Rebuilding L20b and need pistons!

[datzenmike]

3 hours ago, Draker said:

Checking in again, I'm just going to go 20 over with the Lazorite pistons on ebay. nothing exotic.

Now back to whatever else it going on in this thread.

 

Boring is boring. Unlikely you will wear this engine out and rebuild it again so go to the maximum bore and piston size you can.

[Wildcat Walker]

Wiseco.

[Stoffregen Motorsports]

11 hours ago, datzenmike said:

 

Boring is boring. Unlikely you will wear this engine out and rebuild it again so go to the maximum bore and piston size you can.

Right. Unless you damage the engine (overheating, broken ring, run it out of oil) it will probably outlast you, so maximum bore size is always a good idea.

 

[RetroRocket]

[datzenmike]

Were the valves closed all the way?

[RetroRocket]

Yes they are closed all the way. I know it looks like the exhaust valve might not be but they are. When I used the liquid to measure the chamber it held with zero leakage.

 

I did not have a spark plug in the head when I made the clay model. Instead, I had a thread chaser in the hole and it's flat tip was flush with the chamber edge. It made it easier to remove the modeling rather than have the plug tip and ground electrode mucking up the clay and not letting go of the model to extract it. To get the model separated from the head I first removed the thread chaser (the divot in the clay is from the turning of the chaser). To eject the model I let the model set up a bit and then inverted the head and tapped on the mold with a small wooden dowel through the plug hole to get the mold loose and have it fall out onto a plate placed below. Since the spark plug tip/electrode occupies volume but there is some small but actual added volume around the insulator of a spark plug, I'm assuming that it is a wash re + or - any net amount.

 

I'm going to let the model set up over night and it will be much easier to appreciate as a solid. Handling it too much is just asking for distortion. I haven't measured the volume of the piece yet but I'll bet it is close to the chamber + dish volume = 41 cc + 17.6 cc = 58.6 cc; which works out to about 9.25:1 c.r. when the head gasket volume is added in. The deck ht. has a dramatic effect on volume and I want it tight for the quench effect [which is a primary goal in my choosing a closed chamber head and corresponding flat table on the piston top].

 

The 1/2" wooden dowel ($1.48) is passing through the i.d. of the wrist pins and makes it easy to align by sight with the axis of the head. The Z24 head gasket is centered by the locating bits and held in place by a rubber stopper through the gasket at the oil drain-back hole.

[datzenmike]

 There is plenty of clearance between piston top and underside of head. Roughly 1.2mm of gasket thickness with zero deck height. How to Modify Your Datsun recommends not allowing piston tops to rise above the deck by more than 0.3mm to allow for rod stretch at extreme RPMs. If the gasket is 1.2mm then this leaves 0.9 clearance. Of all the stock L series pistons only the L16 rises above the deck (0.1mm)

[Stoffregen Motorsports]

.015" above deck is as far as I would ever go.

 

.010" is ideal.

[RetroRocket]

Thanks. 

 

With what i am doing, or attempting to do, i've realized that depending on what form of working chamber (head/piston top) configuration is going on can make one variable/parameter more dynamic or 'powerful' than some other parameter change. Some other configuration can depend more heavily on change in some other variable/parameter. (re: c.r.   that is the main parameter or goal that is driving the whole process). In the case of the 'quench-based' working chamber i'm setting up, deck clearance is by far the final/ultimate  spec to work with. luckily, a lot can be done fairly easily to fine tune the final c.r. by choosing from a range of head gasket thicknesses.

 

I first assume as a coarse initial parameter, using zero deck ht. calculation because that means at least 0.040" piston-to-head clearance as a given baseline to work around for stroke chosen and rod-sources choices.  btw, I source rods by shopping for the specs i need. I get my numbers together for what dimensions I am looking for [bew, bed, c-c, sed, etc]. another tip when choosing a rod of the c-c length i'm looking for is to work with the bew {big-end width} spec first because that will 'narrow' it down quickly. it can be wider but not narrower. I use what can be most easily fit be it a Saab, Volvo, Toyota, Nissan, Porsche, Alfa Romeo, Kia, etc., etc. This is not the first time that I've done this sort of thing.

