LZ23....good news...bad news

[datzenmike]

Hooked those wires up to the coil....no diff...still has that miss

 

I doubt that would have changed anything. If the fuse blows or the coil fails the other just keeps working anyway.

[HRH]

Yeah, but with one working and one not it definitely runs worse. It made a big difference on my 720, but that was an early version with the Z20S anyway. I dunno, still a miss. Did you check your spark plug wires? I still think the dizzy swap would be a good idea. Those little transistor weirdness things in the hall effect can mess up independently of each other.

[Sealik]

To compensate for a rough running Z24 with only 1 coil wired in...would be to advance the timing...?

2 coils...3-5 degrees

1 coil....8-12 degrees????

Would assume if it was the dizzy my timing marks would be all over the place?

 

The way it's running....it just seems like vacuum...like the intake or exhaust valves leaking, which they are.

Checked the resistance in the spark plug leads...they're good.

 

Wonder if some Seafoam would help...like a gallon of it... ;)

 

I do have a elec problem that just cropped up yesterday though.....not related. I think

Seems my fuel pump relay started to hum, replaced it and cleaned the fuse....no diff.

Clutch in or driving....no hum

[Sealik]

I think I know what the machinist did...well...didn't do properly that is

Last time the head went back, the intake valve guides were replaced...now in theory (someone correct me if I'm wrong) valve seats are machined using a stone to grind the 30 degree seat face onto the seat. The stone is piloted from the guide.

Valve seats were replaced on the previous visit to the machinist

Now...if the replacement valve guides are not positioned exactly as the previous ones....the valve will not seat properly.

The valve seat should of been 'reseated' with the new guides...for proper alignment

Thus the hammer marks on the tops of the valve stems to seat the valves.

Just a theory.........

 

Maybe

[datzenmike]

On a functioning dual plug head there are two ignition sources and it only makes sense that the cylinder will burn in a shorter time and reach maximum pressure sooner. In order to make most use of this pressure on the down stroke, the timing is set for about 3 degrees as you said. Now if you disconnect one plug it will revert to taking longer to reach maximum cylinder pressure so you will need to start the fire sooner. About 12 degrees just like an L series.

 

Whenever the guides are replaced the valve face/seat alignment is disturbed and the seats should be ground to match.

[HRH]

There shouldn't be any hammer marks, but I've seen them before due to valve collapse. They may have been from having one of your tappets too tight previously. You can't seat the valves by hitting them with a hammer, that would open them anyway. Chances are the marks have nothing to do with it. Take a picture of them and post it up, just for amusement.

[Sealik]

There shouldn't be any hammer marks, but I've seen them before due to valve collapse. They may have been from having one of your tappets too tight previously. You can't seat the valves by hitting them with a hammer, that would open them anyway. Chances are the marks have nothing to do with it. Take a picture of them and post it up, just for amusement.

 

 

The hammer (punch) marks were not there when I initially took the head in..(I'm pretty observant)..the third time the head was at the machinist they replaced the intake guides and leveled all the valve stem height(s).

Head was not installed or ran on engine...until (after) the 3rd visit back to the machinist.

So...I didn't have to use 140-190 lash pads.

I took a pic.... I can't find it....but, I will snap another 'ASAP'...was not impressive looking

It seemed like the guy grinding the stems might be having a bout with Parkinsons or something....bad job, not a true 90 degree and looked like there was multiply attempts, different grinding patterns on one top.

I could do a better job with my belt sander.....blind folded... :D

 

When you hammer the stem...the valve opens and closes from spring pressure, not sure why the marks are there...but...

 

Anywho....took the truck out and revved it to 5700 a couple of times....sounded really good.

Then...up to 6000....still sounded good and nothing came out of the engine :D

I taped a microphone underneath the hood and ran the cable to my camcorder to record this 'event'....but no workie.

 

Tomorrow.

 

EDIT....

 

Even the new exhaust valves had the hammer marks

Edited August 23, 2011 by Sealik

[banzai510(hainz)]

Hard to keep track of this. but can you put a L series matchbox and just use a c clamp to hold the dizzy down. and run it. use the main 12v On wire and see what happens,maybe its a different dizzy curve.

