Rebuilding L20b and need pistons!

[RetroRocket]

I'm just using the Z24 gasket as a centering guide as to where to clamp the piston. The dowel will be about 18" long and align with the axis of the head, and therefore the crankshaft as to where to clamp the piston. It is for reference/indexing only re centerline of bore and where I place my piston before clamping it down.

 

My deck height won't be related to a Z24 block or piston in any way. It will be related to Z22 = L20B block height, L20B crank throw, Z20E rod, and Toyota 3ZVE piston compression height. I have calculated that but will verify upon assembly. 

 

I won't be using a Z24 head gasket when I assemble, it will be a L20B or Z22 gasket depending on the brand and diameter of its fire ring and fit to my 87.5 mm bore size.

I will leave that parameter (head gasket volume) as the final factor to tweak the volume (thus fine tune the c.r.).

 

Moving on to relief cutting tool fabrication. It precedes the centering of the piston for casting the model. The valve I am converting to a cutting tool is from a mid-'60s Chevy II 153 c.i. 4cyl (Iron Duke engine) intake valve. I just ordered two more of these so that I could set up coarse, medium, and fine finish tools to use in sequence. Two of these from Rock Auto cost me $12.92 including shipping to my PO Box. SBI 00399 part number. I like that the valve has a generous flat surface on the head (as compared to many other valves) because it allows for good gluing onto the abrasive material doing the cutting.

[RetroRocket]

Custom cutting-tool sized to existing intake valve pocket to machine exhaust pocket to match intake.

[RetroRocket]

Hey Draker are you following this?

There is no guarantee this will work but this is a process . a prototype. a model.

 

I'm going to elaborate on what I was describing in the first paragraph of my post before last about centering the piston for clamping to the head to make the mold.

Pictured below is one of the 87.5 mm pistons crudely placed within the center of a new Z24 head gasket (89 mm bore block). the white paper can be seen as a ring of space around the piston for demonstration. for the actual centering placement for clamping a set of the zero offset pistons will each be centered on the upside down cyl head using a used Z24 head gasket centered (with a gauge rather than by eye, and with the head bolt holes used for indexing the gasket to block. at the same time there will be a nylon or wooden dowel slip-fit through the center-hole of each wrist pin in place (thus all pistons aligned with the axis of the crankshaft). maybe I can place two or more large c-clamps using a softwood block piece about 4" square x 1/2" thick with a couple of thin reliefs routered in for the piston skirts to bed into and then use several clamps using the wood block surface clamped to edge of head or within the valve spring valley. not tight but tight enough and uniform distribution of pressure to hold piston in place and still while forming the fluid-tight cast. I don't show the dowel or all of the other pistons in the pics below but you can form the image of it in place.

 

Once clamped, I can remove the dowel, other pistons & wrist pins except #1 (clamped). Then I can rotate the head oriented spark plug hole-up, support it with whatever to hold it oriented so and then pour my casting media (PerfectCast will be my first trial media) to form my mold.

 

My step before I can do the clamping step is to cut valve reliefs to make each piston top shape uniform. {An intake pocket can work for either intake or exhaust relief; an exhaust pocket can't}.

TBC.

 

 

 

[RetroRocket]

Draker, this would work with an L20B block but only if it were bored from 85 mm to 87.5 mm. That is a huge overbore (0.100" over) which is a waste of good block material turned into shavings. If one were to do what I'm describing it would be more sensible to find a Z22 block 87 mm bore and overbore 0.5 mm to use the STD size 3ZV-E piston or one of the common overbore (88.0, etc pistons available). this would involve converting a NAPS-Z block for use as an LB block vehicle application. choice of compression ratio drives a lot of the selection in that decision.

[RetroRocket]

Or maybe bore and sleeve an L20B block with choice of 87.5 mm, or one or two overbore sizes bigger than STD for i.d. of sleeve. i have never had a nissan block sleeved myself so maybe ask others. I know some machine shops aren't keen on boring the nissan blocks of the era because they were tough material due to nickel content iirc.

[datzenmike]

0.0985" is only 1.25mm of material removed from the cylinder wall. Under 0.050" well within safety limits for an L20B cylinder wall.