 

Some people become apoplectic when they hear what I do. "That can't be done!!", which interprets to: they can't do it and it pisses them off that I can, and do.

 

I try to not need to resize the big end but find something already close enough that i can source a bearing shell to match the rod b.e./crank journal diameter interface. my hunt/screening starts with c-c length, then b.e.w., then b.e.d., then pin dia. when i crunch the numbers for selection. converting to floating pin often makes fitment easier by manipulating bushing wall thickness to fit piston and rod from different applications. Depending on which OEM rod can meet the specs i need, then i decide if it would be easier to procure (or I need more strength) to use an OEM rod or aftermarket performance version of the same application/specs.

 

Back to the topic, i think in this recipe i might go proud on the deck ht. a bit by, say, .4 mm and effectively cut my working clearance from the baseline range of 1 (0.040") to 1.4 mm (0.055") at a zero deck ht. and using a standard readily available head gasket (compressed thickness). This puts piston-to-head clearance at 0.6-0.8 mm (0.015"-0.035"). I want a close quench so will try more for a 0.015" final by selection of head gasket thickness. matching a piston pin ht. to a chosen rod c-c combination and the stroke length is how that gets done.

 

I try to stay between r/s ratio of 1.7 to 1.8 when configuring the setup and I prefer to work with under 90 mm stroke engines with a fully counterbalanced OEM crank (e.g., L20B). This particular engine i'm 'making' here to use in my 510 is not for racing except for an occasional autocross. This is a low budget endeavor. If I would need to have the crank offset-ground to meet my specs requirements I would skip building it due to $$ and figure out another approach. I have a feeling that a 92 mm Z22 crank may be more versatile to come up with my vertical combination here but I'd prefer to use the 86 mm full counterbalance L20B crank and keep the stroke under 90 (just my personal preference for most inline 4 and 6 cyl engines).

 

I may have to put this project on a back-burner for a while because of upcoming back surgery. The trick is to not scatter my notes and parts all over the place so that I can pick up later from where I left off. If it works out maybe i'll put together a kit.

 

TBC...

[RetroRocket]

There are some interesting detail differences between the pistons i've procured during the development of...whatever it is this is...

I don't have a machine shop but it seems to me that the zero-offset stock could be cnc'd to turn the reliefs aspect of the piston top configuration into a symmetric trough.

Better yet just vacuum-cast hypereutectic with the symmetric trough but shallow-up some of the other dish volume to end up with about 12 cc vol and it would make various combo's easier/more practical to adapt the piston to.  I've seen racing piston companies do this to forged piston stock to widen the application range.

 

I am having difficulty determining which spec alloy was used (332, or a raised Si content?)  Are the same pistons available in a range of alloy from another seller? The only zero-offset examples I have now are Enginetech. I don't know who makes them and who makes other brands.  Are the OEM castings any good?  maybe individual R side pistons sourced from Toyota dealers' stock is the best solution to work with in modifying for use in L4/L6 datsun engines.

 

Are there ways to visual appearance or design features which indicate what eutectic range the piston would be?  This to have some expansion characteristics to consider re bore-fit.

 

RE: my present source of core stock: zero-offset 3ZV-E pistons I see that the wrist pin bosses are significantly wider on these than they are on the offset-pin pistons that come in 3L/3R sets. This feature could be valuable if it were combined in use with a wider but lighter strong wristpin (selected to fit spec sought re o.d., length.

 

 At this point I am going to work with a design that employs fitted teflon piston buttons. I encourage you not to do it but don't tell me about it. i have practical reasons. this is a prototype and it includes pin buttons. like an aircraft engine uses.

