LZ22 head spacer shim?

[banzai510(hainz)]

make sure u mark a chainlink w white paint and spocket. as the brit chain links dont line up unless 3 or 4 revolution of mtr. When u pull sproket up it mite get tite and i turn cam to induce slak .long as the marks u make line up

[datzenmike]

That's 1.47mm!!!!!!!!! I could maybe see half a mm or 0.020" If correct that's a removal of 8.7cc from the combustion chamber and an 11.29 compression.  I don't know what to say....

 

 

[ggzilla]

Definitely needs a tower shim (or a head shim if you want lower compression ratio)

 

11:1 is doable on premium pump gasoline with an aluminum head. Although with the open chamber design of the L20B heads you probably will have to reduce the mechanical timing to prevent pinging

[toshts]

53 minutes ago, datzenmike said:

That's 1.47mm!!!!!!!!! I could maybe see half a mm or 0.020" If correct that's a removal of 8.7cc from the combustion chamber and an 11.29 compression.  I don't know what to say....

 

 

Holy, and here I thought the removal of 0.026 was big. I knew the head had already had work, has different types of valve guides. Guess I shoulda checked with it already having shims on the cams when I got it. Yeah I will definitely run premium and low timing, if it gives me problems I'll throw a head saver shim on lol but I think I can get away with it with how it ran on 3.5 cyl

[datzenmike]

The Z series has two things going for it. Hemi heads are extremely detonation resistant and dual spark plugs that speed up combustion thus requiring reduced ignition advance. You might experiment with a colder heat range for the plugs also. There is no real rule of thumb for timing on the hybrid so advance little by little till it pings under hard acceleration and then back it off till it just stops. The increase in engine efficiency from the higher compression will to some extent off set the added cost of premium fuel.  

[toshts]

2 hours ago, datzenmike said:

The Z series has two things going for it. Hemi heads are extremely detonation resistant and dual spark plugs that speed up combustion thus requiring reduced ignition advance. You might experiment with a colder heat range for the plugs also. There is no real rule of thumb for timing on the hybrid so advance little by little till it pings under hard acceleration and then back it off till it just stops. The increase in engine efficiency from the higher compression will to some extent off set the added cost of premium fuel.  

Sounds good, I'll set my timing like that and run premium. Currently running 6 heat range, do colder plugs help prevent preignition? I'm definitely leaning towards just lapping new valves and running it without machining with how much has been taken off this head at this point.

[datzenmike]

In a high compression engine the plugs will run hotter, so hot that they can be an ignition source and cause pinging. The Z24 has two different heat range plug sets. The intake side plugs are cooler than the exhaust side plugs. The exhaust side plugs are over cooled by the in rush of intake valve air. Spark plugs get hot enough to self clean. If the plug is too cold it will build up deposits and fowl.

 

Saying to might have to get cooler plugs. Put the intake side 6s on the exhaust side and buy BPR7ES for the intake side. Up in heat range is colder. 

[toshts]

31 minutes ago, datzenmike said:

In a high compression engine the plugs will run hotter, so hot that they can be an ignition source and cause pinging. The Z24 has two different heat range plug sets. The intake side plugs are cooler than the exhaust side plugs. The exhaust side plugs are over cooled by the in rush of intake valve air. Spark plugs get hot enough to self clean. If the plug is too cold it will build up deposits and fowl.

 

Saying to might have to get cooler plugs. Put the intake side 6s on the exhaust side and buy BPR7ES for the intake side. Up in heat range is colder. 

Gotcha I'll snag some 7s at work tmw then, maybe some 8s down the line to see if it lets me push my timing a little further 

[datzenmike]

Not so fast. See how things are first. It's just an option farther down the line if you have pre-ignition problems.

[toshts]

14 hours ago, datzenmike said:

Not so fast. See how things are first. It's just an option farther down the line if you have pre-ignition problems.

Alright, I'll run the 6s for now and after getting everything going good I'll experiment with the colder plugs.

 

Took the head off today (wedged chain at TDC, just so happened that the bright links lined up) and pleased to see that I don't have nearly as much cleaning as last time with how short the head was on lol. Gonna call my machinist Monday and get a game plan going. 

[toshts]

Took the head in to my machinist today and in some manner I'm just stupid. Valve is infact not bent and there's no damage to the seat/guide. Nothing wrong with the head other than the the insane amount it's been milled. Air was infact only coming out of the intake port not the block breather and that valve was definitely not closing but not from being bent. I double checked the lash before I took the head off and did the testing and I did have 0.008 lash in that valve but maybe I did it wrong? Feeler in-between the cam and rocker? Not sure what was causing it not to close all the way but it sounds most like just messed up the lash? 

 

Live and learn. 

[datzenmike]

 You did say it was coming out the intake port not the block vent.

 

Is it working now?????  What did the machinist say????? If he looked at it and it was not closed he would have found something causing it.  

 

Could have been something pinched between valve and seat. Fell out when, I assume, the machinist took apart.

 

If lash was set somewhere on the lobe it would have been very excessive once the cam turned. The lash pad could have jumped around and caught sideways. Again, when taking apart it may have fell into place and wasn't noticed.

[toshts]

8 minutes ago, datzenmike said:

 You did say it was coming out the intake port not the block vent.

 

Is it working now?????  What did the machinist say????? If he looked at it and it was not closed he would have found something causing it.  