[RetroRocket]

13 hours ago, datzenmike said:

0.0985" is only 1.25mm of material removed from the cylinder wall. Under 0.050" well within safety limits for an L20B cylinder wall.

a mm is about 0.040", No? 

2.5 mm over is about 0.100" and a lot of overbore.

[Crashtd420]

34 minutes ago, RetroRocket said:

a mm is about 0.040", No? 

2.5 mm over is about 0.100" and a lot of overbore.

Think wall thickness... 

If .050 is coming off each side that's a total of .100 on the diameter....

Edited March 11, 2023 by Crashtd420

[Stoffregen Motorsports]

I'm glad you enjoy the process, but me? I have too many projects.

 

Is there a reason you can't do a simple mock up? If it's bore size (haven't had the block bored yet) then maybe buy an extra piston and throw it in the lathe and cut it to fit for a mock up. Doing a mock up could have told you everything you need to know already.

 

Also, a quick way to make a valve relief cutter - weld a couple beads onto a valve, then grind/cut those welds to resemble an end mill. Now you've got a cheap purpose built cutter.

[Stoffregen Motorsports]

For the block, the only thing you need to do to a Z block to get it to work in an L application is to (sometimes) drill a new dipstick hole and plug the old one. Some Z blocks come with both holes drilled, and a plug in one of them. If you're running a header, cut the angled bump off the block under where the two center exhaust ports are so it doesn't hit the header flange. Don't cut too far because you'll cut into the water jacket (ask me how I know). I've built dozens of LZ motors and the blocks are almost interchangeable.

 

.100" over is not a ton for an L20B. It's when you get into the 89mm bore that you really have to be careful. Most times 89mm isn't doable with an L20B, but I think 87.5mm would leave more than enough cylinder wall thickness.

 

A sleeved block is never as strong as one with original as-cast bores. So avoid that if you can.

[datzenmike]

3 hours ago, RetroRocket said:

a mm is about 0.040", No? 

2.5 mm over is about 0.100" and a lot of overbore.

 

2 hours ago, Crashtd420 said:

Think wall thickness... 

If .050 is coming off each side that's a total of .100 on the diameter....

 

 

Exactly. A 2mm over bore is only 1mm removed. Doesn't sound nearly as bad. I have an 87mm  Z22 block that was over bored to 89mm That's only 1mm of metal removed.

[RetroRocket]

On 3/11/2023 at 10:08 AM, Stoffregen Motorsports said:

I'm glad you enjoy the process, but me? I have too many projects.

 

Is there a reason you can't do a simple mock up? If it's bore size (haven't had the block bored yet) then maybe buy an extra piston and throw it in the lathe and cut it to fit for a mock up. Doing a mock up could have told you everything you need to know already.

 

Also, a quick way to make a valve relief cutter - weld a couple beads onto a valve, then grind/cut those welds to resemble an end mill. Now you've got a cheap purpose built cutter.

 

[RetroRocket]

one thousand words.

[RetroRocket]

Recall I'm using Left pistons to sort out my tooling method. The Lefts are useless to me due to their wrong (and compounded) pin offset. This is my first trial. in the first pic are the three grits of ceramic sanding belts glued to the 00399 (SBI from Rock Auto) valves. #36, #80, #120. But I found it easier to start the pocket modification by establishing the shape and depth perimeter by using a dremel carbide tip cutter freehand to remove the most bulk; then switching to a diamond cutting disc to define the extent of the depth. It can be seen how rounded it is shaped from the freehand shaping. Next I chucked up the cutters in the drill press and did sequential coarse, med, fine.

By the time I've sacrificed another left piston I should have arrived at an efficient technique. I may use this prototype to start the volume measuring.

 

I'll try to tape off the sides of the valve reliefs to cc the piston head. But I may try measuring the volume of two sticks of chewing gum, chewing it up, and using half on each side to mold a dam on each side, flush with the piston side and level on top with the top of the machined areas...then let it dry out. The absolute value of the volume of the gum is what matters. That volume will be subtracted during my calculations; whatever the volume is it won't be there in the engine itself.

 

All of this is eye-protection territory and safety first, that should be obvious.