 

Look at the differences between these two pistons: in the pic where you can see that one wrist pin is longer than the other...it isn't.  they are exactly the same length pin. there is a wider boss on one of the pistons {in the photo both pins are flush with the side of their bosses at the end away from viewer.  but it also shows that the area is not being put to use.   But it could be. So i'm looking at alternate pin sources. Regarding rod selection, conversion from a 21 mm pin to a 22 mm pin opens up more selections.

 

Four other features worth noting [and unlike the piston buttons, i am asking for inputs] are: 1) presence v. absence of elastic steel expansion inserts; 2) the shape of the force-absorbing area of the pin bosses is quite different...should the triangulated shape be stronger? 3) the configuration of the oil slots: is one stronger than the other? 4) does one oil slot configuration work better with low-tension rings or for certain use designation?

 

TBC

[RetroRocket]

Monologue addendum:

I may be off on the chamber/piston dish volume due to the paint cup container I'm measuring with. I ordered a 500 ml beaker with 5 ml graduations and will re-check my measurements, plus use some alcohol % to reduce surface tension for accuracy. I am probably over on my measurements now which is good for what i'm trying to do.

 

btw, I described modifying the 3VZ-E (i often transpose the Z and V identifying these pistons) such that the asymmetric valve pocket sizes gets machined into becoming a 'trough' shape so that interfacing with an intake/ex order or ex/intake order can be used in any cyl.

 

I stumbled on these piston configurations that could be useful for a high quench L-series configuration. One has potential at 91 mm dia. to build a Z24 based Z/L hybrid with 0.080" (2 mm) overbore; the other is 86 mm dia. Both are pin ht. = 35 mm ,with 22 mm pins. Unfortunately due to their applications there aren't going to be any hypereutectic or forged versions of these:

https://size.name/en/catalog/porshnya?auto=TOYOTA&engine=3Y&d_out=86#gallery

 

https://size.name/en/catalog/porshnya?auto=TOYOTA&engine=4Y&d_out=91#gallery 

 

The Z20 152.4 mm rods look pretty flimsy so I don't mind coming up with a different rod to use. There is a Kia rod, 150.01 mm c-c that could work using a 1.00 mm undersize rod bearing to take the bed from 54 mm Kia; to 53 mm Nissan. It is the correct bew and uses a 22 mm dia floating pin. as i mentioned, i'll be addressing the floating pin used in a pressed-pin piston by using teflon pin buttons. If it works out then i might have circlip grooves machined into the pin bores.

 

I actually have a set of the 4Y pistons somewhere in storage. i've been considering this project for a long, long time. The numbers haven't changed and won't so hitting "pause" doesn't matter too much.

 

TBC 

[Crashtd420]

How accurate are you trying to measure?

I never liked trying to read the lines on the side for the volume...

 

One thing I figured out trying to prep and cc the head on my engine was to use the weight of the liquid..

I weighed the syringe before and after and the difference was my measurement...

 

1 cc of combustion chamber volume actually equaled 1 gram in weight..

 

I was down to .01 accuracy between cylinders... the trick is measuring everything the same day... temperatures did affect the measurement,  not much,  maybe by .1 to .2 of a gram or cc....

 

This was just water not sure if alcohol has a different weight or not

 

[RetroRocket]

Hi,

I'd like to know within 1 cc but this is preliminary right now. The reason for some alcohol content is to lower the surface tension and make the fluid easier to work with and measure (to make it 'wetter'?). The weight of alcohol is less than water [water weighs a pint-a-pound-the-world-'round] but I suppose I could mix a random % alcohol to water solution, record the weight/volume of that and derive the volume displaced from the weight of the fluid displaced. It wouldn't matter what the H2O:alcohol ratio was exactly as long as I used the same batch. The volume measurement would be reliable as long as the density of the batch doesn't change. It is weight/volume regardless. Your approach is the same and you make a good point re temp, atmospheric pressure, etc needing to be consistent. They aren't huge effects but would compromise accuracy if not held constant for all measuring.

