L20b motor rebuild - Piston and Parts required?

[second chance]

Alright, let me start by saying I have been reading, searching, and re-reading posts about rebuilding a L20b motor....and I'm overwhelmed.

Can someone help simplify the parts required (on a budget) if I need to bore out my cylinders.

 

Correct me if I'm wrong,

Boring 40 over will require 86mm pistons?

I can keep my Crank (stock L20b) and connecting rods, purchase a set of 86mm pistons and ring set....and I should be good?

I think I saw Mike post that 79-80 280zx are dished pistons @86mm and 81-83 280zx are flat top pistons @86mm. What are the advantages/disadvantages of each?

 

What have others done when rebuilding their engines?

Can anyone provide a parts list?

 

Please be gentle. 

Thanks,

 

 

[Yeedog168]

34 minutes ago, second chance said:

Alright, let me start by saying I have been reading, searching, and re-reading posts about rebuilding a L20b motor....and I'm overwhelmed.

Can someone help simplify the parts required (on a budget) if I need to bore out my cylinders.

 

Correct me if I'm wrong,

Boring 40 over will require 86mm pistons?

I can keep my Crank (stock L20b) and connecting rods, purchase a set of 86mm pistons and ring set....and I should be good?

I think I saw Mike post that 79-80 280zx are dished pistons @86mm and 81-83 280zx are flat top pistons @86mm. What are the advantages/disadvantages of each?

 

What have others done when rebuilding their engines?

Can anyone provide a parts list?

 

Please be gentle. 

Thanks,

 

 

The easiest way is: buy my $12k long block from me for $4,500.  L20B, bored 80 over with forged aluminum Venolia pistons, ported & polished head - done by the Electramotive Racing Team, 240Z valves and springs, 3/4 racing cam, balanced crank, spray bar. 

[Stoffregen Motorsports]

Rebuilds are different than custom engines. A rebuild can use stock components and oversized pistons, while a custom engine mixes and matches cranks, rods, pistons, etc.

 

An L20B can go .080" over pretty easily, but finding replacement pistons bigger than .040" over will be difficult. Custom pistons are pretty common these days and can be purchased for about $800-$1000. If you're going that route, find some 6" rods and make a long rod 2100 or even 2200.

[Stoffregen Motorsports]

18 hours ago, Yeedog168 said:

The easiest way is: buy my $12k long block from me for $4,500.  L20B, bored 80 over with forged aluminum Venolia pistons, ported & polished head - done by the Electramotive Racing Team, 240Z valves and springs, 3/4 racing cam, balanced crank, spray bar. 

Really? That's an Electramotive motor? How old is it?

[Danalive]

i rebuilt my l20b recently, it had little to no compression and the head had warped.

 

i got 86mm small dish pistons (4cc instead of l20b 11cc) & rings from swmotorsport in australia, im in the uk and couldnt find anything locally so went with these as rockauto were out of stock of the zx pistons

new rod and main bearings

a gasket kit

new front cover bolts as mine were rusty

new water pump

i think that was it, then i had a local machine shop bore the block for the new pistons and deck the top of it, check it over. also had them place the new pistons on the old rods. then i reassembled myself. 

total cost, with a new head was around £1000. 

 

the different 280zx pistons will give different compression ratios, 

you can work out yours with the ozdat calulator: https://www.ozdat.com.au/ozdatonline/enginedesign/ 

 

 

[second chance]

18 minutes ago, Danalive said:

i rebuilt my l20b recently, it had little to no compression and the head had warped.

 

i got 86mm small dish pistons (4cc instead of l20b 11cc) & rings from swmotorsport in australia, im in the uk and couldnt find anything locally so went with these as rockauto were out of stock of the zx pistons

new rod and main bearings

a gasket kit

new front cover bolts as mine were rusty

new water pump

i think that was it, then i had a local machine shop bore the block for the new pistons and deck the top of it, check it over. also had them place the new pistons on the old rods. then i reassembled myself. 

total cost, with a new head was around £1000. 

 

the different 280zx pistons will give different compression ratios, 

you can work out yours with the ozdat calulator: https://www.ozdat.com.au/ozdatonline/enginedesign/ 

 

 

Thank you Danalive, I will check out this calculator.

