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Early 1974 260z build

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On 1/1/2022 at 12:45 AM, Noll said:

The 260z fuel pump and interlock systems are a fun time for sure, been there done that with mine. There are two fuel cutoffs - one is the alternator as you say, and the other is (for some reason I have yet to figure out) a starter cutout. They're in-line, so if one triggers for some reason no voltage gets to the fuel pump. The 2nd cutoff relay kills the pump while the starter is cranking and a lot of people bypass it (was done on my car long before I got it, jump GW to BW on the relay plug and bob's your uncle).


Assuming the starter cut relay isn't acting up it's either going to be the alternator safety cut or a wiring issue most likely.


I did some tracing of the harness when I was troubleshooting some fuel pump and interlock stuff (interlock being related to cranking not fuel but was working on both at once); if you follow the neon blue wire (multiple colours in the real harness, just did that in the drawing for continuity) back it should give you some spots to check for voltage at plugs etc. you may need to right click>view in new tab to see the full size




You can also disconnect the pump entirely and splice in some hose to just go tank>lines>mechanical pump>carbs for testing purposes, they added the electric pump to try to stop vapor lock IIRC; the car will run fine on the mechanical pump only.

Edit: oh, and in case it helps, here's how I mounted my aftermarket electric pump. Basic square bracket that bolted to where the stock one went, rubber isolators, and a U bend from some nicopp hardline. Probably 1/4 the weight and size of the stock massive bracket.




Cheers on the workman ship Noll...... absolutely impressive.  Good show!  THANK YOU so much for sharing this.  Always nice to see this sort of thing. :)

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31 minutes ago, A to Z said:

Cheers on the workman ship Noll...... absolutely impressive.  Good show!  THANK YOU so much for sharing this.  Always nice to see this sort of thing. :)


Thanks! Just trying to make it a bit easier for other peeps doing the same as I did, I had to trawl through lot of old forum pages and nearly-dead websites for a lot of stuff when I was looking it up haha. I have a full forum thread with a ton of stuff documented over on Ratsun ( https://ratsun.net/topic/71982-project-theseus-a-74-260z/page/31/ ) - didn't have an account here when I started on the car or I'd have made it over here to o(I suppose I could still but 4.5 years of work in one big dump might be a bit odd lol). Keep in mind I knew very little at the start of the build (bought the car on my 19th birthday) and was teaching myself to weld for like the first 1/4 of it all.


@juggernautjoee ah that sucks, hopefully HG or at worst the head as opposed to block issues :(


Handy tip for being lazy like me - mark the orienting hole that the cam gear is in on the front (there are 3 to accommodate for chain stretch, so don't want to use the wrong one), the chain, and the back of the gear and first cam tower and you can do the whole head pull/reinstall without having to touch the front cover or set timing (as long as you use a wedge to the chain doesn't fall off the tensioner inside the cover).





Edited by Noll
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Thanks @Noll.  I took a look at - 


I'll be setting the engine at TDC, marking chain and sprocket points.  And taking pictures of where everything lines up.  Already got a timing chain holding wedge coming, and a head gasket.  I'm gonna hold off on some of the extra stuff like arp studs, intake/exhaust gaskets, etc... Until I get this thing torn down to inspect.

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Well that was one of the easiest tear downs I've done.  Took maybe 1.5hrs taking pictures along the way.  Nothing really gave me any trouble.  In fact, some of the intake and exhaust manifold bolts were finger tight.  Even the nuts holding the exhaust pipe on were easy as pie.  I've never had that happen before lol.  There may have been 1 or 2 intake manifold fasteners missing.  I guess it was a good thing I tore the down a bit.


I did have to use an angled mirror to find a hidden intake manifold bolt back near cylinder #5.  But after that, the rest was cake.  Hopefully this doesn't mean someone already tore this down, found a big issue, then just slapped it all back together and crossed their fingers.


I'm waiting on that timing belt holder tool before I pull the head off.  



Edited by juggernautjoee
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In the old days, you used to make a block out of a piece of wood to certain dimensions and stuff it under the upper timing chain gear to keep everything from moving when removing the head.  I would recommend doing that.


Free horsepower is to be gained by removing those probes from that exhaust manifold.  Mine wouldn't come out, so with a Dremel I cleaned off the outside and make it flush like a bolt, and had them welded shut and ground down again.....now they just look like plugs.  On the inside I again used my dremel and made what was left of the probes flush with the port.   Below is some pics of what I did.  The bottom 3 bolts where the mid pipe connects.....mine snapped off and after so many years, it necessitated having them redrilled and heli-coiled.  A local machine shop did for me for $75 bucks U.S.


Buy the best head gasket you can.  Let's do this once. :)  Do you have the funds and time to have the head worked by a Machine shop?  Valve stem seals should be done, the old ones are bound to be cracked up.  Minimum, a lapping of the valves is a good idea, but of course, hardened seats are what is really needed....no lead in the fuel starves the factory valve seats from the lubricant that leaded fuel was designed to offer.


These engines are tough as nails, but the head is where wear can occur, especially if it never received regular valve lash adjustments.  These old girls also need Zinc/ZDDP engine oil.






timing chain wedge.jpg

Edited by A to Z
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Thanks @A to Z.  You're taking us to school with all this learning.