 

It does seem logical that working with a fluid with a high wt/vol ratio would give the most information or sensitivity to changes in volume, but might also increase surface tension and viscosity. Mercury, for example would be too toxic regardless but a slight change of volume would mean a big change in measured weight as an indicator or parameter. Opposite would be true the less dense the fluid.

 

I mentioned the Toyota 4Y pistons as a potential candidate for Z24/L head conversion based on piston head configuration and I did dig up a set from my storage. With pin they weigh 505g which seems like a lot compared to the 470g 3VZ-E pistons but with the larger diameter (91 v 87.5) and bigger pin mass you can see by the photo why. I'll hunt down the weight specs of the 86 mm 3Y pistons to compare to datsun L pistons of the same dia to see if they are useful.

 

btw, in general, this is a boondoggle. But I'll pursue it until I hit a 'no-go' point. I took the same approach when I modified a 84.5 x 83 (bore x stroke) LD28 engine to a 10:1 petrol efi aluminum head L6. Nay-sayers galore. "You can't do that!!"       Oh?

I used to drive it ('82 Maxima sedan) over the Cascades to take my boys skiing at Stevens Pass. I didn't drive it hard but it could pull hard even right from an idle. It was quite the 'sleeper' car that could drop the jaw of the unsuspecting. There is a photo of it somewhere online. It's dark grey with Infinity G20 OEM wheels. I modified an N42 head to make that engine. If I were to do another I'd use a high quench head (P90 or P79) to configure it instead of open-chamber. I may resurrect that project some day. I took it off the road after someone t-boned me with an Expedition. It wasn't at high speed or any injuries but the Maxima was no match. I still have the car. I might strip weight off of it and do some solo I and II with it some day. The chassis is basically a 280ZX but Maxima of that gen were front-sump and I'd just continue to work with the Maxima chassis rather than adapt to an S30 or S31 car.

 

Woops; off topic. Still, a datsun L is a datsun L.  Here's a pic of the 4Y piston. Note that on any piston that would potentially work as a candidate for the high-quench L engine project, I've learned to orient my view as if I were standing on the right side of the car, where the spark plugs are, the piston must have the front indexing/clocking mark facing front of engine; and the piston quench pad must be away from the spark plug side (so the dish at the spark plug side). It is much easier to just remember that image quickly rather than trying to flip over orientations in my mind from diagrams of chamber shapes and piston tops. If it is a piston source without pin offset there will be no 'front' indicator mark but the quench pad still has to always be opposite the spark plug regardless.

 

I appreciate your input. cheers.

TBC

 

[RetroRocket]

Hey Draker,

cat got your tongue?

speak up. you started this discussion. what happened re the pistons you bought?

[Stoffregen Motorsports]

Draker? I think he bailed out long ago.

[datzenmike]

Draker was here 14 days ago. Reports of his demise are premature.

[RetroRocket]

4 hours ago, Stoffregen Motorsports said:

Draker? I think he bailed out long ago.

who could blame him?

[RetroRocket]

Update on the mission to come up with high Quench piston top to use with closed chamber L-series head for L20B.

 

Here is a pic of a Toyota 3Y piston. it is 0.5 mm (.020") oversize at 86.5 mm which would mean a 1.5 mm (.060") overbore to an L20B, Z20, or L18 block.

Pin ht. (compression ht.) = 35 mm; pin dia. =22 mm; offset pin in proper direction, non-floating. Dish volume TBD (but my guess is at about 5 cc by visual comparison to a L28 N42 series 86 mm with a 10.9 cc dish).  A ball park is good for now.  Use with an L20B (or Z20) crank would need a 149 mm c-c length rod to duplicate the deck position of the L20B stock piston. Since most L rods are 21 mm non-floating pin, an L-series derived rod is sub optimal. There are other solutions to look for. Or, a good question is: can a 21 mm s.e. bore of a stock L-rod be oversized to accommodate a press-fit of 22 mm pin without compromising strength of the small end?

