3.0 and 3.1 liter In-line 6 cyl. FAQ

by Steve Golik IZCC Member #356

August 4, 1997

This FAQ is based on my experience in building a six cylinder 3.1

liter Z car engine. I am by no means an "expert" on this subject,

so this FAQ is not the final authority. Any comments, new

information or additional questions are always welcome.

You may e-mail them to: Steve Golik (goliks@knox.pcec.philips.com)

*How can you build a 3.0 liter (or larger) Z engine?

All the 3 liter (and larger) engines are based around using a

crankshaft with a longer stroke in an L28 (280Z) block. The stroke

of a stock L28 crank is 79mm. Nissan did made an L series six

cylinder crankshaft with a stroke of 83mm. In the USA this crank

was only used in the 1981 (7/80 production date) through 1984

(9/83) diesel Maxima with the LD28 block, hence it is commonly

referred to as "a diesel crank". The Nissan part number for the

diesel crank is 12201-V0790.

*What bearings do you use with the diesel crank, 280Z or diesel

*Maxima bearings?

The dimensions of the connecting rod journals and the main bearing

journals of the diesel crank are the same as the L28 crank (and

L24) crank so you can use Z car bearings. This also means that any

of the L engine series connecting rods will fit on the diesel


I used standard size Z engine main and rod bearings (either 240,

260, 280, or 280ZX, they are all the same). The diesel bearings

appear to be the same as a Z engine, but the rod bearings have a

different part number.

*Do I have to "prep" the diesel crank any?

The diesel crank has a locating dowel on the rear where it mounts

to the flywheel. You must remove this with a hack saw or grinder.

A Z car flywheel will then bolt up. The Z car harmonic balancer

will bolt up with no problem. There is a hole for a pilot bushing

as well, so don't forget to check for it's presence if you are

going to use a manual transmission.

Check the journals for scoring. Very light scratches can be removed

by polishing. See your machinist for details. Inspect the thrust

bearing surface at the center of the crank for wear. The crank can

be checked for straightness with Vee blocks and a dial indicator,

again, your machinist can perform this. However, from what I

understand, Nissan cranks are extremely rugged. You should make

sure that none of the threaded holes are stripped, although this

can be repaired if your machinist has the right equipment.

I had my crank polished, inspected and measured for about $35. My

machinist recommended this before balancing the bottom end, which

I do recommend doing (although it cost me around $100).

*When using the diesel crank, do you have to notch the block so the

*connecting rods clear correctly?

It depends. I had no clearance problems when I built my 3.1 liter,

but other people have. The diameter of the bore is a factor, a 89mm

diameter bore will give you more clearance than a 87mm bore. The

9mm connecting rods have less clearance than the 8mm rods. And

there are probably slight differences in the L28 block due to

tolerances and changes to the casting molds during the production

run of the L28.

So, you must expect to check this during engine assembly and take

appropriate measures if necessary (get the die grinder out).

*How much should I expect to pay for a good _used_ diesel crank?

According to a recent survey of people who had purchased one, they

go for between $300 to $400. One individual said he paid only $150

for one. In my case, I spent $300 for an entire diesel engine. The

junkyards I talked to would not disassemble an engine just to sell

a crank.

*What size (displacement) engine can one get?

That depends on what you decide to bore the block out to:
bore(mm) stroke(mm) displacement(liters) notes
86 79 2.753 stock 280Z
86 83 2.893 5.1% increase
87 83 2.960 7.5% increase
88 83 3.029 10.0% increase
89 83 3.098 12.5% increase
90 83 3.168 15.1% increase 

As you can see from the chart, you can't just drop a diesel crank

in a stock bore L28 and honestly call it "a 3 liter". You must at

least bore it 1mm over.

*It can't just be a "bolt in" job now can it?

