[Mgs] tappet question

[Clayton Kirkwood]

As I said in a different post, I made the mistake of using TDC and BDC too
freely, as I meant the TDC and BDC of the cam lobe, and actually that isn't
accurate, it is degrees before and after the top of lobe, which can now call
BTL and ATL:<)))) (before top of lobe.)  While I agree that the lobe leads
in to BTL and follows ATL is still raised over the bottom of the lobe (BL),
I know the lobes don't extend 180 degrees, 70-90 degrees either side of Top
Lobe and still keep the follower up all the way. As you then kind of  point
out, and what my question was, how far TL can be assumed and then whether
that lined up 180 degrees opposite the other RON valve. I now understand
fully that the follower (I think it's the right word) will stay on the TL
for an extended time or degrees. The last question still remains unstated:
does the TL of valve 8 mean that you have found the BL of valve 1? If I
remember correctly, they aren't 180 opposite, input being before or after
exhaust by some degrees. Is the difference of opposition so insignificant
that it doesn't matter? Close to TL on one valve is also close enough on the
other valve? 

 

 

Hope that is more clear.

 

Clayton

 

 

 

From: PaulHunt73 [mailto:paulhunt73 at virginmedia.com] 
Sent: Tuesday, May 19, 2015 2:22 AM
To: crk at godblessthe.us; mgs at autox.team.net
Subject: Re: [Mgs] tappet question

 

As said elsewhere TDC and BDC are not relevant, if you are referring to the
piston.  If you look at the valve timing the inlet lobe is at its peak
70-odd degrees before BDC, and the exhaust valve is at it's peak about the
same distance after BDC.  So the back of the lobes are under the followers
180 degrees from there, which is more than 70 degrees before TDC and after
TDC respectively.

 

But it shouldn't make a difference, look at the cam profile, and the base
circle should extend for significantly more than half way round the cam, in
theory giving more than 180 of engine rotation where the clearance should be
the same.

 

Note in theory, which is why I said it's one of the reasons why I find the
position of greatest gap to adjust them, which on mine (and others I have
done) can be several degrees either side of the strict RON point.  

 

Also, whilst the dynamic forces on the piston etc. are slightly different on
compression and expansion etc, statically TDC is directly above BDC, how
could it be anything else?

 

PaulH.

 

  ----- Original Message ----- 

 

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?

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/mgs/attachments/20150519/10dfe029/attachment.html>