 

[second chance]

On 9/16/2023 at 9:27 AM, Stoffregen Motorsports said:

Rebuilds are different than custom engines. A rebuild can use stock components and oversized pistons, while a custom engine mixes and matches cranks, rods, pistons, etc.

 

An L20B can go .080" over pretty easily, but finding replacement pistons bigger than .040" over will be difficult. Custom pistons are pretty common these days and can be purchased for about $800-$1000. If you're going that route, find some 6" rods and make a long rod 2100 or even 2200.

Thanks Stoffregen.

[second chance]

On 9/15/2023 at 2:42 PM, Yeedog168 said:

The easiest way is: buy my $12k long block from me for $4,500.  L20B, bored 80 over with forged aluminum Venolia pistons, ported & polished head - done by the Electramotive Racing Team, 240Z valves and springs, 3/4 racing cam, balanced crank, spray bar. 

That's a little outside my budget!

Nice setup though.

[datzenmike]

The L20B is 85mm bore, so 40 'thou' over is 1mm or 86mm.

 

Stock L20B compression is 8.4

 

Using stock dish 11. 36cc 1mm over or 86mm pistons the compression is 8.55

 

Using 86mm  10.9cc early L28 pistons compression is 8.6

Using 86mm flattop late L28 pistons the compression is 10.11

 

Higher compression Is the same as a teaspoon of fuel ignited in a small sealed container compared to being lit in the open. BANG compared to a pfft. The energy release is more sudden and energetic just what's needed to push down on a piston in a very short time.

Higher compression, assuming all things equal except the smaller or no dish, means the combustion chamber is smaller with less surface area to absorb heat, freeing it to do more work expanding the combustion gasses and pushing down on the piston. 

Higher compression means the air fuel mix burns faster so less ignition timing is required however if the compression is high enough it may ping or self ignite from the extra heat of compression and a higher octane gas must be used.

 

[second chance]

18 minutes ago, datzenmike said:

The L20B is 85mm bore, so 40 'thou' over is 1mm or 86mm.

 

Stock L20B compression is 8.4

 

Using stock dish 11. 36cc 1mm over or 86mm pistons the compression is 8.55

 

Using 86mm  10.9cc early L28 pistons compression is 8.6

Using 86mm flattop late L28 pistons the compression is 10.11

 

Higher compression Is the same as a teaspoon of fuel ignited in a small sealed container compared to being lit in the open. BANG compared to a pfft. The energy release is more sudden and energetic just what's needed to push down on a piston in a very short time.

Higher compression, assuming all things equal except the smaller or no dish, means the combustion chamber is smaller with less surface area to absorb heat, freeing it to do more work expanding the combustion gasses and pushing down on the piston. 

Higher compression means the air fuel mix burns faster so less ignition timing is required however if the compression is high enough it may ping or self ignite from the extra heat of compression and a higher octane gas must be used.

 

This is exactly what I was looking for, thank you for answering my questions. 

[510TATION]

On 9/15/2023 at 1:58 PM, second chance said:

Alright, let me start by saying I have been reading, searching, and re-reading posts about rebuilding a L20b motor....and I'm overwhelmed.

Can someone help simplify the parts required (on a budget) if I need to bore out my cylinders.

 

Correct me if I'm wrong,

Boring 40 over will require 86mm pistons?

I can keep my Crank (stock L20b) and connecting rods, purchase a set of 86mm pistons and ring set....and I should be good?

I think I saw Mike post that 79-80 280zx are dished pistons @86mm and 81-83 280zx are flat top pistons @86mm. What are the advantages/disadvantages of each?

 

What have others done when rebuilding their engines?

Can anyone provide a parts list?

 

Please be gentle. 