Well, most of it is. The problem is that now since you have

increased the stroke by 4mm, a 280Z piston when installed on a 280Z

rod would extend over the top of the block by 2mm! Now I have heard

of people milling the tops of the L28 pistons by 2mm to correct

this, but Ron Johnson of Nissan Motorsports said that if you mill

the stock cast pistons this much the top compression ring could get

too hot and eventually fail.

To resolve this dilemma you must use a rod and piston combination

that will allow the piston to protrude the correct amount or just

slightly more so that the pistons can be safely milled. There are

also head gaskets with different thickness available to assist in

this. You also must maintain some amount of piston to head

clearance at TDC.

Another item which must be addressed is the compression ratio. Even

if you obtained the same "deck height" as a stock 280 set up, the

compression would increase because you have increased the sweep

volume of the engine.

*So how do I know if my combination of rod and piston needs to be

*machined, and by how much?

I went through this in detail when I built my 3.1 liter, using a

spreadsheet program. The figure of concern is what I call the

"installed piston height". It is the maximum distance between the

centerline of the crankshaft to the top of the piston with

everything assembled.


installed piston height =

[piston pin height + rod length + stroke/2]

Piston pin height is the distance between the centerline of the

piston pin to the top edge of the piston. Rod length is measured

between the centers of the two circles formed by the big and small


The installed piston height along with the height of the block will

determine the "deck height" which tells you how far the piston will

be relative to the block at top dead center (TDC), or:

Deck height = Installed piston height - block height

This number can be positive or negative. A positive deck height is

where the piston extends above the top of the block. Because of the

thickness of the head gasket, this can occur without the piston

making contact with the head.

Since most people use the L28 block with the diesel crank the

height of this block becomes important. This height is 207.9mm.

For example, in a stock L28 (280Z) the installed piston height is:

38.1mm + 133.3mm + 79.0mm/2 = 207.9mm

And the deck height is:

207.9mm - 207.9mm = 0

You should keep in mind that if you are going to use the diesel

crank then you have changed one of the parameters in the "installed

piston height" equation and must be aware what are the

consequences. What you end up doing is using a rod and a piston

with the correct pin height or one close enough so that you can

mill the top of the piston to maintain clearance to the head.

*What are the important dimensions of suitable pistons?

Here is a chart of most of the Nissan L series pistons (all of

these are cast, not forged):
Engine pin height(mm) piston diameter(mm) application notes:
L28 38.1 86 280Z
LZ22S 35.0 87 720 truck 6/79 to 10/82
LZ22E 32.5 87 200SX 7/81 to 10/83
LZ24 34.0 89 720 truck 11/82 to 10/85
KA24E 34.0 89 240SX

*What about connecting rods?

The lengths of the L28 and L24 connecting rods are 130.3mm and

133.0mm respectively. There was a 140mm length rod that was used in

the 2.0 liter six cylinders (the Fairlady Z engine), but this

engine was not imported to USA, and it also only had the 8mm

diameter rod bolts. All the other L series rods are too long to be

of any use.

*Why should I use 240Z rods?

240Z rods are recommended because they are longer than the 280Z

rods and the theory is that a larger [rod length]/[stroke] ratio

should produce more horsepower. Since you have increased the stoke

of an L28 you should increase the rod length to maintain a more

optimum ratio.

Of course you use the later 240 rods which have the larger 9mm rod

bolts and weigh less than the 8mm rod bolt connecting rods. Early

L24 engines (up to serial number L24-096181) have the 8mm rod

bolts. Therefore, the changeover to 9mm bolts happened sometime

near the end of 1972 model year, so only a 1973 240 engine would

definitely have the 9mm rods.

*Why can't I use the diesel rods?

For several reasons you cannot (and should not) use the diesel

rods. The piston pin diameter is larger than the L series pistons,

it is longer in length than a rod that an L series uses (I don't

recall by how much) and being designed to be used in a diesel

engine, it is considerably more massive than a rod for a gasoline


*Ok, so what pistons/rods can I use to build a 3.0 liter?

