Valve Lash

[Weasel73240Z]

I took my first stab at adjusting valve lash this weekend. I found that most of the valve's were about .002 too tight. Most of the exhaust were at .008 and most of the intake were at .006. I now have them adjusted to factory spec (.008 intake and .010 exhaust - cold). I still feel that something is "holding the car back" over 4,000 rpm's, and I'm curious what effect insufficient valve lash can have on performance?

I did notice one other curious thing when I was taking out the plugs. The #4 plug was fouled, and all of the others were nice light brown, and clean. The valve lash at the #4 was just like the others, a little bit too tight. I've noticed this plug being fouled in the past, when the others look good. If the valves are adjusted correctly, what would cause 1 specific plug to foul over-and-over, while the others all look good?

Thanks for any ideas/help.

[Carl Beck]

Fouled with what? Carbon, Oil, Wet Gasoline?

Carl B.

[Weasel73240Z]

Definitely "wet" fouled, it looks like gas fouled.

[=Enigma=]

Perhaps a bad plug operating intermittently, a leaky plug wire, dirty terminals, a cracked or tracing disti cap. That could explain what's holding you back. Time to check all the wires, clean up the terminals and inspect the cap. Switching the plug to another cylinder might help isolate whether it's the plug, wire, connections or cap if all else fails.

Edited June 30, 2009 by =Enigma=

[Weasel73240Z]

Perhaps a bad plug operating intermittently, a leaky plug wire, dirty terminals, a cracked or tracing disti cap. That could explain what's holding you back. Time to check all the wires, clean up the terminals and inspect the cap. Switching the plug to another cylinder might help isolate whether it's the plug, wire, connections or cap if all else fails.

I finished putting the car back together last night. The valve lash adjustment made an improvement, but theres still something thats not 100% dialed in.

I replaced the #4 plug while I was doing the valve work. I visually inspected the dizzy cap, put the timing light on the #4 to make sure it was firing (it was), and confirmed good plug connections.

I still think the occasional "dead spot" in the powerband is a timing/advance issue. I don't remember there being a dead spot before I installed the ZX dizzy and got rid of the points. Right now I'm at 12 BTDC (initial) which gets me to about 35 degrees total (mech. and vac.) advance. The car idles great, and it pulls great right up to about 4,500 + most of the time. I rarely push it past 4,500 but the car would be glad to, in 1st or 2nd gear.

But sometimes (typically in 3rd and 4th gear it seems) there is a dead spot from around 3,800 - 4,200. On the highway, when taching at say 3,200, if I try to accelerate without downshifting, I feel the "dead spot". I know I'm not getting max. output, and I'm actually thinking about paying someone look at it.

Problem is, finding someone withing 50 miles of me that works on Z's. If any of the New England guys have anyone in mind in southeast MA that knows how to dial these L-series motors in, shoot me a PM. I'd know A & C Imports in NH has a very good reputation, but 100 miles on the highway is a challenge with my tranny/diff. set-up (4-speed w/4.11's).

[Carl Beck]

I rarely push it past 4,500 but the car would be glad to, in 1st or 2nd gear. ........

......But sometimes (typically in 3rd and 4th gear it seems) there is a dead spot from around 3,800 - 4,200. On the highway, when taching at say 3,200, if I try to accelerate without downshifting, I feel the "dead spot". I know I'm not getting max. output, and I'm actually thinking about paying someone look at it.

Hi Paul:

At least one of the problems is - you drive it like an old lady:stupid:

If you want to accelerate when you are running along at 3800RPM - DOWNSHIFT!! and run that puppy up to 6,500 RPM before shifting... While the L24's have plenty of low end torque, they really don't wake-up and run {come fully onto their power band} below 4000-4500RPM.

4500RPM shifts are fine in stop and go traffic in first and second... When you hit the freeway on ramps you should be running it up to 5500-6000RPM in the lower gears - just to keep the carbon from building up on the tops of your pistons.

