L28 Rebuild Help For 1978 280z Honing vs Boring

[Ownallday]

Hey guys, I have an L28 Engine, N42 block and N47 head. My goal was to rebuild the engine and make it a reliable engine that can last a long time. I want to avoid having to pull the engine anytime soon. Power is not my biggest concern however I would like to be above the stock power numbers minimum with this rebuild since it's going to gain a little weight with aftermarket AC. For the most part I will be sticking to the stock efi for smog reasons and would like whatever I do internally to not mess with my ability to pass smog. I have almost all refurbished or new parts for the intake manifold too which should be a big help.

The condition of the block is the cylinder walls are polished, slightly glazed but overall look good with no major signs of scoring or anything. I got a couple of quotes from three machine shops in my area and not a single shop wants to do just a hone job. One shop quoted me $3500 because he wants to put all new parts in it and grind the crank (Which is insane if you ask me for a stock rebuild and does not sound necessary), the other shops quoted me closer to $600 with no parts. Every single shop wants to bore the block which means I need new pistons at 87mm (I think because of how old the car is or they trying to get more money out of me?). As most of you know, pistons are hard to come by for these cars especially domed pistons which I need because flattops will put me at a CR of 10.2 according to OZdat which is too high for California 91 and sounds too high for stock efi. The only 87mm domed pistons I see are forged (overkill) and will cost me more than $1500 (overkill).

My question is can I just ball hone the cylinder walls myself (or one of my co workers with experience honing) and be okay or keep trying to find a shop that will do just a hone and not worry or is a Bore absolutely necessary? Also if possible can anyone chime in and let me know how the stock efi system will react to 9.1 compression ratio? Thinking of potentially decking the block just to raise it if it'll even be worth it?

The N47 head has one exhaust liner missing and decided to just leave it as is since someone had one missing and didn't notice a performance decrease with it and without it. I didn't plan on doing anything to the head but I would like to ask would I see any benefit to porting the head and doing a port match with the intake manifold on the Stock EFI? The head and internals for the most part however look really good.

Thank you!

[dutchzcarguy]

 

1 hour ago, Ownallday said:

the cylinder walls are polished, slightly glazed

Hi, That's not good, they should look like these.. this L28 is now 44 years old and these pic are 3 years old.. It has run 119000 km (i'm sure about the km's) and in excellent condition if you ask me..

 

When your cylinders are glazed and polished looking just a quick hone is not gonna help..

The walls are gone..  You could test the diameter of the cylinders first and look if they are perfect round, inportant spot to test is the lower diam. of the cyl. There where the skirt of the piston sits. if there is any oval you need a rebore.. and new pistons. and yeah it is/can be a expensive hobby. 😬

Have you also done a compression test, a leak test etc.. it can help a lot to know in what condition your engine is..

Maybe some pictures of your cyl.walls? and what you think the engine has run (Mls) ?

 

Edited June 23, 2023 by dutchzcarguy

[grannyknot]

It sounds like you have already removed the head, a compression test before tear down would have answered a few of your questions.

I have deglazed cylinder walls on L24-28 engines before and installed new stock rings on original pistons with good results but those blocks were only slightly down on compression and had consistent numbers across all cylinders.  If your cylinder walls are truly polished with no signs of crosshatching then you are probably looking at a rebore.

At this point you will have to do some careful measuring with a bore gauge to determine where your cylinders are compared to the specs, you also might consider picking up a good used L28 and installing that.

[Patcon]

Well your first issue in my mind is you need to stick with stock efi. That rules out most mods. You can probably tinker with the setup but the problem comes in when you cant tune the system for a deviation.

Also you would be searching for dished not domed pistons.

To really determine the bore condition you would need a way to measure bore ID. 3 places down the bore. Side to side and front to back. If there's no lip at the top of the bore you might could just hone if your measurements are good. But you might hone and then have to bore and re-hone. It sounds like these shops are approaching this from past experience and the highest percentage of success.

As for the crank, if it mic's out, is round and looks good, a light polish would be better than grinding.

It's easier (maybe lazy) of the shop to bore and grind. The upside for them is they know for certain the crank is true and round. They also know the bores are all true, cylindrical,  straight, consistent and without taper. All good things. It also takes some time to do all the checking versus just chucking it uo and punching it out. These old Nissan blocks were made out of really good metal and these shops may not have a lot of experience with how well they hold up

[Ownallday]

7 hours ago, dutchzcarguy said:

 

Hi, That's not good, they should look like these.. this L28 is now 44 years old and these pic are 3 years old.. It has run 119000 km (i'm sure about the km's) and in excellent condition if you ask me..