[RetroRocket]

The piston top looks bad in the pics but looks a lot nicer to visual inspection. It will do for my crude initial volume/calculation. I'll include a photo of the one-off jig fixture I designed next time. One thing I've found is that my valve transformed to cutter works well if I nestle it in the piston/fixture assembly and just hold a very light pressure to use the existing vertical wall of the pocket as a guide to keep the cutter from trying to oscillate or chatter. That is a reason to establish that vertical depth first (using dremel tool) prior to the cutter tool. The angle of the cutter is relative, unmeasured, and indexed to the existing intake pocket angle. The cast aluminum of the pocket matches (parallel) the plane of the cutter tool and can be set by eyeballing it. The angle is being matched to the Toyota engine valve angle and I will check the relationship to the Datsun valve angle when I model it. It is in the ballpark from specs I researched.

[RetroRocket]

I have not been able to find the dish volume specs for the stock 3ZV-E pistons that I'm working with and I want to know at least a crude baseline. I taped clear packaging tape around the piston snugly with the free edge aligned with the piston top so to seal off the sides of the exposed valve pockets, as a dam. I then stretched plastic wrap tautly across the piston top and knicked it with a knife to allow air out as I filled the cavity with measuring fluid. I used 90% isopropyl alcohol (reduced surface tension compared to water) and mixed in a splash of red wine for coloring. I couldn't find any food coloring but the wine was right there in my glass. Malbec. I used a farm store medicine dispenser plastic syringe (note the integral stepped tip, not the tapered tip one) to draw it full of my fluid; invert to purge air out, hold vertical and read starting volume [13.6 cc was where it randomly was]. I dispensed that volume through the hole in my membrane and took up another half syringe full and filled the void to top it off [it took 4 cc more] for a total of 17.6 cc. I did this quickly to get a decent measurement and then took the pics which is why you can see bubbles in the fluid and wrinkles in the plastic wrap from being moved around. Crude but 17.6 cc compared to zero information is good to know.

[datzenmike]

How about spraying with Pam, (as a mold release) place a suitable size blob of clay (plasticine)in the dish. Press it down on a flat surface and it will squeeze out the sides. Trim those sides flush, then peel the clay off. Roll into a shape that will fit a graduated cylinder of water and the increase in water level is proportional to the clay volume.

[RetroRocket]

yeah that should work too. the cookie-cutter approach. I'll give it a try. thanks.    now i don't need to chew-up an entire big pack of chewing gum.    in fact, i could have swiped some of that molasses cookie batter from Susan before it went into the oven.

 

I'm trusting you are right about boring a Z22 block from 87 to 89 mm because I ordered a set of the same 3ZV-E pistons (with zero pin offset) in 1.00 mm oversize (88.5 mm).

The set of six 87.5 mm I'm modifying now might end up in one of my L28's.

 

Do you know if the Z22S block is beefier than the Z22E block? I don't recall if one is siamezed and one not.

[datzenmike]

I believe the Z22S blocks (S for carburetor) in the 720 truck application are the thickest wall and are joined or siamesed, although the joining is only between cylinders and doesn't affect the overall thickness elsewhere. The Z22E (E for EFI) in the '82-'83 S110 200sx are not as thick a wall.

[Stoffregen Motorsports]

There are steam ports between the #1-#2 and #3-#4 cylinders. Those can be bored into if not careful. You can always have the machine shop spread the bores to clear those steam ports.

[datzenmike]

I bored a 720 Z22 from stock to 89mm that's only 1mm or 0.040" off the wall.

 

The bore spacing for all L, Z and KA engines is 95.2mm so 6.2mm or 0.24428" between cylinders when bored to 89mm. Almost 1/4 inch.

 

 Z22 fitted with Z24E pistons. Tons of room..

[RetroRocket]

I'm going to lay this model piece flat and allow to dry and save it.

Next I'll respray the cyl head with PAM and the Piston top, and then put the modeling clay in the chamber and the dish and push it down to make a model of #1 cyl @ TDC compression. It makes it easier that the valve pockets extend to the sides on therse pistons because with pressure the soft clay extrudes any excess out the side. Trim with a knife around perimeter of piston and you are done. Note I left the clear cellophane tape around the piston to save it from nicking while trimming.

[Draker]

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.

[RetroRocket]

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.

A bit overwhelmed Draker? It's like taking a sip of water from a fire-hose, no? Best of luck but you started this thread after all, right?  cheers

[RetroRocket]

does anyone else find this image disturbing, or creepy looking?  yikes.