In my personal experience the harder you run an L16,18,24,26,28 the better they run and the longer they stay on the road. I've never seen one of these engines hurt by running them at anything below 6500RPM.

FWIW,

Carl B.

[motorman7]

Hi Paul:

At least one of the problems is - you drive it like an old lady:stupid:

If you want to accelerate when you are running along at 3800RPM - DOWNSHIFT!! and run that puppy up to 6,500 RPM before shifting... While the L24's have plenty of low end torque, they really don't wake-up and run {come fully onto their power band} below 4000-4500RPM.

4500RPM shifts are fine in stop and go traffic in first and second... When you hit the freeway on ramps you should be running it up to 5500-6000RPM in the lower gears - just to keep the carbon from building up on the tops of your pistons.

In my personal experience the harder you run an L16,18,24,26,28 the better they run and the longer they stay on the road. I've never seen one of these engines hurt by running them at anything below 6500RPM.

FWIW,

Carl B.

Wow! Put me in the old lady category along with my mom. I must say my typical shift point is at 3500 or lower. The only time the engine approaches 4000 is when we are on the freeway driving normal California speeds. And, I don't beleive that I have ever taken it over 5000 RPMs.

I am pretty sure my parents drove the same way as they are typically the slowest car on the road (yes, even in the Z). So slow that I consider them hazardous and always offer to drive (Mom in 70s, dad in 80s). We all were taught the lower shift points were more economical and gentler on the engine (without lugging of course).

FWIW, the engine had absolutley no carbon build up on the pistons and only a bit of white caking on the exhaust valve. Otherwise, the cylinders were very clean.

Boy, I'm gonna have to rev that baby up one of these days when I get it back together.

Rich

[Weasel73240Z]

I rarely push the car over 5,000...and I bet that's true of most guys on here. Not saying that the L-series can't handle 6,500+, we all know that it can, its just not practical for a street driven car to be winding it up to 6,500 very often. Between the color of my car, the sound of my exhaust, and the number of cops in Taunton, I'd be paying speeding/sound ordinance tickets every other week if I was regularly running it up to 6,500 rpm shift points.

Either way, there's clearly something going on around 3,800 - 4,000 usually in the higher gears. I'm going to richen the mixture another 1/2 turn out, and see what I get. I'll keep you posted.

Still wondering what I should running for intial timing and total advance with my set-up. It's a 1973 L24 (stock cam) ZTherapy SU's, ZX dizzy (E12-80) NGK plugs at .045 gap. MSD Blaster 2 coil. Any help would be appreciated. I have tried searching alot, but there's nothing as specific as what I'm looking for. I'd love to hear what guys that are running the same set-up as mine as using for initial timing, and whether they are using vacuum advance, or just mechanical. Thanks in advance for any help.

[Weasel73240Z]

I wanted to follow up on this post. In reviewing my manuals, it looks like the initial timing for my L24 (with D609-56 dizzy) from the factory was 7 degrees BTDC. Looks like the mech. advance gave a total of about 9 degrees of additional advance, and 7.5 degrees more from the vacuum advance. So starting at 7, the total advance should only get to about 23.5 degrees. I think for the most part, ignition timing relates most directly to the camshaft, and that's stock in my car.

When I installed the ZX dizzy, I advanced the timing to about 12 BTDC, based on what I read here. The ZX dizzy has 17 degrees of mechanical advance, and I'm using the vacuum advance (with new breaker plate so it works) and full advance gets me to about 35 degrees BTDC at around 2,300 rpms.

Most of the stuff I read says around 35 total is about right. But, could it be that my hesitation around 4,000 may be from advancing the timing more than the cam can handle? :stupid:

I'd go tweak the timing and take it for a ride, but its raining in MA for about the 28th day in a row so the cars in dry dock. I don't know how you Pacific-NW'erners take it. :classic:

Edited July 2, 2009 by Weasel73240Z