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Questions before contacting the machine shop


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Gentlemen,  I have reached a point in my build where it is necessary to hire a shop. There has been some conflicting information, in terms of what is required, what is prudent and what is extra and how these items are balanced with cost.

For me, the most important goals are engine efficiency and longevity. I am willing to sacrifice some power and torque, for a more efficient or more reliable engine.

1.       Hot tank. Will this service clean all the inner passages of the block, or is that an additional service?

2.        Magnaflux- The engine block was given to me and has certainly been used, however PO did not turbo or otherwise artificially stress the block and claims it hadn’t been over heated. It still seems prudent to check the block for damage, before I put all my pretty new parts in it. My question is how cracked it too cracked. Finally, should I leave that evaluation up to the engine machinist?

3.       The Z24 block will be bored  to 90mm. I will supply the pistons to the machine shop to be matched to the bore. Should I install the piston rings or would the shop prefer to install?

4.       “O ring” the block (Unless this is a very pricey procedure, it seems prudent when increasing compression on a older block.)

5.        “Deck” the block. I want the least amount of material removed, from where the head attaches, to make it “perfectly” flat(Is “Deck” the correct term?

6.       I will supply the crank, the main bearings and the rod bearings and would like the “bottom end” assembled and checked by the machine shop. Is there a specific term to request this service? The crank did not present with scratches or any obvious damage. Are there checks and/or services, best completed by professionals, on the crank as part of a prudent rebuild?

7.       What kind of price should I expect for any portion or all of the work?

8.       Did I miss any parts or services that are best completed to the bottom end while the block is out?

9.       Would it be wise to provide then unassembled head to the machine shop to be matched to the block?

 Thank you for sharing your expertise

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I am not expert, but here is what I know

 

1.       Hot tank. Will this service clean all the inner passages of the block, or is that an additional service?

 

Hot Tanking will mostly clean surface areas and some ports and passages, but the best way to clean them out is with bottle/bore brushes and hot soapy water. 

 

2.        Magnaflux- The engine block was given to me and has certainly been used, however PO did not turbo or otherwise artificially stress the block and claims it hadn’t been over heated. It still seems prudent to check the block for damage, before I put all my pretty new parts in it. My question is how cracked it too cracked. Finally, should I leave that evaluation up to the engine machinist?

 

Let the machine shop check for clearances, magnaflux is usually done when there was an issue to begin with, like severe overheating or overbore. 

 

3.       The Z24 block will be bored  to 90mm. I will supply the pistons to the machine shop to be matched to the bore. Should I install the piston rings or would the shop prefer to install?

 

Leave the rings off as they need to use them to fit them to the bores. 

 

4.       “O ring” the block (Unless this is a very pricey procedure, it seems prudent when increasing compression on a older block.)

 

O Rings are for some severe boost type engines, but not necessary for a street engine. Unless you are seriously going to boost the engine. We run a 548 Inch, Blown Alcohol engine and we did not O Ring the block and heads. We run Cometic head gaskets.

 

5.        “Deck” the block. I want the least amount of material removed, from where the head attaches, to make it “perfectly” flat(Is “Deck” the correct term?

 

Decking is necessary mainly if there is some discrepancies when they check the trueness of the deck. Slight clean up would not be bad

 

6.       I will supply the crank, the main bearings and the rod bearings and would like the “bottom end” assembled and checked by the machine shop. Is there a specific term to request this service? The crank did not present with scratches or any obvious damage. Are there checks and/or services, best completed by professionals, on the crank as part of a prudent rebuild?

 

Have then check the crank and rods and they will tell you what bearings you need. Might range from just a crank polish to having it reground oversize. 

 

7.       What kind of price should I expect for any portion or all of the work?

 

Depends on your local shop, but between $500 and $1000

 

8.       Did I miss any parts or services that are best completed to the bottom end while the block is out?

 

Nope, just make sure it is clean when doing assembly and check your torque specs

 

9.       Would it be wise to provide then unassembled head to the machine shop to be matched to the block?

 

It would be good to have them check the head for trueness and at least have new valve guide seals installed. 

 

Good Luck with your build! 

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JesseC covered it pretty well, I would just add, choose your machine shop carefully.  There are some real nightmare shops out there, personally I try and find a small shop where an old guy is in charge or is doing the work. Once you have found your place the machinist will go over all your questions. Reassembling the bottom end yourself isn't really all that difficult if you have FSM, it also gives you the chance to get the block outside with hot soapy water, bore brushes and hose to make sure there is no sludge or metal chips hiding.

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3 hours ago, Jesse C. said:

Thank you for responding, it is appreciated much,

I would like to interject my rationale for some of my ideas and see if it alters your suggestions, BUT this is not a challenge or debate of your opinion. It is only my attempt at better understanding. Again, I am thankful for your participation.

 

 

2.        Magnaflux- The engine block was given to me and has certainly been used, however PO did not turbo or otherwise artificially stress the block and claims it hadn’t been over heated. It still seems prudent to check the block for damage, before I put all my pretty new parts in it. My question is how cracked it too cracked. Finally, should I leave that evaluation up to the engine machinist?

