Technical Information (MGB 20)

Camshaft Choices and Lifters

Last Modified - 03/05/01

I wish I could bring you information on every camshaft out there, but unfortunately, there are so many grinds available it would be a momentous task to actually check each individual cam (for comparison reasons) using a standardized checking method (.050" lifter rise) to establish valve timing sequences and valve open duration numbers. However, I have concluded that many MGB owners, who are in the engine rebuilding process, will purchase a camshaft that is unsuitable for their particular driving needs and, most importantly, unsuitable for the appropriate engine operating RPM range. So, before you make this very important decision, you should be aware of several factors, which should be helpful and guide you in the right direction. In the following, we are going to concentrate on camshaft profiles that are suitable to street and street performance driving conditions. Camshafts, for racing applications, are not covered in this article.

Trying to strike a balance between fuel consumption, performance and acceptable exhaust emission levels is very difficult, therefore, some compromises have to be made.

Let us take a look at the MGB/MGA cylinder head with its' siamesed intake port design, by virtue of this shared design, the intake flow dynamics result in #1&4 cylinders trying to "rob" their adjacent cylinders i.e. #2&3 of their incoming mixture charge. This was all kept nicely under control by retaining a mild duration (214 deg @ 0.050" lifter rise) single pattern camshaft, together with the H4 or HS4/HIF4 SU carburetor(s) and intake manifold assembly. Incorporated in the manifold's design is a balance tube, who's primary job is to balance out cylinder pulses. Installing higher duration camshafts will always have a tendency to increase the "robbing" effect that we have mentioned above, however, this balance tube continues to offset this abnormality.

Installing side draught carburetors, such as Weber DCOE or Mikuni 40/44PHH, especially with the long intake manifold, is a different set of circumstances altogether, with no balance tube incorporated in the intake manifold design to take care of the cylinder pulses, we compound this "robbing" problem. With this type carburetor setup the more camshaft duration you add into the camshaft design, the greater these effects become and, consequently, the cylinder balance power will not be equal for all four cylinders.

Valve Lift
You will benefit from higher valve lifts on the stock cyl/head and way of increased camshaft lobe lifts or higher rocker arm ratios or a combination of both can accomplish this. Before making this decision, remember, it makes absolutely no sense to lift the intake, or to some degree the exhaust valve, beyond a point where the CFM flow rate increase decreases proportionally to decimal inches of valve lift. This max CFM flow rate will occur at approximately .375" (stock MGB cyl/head 1963-71 and 1975-80) and .400" (stock MGB cyl/head 1972-74 1/2). Further cylinder head work can be carried out to increase these CFM flow figures (a good reference source for this is Peter Burgess book " How To Power Tune MGB 4-Cylinder Engines For Road & Track ").

Roller Rockers
We have already pointed out the benefits of using roller style rocker arms in technical article technical article MGB16 "Rocker Arms".Where the customers' budget allows, we install 1.55:1 ratio rockers on all engine rebuilds.

Camshaft Lobe Lifts
We recommend that lobe lifts be kept in the region of .290" max or less, remember that high lobe lifts come at the expense of reduced lobe heel diameters and also extreme pressures at the lobe nose/lifter interface..

Camshaft Intake Duration (Street and Street Performance)
Based upon the "robbing effects" that occur within the siamesed intake ports (1/2 & 4/3) we recommend that the intake duration be no more than 225 degrees @ .050" lifter rise for any given carb/intake manifold combination.

Camshaft Exhaust Duration (Street)
In order to reduce valve overlap, which will promote good gas mileage, increase idle vacuum (HG) and reduce exhaust emission levels. We recommend that this be in the same region as the intake duration above.

Camshaft Exhaust Duration (Street Performance)
We recommend that this be greater than the intake duration, around 235 degrees, again measured at .050" lifter rise.

Intake/Exhaust Valve peak lift
The OEM single pattern camshaft specifications are as follows:
Duration 214 degrees @ .050" lifter rise.
Lobe lift .264".
Lobe centers 107.5 deg.
Exhaust valve peak lift 105 deg BTDC.
Intake valve peak lift 110 deg ATDC.

Ideally, intake valve peak lift should take place at maximum piston velocity (76 degrees ATDC) unfortunately, due to engine 4 stroke design constraints this is not practical, However, we should advance the intake valve peak lift over that of the OEM 110 deg ATDC figure.
Let us take a look at the OEM camshaft phasing. The camshaft lobe centers = 107.5 degrees (105 deg Ex peak BTDC + 110 deg In peak ATDC = 215 crankshaft degrees, however, divided by 2 = 107.5 camshaft degrees).

Now, If the OEM camshaft phasing had been, let us say 107.5 deg BTDC (exhaust valve peak lift) and 107.5 deg ATDC (intake valve peak lift) then both valves would be open an equal amount when a particular cylinder is at TDC during the overlap (exhaust/induction) period, this is commonly referred to as "spit-overlap". From this we can conclude that the OEM 110 deg ATDC (intake valve peak lift) is actually -2.5 deg retarded (107.5 - 110). If the intake valve peak lift was 105 deg ATDC then we would be +2.5 deg advanced (107.5 - 105). The intake valve peak lift is always referred to "advanced", "split" or "retarded" in respect to the camshaft lobe center angle. All camshaft regrinders will indicate this position in their camshaft specification literature.