 

175 sounds good across the board,this indicates good to me. It compresses and goes BANG. If bad I think exessive blowby would be detected

[Sealik]

What is a good reading on a leak down test....less than 5 percent?

Over 45 would be of concern...? :lol:

Not that it matters...but tank pressure to tester was set at 90 lb...thus the tester set at 10 lb less.

[datzenmike]

15% to 20% I think is a pass.

[Sealik]

Tested 1 cylinder yesterday before it started raining and unless I fucked up the process.. :D ..the result was good.

2 lbs...or about 2 percent loss.

My compressor hose had a slight leak, still maintained pressure...but shall fix before I proceed.

I know that cylinder I tested had a bad leak prior.....I guess my running the crap out of the engine helped seal it up a bit.

[datzenmike]

I think you compare the line pressure available to the pressure when connected to the cylinder. The cylinder will always leak down some but 2% seems too good.

[Sealik]

Ya...I shall retest to confirm :D

There are 3 types of testers.

Tester with 1 gauge

Tester with 2 gauges....low pressure though, about 35 lbs I think.

Then the high pressure with 2 gauges...(better)....which I have

 

 

Plug compressor line (set at 100 lbs) into fitting on left, turn regulator to 90 lb, connect to engine.

Right gauge instantly reads cylinder pressure

[Sealik]

LZ23 Leak Down Test Results...not what I was expecting :blink:

 

Compressor at 100 lbs, connected to regulator, regulator set at 90 lb

All cylinders read 87+ lbs....3 percent loss.

Could hear a small hiss through top of TC cover....coming from pistons.

 

 

 

Soooooo....I'm thinking to confirm the 'accuracy' I'll roll my old truck in with 480000 on it.

This has got to have major leakage...?????/...nope.

Z24 at TDC...attached the leak down tester to No 1 exhaust plug hole.....nothing...zippo, can't hear any leaks and the gauge never dropped.

WTF.....?....(scratches head)

 

Sooooo...bring in another candidate....my Z24 EFI, strong motor with about 200000km on it.

TDC...attached to No 1 exhaust spark plug...etc.

86 lbs...which is a 4 percent loss...not bad....very good actually...can hear the air escaping

I then attached the compressor (100lbs) line straight to the fitting at the plug....no difference in sound (hiss) coming from engine.....hmmmmmm.

 

So what the fuck happened on the second test?????

I knew the 'old girl' ran pretty good....but zero loss of air pressure???

 

Anywho...the rest of the results

LZ23 compression test

Cam sprocket at No 3.....484 cam lift

 

No 1... 173 - wet 189

No 2... 175 - wet 187

No 3... 170 - wet 186...reset the valves after...No 3 intake was a little loose.

No 4... 174 - wet 190

 

I did notice (after they were pulled) one spark plug had soot on it.

I'll run the engine again to determine which one....I'm thinking insufficient spark???

Buy a new cap and rotor....even though they ran fine on another engine

 

[datzenmike]

Doug should be over 10%. You have that cylinder at TDC??

 

[Sealik]

Doug should be over 10%. You have that cylinder at TDC??

 

 

 

Actually....I saw that video a few times already in my research.... :D

He's using the low pressure tester....same poop different pile.. ;)

 

Yup...had all engines at TDC......ready to fire

 

You can see No 2 cylinder here.....lobes 10 and 2....TDC

 

[wayno]

IF you read this post before I deleted it, disregard my previous ignorant rambling, I read the entire thread. :lol: :lol: I hope you figure it out, I am fortunate to have the shop I use in my area, when he gives me my parts, it is usually right, unless there was a lack of communication, then it was an issue of WHAT was supposed to be done, rather than if it was done right. I have always wondered about how the Z block 8 plug dizzys worked, if it is strait forward, or a strange setup.

[Sealik]

IF you read this post before I deleted it, disregard my previous ignorant rambling, I read the entire thread. :lol: :lol: I hope you figure it out, I am fortunate to have the shop I use in my area, when he gives me my parts, it is usually right, unless there was a lack of communication, then it was an issue of WHAT was supposed to be done, rather than if it was done right. I have always wondered about how the Z block 8 plug dizzys worked, if it is strait forward, or a strange setup.

 

 

Crap...never read it. :D

 

Pretty sure you're not the only one with 'ignorant rambling'...I myself for one...'guilty as charged'. :lol: :lol:

The valves/pistons were leaking before I upgraded to heavier springs and taller retainers.