 

There was a 148.6 mm c-c rod used in some NAPS-Z engines, 21 mm pressed pin and I think I have a set but I wrote with a Sharpie: "whimpy rod" on them.

 

The piece de le resistance/ coup de grace is to find a piston-rod assy from another engine source that happens to coincidentally meet the needed specifications to fill the niche, and transplant it.

 

So far though, on this quest, the 87.5 mm 3VZ-E pistons with machined modification to make valve reliefs symmetrical to one another looks good...but would likely be a better idea if a Z22 block were used since 0.5 mm overbore to 87.5 mm is easy and o.s. pistons in that application are readily available to increase to 88.5 mm bore and gain some displacement. Plus they are already 21 mm pin pistons, so they may hold more promise than the 3Y pistons with 22 mm pin.

 

The question becomes: what is the most efficient means of machining to convert the piston-top configuration of a 3VZ-E piston into the same shape as I did with the improvised crude relief-cutting tool I made and used for a prototype (practiced using a sacrificial 'L' piston as pictured; actual would be only 'R', or zero offset 3VZ-E), but instead using CAD to machine and churning them out efficiently en masse?

 

Any suggestions? (I know nothing about machining techniques). It seems like if something was set up to produce one example, then times that number (however many you want) is just a matter of setting up a 'repeat' task button for next piston blank.

TBC

[Stoffregen Motorsports]

Rods can be "floated" by honing the small end. You'll then have to drill (and chamfer) an oiling hole in the top of the rod. We've used modified stock L rods in high revving race engines with success.

 

For piston machining, I think I mentioned the valve turned into a cutter trick, but this means having the pistons in the block.

 

The most effective and repeatable machining method requires a mill and a piston vice. New ones are expensive ($600 - $1200), but you could make some soft jaws for a normal milling vice and do it that way, or buy an old used piston vice.

 

Here's one on ebay.

[datzenmike]

 

 

 

 

[Stoffregen Motorsports]

Yep, that's one way to do it.

Edited April 17, 2023 by Stoffregen Motorsports

[RetroRocket]

I've floated pins like you did by creating an oil hole and honing the small end for pin to float. i've done this right onto the rod without a bronze bushing but I'd prefer the bushing,

What I'm faced with now, since my pistons don't use end-clips is to have grooves machined in pin bores for clips, or use pin-button retention, or stay with a pressed pin but now the pin will need to be 22 mm; not 21 mm. One piston I'm working with, toyota 3Y 86 mm uses a non-floating 22 pin but I want to use it in a Nissan small end = 21mm non-floating rod end. I need to press a 22 mm pin into the 21 dia small end rod by boring it enough to accommodate proper press-fit. Is that commonly done? Would boring the small end from 21 mm to 22 mm for press fit be a problem?

 

Is there a wall thickness standard range for pin bushings?  What is the acceptable limit for thin bushings vs thick wall bushings? i.e., if a rod has a 23 mm bushing i.d. but I want to use a piston with a 22 mm pin, can i press out the 23 mm i.d. bushing and replace it with a 22 mm i.d. bushing (with double the wall thickness)? Would a different alloy for the bushing be recommended when using a thicker wall bushing?

[Stoffregen Motorsports]

Even racing engines don't need bushings. It would take an entire lifetime of daily use to wear the rod or the pin without a bushing. As a matter of fact, the bushing will wear faster than the rod without a bushing.

 

I know you can open up the stock rods. A full mm shouldn't be a problem for what you're doing.

 

I hate buttons. They are so 1970's...

