicator only. Of course, this applies to standard components in good condition only. Milling the head or cylinder, or using non-standard or badly worn parts will affect actual timing.

Is ±11° good enough for you?

Big valves cannot be used in most cases. As overlap increases, valves come closer together. In our experience, an unrestricted profile will do more for performance than oversize valves. More latitude for cam timing variations are possible with stock valve sizes, too.

Carefully designed and tested profiles prevent excess stress and premature float. Extreme, power-robbing valve spring pressure is not required.

To test for adequate valve to piston clearance with any cam, rotate the nearest cylinder slowly to the overlap (exhaust closing, intake opening) position. Rotate the motor slowly, stopping every few degrees, from 35° BTDC to TDC (top dead center). Each time you stop, depress the exhaust valve follower (a padded screwdriver works well) until the valve contacts the piston. The point at which the valve moves the least is your minimum clearance and it may now be measured. In no case should it be less than 1mm (.040"). Reverse the procedure (TDC to 35° ATDC) to check intake valve clearance. Advancing the cam (forward in relation to motor rotation) will increase exhaust and reduce intake clearance. Retarding the cam has the opposite effect.

CB750 'SS' SERIES CAMSHAFTS

'SS-1' GRIND

High 11, low 12 second 1/4 mile times (used with 811cc Bore Kits) yet as smooth and tractable as a stock machine! This is definitely the cam for those riders who are worried about their "hot" cams.

May be used with stock valve springs for economic applications. Of course, we recommend a complete racing valve spring set for an even wider margin of over-rev protection.

Camshaft Only	PART # 19-101
Cam & Racing Valve Spring Set (Except F2)	PART # 20-101
Cam & Racing Valve Spring Set (F2 Models)	PART # 20-201

Note: The SS-1 may be safely used in F2 (large valve head) models, without valve modification.

'SS-2A' GRIND

For maximum acceleration. Preferred by those who are serious about drag racing, yet need a certain degree of tractability. Best power from 6,500 up. Racing valve spring set is recommended.

Camshaft Only	PART # 19-102
Cam & Racing Valve Spring Set (Except F2)	PART # 20-102
Cam & Racing Valve Spring Set (F2 Models)	PART # 20-202

For the best performance and reliability use them cams with Action Fours high compression big bore kits.

CB750 K-H CAMSHAFTS

Kenny Harmon's 35 years of cam design and grinding experience are manifest in these excellent profiles. 750 Honda cams from K-H have become an industry standard for quality and performance. All cams are precisely indexed for "spot-on" timing.

'D' GRIND

A famous grind. Excellent for riders who desire a major H.P increase, but insist on a wide range of us. Well balanced with reasonable idle and "low end" and a major increase in acceleration. Long exhaust duration allows for sustained high speed cruising without excess combustion chamber temperature.

May be used with stock springs if desired. For greatest reliability our racing valve spring set is recommended.

Camshaft Only	PART # 19-103
Cam & Racing Valve Spring Set (Except F2)	PART # 20-103
Cam & Racing Valve Spring Set (F2 Models)	PART # 20-203

'F' GRIND

For the greatest H.P possible, consistent with sustained use. Extra long exhaust duration and substantial intake area provide record setting H.P, as well as efficient temperature control.

The best choice for road racing and other "top end" applications. Best power 7-11,000 RPM.

May be used on the street or for drag racing with very low gearing. Should be used only with racing valve spring set.

Camshaft Only	PART # 19-104
Cam & Racing Valve Spring Set (Except F2)	PART # 20-104
Cam & Racing Valve Spring Set (F2 Models)	PART # 20-204

SUPER 'F' GRIND

The ultimate DRAG RACING ONLY cam. ABSOLUTELY NOT FOR STREET USE.

Extreme valve lift is combined with over 300° intake and "short" exhaust timing to get off the line hard and accelerate to high RPM.

No compromises in profile design whatever. This cam is not suitable for for any sustained use. Should only be used with complete racing valve spring set.

Camshaft Only	PART # 19-105
Cam & Racing Valve Spring Set (Except F2)	PART # 20-105
Cam & Racing Valve Spring Set (F2 Models)	PART # 20-205

For the best performance and reliability use them cams with Action Fours high compression big bore kits.

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It is the sole and exclusive responsibility of the purchaser to determine the suitability of any part, product or work for his or her use.
The purchaser shall assume all legal, personal injury risk and liability and all other obligations, duties and risks therewith. There is no warranty on High Performance products.

Begins Intake Event Sooner - Advancing	Delays Intake Closing Event - Retarding
Open Intake Valve Sooner	Keeps Intake Valve Open Later
Builds More Low-End Torque	Builds More High-RPM Power
Decrease Piston-Intake Valve Clearance	Increase Piston-Intake Valve Clearance
Increase Piston-Exhaust Valve Clearance	Decrease Piston-Exhaust Valve Clearance

Begins Intake Event Sooner - Tightening lobe center	Delays Intake Closing Event - Spreading lobe center
Open Intake Valve Sooner	Keeps Intake Valve Open Later
Builds More Low-End Torque	Builds More High-RPM Power
Decrease Piston-Intake Valve Clearance	Increase Piston-Intake Valve Clearance
Increase Piston-Exhaust Valve Clearance	Decrease Piston-Exhaust Valve Clearance

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