In reading build threads, here and on other Nissan/Datsun sites, the Z24 block seems to be susceptible to hairline cracks around the spark plug area. I remember reading on Ratsun where one builder discovered cracks in 3 of  4 Z blocks. Some responses said that hairline cracks were not an issue, others said ignoring the cracks was building a time bomb.

 

The first stage is to get a vehicle operational, right now I have a couple rollers. I do not want to keep pulling engines for improvement, so I am trying to get a solid build. Increasing compression a bit, feels like free money, since the surfaces should be trued up as part of a total rebuild. I'm on the fence about running premium gas. I know my Sentra likes it, I haven't run the numbers precisely, but when have a big stretch of highway miles coming up, I fill with premium gas and mpg improves. Improve enough to justify the cost of premium gas, not sure. So, I am looking to increase compression to where premium gas is nice, but low grade gas will work in a pinch. As I understand it, a KA ECU and a knock sensor will address the premium gas low grade gas situation. At this point it seems compression over 9 but less than 10 would be about right.

Again, the first stage is to get  something back on the road and for that "better" is the enemy of "good".

 

4.       “O ring” the block (Unless this is a very pricey procedure, it seems prudent when increasing compression on a older block.)

The flow of the Z block would like a turbo, and there are papers published on the internet (therefore unquestionably true) that the addition of a small turbo to a high compression engine will increase efficiency resulting in increased mpg. But, if the air fuel ratio is leaned out to far, the engine becomes a bomb. If O rings are not cost prohibitive (no more than 1-2 hundred) having a crack free O ringed block would give confidence to try this at some point down the road.

 

5.        “Deck” the block. I want the least amount of material removed, from where the head attaches, to make it “perfectly” flat(Is “Deck” the correct term?

 

Decking is necessary mainly if there is some discrepancies when they check the trueness of the deck. Slight clean up would not be bad

When talking with the machinist, it would be better to say I want the surfaces of the block and the head "trued" instead of asking for the block and head "decked" correct? If the surfaces on the block and head are true is it necessary for either to be  "blocked"?

 

6.       I will supply the crank, the main bearings and the rod bearings and would like the “bottom end” assembled and checked by the machine shop. Is there a specific term to request this service? The crank did not present with scratches or any obvious damage. Are there checks and/or services, best completed by professionals, on the crank as part of a prudent rebuild?

 

Have then check the crank and rods and they will tell you what bearings you need. Might range from just a crank polish to having it reground oversize. 

I already have new standard size, crank, rod, and main bearings. Could  this be an excuse to purchase new rods? It is my understanding that absent scratches cranks rarely wear, new rods should guarantee the ability to use the purchased bearings. Is that good reasoning? 

 

7.       What kind of price should I expect for any portion or all of the work?

 

Depends on your local shop, but between $500 and $1000

Dang that's a big spread. 500 would be great, I would drop it off today, 1000 would sting and require spousal involvement.

 

9.       Would it be wise to provide then unassembled head to the machine shop to be matched to the block?

 

 and at least have new valve guide seals installed. 

Do you mean the valve seats installed? I have replacement seats that are metal rings, I'm pretty sure press in and are lapped to match the new valves. I also have valve guides that are brass tubes and seals that are blue rubber type material. I have acquired all components to complete a head rebuild, except valve springs. I have the springs off two other Z24 heads, and have been on the fence over the need to purchase stronger springs, replacement stock springs, or replacement of just the inner or outer springs, to run one new and one old for each valve. I looked into higher compression springs but the applications they are recommended for are high rpm. I want to keep my Z motor lower rpm.

 

Thank you

 

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2 hours ago, grannyknot said:

JesseC covered it pretty well, I would just add, choose your machine shop carefully.  There are some real nightmare shops out there, personally I try and find a small shop where an old guy is in charge or is doing the work. Once you have found your place the machinist will go over all your questions. Reassembling the bottom end yourself isn't really all that difficult if you have FSM, it also gives you the chance to get the block outside with hot soapy water, bore brushes and hose to make sure there is no sludge or metal chips hiding.

I like your thinking and always appreciate when presented with an obvious answer for some reason I was missing. Of course the "super clean" of the motor should happen AFTER machining, because metal flakes and stuff can do more damage than dirt. The pre machine clean is just to keep the machine shop happy and not being labeled one of "those guys". For some reason I thought the big cleanout should happen before machining. Thanks for squaring me away

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38 minutes ago, Crashtd420 said:

Another good thing to do to really clean out the block is to remove all the freeze plugs and flush it that way.... 

 

Also the oil galley plugs are good to remove for cleaning... new ones are available to replace when done...

 

 

Good call, I picked up the brass plug set for the Z24. Is there a trick to removing the old ones. They appear to be press fit. I will youtube it, if it is a lengthy answer.

