[Mgs] tappet question

[Richard Ewald]

Houston we have a problem with terminology here. 
TDC and BDC refer to the position of the piston in the bore, or in the firing stroke. Period. 
Piston at the exact top of its stroke?  The piston is at TDC. At the exact bottom of its stroke? BDC. 
#1 at the top of its stroke on compression?  The engine is at TDC. 
What you are referring to is the valve being on the lobe or the heel of the cam. 
If you doubt that when #s valves 1 & 3 are on the top of the lobe that valves 6 & 8 are fully on the heel feel free to rotate the engine several degrees one way or the other and see if the gap gets bigger (it won't) 
This is because a camshaft is a circle (base circle) with a bump on one side. Anywhere on the heel is going to give you the same clearance. 
There are even some engines that instruct you to put the engine @ TDC #1 adjust half the valves then rotate the engine 360 degrees and then adjust the other half. 
Rick


Sent from my iPhone

> On May 18, 2015, at 10:03, Clayton Kirkwood via Mgs <mgs at autox.team.net> wrote:
> 
> Regarding Rule of Nine, I understand having 8 all the way up to set 1. But there is a significant rotation between “real close to the top” in front of, and after TDC. This can be seen with rotation the engine and seeing very little to no movement. Also, if I am not mistaken 8 TDC is not perfectly in line with BDC of 1; there is a bias. This means that when 8 is TDC, 1 is not absolutely BDC ready for measurement. So the question is, how do you ensure, with all of that slop, that you truly have BDC?
>  
> TIA,
>  
> Clayton
>  
> 
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