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850 Commando cam shaft variations

Submitted by paul_wolf on Sat, 18/04/2020
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Commando

After 2 valves seats dropped down and got smashed to bits and damaged the head and a piston,i decided to strip the complete engine and discovered that the right hand inlet lobe on the camshaft was badly worn.After looking at the cost of standard camshafts i bought a standard Commando Hepolite camshaft from Wassell.When it arrived i noticed that it looked slightly different so i fitted it to the crank cases with the crank and attached the cylinders with a piston  a DTI gauge and a timing disc and put the DTI gauge on top of a push rod.

The Norton workshop Manual info for a standard cam are. with a .013" cam life

Inlet opens BTDC 50deg    Hepolite cam 50deg 

inlet closes ABDC 74deg   Hepolite cam72deg  

Exhaust opens BBDC 82deg Hepolite cam 75deg

Exhaust closes ATDC 42deg Hepolite cam 42deg 

and the lift of the cam is 0,325in

 

 

Submitted by peter_shand on Sat, 18/04/2020

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Are you taking into account the manual states 'measured at .013" cam lift'  This is to stop the confusion of when the opening and closing ramps have moved out of the way. 

remeasure your original cam and see if this affects your first reading.  Then you are comparing like for like (at least with the manuals figures)

How manufacturers measure their respective cam shafts can differ from each other. They usually quote the cam lift when the measurement is taken.   

Getting into cams is like opening Pandoras box! Lobe phasing ,lobe shape, opening ramps, duration, lift rate, timing diagrams etc etc     

There are various books available on camshafts. 'How to choose camshafts and time them for maximum power' is a good starter for ten.  

R.E. Wassel parts. I stand to be corrected but don't Wassel own the Lucas brand now? So are they the only manufacturer of alternators and rotors for commandos?     

Submitted by john_holmes on Sat, 18/04/2020

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I stand to be corrected but don't Wassel own the Lucas brand now?

No, they have a license to use the Lucas name on old Motorcycle electrical parts, Lucas TM is still owned by whatever multinational outfit owns them but they have rented it out.

So are they the only manufacturer of alternators and rotors for commandos?   

No, LAP, formed by some ex Lucas employees, took the tooling with them and still make alternators and rotors in the UK. But they cannot use the Lucas name, they are listed on the TMS motorcycles online store as UK made rotors and alternators. Wassell/Lucas rotos and alternators are made in the far east from new tooling. I only buy LAP alternators and rotors.  

Submitted by peter_shand on Sat, 18/04/2020

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Paul

Basically reset your dial gauge to zero when your cam reaches .013" lift. Then take your readings from there until the dial gauge reads zero again. This prevents the opening and closing (sometimes called quietening ramps) ramps that are ground into the cam on manufacture affecting the readings.

If the cam in the manual was measured how you have been doing so it would be quite different from the figures quoted in the manual and probably similar to the figure you are seeing on your original cam.  

You have been measuring the opening ramp (75deg BTDC to 50 deg BTDC) then the lift (.300" plus)and then the closing ramp (74deg ABDC to 80deg ABDC)

Regards

Peter   

Hi Peter,I was forgetting .013" cam lift after rechecking the new Hepolite cam is pretty close within a few degrees and  some lobes spot on.After being on it all day sometimes you need to walk away and have a cup of tea and then it all makes sense.Engine rebuilding tomorrow.Thanks Paul

 


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