There are a few options: One is to use 240Z rods and LZ22S pistons

(87mm diameter) which were used in the Nissan 720 truck from 6/79

to 10/82. The part number is 12010-06W11. These have a dish of

9.3cc. The installed piston height is:

35mm + 133.0mm + 83mm/2 = 209.5mm

And the deck height is:

209.5mm - 207.9mm = 1.6mm

In other words, the pistons will protrude about .063" (1.6mm) above

the top of the block when everything is assembled and installed.

As a result, you must use the 2mm thick HKS head gasket. This

results in a compression ratio of 9.6 to one with an N42 head

(44.6cc combustion chamber volume) and 9.9 to one with an E31 head


Another option (especially if you want more compression) is to use

the 280Z rods, 280ZX (flat top) pistons (in a +1mm, or 87mm

diameter), and the 2mm thick HKS head gasket. If the pistons are

milled 1mm the compression ratio with an N42 head becomes 10.6:1.

Yet a third option is to use the LZ22S pistons with 280Z rods and

the stock 280Z head gasket. The installed piston height is:

35mm + 130.3mm + 83mm/2 = 206.8mm

And the deck height is:

206.8mm - 207.9mm = -1.1mm

In other words the pistons will have a negative .043" (1.1mm) deck

height so the compression ratio will only be about 8.6 to one (with

an N42 head). The top of the block can be milled to increase the

compression ratio, but several concerns must be addressed: the

timing chain slack will increase, the heads bolts might bottom out,

the oil passage restrictor plugs would have to be pressed further

down into the block, and the keyholes used to position the head in

the block would have to be re-machined, etc, etc. Needless to say,

this is not a popular approach, but it has been done.

*What about a 3.1 liter?

To build a 3.1 liter you must use 89mm diameter pistons and the

"Big Bore" head gasket. Use either KA24E pistons or LZ24 pistons.

The 280 block must be overbored by 3mm (about .120"). Again, use

240Z rods. All of these pistons have a 34.0mm pin height.

The installed piston height is:

34.0mm + 133.0mm + 83mm/2 = 208.5mm

And the deck height is:

208.5mm - 207.9mm = 0.6mm

So, both of these pistons will protrude, but only about .025"

(0.6mm) above the block.

*Isn't a 3mm overbore risky?

Nissan Motorsports recommends that you have the bores "sonic

tested" or measured for thickness, but only before you take MORE

than a 3mm "bite" out of them. It's still probably something you

might consider doing. Sonic testing will check to see if any

shifting of the sand molds occurred during manufacture. You may

have to contact several machine shops to get this done, as it is

not a standard automotive machine shop operation.

I have heard of overbores of 4mm (.160")! without hitting water

passages. The real problem is how much flexing you can tolerate.

All engine blocks flex during operation. Removing metal from the

bores reduces overall block rigidity, allowing the rings to stop

sealing. This is mainly a high rpm phenomenon.

I really don't know what is the minimum thickness you need around

the bores for a Z engine. Rick Voegelin in "Engine Blueprinting"

recommends a minimum of .180" wall thickness for a small block

Chevy. He says what you want is consistency from bore to bore.

Measure the wall thickness in four places (ninety degrees from each

other) near the top and bottom of each bore.

*Tell me more about the LZ24 pistons?

These are the pistons I used in my 3.1 liter. As I said above, when

installed in an L28 block with 240Z rods these pistons extend about

.025 inches above the top of the block. I did not mill the pistons

to reduce this. This piston has a fairly large "dish" of 15cc.

The calculated compression ratio with an unmilled N42 head is 9.3

to one. Using an E31 head would increase this to 9.6 to one. I used

a milled N42 head to obtain a 9.4 to one ratio.

The Nissan part number for the LZ24 piston is 12010-30W01. They

were used in the 720 truck built from 11/82 to 10/85. They list for

$38.50 each. The part number for the ring set is 12033-30W10. They

sell for $91.39 for a set to cover four pistons. You must order two

sets of rings for a six cylinder engine!