 

Now oil galley plugs, I am drawing a blank on where they are located. I think there is a tutorial on some Zcar website that breaks it down. I spent some time attempting to find a universal plug to use for the oil galley and to plug the IGR holes in the intake manifold and found myself in a world of bullshit. The differences between pipe thread and non pipe thread and 1/2 that wasn't half inch depending on the plug. I found some gunsmithing thread that would work but didn't install. While I have and will resort to crazy one off custom fixes. So many times, when something goes wrong, years down the road and I have to remember how I pieced something together, I only remember, why I did something a certain way, after I have spent many hours,fighting it.

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1.       Hot tank. Will this service clean all the inner passages of the block, or is that an additional service? Either you or someone else will appreciate a clean block to work on. Hot tanking usually involves pulling the oil gallery plugs to get the cleaning solution out after. I mean 100K miles of filtered oil pushed through.... how dirty can it really be????

 

2.        Magnaflux- The engine block was given to me and has certainly been used, however PO did not turbo or otherwise artificially stress the block and claims it hadn’t been over heated. It still seems prudent to check the block for damage, before I put all my pretty new parts in it. My question is how cracked it too cracked. Finally, should I leave that evaluation up to the engine machinist? Probably tens of thousands of running L blocks out there with undiscovered cracks and they are fine. Yet people take them apart find a trivial crack and lose their shit over it. Most cracks are between water jacket and head bolt holes.... where's the water going to go????? A machinist will err on the side of caution because his work will be guaranteed so will reject every block for the slightest defect. If this will turn 8k that might be different. Far as I'm concerned a crack indicates the block has stress relieved itself.

 

3.       The Z24 block will be bored  to 90mm. I will supply the pistons to the machine shop to be matched to the bore. Should I install the piston rings or would the shop prefer to install? If the shop is installing the pistons let them do it. If you install the rings I doubt they will remain where you set them and they'll have to check them anyway. If forged pistons the side clearance is wider than if using hyper-eutectic. A shop should know this. Ring end gap is critical to the end use of the engine. Street, or race with power adders, let them know.

 

4.       “O ring” the block (Unless this is a very pricey procedure, it seems prudent when increasing compression on a older block.) What would be the cost in money and time of replacing a blown head gasket?

 

5.        “Deck” the block. I want the least amount of material removed, from where the head attaches, to make it “perfectly” flat(Is “Deck” the correct term? Yes correct term. You have 0.45mm of deck that can be removed before the piston even comes up level with it. That's about 0.017". You can safely take about 0.3mm more as there is about 1.2mm of crushed gasket thickness between the block and the head. The piston can rise above the deck almost 0.11" if you want to maximize compression, so you have lots of room. Otherwise say take 0.010" off.

 

6.       I will supply the crank, the main bearings and the rod bearings and would like the “bottom end” assembled and checked by the machine shop. Is there a specific term to request this service? The crank did not present with scratches or any obvious damage. Are there checks and/or services, best completed by professionals, on the crank as part of a prudent rebuild? They can check the clearances but the rods may need 'sizing'. They tend to oval and the caps and/or rods need milling to close up the clearances... if needed.

 

7.       What kind of price should I expect for any portion or all of the work?

 

8.       Did I miss any parts or services that are best completed to the bottom end while the block is out?

 

9.       Would it be wise to provide then unassembled head to the machine shop to be matched to the block? All the head needs to be is flat. New guides and valve seats and seals. You can assemble the rest of the head yourself and install it. Depends what you are doing. Ask the machinist.

 

 Thank you for sharing your expertise

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A shop where you have to wait a month or two to get your work done is a good rule of thumb. It means people know where to go for good work.

 

0oGRI1z.jpg

 

This is the rear oil gallery plug location. The starter would be down there on the upper right. I tapped this one to fit a pipe plug. It will never leak, not that the stock ones ever do, but you can remove for cleaning at a later date, not that you ever will.

 

t1iYVhU.jpg

 

This is the front oil gallery plug location. To help, the little threaded hole under the brush is the bottom bolt that holds the timing chain tensioner, I think. The hole to the lower left of the brush is the oil under pressure from the pump to the oil filter.

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A couple quick points: if you don’t know anyone that works at a shop, call a couple trusted shops in your area and ask what machinist they use. If you know someone that works at a shop, see if they can get it in under their shop name, you’ll get it way faster. I just had a little tuning and testing done on a head, I got it back in two days because the shop I work at has a great working relationship with the machinist. The old guy theory is spot on, our machinist is in his 70’s easy, and he’s built most of the local race engines for decades. 

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On 8/3/2021 at 10:03 PM, datzenmike said:

A shop where you have to wait a month or two to get your work done is a good rule of thumb. It means people know where to go for good work.

 

0oGRI1z.jpg

 

This is the rear oil gallery plug location. The starter would be down there on the upper right. I tapped this one to fit a pipe plug. It will never leak, not that the stock ones ever do, but you can remove for cleaning at a later date, not that you ever will.

 

t1iYVhU.jpg

 

This is the front oil gallery plug location. To help, the little threaded hole under the brush is the bottom bolt that holds the timing chain tensioner, I think. The hole to the lower left of the brush is the oil under pressure from the pump to the oil filter.

DatzenMike, That looks suspiciously like a cleaning rod and brush for, let's say in an obtuse way to avoid keyword bots---a bang stick. 

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