Let us continue to use the OEM camshaft as our example and do some camshaft phasing experimentation. I have decided to install an offset keyway to the camshaft to attain the following: 103 deg ATDC (intake valve peak lift), 112 BTDC (exhaust valve peak lift) having now achieved a 7 degree shift over the original OEM Intake 110 deg ATDC position. And a 7-deg shift from the OEM Exhaust 105 deg BTDC position. This 7 degree shift for the intake and exhaust valve position work to the advantage of the intake CFM flow rate (remember max piston velocity) and to the disadvantage of the exhaust CFM flow rate.

The critical area in the exhaust CFM flow rate is the flow at low exhaust valve lift heights (i.e. approaching TDC) and we have now compromised this by closing the exhaust valve earlier. To figure out how much we have restricted the exhaust flow CFM by this early valve closing we would have to know how far the exhaust valve was originally open at 105 deg BTDC and compare this to the new exhaust valve open height at the same 105 deg BTDC. We know it will be less, but how much less? If we had the cylinder head CFM flow bench tested prior to assembling our engine, we could actually compare the exhaust valve CFM flow rates for these two exhaust valve open heights.

Another point often overlooked during the engine rebuild process, is, we invariably increase the engine bore size (reboring) which in effect increases the engine swept volume. So, theoretically, we are trying to flow a greater volume of exhaust gases, when compared with the original bore size, thru a reduced area.

So, do a little homework and make decisions, before attempting to rebuild your engine, as to component selection, such as camshaft choice, high ratio roller rockers, exhaust valve sizing/porting etc, etc.

Camshaft Recommendation (Street)
Part 6625075-15 single pattern (Elgin Camshafts stock OEM grind) 217 deg duration @ .050" lifter rise.
.262" lobe lift.
107.5 deg lobe centers.
Intake valve peak lift 103 deg (minimum) ATDC.
Exhaust valve peak lift 112 deg BTDC.
Cam timing @ 0.050" Intake 5.5 deg BTDC & 31.5 deg ABDC.
Exhaust 40.5 deg BBDC & 5.5 deg BTDC.
Overlap 0 deg.
Valve clearance Int/Ex .013" hot.
Use with 1.55:1 roller rockers, GCR 9:1, LCB exhaust header with free flow system. Good Street grind with plenty of torque.

We recently rebuilt a MGB street engine (+.020") 9:1 GCR with the above camshaft, A stock cyl/head 68-71, with 3 angle valve job (Intake 1.565" Exhaust 1.344"). Over and above the camshaft, I would like to take the opportunity to list the components that made this particular MGB a real pleasure to drive.

Compression Ratio 9:1
* Roller Rockers 1.55:1    Part # 1.55:1/KIT
* LCB Exhaust Header   Part # EXL18
 Free-Flow 2 inch exhaust system (Glasspack F18 front. F15 rear)
* Maniflow intake manifold   Part # SUB4-2
 1.5" HS4 carbs with #6 metering needles   * Part # AUD1005 (2) Fixed
* K&N Air filters Part # 222-950(2)   * SEE MGB19 FOR FURTHER INFORMATION
* Velocity Stacks   Part # 222-970(2)
* Total package for these items $1,000 approx

Part 671018X289 single pattern (Elgin Camshafts) 222 deg duration @ 050" lifter rise. .289" lobe lift.
110 deg lobe centers.
Intake valve peak lift 105 deg (minimum) ATDC.
Exhaust valve peak lift 115 deg BTDC.
Cam timing @ .050" Intake 6 deg BTDC & 36 deg ABDC.
Exhaust 46 deg BBDC & 4 deg BTDC.
Overlap 2 deg.
Valve clearance Int/Ex .016" hot.

Use with 1.55:1 roller rockers, GCR 9:1, LCB exhaust header with 2" free flow system. Requires exhaust CFM flow increase. Exceptional torque.

Further information from Elgin Camshafts has indicated that, due to the 671018X289 camshaft lobe ramp design, we can actually run valve clearances as low as .012" on both the intake and the exhaust. This has the advantage of being able to increase the intake and exhaust valve open duration. As a rule of thumb, every .001" decrease in valve clearance will result in approximately 2 degrees of valve open duration.

With this change comes increased valve overlap, with possibly lower engine idle vacuum readings and decreased gas mileage.

The above would allow the enthusiast the ability to tailor his driving needs for the occasional autocross etc.

Camshaft Recommendation (Street Performance)
Use 671018X289 with .012" intake and exhaust valve clearance.

Our earlier recommendation Moss part 222-270 dual pattern (Crane part 342-0010) did not perform as forecasted. So, subsequently we no longer install this camshaft.