Yeah I was planning on plugging up those ports for sure.  My 83 S10 had these exact same things on the exhaust manifolds.  We'll see if I get lucky and they come out with little work.  If they don't, and the plan is still to keep this motor, I would also consider finding some headers.  But that all depends on what I see once I get this head off.


And when it comes to head work, I've got a message out to someone selling a P90 head.  I'm 99% sure I have dished pistons, so I'd be taking that thing to a machine shop anyways to get it shaved down to up the CR.  If that falls through, then yeah I'm going to just send this unit along to have it cleaned up for sure.

Edited by juggernautjoee
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So here is the news.  Cylinder 5 exhaust valve has a hole right on the edge of the valve seat.  I would say it could be repairable, but that location doesn't seem like a great spot.


The water jacket holes were pretty clogged up.  But after popping out the freeze plugs and flushing it out with a hose, it's pretty clean now.  


The head gasket itself looked decent.  I couldn't tell where it was torn, or had any soot build up where it could be leaking.  


So now I'm in the dilemma of finding a head for this thing.  I know the shaved P90 is the best, but they're basically impossible to find.  The guy I was talking to about one already sold it.  I see plenty of P79 heads, and I've got a local N47 head near me.  But those have the round exhaust ports, so I'd have to source some headers or a manifold.


The guy with the local N47 head also has a dished piston F54 block, J tube, exhaust manifold for turbo, intake manifold, and a turbo.  I could just slap those things on this and then figure out how to manage it via megasquirt or something like that.  I'm at a crossroads and don't know what to do.


I know I said an LS could happen, but all the mounts and crossmembers really add up.  And I'm trying to get married this year lol.


I think the best course of action is to grab that N47 head for ~$75.  Take it to the machine shop to do a valve job on it and freshen it up.  Hopefully ~$150.  Then either try and find someone selling a round port manifold, or fork out the cash for some headers.  If I decide to go LS or something else in the future, I can always sell the headers to recoup some money.



Edited by juggernautjoee
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19 hours ago, calZ said:

You can use a square port manifold on a round port head I believe, just not the other way around. As long as the square gasket holes are larger than the round ports, it'll work. 


Nice.  Well that'll save me a couple hundred bucks.  I assume this also applies to headers as well?



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I think I got a good deal on all these parts for $300 (Ignore the head at the top.  That's the broken one)


I wasn't planning on going turbo or fuel injection, but I couldn't pass up a deal on all of it.  I'll probably keep those parts on the shelf until I can make a decision on what path I want to go.  He also has a clean F54 block (dished pistons), and a nice zx hood.  I'm gonna hold off on those for now.


The N47 head is in much better shape, and cleaner than my N42.  I need to look for some stamps or markings on the cams to compare them.  Do the turbo cams out of the ZX's differ much than the earlier ones?  I assume they have a shorter duration.  I'll have to research that.








So the cam that is in the N42 has 3 markings.  H and E30 in the cam itself, then an A on the back of the lobe on the rear.  The cam in the N47 head has a B.


I found http://xenonzcar.com/s30/cams.html - Which explains what the cams are.  Looks like I'm going to need to swap the cam over for sure.  The turbo cam has less duration and lift, which makes sense. But I need to get this thing running NA first.

Edited by juggernautjoee
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Got all the lash set.  Cleaned the new head.  Started lubing up and putting all the new head bolts in.  Missing 1 washer.  Found a couple that could work if I stacked them, but they're cheap and will probably flex.  I'll just head to the hardware store tomorrow to find something better.  Maybe a couple grade 8's if I can't find the right thickness.







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Well, things snowballed today.


Got the head on, torqued to spec.  Put a new water pump on.  Went to put the cam gear on, and it just would not give me enough slack to slide on.  I tried prying up with a long screwdriver to get some leverage.  Nope.  So I look down the hole and see that the chain tensioner had popped out.  Big oof.


I tried my hardest to get it back in from the top, but just couldn't do it.  Sigh


So I had to take off the water pump, AC compressor & bracket, alternator (to get some room), distributor, oil pump and the radiator/condenser out (to get an impact on the crank bolt)


But now I can just line up the timing chain and sprocket all in one go.  Which is nice.


What isn't nice is that I gotta make sure I get all the replacement gaskets for everything that was taken off.




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Decided to take a gamble on an ebay header and an aluminum radiator.  I was going to slap a header on this thing anyways, might as well do it now when everything is off.  And the current rad has a ton of missing/bent fins.


Got some header wrap too of course.


We've got a few warm-ish days ahead, so hopefully I'll make some more progress.

Edited by juggernautjoee
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Well the ebay headers I bought don't seem to fit with the carb'd intake manifold.  They fit fine with the FI intake I have.  I assume the 240z/260z headers hug the block a bit more.  I could probably clearance them, but I'll just weld up the the holes on the exhaust manifold and run that until decide to swap them over.  


That winter storm is coming right through us here just south of Cincinnati, so I don't think I'll get around to working on it much over the next few days.

Edited by juggernautjoee
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