 

When your cylinders are glazed and polished looking just a quick hone is not gonna help..

The walls are gone..  You could test the diameter of the cylinders first and look if they are perfect round, inportant spot to test is the lower diam. of the cyl. There where the skirt of the piston sits. if there is any oval you need a rebore.. and new pistons. and yeah it is/can be a expensive hobby. 😬

Have you also done a compression test, a leak test etc.. it can help a lot to know in what condition your engine is..

Maybe some pictures of your cyl.walls? and what you think the engine has run (Mls) ?

 

Hello, basically what I'm fearing. What I thought would be a $500 job is turning into thousands 😔. To my eye it looks very slightly glazed. I know the engine was running prior as I bought the engine off a YouTuber and he had video of this engine running good. I will provide some pictures maybe you can give some insight based on the pictures. Have yet to remove the pistons so the measuring will have to wait another week or two depending on what happens. 

I have not done a compression test based on the fact that I recently bought the engine from someone but I just know it was running good based on what the guy showed me.

 

[Ownallday]

4 hours ago, grannyknot said:

It sounds like you have already removed the head, a compression test before tear down would have answered a few of your questions.

I have deglazed cylinder walls on L24-28 engines before and installed new stock rings on original pistons with good results but those blocks were only slightly down on compression and had consistent numbers across all cylinders.  If your cylinder walls are truly polished with no signs of crosshatching then you are probably looking at a rebore.

At this point you will have to do some careful measuring with a bore gauge to determine where your cylinders are compared to the specs, you also might consider picking up a good used L28 and installing that.

Compression is something I wish I had the luxury of knowing but I bought the engine used and previous owner never got any readings. The only information I have based on the engine is it ran good. I wasn't able to find any info on people just doing a hone and getting good results so to hear that gives me some positive news. I posted some pictures hopefully they are good enough to get some insight on the walls conditions. They are perfectly 86mm btw according to the gauge at the top of the walls.

1 hour ago, Patcon said:

Well your first issue in my mind is you need to stick with stock efi. That rules out most mods. You can probably tinker with the setup but the problem comes in when you cant tune the system for a deviation.

Also you would be searching for dished not domed pistons.

To really determine the bore condition you would need a way to measure bore ID. 3 places down the bore. Side to side and front to back. If there's no lip at the top of the bore you might could just hone if your measurements are good. But you might hone and then have to bore and re-hone. It sounds like these shops are approaching this from past experience and the highest percentage of success.

As for the crank, if it mic's out, is round and looks good, a light polish would be better than grinding.

It's easier (maybe lazy) of the shop to bore and grind. The upside for them is they know for certain the crank is true and round. They also know the bores are all true, cylindrical,  straight, consistent and without taper. All good things. It also takes some time to do all the checking versus just chucking it uo and punching it out. These old Nissan blocks were made out of really good metal and these shops may not have a lot of experience with how well they hold up

Yeah I know I'm very limited since Im staying stock, there isn't really any information on how these engines perform with more compression, port, etc etc with stock EFI. The only thing I know I'd be able to tinker with is the afm, timing and could possibly get an adjustable fuel pressure regulator but that's about it. I already have shorter gearing trans and lightened flywheel and electric fans etc..

My bad that was a typo, dished is what I meant. For the most part I know the first guy only does work if he does everything according to my friend mainly because he is known for making good builds but I doubt he has touched an L series. For the most part a polish on the crank is what I had in mind but the shops I believe they only want to grind and not just polish but I have yet to see the condition of the crank.

I know these blocks are very strong as I've almost never heard of one of someone running into serious major issues on a stock build at least. I supplied some pictures of the walls. If I could find 87mm pistons for less than $800 maybe I'd be willing to take the extra steps

[Racer X]

As mentioned, accurate measurement is paramount to deciding what needs to be done when reconditioning an engine. Disassembly, cleaning, and then measuring the cylinders, rods, pistons, crank, deck, bearing journals, cylinder head surface, valve guides, etc.

I see some scoring in at least one cylinder, can you catch a fingernail in it?

Also, the engine has a lot of carbon buildup on the pistons, and in other pictures there is evidence that this is a high mileage engine, and that it didn't see regular oil changes.

Without actually doing the above, I cannot say what needs to be done, but it does look like the engine will require more than a ball hone on the cylinders and slap it back together.

