L28ET F54 Cylinder Liners... Why?

[thehelix112]

Hey guys,

 

I freely admit I know very little about cylinder liners. I think I understand what they are, and where they are well enough. But what I don't understand is WHY they are there? Ie, why did Nissan see fit to equip the L28ET F54 block with cylinder liners, but apparently few other blocks?

 

What advantage do cylinder liners give? It appears to me that they simply reduce the amount of metal that is actually holding the bores straight as opposed to a non-linered block?

 

Phred/katman/johnc/et. al?

 

Dave

[cooks240z]

This centrifugal casting process consists of pouring the molten iron into a rotating mold. The impurities are spun to the outer surface which is then machined off. All liner surfaces are fully machined to ensure that only quality material remains.

 

Cylinder liners for turbocharged engines are induction hardened and tempered on the inner surface to reduce wear. Liners for naturally aspirated engines do not require this additional hardening operation but still provide long life.

 

The cylinder bore is machined and plateau-honed to produce a crosshatch pattern which retains oil. This aids break-in of piston ring surfaces and promotes precise limits, minimizing oil consumption and eliminating ring scuffing. Automated measuring equipment precisely measures diameter and roundness through the liner bore so that liners can be matched to pistons for best performance.

 

The matching of liners and pistons for service in many four and six-cylinder late model engines is only one of the elements which is engineered into the cylinder block cylinder liner and piston assemblies in order to promote greater engine durability. Through extensive laboratory testing optimum liner machining tolerances have been developed.

I pulled this from my bookmarks. cheers..

[thehelix112]

Good info, but it begs the question: Why would a turbocharged engine have more wear on its bores?

 

Dave

[Mack]

higher cylinder pressures.

[thehelix112]

Forgive me, but I'm not seeing the connection? Is this because the pressure goes down those holes that exist in some pistons which apply pressure to the rings (and hence bore) to improve seal?

 

Dave

[Mack]

Im going out on a limb here, and Im just guessing - not trying to be a dick- but I would guess that in a turbocharged engine with high boost pressures the increased cylinder pressures may cause the pistons to rock more or with a bit greater force, increasing the pressure the skirt puts on the bore.

[tfreer85]

Okay, I'm going to take a stab at this. Forgive me if my memory doesn't serve me right. When a piston moves up and down in a cylinder it doesn't move symetrical the the Y-axis, due to the rotation of the crankshaft and the movement of the rods. What this does is create piston-skirt side loading on both the upstroke (compression) and downstroke (ignition/combustion). This wear pattern is called out of round, often times creating an oval shape at the top of the cylinder walls. Depending on rod/stroke/piston skirt length/etc. depends on how much of this wear is incurred. When you add boost to a motor, it increases the pressure not only on the rings but also on the side-skirts of the piston (more power = faster piston movement more aggressive combustion increasing the stresses on the motor) which in turn creates more friction on the cylinder walls which equals more wear. This is also another reason why ceramic or teflon type coatings have become popular on pistons skirts is to minimize friction and also the wear involved with that friction.

 

Hope I haven't offended anyone or haven't left out any loop holes. Again this is just what I remember from my engine overhaul class 3 years ago, hope it helps.

 

Tyson

[thehelix112]

Hmmm.. i don't think so. Turbocharged engines don't see that much more cylinder pressure. They see slightly more pressure, but for longer (more charge to burn).

 

And forgive me if I'm wrong, some basic engine knowledge lacking, but a piston skirt should never rub on the bore. It should be held in place by the rings?

 

 

Dave

[Mack]

naw, piston skirts get scuffed all the time.

 

 

infact,. piston skirts can actually break clean off.

 

perhaps the peak pressures over more time might have something to do with it.

 

NIssan does tend to over-engineer things.

[proxlamus©]

increased pressure = increased heat

 

increase heat = increase wear and tear

 

my guess

[tfreer85]

Hmmm.. i don't think so. Turbocharged engines don't see that much more cylinder pressure. They see slightly more pressure, but for longer (more charge to burn).

 

And forgive me if I'm wrong, some basic engine knowledge lacking, but a piston skirt should never rub on the bore. It should be held in place by the rings?

