Setting Tappets

[Barnsey]

Dear All,

   I have set tappets up before but it has been a while.  According to Rupert Ratio I should turn the engine until the inlet is just closed before setting the exhaust.  This doesn't seem to make sense to me as the exhaust is already pushing open at that point (due to valve overlap) .  It seems to me to make more sense to set up the exhaust when the inlet is fully open.  Is this a mistake on the part of Rupert, or have I mis-understood something? 

  Regards,

    Ian

[Spaceman]

The conventional way of adjusting the valve clearances is with the engine at TDC on the compression stroke - at this point both valves will be fully closed. However, doing it the way RR suggests is equivalent because both methods ensure the tappet is positioned on the base circle (lowest lift point) for the cam lobe corresponding to the clearance being measured.

[Barnsey]

OK, Thanks Spaceman,

  That makes a lot more sense now, and saves removing the side cover to check TDC.   I think that is how I did it on my Honda.

         Regards,

                Ian

[JulianS]

This service sheet from BSA shows how to set the valve clearances and ensure that they are set whilst the follower is on the cam base circle. If not set on the base circle the follower may already be rising on the cam quieting ram and cause an incorrect setting and more valve gear noise.

[Barnsey]

Excellent!, Thank you for the scanned sheet Julian!

  I think I can see the cause of my confusion.  Basically the valve sequence is inlet, exhaust and then a dwell.  It should be exhaust inlet and dwell.  I am thinking that the push rods might be reversed. 

  Is this actually possible? 

  I hope it would be possible to correct it by slackenning off the tappets and not require removing the side covers from the engine again!!!!.  There was some work in putting it all back together!    I'll call that a lesson for the future. 

   Ian

[Spaceman]

The base circle extends for at least 180 deg for either cam lobe. The BSA approach simply positions the respective tappet in the middle of the base circle for each cam lobe, whereas, the TDC method positions the tappets about 45 degs from the middle of each base circle but it is still on the base circle. I think the only difference between the two approaches is whether it is easier to set the engine at TDC on the compression stroke using a pencil down the spark plug hole or whether it is easier to go by the opening or closing position of the opposite valve. I tend to use the Haynes approach and adjust at TDC on the compression stroke.

[Derek996]

Use a pencil or whatever to find TDC on the compression stroke. Then rotate the engine backwards to find the point where the inlet valve has just closed. This is the position for setting the exhaust tappet clearance. Then rotate the engine forward until the exhaust is just on the point of opening. This is the position to set the inlet tappet clearance.

[Barnsey]

Thanks Derek,  Do I need to remove the left side cover to rotate the engine backwards?  Maybe I can just remove the small plastic cover on that side although I wouldn't see the timing marks then.

   Anyway, it turns out that the push rods were indeed reversed  (DOHH!) .  I swapped them over and everything makes sense. 

  The tip for using a pencil through the spark plug hole is super handy too. 

  It looks really fiddly to set the tappets with the engine in the bike, so I have ordered an adjuster tool, so expect more posts next weekend.
For now it is Sunday afternoon so wine calls.......

   

[Derek996]

Thanks Derek,  Do I need to remove the left side cover to rotate the engine backwards?  Maybe I can just remove the small plastic cover on that side although I wouldn't see the timing marks then.

   Anyway, it turns out that the push rods were indeed reversed  (DOHH!) .  I swapped them over and everything makes sense. 

  The tip for using a pencil through the spark plug hole is super handy too. 

  It looks really fiddly to set the tappets with the engine in the bike, so I have ordered an adjuster tool, so expect more posts next weekend.
For now it is Sunday afternoon so wine calls.......

My bike is a B32 but the procedure is the same. To move the engine I just select top gear and turn the rear wheel in the appropriate direction.