A problem with using these pistons is that there is insufficient

clearance between the top "eye" of the rod and the piston pin boss.

However this is easily solved by removing a very small amount of

material from both sides of the small end of the connecting rod. Of

course re-balancing is necessary.

*Tell me more about the KA24E pistons?

This piston was used in the 240SX. This piston has a floating pin

and clips to retain the pin. There are two versions of this piston,

a "dished" and a "flat top", but both have the same piston pin


Part number 12010-30R10 has a 2.8cc volume dish and part number

12101-40F10 has no "dish" and hence one could obtain a higher

compression than with the dished KA24E piston. These are the

pistons that Nissan Motorsports sell in their "3.1 liter kit".

However, with a N42 head and a 1mm thick head gasket, the

calculated compression ratio would be 12.0 to one! Using the 2mm

thick HKS head gasket would lower this to 10.6 to one. Milling the

tops of the pistons by .025" would reduce this further to 10.0 to


There is another part number, which was used on the truck

(Hardbody) version of the KA24 engine, part number 12010-86G20.

This piston is also a "flat top" and appears to be very similar to

the 12101-40F10 piston (it also has the same pin height). I have

been told that it uses a pressed piston pin rather than a floating


*Can I build a motor even larger than 3.1 liters?

You can get both the L24Z and KA24E pistons in a 1mm oversize

(90mm). This would give you 3.168 liters of displacement (usually

rounded up to 3.2 liters). But according to two sources, a 4mm

overbore is very risky. A 3mm overbore is the practical limit.

*Why should I use a lightened flywheel?

Most everyone who has built a stroker engine recommends using a

lightweight flywheel (10 lb. or less) to prevent failure of the

harmonic balancer or the crankshaft key due to cracks.

I used the HKS flywheel, sold by Motorsport Auto (phone 800-

633-6331) and others.

*What if I use the stock L28 crankshaft and bore the L28 block out


This will result in a displacement of 2949cc. Using 240Z rods and

the KA24E pistons would result in a calculated compression ratio of

9.6 to one with an N42 head and the 1mm head gasket. The deck

height is a negative .055". Again, the block could be milled to

increase the compression ratio.

*What about stroking an L24 block?

I have not actually done this, nor do I know anyone who has but,

according to a "paper design" you could use the diesel crank with

a bored L24 block, 280Z rods, stock 280Z head gasket, unmilled E31

head and unmilled LZ20S (PN 12010-W4001) pistons. This would result

in a compression ratio of about 9.9 to one. The L24 block would

have to be bored out 2mm to 85mm, giving you an overall

displacement of 2826cc's.

*Tell me more about this "Big Bore" head gasket?

This gasket is made by HKS (phone 310-328-8100) and is available in

either a 1mm or a 2mm [compressed] thickness. It is sold by Nissan

Motorsports and Motorsport Auto for around $100 for the 1mm version

and $125 for the 2mm one. The Nissan part numbers are 11044-91MM1

(1mm) and 11044-91MM2 (2mm). You can order it through any Nissan

dealer. The Motorsport Auto part numbers are 10-2456 (1mm) and 10-

2458 (2mm).

This gasket is a all metal, multi-layer design with the pieces

being riveted together in a "sandwich" configuration. The rivets

are outside the engine, so they do not interfere with the head-to-

block seal. However, one of the rivets does interfere with the rear

heater hose brackets on the right side of the block.

You MUST use this gasket if you bore is increased to 89mm or more.

The bore size of the stock head gasket measures about 89mm and

should only be used in engines with a bore of 88mm or less. The

bore diameter of HKS gasket is 91mm.

BTW, the compressed thickness of the stock L28 head gasket is


*Does the engine run hotter (water temp) in the 3 liter?

I have had no problems with the engine water temperature being any

hotter than before. I use a four core radiator with only the stock

fan and clutch unit.

*What about the stock induction system and stock exhaust. Can they

*handle the increased air flow of the larger engine?

