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Another Z to see the roads again...


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I decided to start this thread to provide some background on some of the work I am doing/planning.

My car is an early production 76.  Back in 95, at the advice of Z Doc (Roanoke), I swapped motors from an 83 ZX, with the .080 head cut, early 280 valves, etc. and not much else in terms of performance.  The car ran well, but not as well as I imagined it would, and it was okay.  After a year or so and about 10-15K miles of daily use, I could no longer live with the rust, so I took the car off the road for a complete restoration.

As life would have it, my plans got side-tracked.  I started a business and never had the time to restart the Z project until now.

So I went into this project knowing I had a good motor.  Figured I'd disassemble and clean it, new gaskets and seals, have the cylinders honed and replace the chrome-moly rings with Total Seal (the rings never seated well).  Well, to my utter surprise and disappointment, what I found was not what I was expecting.

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The first issue I found was the headers had developed leaks.  Not really surprising, and no real problem as I am replacing these with Sean Dezart's.

Look closely though at the exhaust runners, then look at the water pump cavity and the scoring of the material.

 

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Then the pistons.  I knew the rings didn't seat, but that's a lot of oil.  I only ever saw blue smoke on shifts.

No more than 15,000 miles. 

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Well, that was the top side.  Now the bottom side.

The journals are not terrible but they had been polished.

I am not sure what the debris is on the pick-up screen, but I did save it.  At some point I will clean it of oil and examine it closely, just for edification if nothing else.

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2 minutes ago, ETI4K said:

Well, that was the top side.  Now the bottom side.

The journals are not terrible but they had been polished.

I am not sure what the debris is on the pick-up screen, but I did save it.  At some point I will clean it of oil and examine it closely, just for edification if nothing else.

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That doesn’t look good 

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My machine shop still has the motor (since January).  No rush on my end.  The good news is the cylinders were not scored, the crank journals polished out okay, the cam polished out withing spec, and the pistons are okay.

Unfortunately the towers did not fair so well.  Three of them are out of spec by .003 and each is a different size.  There is also some question that I am still trying to get to the bottom of, but it may be that the head was cut more than .080.  Like maybe another .028.  The problem is the towers were only shimmed .080.

Adding to that, the head needs three guides, and the exhaust valve seats are beat up pretty well, so a real valve job is needed.  So, in reply to @Derekquestion, I figured if the head is in for that much work, I'd prefer to have everything to spec and nice and tight.  I can make the bearings and install them so that saves me a few hundred dollars (the machine shop in OH told me making them would be a T&M job - so that's a guess).  I am familiar with the pain off trying to shoot that hone in the right direction, though I have never done it.  I think the guy quoted me less than $200 to do that work only.

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I would suggest getting another head . You are going to have a difficult time reinventing the wheel . You should be able to measure head thickness . 
Making your own bearings ? 
In all the years in these sites I’ve never heard of anyone putting bearings in the cam towers . 

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Posted (edited)

Always open to ideas and changing my plans accordingly, though sourcing another head in decent condition sounds iffy.

The only bit that my head has me concerned about is the water pump cavity.  It will certainly reduce pump efficiency.  I know there are epoxies that are up to the task of repairing it, but I'm not keen on that idea.  It could be welded and machined back, and I could do that, though it is certainly a non-trivial undertaking.

 

 

Edited by ETI4K
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I've not heard too much on exhaust seats being worn out. Intakes that are bronze, definitely but not exhaust. I guess if the adjustment was really off they could get damage? My machinist told me the big intake seats are the same as a Dodge hemi motor so they were cheap as that's a popular motor nowadays. I too would look for an older head and start over. I know where an n42 is in an older junkyard for $100 and that includes the n42 intake. My $.02.

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You should measure the head thickness and check flatness.  If it's too warped you might not be able to get it straight with more cutting.  I seem to recall that the heads all started at 108 mm.  Add up your cam tower work, valve work, skimming if necessary, etc., and see what the math looks like.

The oil on your pistons could be bad valve seals.

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13 hours ago, ETI4K said:

My machine shop still has the motor (since January).  No rush on my end.  The good news is the cylinders were not scored, the crank journals polished out okay, the cam polished out withing spec, and the pistons are okay.

Unfortunately the towers did not fair so well.  Three of them are out of spec by .003 and each is a different size.  There is also some question that I am still trying to get to the bottom of, but it may be that the head was cut more than .080.  Like maybe another .028.  The problem is the towers were only shimmed .080.

Adding to that, the head needs three guides, and the exhaust valve seats are beat up pretty well, so a real valve job is needed.  So, in reply to @Derekquestion, I figured if the head is in for that much work, I'd prefer to have everything to spec and nice and tight.  I can make the bearings and install them so that saves me a few hundred dollars (the machine shop in OH told me making them would be a T&M job - so that's a guess).  I am familiar with the pain off trying to shoot that hone in the right direction, though I have never done it.  I think the guy quoted me less than $200 to do that work only.

I don’t see how the journals polished out . They would have cut to clean up the scratches in those pics . 
the scoring behind the water pump is not part of the head . That’s the timing cover that will need to be replaced .

you need to find out what you have before you spend money on junk . Find out how thick the head is and if it’s flat . Then a pressure check . If the towers are bad , it’s probably because the head is -or was warped . Not sure I would cut any more than .080 . 
 

Shameless plug . I do have a p90 for sale  that is shaved and ready to roll and it’s shaved .080 - with good towers ! Just PM me if interested . 