 

 

Dave

 

Turbocharged/boosted applications recieve significant more pressure than a NA motor. Naturally Aspirated motors never function at full capacity of atmospheric pressure of 14.7lbs, if you're lucky to be near/below sea level your motor will function near 100% efficiency, but WILL NOT due to physical realistic restrictions on ANY NA motor. When you add a turbo or boost you add onto your appx 10lbs of intake pressure (in the clyinder of an NA) and multiply it by the amount of boost your feeding it, increasing the motors combustion efficiency. Pistons rings are to increase seal for compression, combustion, exhaust expulsion, less oil mixture in the combustion process, they are not intended to hold the piston "in place." Whether you intend a piston skirt to rub the cylinder wall or not, its going to. According to "Automotive Engineering" by Tim Gilles

 

"Piston pins are often offset appx 1/16" from the piston centerline. The connecting rod changes to the other side between the compression and power strokes. When the piston rocks from one skirt to the other at TDC (top dead center) the side of the piston that is "thrust" against the cylinder wall changes. The compression stroke does not exert as much force on the piston skirt as the pwer stroke. For theis reason, the side of the piston that pushes on the cylinder wall during the powers stroke is called he Major thrust surface. The wrist pin offset toward he major thrust side is to reduce teh tendency of the piston to "slap" as it rocks between teh minor and major thrust surfaces at TDC.

The connecting rod pushes the minor thrust surface cylinder wall on the compression stroke. Pin offset causes more of the combustion pressure to be exerted on the "larger" half of the piston head. This results in piston contacting the cylinder wall at the bottom of the major thrust surface. As the piston starts down, the upper half slides smoothly into contact with the major thrust surface."

 

Tyson

[Tony D]

I'm missing something here: where did you get the idea that the F54 has liners?

 

Is this from the parts manual, showing liners?

 

They have that for ALL the L-Engines. They are service replacement units, if an engine looses a piston and damages one bore at low mileage you can repair the block to standard specification without replacing all six pistons by using one of the service replacement liners to restore standard bore dimensions on the damaged cylinder without having to overbore all six and the resultant component costs.

[thehelix112]

Tony,

 

Interesting. I am talking specifically about 280ZForce's old block (he has sourced a replacement and donated his existing F54 to me). Check this pics in his thread http://forums.hybridz.org/showthread.php?t=119614 such as this one: showing the liners from the top

 

And this one, kinda showing the liners from the bottom

 

I have another F54 block in Australia, that doesn't appear to have liners. I just recently found out the F54 block came to Australia in the Nissan Patrol, so assumed that the patrol version was different to the US/JDM F54.

 

Do you have pics of US L28ET F54 blocks that are not linered? Or are you saying over the course of the life of Justin's block each individual cylinder failed independently?

 

Dave

[Tony D]

Those likely are aftermarket sleeves, installed for one reason or another. They are not stock. My bet is if you blueprint the deck height on the block you will find the height is shorter referencine crankshaft centerline to deck height from the decking operation after installing dry liners.

 

This was a common procedure for JDM engines when bores got too close to the wall thickness limitations of the skimpy walled F54. That's why most JDM builders specify N42 Blocks for big bores: much thicker walls when overboing 2mm+.

 

Chances are good the machinist who bored the block tested the cylinders and found the support lacking, so decided to sleeve the bores with higher quality materials of sufficient thickness to support expected loads at the bore diameter desired.

 

L20A blocks would be overbored and LD28 Liners installed to make 2.4L engines (using the L24 Crank) without moving the vehicle's tax class from the 2-Litre Rating in the JDM. Same thing here on the F54 I'm betting---walls as-cast were simply too thin, so they linered the block instead of looking for another one, or getting the N42 which the internet myths say "are terrible"...

[thehelix112]

Tony,

 

Ok. So your `one reason or another' in this case is `support expected load'?

If the liners are purely there to reduce wear, the exactly what are they supporting?

 

I can't see how linering a block makes the block any more capable of supporting more lateral piston thrust. I can see how, if linering with harder materials, it could make it more wear resistant.

 

In fact, I can only see how linering makes the block LESS capable of resisting thrust forces, as the liner itself is not tied into the block at all, so you are simply removing material that distributes the thrust forces.

 

Also, how does posting come into play on the L28 (F54 specifically). Obviously, if the thrust forces are greater on the power stroke, then posting becomes more important on the manifold side of the engine (the side the power-stroke thrust forces are applied to correct?). I recall the bloke who welded the crank and bored out a touch to make the L34 said he posted the block. Is this a common procedure in racing engines?

 

I am mostly concerned about block rigidity on my engine above all else. If posting is going to improve that, and it would seem to(?), then that sounds like a good idea to me. But then why isn't it common practise amongst severly overbored L-engine builders? Or is it?

 

Dave

[Tony D]

The F54 has (relative to the N42) VERY thin walls. If you overbore to the limit, then there is insufficient wall thickness to support the expected loads.

