"Rocking" Valves Question

[double_ender]

Adjusting the tappets and fuel pump on the Volvo 7b the book talks about turning the flywheel untill the valves on cyl 1 are "Rocking". Is this when the valves are closed and the rockers have movement, or when the valves are open and the rockers have rocked down tight?

Answers much appreciated
Malcolm

 

[Shiver Metimbers]

The term "valves rocking" is, when one valve is closing the other is opening.

 

[VicS]

Yes its the point at which the exhaust valve is closing and the inlet valve is opening.
You then rotate the crankshaft 1 complete turn, both valves will then be closed and the gap that you are measuring will be at its maximum.
The adjustment is correct when you can just feel some drag on the feeler gauge.

 

[alan17]

It is often referred to as "valve overlap" which I think is a clearer description.

 

[Lakesailor]

Vic pointed out my mistake in this post. Go on to the rule of 5 post later.

 

[Trundlebug]

An alternative rule is the rule of 9 (on an eight valve engine) or 13 on a 12 valve engine etc.

When valve no. 3 is fully open, adjust no. 6 (3+6=9) Then rotate a bit until another valve is fully open.

Subtract that valve number from 9 and adjust that one. Keep going until you've done them all. Saves a heck of a lot of excess turning, but I always get confused about where I started, so best to make a note of it!

As I understand it, this rule will work on any engine, although not completely sure about V8's or V12's as I haven't tried it on them.

 

[Lakesailor]

Logically it would become the rule of 5 on a twin cylinder, and I have heard it referred to as that.
I haven't bothered to work it out but I seem to remember that firing order has an effect on this rule of thumb. V8 engines can have flat plane cranks or offset cranks and it effects the firing order. Or maybe I'm just getting senile.

 

[paulm299]

An alternative rule is the rule of 9 (on an eight valve engine) or 13 on a 12 valve engine etc.

To avoid confusion about which tappet has been adjusted , Mark it with chalk as you adjust them

 

[VicS]

save time and effort by adjusting the tappets on cylinder 2 when the valves are rocking on cylinder 1 and vica versa

Oh no no no.

When the valves are rocking you are at about TDC between the exhaust stroke and the induction stroke, Now turn the engine one complete turn and you are at about TDC between the compression stroke and the power stroke. Thats the point at which to adjust the tappets.

When one piston is at the top of its stroke the other is at the bottom !

DO IT THE WAY THE WORKSHOP MANUAL SAYS.

 

[double_ender]

Many thanks everyone for the replies resulting in a refreshment of my memory from when I "did" the tappets years ago on the A40 and my father's Standard Eight. My boats in those days had a Vire engine, and then a Stuart 8 when tappets weren't a problem! Happy Days!

Thanks again
Malcolm