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12 minutes ago, madkaw said:

the scoring behind the water pump is not part of the head . That’s the timing cover that will need to be replaced .

Well, of course you are correct.  I know that, but somehow my feeble mind typed it out anyway.  Yes, I'm a nimrod.

I haven't seen the crank and I too can't see how the scratches would clean up by polishing.  I got that info from the shop owner, not the guy who did it, so we'll see.  Cutting it again wouldn't be the end of the world.

Anyway, I plan to mic the head tomorrow or Thu.  More to tell then

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@siteunseen
The exhaust seats show some good pitting (I'lltry to get some pics). 

These were cut clean with a 3-angle finish way back when.  They may clean up with a valve job.  I suspect the time on the engine stand had something to do with it but that's really just WAGuessing.  I have never seen pitting this bad before.

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Anyone notice the debris at the water pump cavity in the TIMING COVER 😉?  Or at the exhaust ports?  How about these pics of what was a brand new oil pump...

Truly, now a wasted pump. Some serious debris has been through this motor.  Why did the oil filter not catch it?  Perhaps bc it went into bypass during winter starts and that 5hit went right on through to ruin the oil pump, timing cover, cam towers, and score the cam and crank journals.  Maybe more.

What I've not commented upon is the fine grit I found in the oil pan.  I've spent a lot of time reflecting on what was going on at that time in my life ('96 - '97) to try to understand what might have happened.  I've considered my negligence or oversight by allowing debris in the area while building this motor, machine shop debris left in passages (again, my oversight for not clearing it), sabotage by employees (I had received several serious threats), contaminated oil and antifreeze (IMPOSSIBLE), and so on. 

My principal concern is to avoid it happening again!  The cost to have the original machine work done was painful then, now it'll be much worse.

More later...

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I have an aluminum pump on my 240 and Melling steel pump on my 280. I haven't had them apart since the rebuilds but it does look like you have some extra pitting. Could be coolant mixed in with the oil. Just a guess but that's what it does to the water pumps that I've seen with head gaskets gone bad.

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I've seen oil pumps look like that.  If I see any denting, I pitch it and buy new.  Every dent will result in lost flow/pressure.  It should be pristine.  

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There was zero leakage of oil or antifreeze.  I am certain the pitting and gouges are from debris.

The pump gears are hard, but not like tool steel.  A file scratches them.

So, I finally got to measure the head today.  Got in onto the bench and was rolling it into position and guess what I saw?  Metal filings and glass beads in a water passage.  Interestingly, the same machine shop did the work back in '96.  Maybe cleaning after milling ain't a happening thing.

I didn't find any metal in the oil pan, but definitely hard, rough, very small particles.  Also, when I built this motor I capped it off with a polished valve cover from MSA.  My search for the source of debris turned up a problem with that valve cover.  The vent baffle perimeter is sealed with a material that is extremely hard (probably started as firm and flexible).  I found several pieces of that sealant in the debris field.  The pieces are quite brittle.  If some of these made their way through the motor, I could easily see them causing this damage.

If that is true, then any valve cover is essentially a time bomb.  As if there aren't enough things to keep us awake at night. 🤯

Oh yeah, measured the head.  It's been cut a total of .106" with .007 off the top (machine shop just did it) and the balance off the bottom.  Combustion chamber now measures 43.5cc.

 

 

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13 hours ago, ETI4K said:

The vent baffle perimeter is sealed with a material that is extremely hard (probably started as firm and flexible).  I found several pieces of that sealant in the debris field.  The pieces are quite brittle.  If some of these made their way through the motor, I could easily see them causing this damage.

I've polished a few valve covers now and it's always a good idea to chip off the rest of that original hard epoxy sealant and remove that vent baffle so you can clean the accumulated muck behind it, on a couple of them I found glass beads from a previous restoration.  I used a permanent flexible sealant like ThreeBond or Motoseal on the baffle after reinstalling.

Even when I get a head back from the machine shop and it has been been sealed up with cling wrap it still has to go through a complete cleaning process. 

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On 4/29/2021 at 2:55 PM, ETI4K said:

Oh yeah, measured the head.  It's been cut a total of .106" with .007 off the top (machine shop just did it) and the balance off the bottom.  Combustion chamber now measures 43.5cc.

 

 

 

 

 

 

My P79 is right at .080 and with a standard Nissan head gasket is on the verge of ignition ping if I go anything past 12 degrees base timing(my vac advance is currently bypassed due to busted diaphragm).

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Is that your combustion chamber volume?  If so, what do your compression numbers look like?

I think the reason the head didn't explode when I drove it is because they also cut the new pistons to have .000 protrusion from the deck surface, that's about 25 mils, so it kept the same compression ratio (close anyway).

This whole thing is beginning to look a lot like a CF.

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It's right at 10:1,  I haven't checked compression yet.  I put about 150 miles on it since the build and started prepping the car for paint. 

That's good that your pistons are cut.  Hopefully you can salvage it.  Sounds it's got the bones for a pretty good build.

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The motor is on hold for the time being until I get the rest of the parts from the machine shop.  Decided to go with a replacement head since a good one became available.  Thanks @madkaw
Got some work done on the replacement floor pans.  Decided to remove the driver's side hump in the tunnel.  I still have to make and weld in new sections for the reinforced rear corners, but it's mostly down to blending the welds, a little flattening, and then get the floor supports in. 

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