 

In this case, linering (and I somewhat mis-stated saying 'dry liner', these may indeed be 'wet liners') will give you a bore of sufficient wall thickness for all loads, compared to the bored F54 block.

 

I forget the specifics, but the wall thickness on an N42 is something along the lines of 0.400". IMO, that allows a significant overbore wihout regard for core shifting.

 

The F54, on the other hand has cylinder wall thickness less than that, I'm not sure but some say on the line of 0.0250".

 

Obviously each block on a 3mm overbore (0.120") will have SIGNIFICANTLY different wall thicknesses. On an N42, you may be looking at 0.300", but on the F54, only 0.130". Generally on a high-quality wet liner you will have at least 0.125 to 0.180" of seriously high-grade spun-cast ductile iron which is MUCH stronger a metal than the general cast-iron block. It holds up better, and therefore would be a better support at that thickness than the cast block at 50% as much more thickness!

 

This is why the JDM boys use the N42 almost exclusively in big-bore high-boost turbo applications. It is not uncommon to see an engine detonate there and blow the cylinder, then hydrolock. Nasty business.

 

So given these examples, and throw in a core shifted block that has thin spots at the base or top of the virgin-bored block you can see that a competent machinist would likely decide (for lack of another block to use) simply keep on boring another 0.200 or 0.250" beyond the original bore size, liner the block giving rigid and true bores, and call it done.

 

Darton has made a big business of high-tensile sleeves to put in aluminum blocks, as well as iron blocks. Having a sleeved block for racing in many ways is preferable. If it comes time to remanufacture the engine, you simply order up another set of liners, LN2 the old ones and shatter them out, press in a new set and deck the block.

 

You have then, the same seasoned block, dimensionally identical as what you had before, with fresh new bores.

 

Keep in mind the S20 engine in the 432 had Wet Liners (liners that run directly on the coolant system, and not in a metal sleeve of the block casting for their whole length) primarily because it was a racing-specific vehicle and overboring was NOT an option. When you have 1998 CC's on a 2.0L maximum displacement racing class liners are your only option. It makes refreshing the engine simple: press the old liners out, o-ring and press in the new liners, reassemble the engine and you are ready to go racing.

 

The issue you ahve is you have an F54, with thin walled cylinders. The common practice for big displacement engines is to use the N42, not the F54---simply due to the wall thickness issue mentioned above. So, for the vast majority of engine builders, they will use another block. Here in the USA, there is a myth of 'F54 Superiority' and that really only applies to Stock-Bore Applications. The cooling the cylinders get is somewhat more equal in the F54 with a stock bore. Knowing this redesign was effective, Nissan cut wall thickness accordingly. In the N42, wall integrity and thermal distortion was countered with metal mass (thick walls). Once you redesigned the coolant flow, you didn't need the mass, so they eliminated it as any good engineering student would tell you to do---saves money!

 

The liners aren't there to reduce wear, I never said that. Someone else did, and that is in another application (think domestic crap...V8's specifically the SBC) In the V-8 world the metal used to cast blocks is NOWHERE near as high-quality as Nissan used in the L-Engines. in those applications, the spun-cast ductil iron cylinders, indeed are harder and wear better long term than the virgin metal in the OEM block. I mean, I've seen Ford 460's with almost a 1mm RIDGE at the top of the bore where ring travel stops (and only at 150,000 miles!!!!!!!) I mean 'ridge reamer' is an American and British invention! LOL You definately don't need on on any Nissan L-Block.

 

I hope that made sense.

[Tony D]

Oh, and this:

 

"I can't see how linering a block makes the block any more capable of supporting more lateral piston thrust. I can see how, if linering with harder materials, it could make it more wear resistant.

 

In fact, I can only see how linering makes the block LESS capable of resisting thrust forces, as the liner itself is not tied into the block at all, so you are simply removing material that distributes the thrust forces."

 

The liners are tied hard and fast at the top and bottom through interference fits. They don't 'drop in'---usually they are chilled to -40 while the block is either at room temperature or heated to operating temperature and then PRESSED IN with a hydraulic apparatus. This give more than enough interference fit to lock the block and liner together as integral parts of the same assembly.

 

When this occurs, the 'unsupported' portions of the liner between the top and bottom of the block they are in function as surrogate cylinder walls. You seem to be making the assumption that they are somehow loose in the block flopping around, and this is far from the case. The liner walls are every bit as stable as the OEM cast cylinders. In fact, piston thrust loads are not really that great, and rarely come into play at all. You could support them on the thinnest of tubing.