Thanks,

 

 

are you doing just a stock build? you did mention that you want a budget build so I am assuming you want to keep it simple right? you already have the pistons and rings that you'll be using. if so I would just have the shop check the crank shaft checked and if it checks ok have them polish it. have the shop swap out the connecting rods on the new pistons and have them bore and hone the cylinders or just do that your self. installing everything is pretty easy as long as you follow the manual and recommendations. I'M sure you know what you're doing so should be a fun project if everything checks out ok you should need the basic components like main and rod bearings, pistons and rings main seals and freeze plugs and a complete gasket set. once you have the short block done than check your cylinder head and have everything checked as well. replace components as needed and now for the fun part...engine installation and breakin. good luck on your build and hope it all goes well for you 

[510TATION]

On 9/15/2023 at 1:58 PM, second chance said:

Alright, let me start by saying I have been reading, searching, and re-reading posts about rebuilding a L20b motor....and I'm overwhelmed.

Can someone help simplify the parts required (on a budget) if I need to bore out my cylinders.

 

Correct me if I'm wrong,

Boring 40 over will require 86mm pistons?

I can keep my Crank (stock L20b) and connecting rods, purchase a set of 86mm pistons and ring set....and I should be good?

I think I saw Mike post that 79-80 280zx are dished pistons @86mm and 81-83 280zx are flat top pistons @86mm. What are the advantages/disadvantages of each?

 

What have others done when rebuilding their engines?

Can anyone provide a parts list?

 

Please be gentle. 

Thanks,

 

 

are you doing just a stock build? you did mention that you want a budget build so I am assuming you want to keep it simple right? you already have the pistons and rings that you'll be using. if so I would just have the shop check the crank shaft checked and if it checks ok have them polish it. have the shop swap out the connecting rods on the new pistons and have them bore and hone the cylinders or just do that your self. installing everything is pretty easy as long as you follow the manual and recommendations. I'M sure you know what you're doing so should be a fun project if everything checks out ok you should need the basic components like main and rod bearings, pistons and rings main seals and freeze plugs and a complete gasket set. once you have the short block done than check your cylinder head and have everything checked as well. replace components as needed and now for the fun part...engine installation and breakin. good luck on your build and hope it all goes well for you 

[510TATION]

1mm equals 0.039 inch so yes this is correct for a 0.40 over bore for the 86mm pistons 

[second chance]

5 minutes ago, 510TATION said:

1mm equals 0.039 inch so yes this is correct for a 0.40 over bore for the 86mm pistons 

Thank you.

[second chance]

7 minutes ago, 510TATION said:

are you doing just a stock build? you did mention that you want a budget build so I am assuming you want to keep it simple right? you already have the pistons and rings that you'll be using. if so I would just have the shop check the crank shaft checked and if it checks ok have them polish it. have the shop swap out the connecting rods on the new pistons and have them bore and hone the cylinders or just do that your self. installing everything is pretty easy as long as you follow the manual and recommendations. I'M sure you know what you're doing so should be a fun project if everything checks out ok you should need the basic components like main and rod bearings, pistons and rings main seals and freeze plugs and a complete gasket set. once you have the short block done than check your cylinder head and have everything checked as well. replace components as needed and now for the fun part...engine installation and breakin. good luck on your build and hope it all goes well for you 

I am trying to keep it simple and budget friendly. I just wanted to make sure I was understanding the information I collected from all my research correctly. I'm looking forward to getting started on this, it's been too many years since I ventured into engine work.

[510TATION]

33 minutes ago, second chance said:

I am trying to keep it simple and budget friendly. I just wanted to make sure I was understanding the information I collected from all my research correctly. I'm looking forward to getting started on this, it's been too many years since I ventured into engine work.

Ok Cool. I wish you the best of luck. doing your own build is quite fun but can also be challenging. if you are Mechanically inclined and you are getting into engine rebuilding the L20B is a good engine to start with as the datsun L series are easy to work on and pretty straight forward. watch videos on youtube as there are many and very detail and easy to follow i personally have not made any videos as i am not good at doing them but there are really good channels to follow 

 

Cars, Bikes, and Coffee on youtube has lots of info on the L28 and sutch. the datsun Z engines are built in the same way as an L16,L18 and the L20B to name a few

[second chance]

I also have the option of using an A87 head or a W58 head. What would be my best option between the two? Are there pros and cons to using one or the other?

[510TATION]

not sure what's best but I am a big fan of the A87 especially if it is a closed chamber. the A87 has the squared exhaust ports and no baffle inserts. the w58 has the inserts and round exhaust ports. 