We were unaware at the time that the camshaft lobe material required a lifter with a minimum hardness Rockwell RC scale of 60. Iskenderian was the only company making such a lifter (part SP-002). Unfortunately, they have been discontinued for many years. Consequently, using this camshaft with lifters less than 60RC will result in lifter failure.

Also, this camshaft requires a valve spring seat of 90# and 172# at full valve lift. Any increases in seat or full lift #s will result in possible rapid lifter failure. The maximum operating engine 5200RPM must be strictly adhered to.

I am going to leave the following original text information in place just for reference purposes only.

Although to date (05/31/98) we have not actually installed the below camshaft into a rebuilt engine, we did however took a close look at its profile and found that the intake profile to be almost identical to camshaft part # 671018X289 which is the camshaft we have been using for many years as an alternate camshaft for street applications. The exhaust profile also meets our current criteria for exhaust CFM flow.

Moss part 222-270 dual pattern (Crane part 342-0010) 222 deg duration (intake) and 232 deg (exhaust) @ .050" lifter rise. .280" intake lobe lift and .294" exhaust lobe lift. 110 deg lobe centers. Intake valve peak lift 105 deg ATDC. Exhaust valve peak lift 115 deg BTDC. Cam timing at .050". Intake 6 deg BTDC & 36 ABDC. Exhaust 51 deg BBDC & 1 deg ATDC. Overlap 7 deg. Valve clearance (hot) Int .014" Ex .016".

Use with GCR 9:1 and all components listed for previously mentioned camshaft part # 6625075-15 and 671018X289. No reason why this should not be an exceptionally good street performance grind.

Part 7008-10 single pattern alternate camshaft that we have used for many years with good results.
224 deg duration @ .050" lifter rise.
.278" lobe lift.
108 deg lobe centers.
Intake valve peak lift 103 deg ATDC.
Exhaust valve peak lift 113 deg BTDC.
Cam timing @ .050" Intake 9 deg BTDC & 35 deg ABDC.
Exhaust 45 deg BBDC & 1 deg BTDC.
Overlap 8 deg.
Valve clearance (hot) Int .010" Ex .012".
Suggested components as outlined previously.

Numerous other camshaft profiles that are available will probably work just as well as the ones I have outlined above, Unfortunately, we are unable to give any information on their characteristics, but we wouldn't be surprised in the possible similarity of their profiles, when related to the above.

Many camshaft regrinders establish their valve lift specifications by multiplying the cam lobe lift by the OEM rocker arm ratio of 1.426:1. If you read technical article MGB16 "Rocker Arms" you will understand why there is no way you can use this number to establish this valve lift. In all my years of engine rebuilding I have never been able to confirm this theoretical figure of 1.426:1.

One final note, Always degree your camshaft directly at the camshaft do not use any references in regards to valve clearances to establish phasing positions.

For camshaft profiles Part 6625075-15, 671018X289 and 7008-10 contact Elgin Camshafts at 650 364 2187. Be sure to request that your camshaft be nitrided (heat-treated).

Camshaft Lifters
There were two types of lifters were fitted to the MGB engine i.e. long style with short pushrod (up to 18V engines) and short style with long pushrod (18V engines). Use the 18V-style combination only. We find a very high failure rate with the long style and I believe have come to the conclusion for this failure.

Firstly, a camshaft lifter must be allowed to rotate to eliminate rapid wear on the lifter face and subsequently the camshaft lobe nose. This is taken into consideration in the design of both components. The lifter face is radiused and the camshaft lobe nose has a slight taper machined to it, However, the main criteria is the actual contact centerline between the lifter and the lobe nose, this centerline contact should be offset, and in conjunction with the lifter radius and lobe taper design will promote rotation of the lifter.

Back to the problem with the premature failure of the tall type lifter.
If you check the centerlines of the camshaft and the rocker arm adjusting ball (when viewed from the front) you will see they are different, resulting in pushrod lean towards the valve. If you give this some thought, then there must be some side loads associated with this lean and this side load must be transmitted to the lifter. Consequently, pushrod lean on the longer lifter is greater than the shorted lifter. This can be understood by simply making a drawing. The longer lifter also has a greater surface contact area than the shorter lifter. So, therefore, the longer lifter suffers from greater sideloads. This sideload pressure also increases with increased valve spring #s and increased valve lifts by way of higher camshaft lobe lifts and or increased rocker arm ratios.

We have not ruled out the fact that lifter hardness plays an important part in lifter failure. Here at British Automotive we have every single lifter hardness tested (Rockwell C scale) and yes some lifters do not pass this test. Recently we had a batch of 50 lifters tested and 2 did not pass the test, can you imagined these 2 lifters finding their way into 2 separate engine rebuilds. That is a hell of a lot of work to redo for the price of $1 the price for the hardness test. So, be sure to have your complete set of lifters checked and throw out any that don't register in the region of 55 on the Rockwell C scale. Alternatively, we can supply the set (8) Part 2A13/HP (see price list) which also incorporate a small bleed hole in the lower portion of the lifter, which allows for better camshaft lobe lubrication and allows accumulated oil within the lifter to drain out.