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Installation - Hot Road Cam

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Fitting Instructions for Hot Road Cams


If you feel any of this is too involved, give the job to an expert! 

These cams have been designed to give a “fast road” performance, and are deliberately not full race profiles, with all that that means… power loss and temperament at low to mid rev ranges. 

The standard Norton timing chest does not provide for much increase in cam lift. Check the clearance between your existing cam at full lift and the follower when raised to its full extent. If there is not room for the additional 0.054” lift of these Hot Road Cams, the cam follower block will need to be shortened. (Any cam with less lift is extremely unlikely to give comparable performance.)   

I and several other people have fitted these cams without needing to increase the cam follower movement, BUT...

Let us assume that you do need to shorten the cam follower blocks.  Fitting and timing these cams is a job that can only be undertaken with the engine out and stripped. With the timing side crankcase separated, remove the cam bushes and the cam follower blocks. This involves drilling out the cam block locating pin, heating the cases and unscrewing the block. The bottom end of the cam follower block can then be ground to make provision for the additional lift. About 1.5mm should be enough, but refer back to your earlier measurements.   

 Tappet Blocks.jpg (54396 bytes)

Reassemble the followers and follower blocks. 

Check that the new cams rotate freely.


Timing Instructions for Hot Road Cams


Rebuild the engine, but do not fit the head. Set up a degree wheel on the crank and determine TDC. (The best method is with a dial gauge or vernier calliper measuring a certain piston drop either side of TDC and splitting the difference) 

The cams have three keyways to enable timing “between” the teeth. It is necessary to find which keyway gives the most accurate timing. Original cam pinions are a very tight interference fit and require a press to remove. A local engineer will be able to help. Once off, the cam wheels should be polished on their interior surface until they are only a firm hand push on the shafts. 

Fit the cam wheel using any one of the keyways on the cam shaft. 

Fit the assembly into the timing chest 

Set up the dial gauge to measure cam follower movement. 

bulletThe Exhaust cam should give full lift at 103 degrees BTDC
bulletThe Inlet cam should give full lift at 101 degrees ATDC

If this is within a couple of degrees, strip and reassemble the cam and pinions on the same keyways with Loctite. Alternatively reassemble using the second and then third keyway until the best timing is obtained. Use the best keyway and Loctite in position.

Checking Valve to Piston Clearance.

Standard pistons should not need modification, but this check is essential! 

Assemble the Cylinder head using Amal Concentric Carburettor springs in place of the valve springs. 

Fit the head without pushrods. 

Set the piston at TDC. 

Measure the valve travel, seat to piston. Assuming standard rockers with a 1.32:1 ratio, this needs to be 0.354” times 1.32 plus 0.060 for safety. That is 0.530” travel. 

Pocket the piston if necessary.


Check Valve Springs

Again, it is unlikely that any problem will be encountered, but this check is essential.

 With the additional lift it is conceivable that the valve springs could become “coil bound” This is unlikely, but you must ensure that this is not so. Feeler gauges at full lift between the spring gyres) Solutions include machining the extra 0.080” or so from the ally of the cylinder head under the valve spring collar.