 

What you will notice on most cylinder liners is the upper portion is considerably thicker than the lower portion. The lower portion only handles thrust loadings, but the upper portion handles cylinder pressures directly. THIS is where a cylinder liner can shine. Nitromethane Dragsters have SERIOUSLY thick upper combustion chamber and power stroke depth liners, that taper quickly to almost nothing (comparatively) below the lower ring travel area. That is the difference between supporting thrust loadings, location of the liner in general, and Combustion Pressure.

 

Combustion Pressure (and more specifically, Detonation Pressures) can/will/have caused thin cast walled blocks to literally split open. The cure for this is liners of sufficient wall thickness installed into the same block, held fast by the deck and main cap girdle area of the engine. I have personally split both VW and Corvair overbored 'cylinder jugs' running 25psi+ of boost. I've also blown the case studs out of both of them doing the same stupid crap... "Splitting a Jug" was a concern with Corvairs on 0.060" overbores if you boosted enough and even slightly detonated...once! If you could look at the thickness of the cylinder walls on those particular applications you would get a pretty good idea of what the absolute minimum wall thickness should be for any water-cooled application. They warp and overheat when the walls get thin, then you blow by...then you detonate and split a jug... Thicker cylinder walls stay round, thin ones don't.

 

I'm glossing over this a lot. This is the tech link to Darton Sleeves, and it has a load of information on it as to why and how, and etc etc etc. Spend some time there and you will get a pretty good idea what is going on with cylinder liners/sleeves. They talk a lot about abrasion resistance, but containing pressure is of primary concern as well. In this case, with the F54 block, on your application, my bet is someone was concerned about wall thickness after boring to piston diameter, and pressure containment/bore concentricity/ring sealing is why they linered the block.

 

http://www.darton-international.com/tech_ctr.htm

[thehelix112]

Tony,

 

Just to clarify, I am not interested in maximising displacement, I am interested in maximising block strength. From some other readings I have done (on the net, and often 3rd/4th/5th etc hand information), it would appear that the siamesed bores in the F54 where specifically placed to improve block rigidity.

 

In the case that you install wet liners, what are these bore braces then attaching to? Wouldn't they just fall out?

 

If so, in terms of block rigidity, it would seem optimial to leave as much of the F54 block intact (people talk about keeping the overbore no higher than 1mm).

 

I assume that the siamese bores provide some longitudinal force transfer, which can also be added using posting?

 

Does anyone have any information on posting the L bores? Linered or not.

 

Dave

[Tony D]

Did you go to the link I referenced? That directly answers your question.

 

The F54 has a lot of myths surrounding it. Siamesed cylinders notsomuch, but improved cooling around the bores yes. Due to the improved cooling to keep the bores round, the decreased the wall thickness (as stated earlier)

 

No matter which way you slice it, the metal used in the OEM casting is not as strong as the metal used in the liners. I can't conceive why you are hung up on logitunidal force transfer they are siamesed in the non-thrust direction.

 

I'm missing some transferrence in your question, originally your question was why the liners were in the block you had, and I addressed it as best I could.

Is this another question you've moved on to?

 

You really need to read the link I referenced to understand how liners work. If they could pull over 800HP out of a non-posted, linered block, why do you need it, and what are your plans that make you think you need it?

[thehelix112]

Tony,

 

I did indeed read all the articles from the link you posted, but alas, didn't see anything pertaining to siamesed bores, nor posting, which are the two things I have questions on.

 

I thank you for answering my questions about liners, and for the link. I have learnt a lot.

 

The transferrence you are talking about is my point about how the siamese joins would be affected by the installation of wet liners. I realise the joins are in the non-thrust direction, which is exactly my point. As I am picturing it, the only place the joins are connected to are the bores. Ie, they are horizontal tabs if you like that just connect one bore to another.

 

Now lets say you grind all the original bore out to install a wet liner, what do you have at the join? You just have a little tab hanging in space. Then you fit the liner, and go to grind the original bore out from the other side, at this point our little tab is only connected to the material you are grinding out, and as soon as that material has gone, it is no longer connected and drops to the floor?

 

Thats how I am picturing it, am I wrong?

 

If that is the case, I don't want to fit wet liners, as I can see the benefit of having siameses bores (in terms of block rigidity), however small.

 

That then leaves me with F54 bores, with dry liners if I choose to. Ideally I would like to be able to run around 88mm bore, for its benefit in terms of valve deshrouding. Which leads me to posting. 88mm, including liners, is getting the F54 walls a tad thin. So how can I improve it? Posts.

 

I don't know much about them but they seem logical?

 

Dave