Pretty east to determine when there were no rockers installed, piston is up at TDC and there is a shitload of air coming out of the engine.

Guess the higher RPMs after the fact remedied this issue...because now...just a light hiss

Figured that air loss was my miss....nope

If I didn't know better...it's a vacuum leak, and I just can't find it.

Was suggested the Z24 dizzy is the problem...but, I believe the advance curve has nothing to do with idle.

Would most likely miss on acceleration????

I'll change the cap and rotor....if no improvement....back to an L dizzy if I can find one.

Nothing else left to check

 

But...I do have a couple more ideas....gonna try them today.

[wayno]

Crap...never read it. :D

 

Pretty sure you're not the only one with 'ignorant rambling'...I myself for one...'guilty as charged'. :lol: :lol:

The valves/pistons were leaking before I upgraded to heavier springs and taller retainers.

Pretty east to determine when there were no rockers installed, piston is up at TDC and there is a shitload of air coming out of the engine.

Guess the higher RPMs after the fact remedied this issue...because now...just a light hiss

Figured that air loss was my miss....nope

If I didn't know better...it's a vacuum leak, and I just can't find it.

Was suggested the Z24 dizzy is the problem...but, I believe the advance curve has nothing to do with idle.

Would most likely miss on acceleration????

I'll change the cap and rotor....if no improvement....back to an L dizzy if I can find one.

Nothing else left to check

 

But...I do have a couple more ideas....gonna try them today.

 

I am going to mention this even though it's probably stupid to, but it may help other people in the future as I have made this mistake in the past. One of the first things I thought of when you said the leak down problem went away after running it is a bent valve, the most comman way to bend a datsun OHC valve is to sit it on its face with the cam in the head, as some of the valves are held open, when the weight of the head rests on these valves they bend. How it usually happens is when it gets picked up from the machine shop, it gets thrown in the truck/car on its face because that is logicly the most stable way to transport it, when it's the worst way if you hit any bumps. If the cam isn't in the head, then no problem, as no valves are open.

When ever I see a head sitting on it's face I cringe, some ratsuners have posted oics. of a fresh head sitting on its face on ratsun.

As for my babbling comment before that I deleted it, I had mentioned that #2 cylinder was not the one that was supposed to be at TDC to time the engine, although it is entirely doable I am sure, but I had not read the entire thread and went by this photo, which you mentioned something about 10 and 2, which was for the leak down test, not to time the engine. :lol: :lol: I deleted my comment as fast as I could after I read the thread. :D

 

[Sealik]

Ya...I was initially thinking a bent valve, compromised/misaligned valve/seat....rings

Maybe just some crud in there from under revving???...No clue :blink:

With the lobes at 10 and 2...there is (approximately) 8 and 10 thousands between cam and rocker....thus the valves are totally seated for a leak down test

Each cylinder has to be exactly at TDC....not 1, 2+ degrees either way....because if you're not, soon as you plug in 90 lbs, the engine will start turning over

[Sealik]

Sooooo...after swapping out the Z dizzy for the L

 

 

No difference...still misses....figured as much before the swap... :(

 

http://youtu.be/8DW-tmSYxuM

 

Not sure what to check now....nothing left.

Out of plan 'B's

 

Suggestions????

[wayno]

Do you know which cyl. is missing?

[Sealik]

Do you know which cyl. is missing?

 

I put the timing light on each spark plug lead, couldn't see any diff.

Plugs are all the same and look good

 

Edit

 

Although.... I did pull the plugs last week for the leak down test.....and 1 had soot on it.

Didn't notice which cylinder it came from though... :huh:

[wayno]

I put the timing light on each spark plug lead, couldn't see any diff.

Plugs are all the same and look good

 

Edit

 

Although.... I did pull the plugs last week for the leak down test.....and 1 had soot on it.

Didn't notice which cylinder it came from though... :huh:

 

First thing you need to know now is which cyl. it is. When is the miss the most noticable, low, mid, or high rpms?

[HRH]

This may seem silly, but did you check or replace your spark plug wires? If you hook up a scope to it, you can see where they drop off if they're compromised. Even new wires can have a bad lead. Rare, but can happen.