Well, I am using the triple Weber carb setup with the Motorsport

Auto "6-into-1" header and a 2 1/2" exhaust system, so I'm can't

answer your question, but even if you retain your stock induction

and exhaust with your 3.0/3.1 liter, you will still benefit from

the increased lower rpm torque as a result of the larger

displacement and longer stroke.

*What about the performance of a 3 liter engine?

In my 260Z a 3.1 liter with 9.4 to 1 compression replaced a 1mm

overbored L28 block I had in the car which had just over a 10 to 1

compression ratio. In my opinion the horsepower is the about same.

There does seem to be more bottom end torque, which is what you

would expect. I did not dyno either engine, however. Bowling's

horsepower computer program, shows that both engines should


almost exactly the same peak horsepower.

*How much did it cost you?

It does take a LOT of money to build a 3 liter. I did not pay

anything for the L28 block. It came out of a friend's car and he

just gave it to me after we installed another engine in his 280Z.

I paid $300 for a used crank, $100 for the head gasket, and $220

for the flywheel. I got a deal on the pistons, only $15 a piece.

Then there was $35 for piston rings (another good deal) and $60 for

a set of good used 240Z rods.

I spent around $350 for the machine shop work. Of course, if you

are going to bore an L28 block just 1mm over, the machine shop

costs are the same. The only "extra" shop charges was the work done

to the rods and the re-balancing. There was $50 for new bearings

and $25 for the gaskets I needed. Let's see, that comes to a grand

total of $1,230!!

Of course if one were to rebuild an L28 using oversized pistons the

cost differential would be only be around $650 or so.

*Who sells a 3 liter "kit"?

Arizona Z's (phone 602-844-9677) latest catalog features a 3.1

liter kit. The crank is a custom made from 4340 chrome moly. It has

a 83mm stroke, the same as the diesel crank and sells for $2395.

The pistons likewise are custom made. They are forged, 89mm in

diameter, with a flat top (no dish) and have a zero deck height

when installed with 240Z length rods. The piston pin is a full

floating design that is 1mm smaller in diameter than a L series

piston. The pistons run $95 a piece (includes rings). They also

have chrome moly rods that are lighter than the stock 240 rods.

These cost $169 each. Total kit cost is $3979.

I would think that you can utilize a used diesel crank and used

240Z rods and save some money. They will sell you the pistons

separately. The rods would have to have a bushing pressed in by a

machine shop and then machined, but this is a fairly standard


They are also working on a 3.2 liter kit which will feature another

set of custom pistons and rods and a crank with an 85mm stroke. The

rods will be slightly longer in length to maintain the rod

length/stoke ratio, and this of course, means a different custom

piston with a relocated pin. No price info yet.

As I said above, Nissan Motorsports (phone 310-538-2610) sells the

diesel crank, 240Z rods, flattop KA24E piston and rings for their

"3.1 liter" kit. Part number is 99996-28BBK. The cost is $1800. You

can also order the exact same kit from Motorsports Auto for the

same price.

There was a 3.1 liter and a 3.2 liter kit offered by Jim Cook

Racing that are no longer available. They used custom made pistons

in either 89mm (3.1 liter) or 90mm (3.2 liter) diameters.

*What is the cheapest route?

I would get the following from a junk yard: the diesel crank, a

280Z (or ZX) block, late 240Z rods and a 240 flywheel. Use

aftermarket versions of the pistons (and rings) suggested above. If

you build a 3.0 liter and you can use the stock 280Z head gasket,

Felpro makes an excellent replacement, and it's cheaper than the

factory one.

The 240Z flywheel must be lightened by a machine shop. I doubt they

can safely reduce the weight down to 10 lbs, but every bit they

take off will help. The machine shop work for either a 3.0 liter or

a 3.1 liter should be about the same, IMO. Both versions must be

bored and honed, and although you must remove more metal on a 3.1

liter, most shops charge a flat rate for boring jobs.