Valve Adjusting

[kinfish]

Gus,

First time I saw this thread about your issue with zero compression in cylinder #4.

Those valve seat rings are tight fit in head ....... freeze them and press in. Sounds like your problem could be a dislodged valve seat. If you know somebody that has access to a borescope you could insert it and check out inside.

When you are convinced that head must come off you can borrow my plastic device which i bought from MSA and is used to keep the timing chain in place on the crank pulley and chain tensioner. If you forget to use it you will need to pull the timing cover to get chain back in place.

I had my head rebuilt by Bill DiCondino of Extreme Cylinder Heads in Palm City. He owned a small shop in 2002 and did fine job on my head rebuild with mild cam. Rebuild required replacement of all 12 valve seats. I have some of his business cards and believe he is still at same location because he ironically was a high school classmate of the guy who just painted my Z this spring. In 2002, Bill's business was focused on competition and exotic car heads and was not interested in doing routine stuff. He ain't cheap but does good work ..... but don't rush him .......my job took about 5 weeks.

Working in your open air garage in July or August promotes weight loss thru sweat. Took me 3 weeks plus to put all the stuff back on my car after paint.

[westpak]

yeah this took the wind out of my sails

Ron that would be great if I could borrow the tool, I was going to order one but know I will have to order more stuff later when I put it back together so one order would be nicer, let me know how I can get it from you.

I do know people with boroscopes I will have to see if I can borrow one

[westpak]

well thanks to Ron's great suggestion on the borescope I got a hold of one to check out the engine without taking it apart first. Unfortunately it answered some questions but left me without a solution.

I turned the crank to check the valves when fully open and closed and both the intake and exhaust valves on this cylinder operate fine and appear to close fully, and there is no sign of a valve seat dislodged or anything keeping a valve from closing.

Then I checked the piston and it was hard as it had some carbon on it, I saw a spot that almost looked like a small hole but could not verify so I decided to spray some carb cleaner in there and cleaned up and there was no hole, I think it was some carbon knocked off with the borescope. So once cleaned up a bit I could see there was no hole but did see what looked like a dent but it was off to the side and the borescope was a rigid one so I could not get closer, so it is either damage from hitting an intake valve or a valve relief notch.

I have searched without success, does the stock 1971 L24 have notches? does someone have a picture of a stock 1971 L24 piston top so I can compare to what I am seeing?

[Carl Beck]

A small carbon deposit/chunk can get lodged between the valve and valve seat - thus preventing the valve from fully closing.. In the old days, local mechanics would start the car, warm it up, and then mist water vapors into the carb intake while increasing the RPM... They just used a spray bottle...

I'm not recommending this - just mention it to show how common a problem it used to be... I still can't believe that given that cars history, and mileage - that anything serious could be causing the problem...

Since you already have the intake/exhaust manifolds off - go ahead and pull the engine and put it on an engine stand. Pull the head, clean up the piston tops - and send the head to a good shop to be checked. The E-31's were noted for cracking around the exhaust valves. At the same time you can pull the front cover and pan - clean, detail (repaint the block, bead blast the front cover - and reseal the engine). replace the front and rear main seals, freeze plugs etc.

Clean/polish the engine compartment - and reinstall the engine..

FWIW,

Carl B.

[westpak]

well I was hoping to avoid that or at least do it later when I would do the complete car, right now I was just wanting to get her running and drive for a while, I have all the suff to install, already did the rear brakes, but if the engine has to come out to get done then that puts me on part 2 of the plan and skip part 1 which was just to get her running with a lot of the systems redone or replaced but not refurbishing everything like links, brake shields............

So if I go this way I would probably just stop and tear her down to do the full job, but being that big I would probably put off a year while I do some things the 300ZX needs due to age.

do you have a pic of the top of the piston so I can compare to what I am seeing?

I also hate to just take apart the engine before I find out what is wrong

[kinfish]

Here is a shot of my L24 block with head removed. Shows #1 cylinder with piston at TDC. Black areas are dykem I used to layout of potential contact point of exhaust valve with rim of block. I installed 35 mm exhaust valves on rebuild and experts recommend notching block for clearance (OEM valve size was 33 mm).

That white stuff in cylinder #2 is shaving cream. I used it to entrap the metal filings from the notches I installed with a dremel. Clever suggestion and it worked ....... a tip from an old timer on the web.

I do not remember any notches in pistons.

[westpak]

thanks for pics Ron, I am going blind looking through the borescope, I rechecked and I think the abnormality in the surface was an optical illusion from the scope, I could not see it again.

I also checked the valves by turning the crank 1/4 of a turn at a time and sticking the scope in to check the valves and could see them open up easily, again no seats lose, and they seem to close fully, I could not see a gap at all.

I am not familiar with older engines or carburetors at that, but the engine including the intake/exhaust ports as well as the valves look like they have a lot of carbon build up for only 34k miles. I am thinking of cleaning intake and exhaust paths as well as valves and pistons with some carb cleaner, then change the oil, lube the pistons a bit and try it again and see, I just don't see why the piston would not have any compression specially 0

Edited November 18, 2008 by westpak

[srbigbutt]

I took my Z out for a spin today and when I was close to home it started knocking, so I got home and took the valve cover off and saw the same thing pictured in post 1. Retainer on #5 had popped off. How exactly do you get that thing back in?

I will then adjust the valves and hope to god everything is back to normal. I'm new to adjusting valves and hope its pretty straight forward.

[srbigbutt]

Nevermind. I got it back in. Put the VC back on and started it up and it seemed to run smoothly. I will be doing my first Valve adjustment during the holidays and I hope everything turns out ok.

[srbigbutt]

Ok I need some help. I put the lash pad back in place, did a cold valve adjustment and then a hot valve adjustment. Spark plug in #5 where the lash pad fell off was bent so I replaced all 6 with new NGK plugs. Installed new valve cover gasket and then started it up. Ran fine and I was happy and thought I was done. Decided to take her for a drive around the block and it ran perfect until I got back in my driveway. It started to hesitate and stumble real bad. I can hear the AFM flapping and it felt like it wanted to die. Now it just runs like crap when I start it.

Did I do something wrong with the valve job? I'm pretty sure I did everything as documented. Kinda strange that it ran fine for a while. Could it be a vacuum leak or is something else wrong? Any advice would be helpful.

[tibZ]

I would guess there was a reason the lash pad fell off in the first place. Normally with everything operating correctly there is no reason for that to pop off. Mine was due to a major slude problem. Also spark plugs don't get bent for no reason. I suspect you have a serious valve-train/ timing issue that you need to check out before you start that car again.

Mike

[ChrisZ]

thanks for pics Ron, I am going blind looking through the borescope, I rechecked and I think the abnormality in the surface was an optical illusion from the scope, I could not see it again.

I also checked the valves by turning the crank 1/4 of a turn at a time and sticking the scope in to check the valves and could see them open up easily, again no seats lose, and they seem to close fully, I could not see a gap at all.

I am not familiar with older engines or carburetors at that, but the engine including the intake/exhaust ports as well as the valves look like they have a lot of carbon build up for only 34k miles. I am thinking of cleaning intake and exhaust paths as well as valves and pistons with some carb cleaner, then change the oil, lube the pistons a bit and try it again and see, I just don't see why the piston would not have any compression specially 0

I don't know how long you are in the progress of solving this, my advise to you on this is to do the following:

Pour some gas or diesel in the intake runner, with the intake valve closed, wait for an hour and see if there is any fluid on top of the pistons or if it's still in the runner, then do the same with the exhaust, if both valves can hold up the fluid you can pour some on the top of the piston to check if the rings are leaking.

Hope this will help

Chris