Average cost for machine work

[TimmyG]

How much could I expect to pay for machining the block and head? I have rebuilt a z24 many years ago. Just don't know what machining costs to expect nowadays. 

 

I've found a dirt cheap 83 king cab with a blown head gasket. Trying to work out the math if its worth it. Thanks!

[datzenmike]

 There should be no machine work replacing a head gasket. Z24s often blow every 100K or so. Do you suspect a warped head or are you planning to rebuild it? You can mill a warped head yourself in less than an hour, by hand without any tools or special knowledge. 

[TimmyG]

If the head gasket blew I would likely go through the whole motor at that time. I know nothing about how to mill a warped head at home, either. 

[datzenmike]

I said it doesn't take any skill. Get a thick piece of glass. A stereo cabinet door, a glass table top. Use spray adhesive and several sheets of 80 grit emery paper. Loosen the rockers so the valves and closed. Place the head on the sand paper and pull towards you using the opening for the cam sprocket, then push away. After a couple of dozen passes check the surface and blow away the aluminum 'dust'. or it will act like ball bearings. The head is heavy so you don't have to press down, just push and pull horizontally.

 

After 20-30 passes, you can see the middle is the highest on this L series head. Allowable warp is 0.004". This was 0.015 or 4 times the allowable.

 

 

Another 20 passes...

 

Eventually only the high spot in the middle.

 

 

Going....

 

Gone...

 

It goes fast at first but as the low spots get smaller there is more and more to remove. I think 45 min? Remember to blow away the aluminum particles every 20 or so passes. I already had the glass so this cost me about $6 for the sand paper. Once level I switched to 150 for the great finish. I doubt you will need this much removed.

[bottomwatcher]

They don't stay dirt cheap for long. Nice write up Mike. You may find a runner if someone is swapping. I took a perfectly good running naps z24 to the scrap yard because I had no use for the gutless wonder and nobody else wanted it either.

[datzenmike]

When done, I couldn't get a 0.003" feeler gauge under an industrial straight edge.

 

Timmy, before unbolting the can sprocket, make sure you familiarize yourself with how to stop the timing chain tensioner from falling out. There are cheap plastic tools that prevent this. Not doing this adds hours of extra work to fix.

[banzai510(hainz)]

If head is WARPED bad the cam will bind above if installed it straight in or will be hard to turn(with out the valves installed)

[TimmyG]

19 minutes ago, datzenmike said:

When done, I couldn't get a 0.003" feeler gauge under an industrial straight edge.

 

Timmy, before unbolting the can sprocket, make sure you familiarize yourself with how to stop the timing chain tensioner from falling out. There are cheap plastic tools that prevent this. Not doing this adds hours of extra work to fix.

I really appreciate that tip. I do remember this from the z24 I rebuilt years ago.

[datzenmike]

Mine was just a high spot in the middle. A pucker. Cam spins perfectly by hand. Sanding down also does not require the head to be dismantled and the cam and towers removed for milling. The closed valve would keep anything out of the ports anyway. There's no clean up of the head after either. All you make is fine aluminum grit like sand.  

 

Remove the head with the intake manifold on. Remove after it's off. Easier.

The cost for changing a HG is about the cost of the gasket.

[Madkaw]

I respect your knowledge here , but I think you make it sound too easy and that’s when shit happens . I could see all kinds of disasters with aluminum like sand blowing around everywhere- especially with some oily surfaces to stick with. For a confident wrencher this might be easy to think of all the hazards ,  but maybe not the novice .

[datzenmike]

It's an aluminum grit not light enough to blow around. Do it indoors. It was as easy as I described except for the 20 or so push and pulls between pictures. Try it and you'll say the same thing. I used the same apparatus to level the two surfaces of the thermostat housing and the cover.

 

[Charlie69]

Mike, I just shipped you 4 heads to flatten.  Can you have them done in 2 days after receiving them. I will pay shipping both ways.

 

Thank you,

Charlie

[TimmyG]

6 minutes ago, datzenmike said:

It's an aluminum grit not light enough to blow around. Do it indoors. It was as easy as I described except for the 20 or so push and pulls between pictures. Try it and you'll say the same thing. I used the same apparatus to level the two surfaces of the thermostat housing and the cover.

 

This is a pretty neat trick, actually. Thx

[TimmyG]

Random question, have y'all seen this scenario before? Motor jumps time when cam gear slips off the dowel on the front face of the cam? I remember this happening to me, but not sure how exactly it happened... dowel slipped forward or backwards maybe... is the dowel not cast into the cam design ? 

Edited August 6, 2019 by TimmyG
Pic

[datzenmike]

It's a press in pin. It might shear off but it won't slip off. The pin is for alignment, the torque on the nut that holds it is enough to hold the sprocket on 120-150 ft lbs. That's on there!!! It must have been off and not properly torqued on.

[TimmyG]

2 minutes ago, datzenmike said:

It's a press in pin. It might shear off but it won't slip off. The pin is for alignment, the torque on the nut that holds it is enough to hold the sprocket on 120-150 ft lbs. That's on there!!! It must have been off and not properly torqued on.

That makes more sense. I remember hearing a loud clank after firing up the motor for the first time after overhaul. Motor died. I had a bad feeling... except I happened to have a nissan mechanic with me and he knew exactly what it was. We reset the cam sprocket and good to go after that. Ran good until I sold it years later. 

[Genaro]

13 hours ago, Madkaw said:

I respect your knowledge here , but I think you make it sound too easy and that’s when shit happens . I could see all kinds of disasters with aluminum like sand blowing around everywhere- especially with some oily surfaces to stick with. For a confident wrencher this might be easy to think of all the hazards ,  but maybe not the novice .

 

Hi, 

I disagree... Myself being a total newbie, i was able to disassemble, diagnose and rebuild my truck's engine with the help of the guys from this forum and the Nissan manual... I see many other posibilities for mistakes/fu**-ups/risks while removing and reinstalling the head and everything that such tasks requires than flattening it with this procedure. 

I think that someone that cannot do this safely and reliably, should not try to fix his engine at all...! 

Thats my humble opinion, of course...

[banzai510(hainz)]

I guess the dowl can sear or be loose and pop out.

[TimmyG]

1 hour ago, banzai510(hainz) said:

I guess the dowl can sear or be loose and pop out.

It may have popped out. Anyway, it's been a long time and I just remember this being the problem. Wondered if it had happened to anyone else.

[banzai510(hainz)]

I think I seen a sheard pin before on here. when he guy took the cam sprocket off somebody notice no pin

[Madkaw]

20 hours ago, datzenmike said:

It's an aluminum grit not light enough to blow around. Do it indoors. It was as easy as I described except for the 20 or so push and pulls between pictures. Try it and you'll say the same thing. I used the same apparatus to level the two surfaces of the thermostat housing and the cover.

 

 

. Place the head on the sand paper and pull towards you using the opening for the cam sprocket, then push away. After a couple of dozen passes check the surface and “blow away “the aluminum 'dust'. or it will act like ball bearing.

 

Actually - this is what I was referring too. 

 

Yes - have some this many times - though not a cylinder head .