 

Find a good machinist who is familiar with the L series engine, and have a discussion about your expectations and budget, and what needs to be done.

 

[Racer X]

9 hours ago, Ownallday said:

I got a couple of quotes from three machine shops in my area and not a single shop wants to do just a hone job. One shop quoted me $3500 because he wants to put all new parts in it and grind the crank (Which is insane if you ask me for a stock rebuild and does not sound necessary), the other shops quoted me closer to $600 with no parts. Every single shop wants to bore the block which means I need new pistons at 87mm (I think because of how old the car is or they trying to get more money out of me?).

How can any competent machinist say the crank needs ground, or the cylinders need bored, if he hasn’t actually inspected and measured them?

 

9 hours ago, Ownallday said:

 

As most of you know, pistons are hard to come by for these cars especially domed pistons which I need because flattops will put me at a CR of 10.2 according to OZdat which is too high for California 91 and sounds too high for stock efi. The only 87mm domed pistons I see are forged (overkill) and will cost me more than $1500 (overkill).

 

A domed piston will net a higher compression ratio, not lower, requiring even higher octane fuel. 
 

Why not use pistons with the same top configuration as the original?

 

Also, using EFI or carburetors won’t make any difference regarding compression ratio and fuel requirements. It will still be a fuel/air mixture entering the combustion chamber.

 

Edited June 23, 2023 by Racer X

[Ownallday]

41 minutes ago, Racer X said:

As mentioned, accurate measurement is paramount to deciding what needs to be done when reconditioning an engine. Disassembly, cleaning, and then measuring the cylinders, rods, pistons, crank, deck, bearing journals, cylinder head surface, valve guides, etc.

I see some scoring in at least one cylinder, can you catch a fingernail in it?

Also, the engine has a lot of carbon buildup on the pistons, and in other pictures there is evidence that this is a high mileage engine, and that it didn't see regular oil changes.

Without actually doing the above, I cannot say what needs to be done, but it does look like the engine will require more than a ball hone on the cylinders and slap it back together.

 

Find a good machinist who is familiar with the L series engine, and have a discussion about your expectations and budget, and what needs to be done.

 

Okay, I will go ahead and see if my co worker is capable of doing that otherwise I will see what other machine shops can provide in terms of measuring.

My fingernail does not catch any of it at all. I do believe it is a high mileage engine just unsure how many miles. 

I will call around some more and see if I can find someone who can do the measurements if my co worker doesn't have the proper tools to do it.

1 hour ago, Racer X said:

How can any competent machinist say the crank needs ground, or the cylinders need bored, if he hasn’t actually inspected and measured them?

 

A domed piston will net a higher compression ratio, not lower, requiring even higher octane fuel. 
 

Why not use pistons with the same top configuration as the original?

 

Also, using EFI or carburetors won’t make any difference regarding compression ratio and fuel requirements. It will still be a fuel/air mixture entering the combustion chamber.

 

I think they just mentioned thats what they want to do, not sure why or how.

That was a typo, I meant dished pistons my bad.

So more compression won't make any change power wise if I cant adjust afr?

[Zed Head]

Similar conversations have happened over the last few years.  You better check parts availability before going too far.  Oversize pistons are not readily available.  You could end up with a freshly machined block but no parts to put in it.  Your engine will sit at a machine shop in out-of-stock parts jail, with a big bill waiting.

I see what looks like rust pitting in addition to scoring.  Looks like an expensive starting point.  Probably better off to find a different used engine.  They still pop up here and there.

https://www.rockauto.com/en/catalog/nissan,1978,280z,2.8l+l6,1209260,engine

 

[Patcon]

I agree with the others on the wall condition. Vertical lines would concern me. Possible ring scratches or skirt dragging. Also the mottling at the top of the cylinders concerns me. Not really sure what that is, possible corrosion damage?

I absolutely agree with Racer, that its hard to tell what the engine really needs with out Mic'ing it. Also be careful on grinding the crank. I had a hard time finding over sized bearings on a L20 build

[Zed Head]

If it was my project I would put a list of parts needed together, with costs.  Add them all up and compare to what a good used engine will cost.  Evaluate against what your goals are.

I put a short list together of the various parts I bought for my car when I was getting it back in to shape and the final number was pretty big.  The small stuff adds up quick.

Here's the basic engine that you are starting with, for comparison.

https://www.ebay.com/itm/145108452163?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=743dF1EpST6&sssrc=2047675&ssuid=&widget_ver=artemis&media=COPY