 

Could have been something pinched between valve and seat. Fell out when, I assume, the machinist took apart.

 

If lash was set somewhere on the lobe it would have been very excessive once the cam turned. The lash pad could have jumped around and caught sideways. Again, when taking apart it may have fell into place and wasn't noticed.

Lash was set at TDC for each cyl. Heads still at the shop, having him put the holes in the hg this time as I didn't like how messy mine were. I double checked the lash at TDC and made sure it didn't jump the pad, ran again still stayed open, took cover back off and was still in pad. Honestly something stuck between the valve and seat seems most likely but there's no damage to either the valve or seat so unsure. It sounds like user error of some kind I just wish I knew what so I don't do it again. Thinking I set the lash with the head off the car, spin it over and inspect to make sure it's closing all the way, and then reinstall when I get it back?

[datzenmike]

So did he say it's working ok now?

[toshts]

3 minutes ago, datzenmike said:

So did he say it's working ok now?

Last I heard he said everything looked great and there was nothing wrong with the valve or anything else, that it was sealing good. Still waiting on the call to pick it up

Edited August 6, 2025 by toshts

[datzenmike]

Well then, it was just an intermittent problem that solved itself. 

[toshts]

Heads back on

 

 

Benefit to having such a ridiculous amount milled off the head is the cam was way easier to get back on than the z24 I did a bit ago. Still fought me a little but way less. 

 

Gonna set the lash then get the manifolds and fluids in, well see how far I get today before I gotta run errands.

[datzenmike]

If you used tower shims just ignore this.

 

 

Set TDC compression #1 like you have, but only in a clockwise direction up to the mark. If you overshoot the timing mark back up and do again. This wil assure that ALL the timing chain slack is on the tensioner side and the left side has none. Now look through the top hole of the sprocket. Should look like this...

 

 

Note that the small notch in the sprocket is just slightly to the right of the small horizontal line above it. Excessive milling of the head will add slack to the chain which has now been moved over to the tensioner side and the cam sprocket effectively will have rotated the cam counter clockwise moving the notch to the left upsetting the cam timing. If the notch has moved over to the left, move the sprocket to the next number up. In this case from 2 to 3. 

 

Chain stretch or milling the head causes the cam to be late. This enhances high RPM top end running but removes low and mid range power and torque. Factory L20B is set on #2

 

 

 

[toshts]

I am so confused guys.

 

Cam towers shimmed. 

 

Valve lash set extra wide at machinists recommendation,  0.010 on both intake/exhaust while cold.

     - Vid of lash after it warmed up https://drive.google.com/drive/folders/1sNm08DyX0IU4ebcFwyFx7GPM8VKDsSFN?usp=sharing

 

Cam timing set about as perfect as I could hope for 

 

 

 

And the valves still not closing. Runs just about the same as before, pulled the valve cover set cyl 3 to tdc and did the same test and air went out the intake. Compression tester broke after using it on a different 720 with a blown head gasket, shot enough coolant out of the spark plug holes to drench me pretty good but no compression readings this time. 

 

Any further ideas?

 

 

 

[datzenmike]

Can you wiggle the #3 rocker with 0.010" clearance??????? 

 

Can you actually see space between the rocket tip and the lash pad?????

 

 

If YES then the rocker is not in any way holding the valve open. 

 

Take some rocker arms off and place a straight edge across the valve tops. Is #3 sitting lower than the others? like it's caught on something and not closed?

 

Try prying the #3 valve up, any chance that it moves and closes??? 

[toshts]

1 minute ago, datzenmike said:

Can you wiggle the #3 rocker with 0.010" clearance??????? 

 

Can you actually see space between the rocket tip and the lash pad?????

 

 

If YES then the rocker is not in any way holding the valve open. 

 

Take some rocker arms off and place a straight edge across the valve tops. Is #3 sitting lower than the others? like it's caught on something and not closed?

 

Try prying the #3 valve up, any chance that it moves and closes??? 

Can in fact see and wiggle the rocker with 0.010 clearance, was able to with the 0.08 I had before too along with seeing the space. I'll pull some rockers and give the straight edge a try either tomorrow or Thursday along with trying to pry it up.

[datzenmike]

There will be some height variances depending on how the valve seats were cut or seat and valve wear. Looking for something obviously different. 

 

If the machinist said nothing wrong then perhaps the valve is capable of being closed but hangs up when the cam turns. If this is the case try prying the valve spring upward to seat the valve. 

[toshts]

16 hours ago, datzenmike said:

There will be some height variances depending on how the valve seats were cut or seat and valve wear. Looking for something obviously different. 

 

If the machinist said nothing wrong then perhaps the valve is capable of being closed but hangs up when the cam turns. If this is the case try prying the valve spring upward to seat the valve. 

Tried prying up on it and it didn't lift it at all, didn't have time to pull stuff out but a visual inspection with my phone camera resting on the same parts of the intake it looks identical height wise to the exhaust valve next to it, I know that doesn't mean much but when I was loosing 100psi on that cylinder I would expect it to be a big difference. Gonna pick up another compression tester today and give it a go again. 

[datzenmike]

Weird!

 

How about a bore scope down the intake port? Give the valve and seat a good looking at. 

[toshts]

33 minutes ago, datzenmike said:

Weird!

 

How about a bore scope down the intake port? Give the valve and seat a good looking at. 

Boroscope was dead when I went to try this morning, threw it on the charger before I left for work and will check when I get home