4.2 engine question on dwell and vacume

[autoalain]

Folks, me again, 67 FHC, now, I'm an old chev guy, 1st time on my final setup of running engine(yea), 4.2,
on my chev engines I would disconnect vacuum and set up timing to the book, also use a dwell
meter to get points dead on correct, but,, I have manual and it does not give the dwell,
so now do I dis- connect vacuum to do timing and does someone know the dwell setting on points.
thanks. Mike.

[bitsobrits]

Dwell is a function of the lobe separation in the distributor and the shape of the lobe (along with point gap of course), and is pretty uniform across makes, based on the cylinder count.

Dwell setting for any 6 cylinder engine should get you close enough, so should be in the 30-35 degrees range.

And remember that dwell increases (point gap decreases) with wear on the rubbing block of the points, so start with dwell towards the low end of the range, and you won't have to reset the points as often.

And you probably already know that you set dwell first, before final timing, as changing dwell will impact timing a bit.

[autoalain]

Hi Steve, what about vacuum, do I disconnect when setting timing or just do it connected??

[bitsobrits]

Disconnected, and plug the vacuum line to the engine when setting timing at idle. Connected when checking timing advance at various rpms.

From a timing standpoint, there is nothing special about the XK engine, other than #1 plug is the one closest to the firewall. Keep that in mind should you ever change plug wires.

One of the 3 E types I've owned was bought at a deep discount because the prior owner was convinced there were deep issues with the engine. Turns out he/someone had the firing order wrong. A simple plug wire swap at the cap later I had a sweet running car.