[datzenmike]

Other than the round exhaust port outlets and the liners the W58 is basically the same as the A87 though some A87s have smaller exhaust valves. No way to know without removing the head. The A87 intake valves are the same size as the W58 but the ports are smaller. This would give good mid range port velocity in an L18 which is what they were used on, but choke off high speed power some on an L20B. They can be ground out, ported, from their 1.25" to 1.375"

 

I've cut the liners from a W58 before. You have to remove the valve but the liner metal slices easily with a 6" chisel. Round exhaust will work with a square port exhaust manifold. Use the square gasket.

 

Closed chamber heads only work properly if running flattop pistons, otherwise it only ups the stock compression from 8.4 to 8.9 and will ping if you don't reduce the timing. Open chamber means there is open combustion chamber above the entire surface of the piston top. A closed chamber head has a combustion chamber smaller than the piston top so there are areas where the piston top is only separated from the head by the thickness of the head gasket. At TDC air caught between the piston top and the head surface is violently pinched out into the smaller combustion chamber promoting beneficial swirl and homogenized mixing of the fuel air mix. This reduces rich or lean areas, hot spots and carbon deposits which increase combustion efficiency. The smaller surface area of the closed chamber head naturally absorbs less heat (quench) from combustion freeing it to expand combustion gasses and push down on the piston. Stock L20B pistons have a huge 11.36cc dish so this pinch or squeeze is much reduced than if you have a flattop piston. 

[second chance]

2 hours ago, datzenmike said:

Other than the round exhaust port outlets and the liners the W58 is basically the same as the A87 though some A87s have smaller exhaust valves. No way to know without removing the head. The A87 intake valves are the same size as the W58 but the ports are smaller. This would give good mid range port velocity in an L18 which is what they were used on, but choke off high speed power some on an L20B. They can be ground out, ported, from their 1.25" to 1.375"

 

I've cut the liners from a W58 before. You have to remove the valve but the liner metal slices easily with a 6" chisel. Round exhaust will work with a square port exhaust manifold. Use the square gasket.

 

Closed chamber heads only work properly if running flattop pistons, otherwise it only ups the stock compression from 8.4 to 8.9 and will ping if you don't reduce the timing. Open chamber means there is open combustion chamber above the entire surface of the piston top. A closed chamber head has a combustion chamber smaller than the piston top so there are areas where the piston top is only separated from the head by the thickness of the head gasket. At TDC air caught between the piston top and the head surface is violently pinched out into the smaller combustion chamber promoting beneficial swirl and homogenized mixing of the fuel air mix. This reduces rich or lean areas, hot spots and carbon deposits which increase combustion efficiency. The smaller surface area of the closed chamber head naturally absorbs less heat (quench) from combustion freeing it to expand combustion gasses and push down on the piston. Stock L20B pistons have a huge 11.36cc dish so this pinch or squeeze is much reduced than if you have a flattop piston. 

Thank you once again, this is great information!

[datzenmike]

Not saying an A87 is bad at all but it's really an L18 head used on all L18s and for one year only on the '74 610's L20B. All L heads will swap and work. In the '70s while having my L20B head milled flat I used the 210 head off my 510. The Nissan dealer told me it wouldn't work so I put it on and dove down and showed them. He called the mechanics out of the shop to look at it. The 210 has the smallest ports and valves of any L head and the combustion chambers are very small. The compression was 9.25. It ran the same and didn't ping. At the time I didn't know this but ignorance is bliss.

[Stoffregen Motorsports]

Call me names if you want, but I hate the round port heads.

[second chance]

52 minutes ago, Stoffregen Motorsports said:

Call me names if you want, but I hate the round port heads.

Care to share why? 

[Stoffregen Motorsports]

Old school I guess. They never worked as good as a properly set up A87 or W53, or even U60 head.

[second chance]

I need some advice and insight.

 

I just inherited a cam that was ground by a shop and never installed. The box says 81° 45° 45° 81°.

 

Can anyone help me out, what do these numbers mean?

 

What's the advantage or disadvantage of running a ground cam?

 

W58 head

 

Stock valves

 

L20b with L28 dished pistons (+.020)