[RetroRocket]

Buttons are not a solution I am seeking out, they are a default solution only. I can convert a rod to be floating-pin easily enough but I do that in order to use a piston that is already a floating-pin application and has circlips. I could use that same piston in a pressed-pin style rod, just don't install the clips; but what I frequently run into as an impasse is needing to use a piston without machined grooves for retention clips that I need to pair to floating wrist pin style rod.

 

I am assuming that having circlip grooves machine-cut into the pistons would be more costly than I want to spend. My approach is toward spending little money but having a unique results by cross-referencing specs I need to some that already exist in use in some other car engine somewhere. And then pirate those components from their intended use and patriate them to their new home: in my engine.

 

I haven't canvased local machine shops yet because I would only have this done by someone already experienced, not experimenting with it. Maybe someone here knows who can do this at a reasonable price and with reliable quality results. I can USPS Flat Rate Priority Mail back & forth my batch of bare pistons and their pins to keep shipping costs low.

 

But if machining in clip grooves is as expensive as I anticipate it is, I've wondered if teflon buttons configured with a slip-fit into the i.d. of the pin, with a light weight light-tension ss spring fit between them (within the pin's i.d.) could be a possible solution. This would be a dumb-luck added function to lend stability, even if minutely, to piston lateral forces in the cyl bore by incidentally and indirectly quell vibration resonance of the piston slap even though it occurs at 90 degrees away: the thrust axis of the piston.

 

The spring essentially would function to keep the wrist pin centered laterally with respect to the lateral axis of the small end of the rod (and to the cyl bore). Which is what a pin pressed into a rod does; and what a floating pin does by limiting end movement at two fixed clips in the piston; and what a piston pin button does with a fixed clearance to the cylinder walls. Ultimately they all function to keep the wrist pin centered laterally between the walls of the engine bore. 

 

Traditionally, teflon and aluminum pin buttons are fit to the pin such that the overall side clearance to the cyl walls is a fixed amount. The theoretical advantage of what I'm describing with the internal spring is that fewer buttons could be made for a given engine bore (the cyl bore stll dictates the radius of the button face) the wrist pin i.d. bore still dictates the button shaft o.d., But variances of wrist pin lengths could be adjusted by shimming the internal spring effective length rather than by machining each button specifically to fit each wrist pin's unique length. This approach could also expand the ease of adapting a range of pin choice lengths that otherwise would be beneficial due to their weight or material strength advantages. To adapt these for a range of application, just change the spring end-shim washer thickness; rather than make each button with a unique button head-to-pin end thickness.

 

Alternatively, forget the spring concept and just vary the thickness of shim washers that go between a boss below the head of the button and the flat end of the wrist pin.

The shim washers could be used in conjunction with a teflon ring in choice of thicknesses for larger discrepancies in pin lengths. An overall benefit would be to eliminate one of the parameters of a custom fitment and broaden application of one design.

 

Machining grooves for circlips is looking better all the time...

TBC

[RetroRocket]

On 4/16/2023 at 9:27 AM, Stoffregen Motorsports said:

Rods can be "floated" by honing the small end. You'll then have to drill (and chamfer) an oiling hole in the top of the rod. We've used modified stock L rods in high revving race engines with success.

 

For piston machining, I think I mentioned the valve turned into a cutter trick, but this means having the pistons in the block.

 

The most effective and repeatable machining method requires a mill and a piston vice. New ones are expensive ($600 - $1200), but you could make some soft jaws for a normal milling vice and do it that way, or buy an old used piston vice.

 

Here's one on ebay.

It looks bad but did you see that stuff I used many posts ago? EVAPO-RUST Gel Rust Remover? It is not supposed to separate into globs of ....they resemble bay scallops.... but it does.[ That can actually be an advantage because you can use chopsticks to apply a pledget essentially to a site where it needs to be fed the stuff.]

 

The funny part is that because it has already become separated (but buyer was expecting a gel)  is supposed to be a 'gel'; and they return it and get their money back. Probably a lot ends up on the clearance rack in chain auto stores.

 

That would make a great door stop.