The Ratsun Rebuild a good idea?

[datzenmike]

The Z20 block and crankshaft are the exact same as the L20B so all you need is an L head, L engine brackets, L timing cover, L20B timing chain and 521 oil pan and pick up tube to make it outwardly an L20B.

[sick620]

3 hours ago, datzenmike said:

The Z20 block and crankshaft are the exact same as the L20B so all you need is an L head, L engine brackets, L timing cover, L20B timing chain and 521 oil pan and pick up tube to make it outwardly an L20B.

Ok yes I understand this, but in this orients  the 240mm flywheel is still larger than a l20b flywheel at 225mm correct? … you have worries of the 240mm flywheel fitting the l16’s 4speed bellhousing … but it should fit in that 5 speed fine? 

[datzenmike]

The flywheels are physically the same dimensions but the pressure plates are vastly different in diameters. I've heard the 240mm does not fit where the 200mm was on the 521. It might, or with some clearance grinding. It will with the 71B 5 speed, yes. You will need to shorten the 521 driveshaft approximately 5.5" and modify the transmission mount. I had an L20B in my 521 and a 5 speed would have been nice. This would be maximizing your 521 using what you have available.

 

If you want simple rebuild the L20B and put it in using the 521 oil pan. It's that simple.

[sick620]

Yeah plan is rebuild the l20b ratsun style so if I have any more questions I’ll ask em here, slap that in the 521 with its original tranny for the time being…

 

put the z20 as is in the 720 for now as a z20 and either bell housing swap the tranny or let it sit at an angle and bend a shifter for it (720 Is just going to be a old truck for hauling Craigslist finds etc don’t care much about how nice it is as long as it works) if I ever care about making the 720 nice I’ll probably convert the engine to an l series with head swap etc

[sick620]

So the z20 I got that was a known good runner was sitting outside and neither me nor my friend I got it from thought to see if any water got inside from it sitting outdoors .. it was all the way full of water two cylinders were pretty rusty engine hardly turned over… a quick light hone in one cylinder seems like rust will clean up with no pitting, but Guess we will see plan on doing full hone tomorrow… any ideas on how to get this block heater out of freeze plug hole? Tried a punch with no luck just making a hole in it… 

[sick620]

On 2/27/2022 at 9:25 AM, Stoffregen Motorsports said:

You can have the ridge power honed, but that requires the same amount of effort as having it bored and honed with new pistons. Literally, the same wait time, the same machine, everything but the new parts. Installing the rods on the pistons is another job for the machine shop, unless you have a rod vise and a piston press, which you can make easily at home. If after honing out the ridge, the bores are still within spec, you'll save a few hundred bucks by being able to re-use your pistons and not having to have the new ones installed on the rods.

 

I draw the line at the ridge in the top of the bore. A ridge can break rings.

 

So your Ratsun rebuild has just hit dead man's curve. Continue or change course?

ok so I just started honing this second block to see if it’s worth just running as is and it had a lot of rust in Two of the cylinders… running the hone down it for a minute shows pitting from the rust, the worst of which is where the ring was sitting and left pitting in a ring that you can’t quite catch a fingernail on but is obviously there and like an inch worth at the top of light pitting all around the cylinders… this is probably my second block now that must be bored in order to re use am I right?

 

first photo is good cylinders that are honing nicely, second is the worst cylinder 💩 

[datzenmike]

Buy over size Z20 pistons and make sure they are for a 720 application. Give to a machinist and have the block bored to fit. They will finish hone to the exact piston to wall clearance which is 0.001" to 0.0018". In effect you will have a brand new engine capable or hundreds of thousands of miles.

 

I've done quick hone and ring jobs and within 10k it was showing signs of oil consumption and by 20k I was back where I started. You have to figure that the engine was perfect from the factory and after 150k or more miles it's never going to be only the rings that wore out, you are never going to have a like new engine. Hone and ring is a cheap way to get another 20k for the cost of some rings and a head gasket. Back in the 70s I did my 521 for less than about $100 for rings, main and rod bearings and gaskets.    

[Stoffregen Motorsports]

Without being there to see it or measure it, I'd have to say it needs to be bored. And...when spending the money to have a block bored, go all the way for the added displacement. That would be .040" or even more if you find the right piston with the right pin height and dish/dome.

[datzenmike]

Nissan pistons come in 0.5 and 1.0 mm over sizes. A 1mm oversize is about 0.5mm removed from the cylinder wall. About 0.020".

 

The Z20 pistons appear to be 85mm bore, 31.75 pin height and 13cc dish.

 

The Z22 in the later* S110 200sx was '87 mm bore and 32.1mm pin height. The dish is unknown but the early Z22 was 9.32 so it can't be much different. This is a 2mm bore increase which is only 1mm or 0.040" removed from the walls.

 

While the Z22 piston will sit slightly above the deck it's only 0.15mm or 0.006" nothing. If you bore your Z20 block to 87mm and run these Z22 pistons you would have a 2,042 displacement engine. If the Z22 pistons are 9.32cc dish the compression would be 9.411. 

 

* January 1982 and on, S110 200sx Nissan Part number 12010-D8101 in standard bore 87mm.

If you want these they come in 1mm over size also. You can keep boring to 88mm or 1.5mm removed from the walls, about 0.060" This would increase the displacement by another 49cc. The 1mm oversize Z22 pistons are 12010-D8103.  Just sayin'.... 

 

 

 

[Stoffregen Motorsports]

Pistons can be up to .015" out of deck. I'm not sure what the deck height of the L20B/Z20 piston is, but the Z22 piston would be .013" taller, and could easily be machined to fit or left un-cut to be at or under the .015" out of deck rule.

[sick620]

On 3/11/2022 at 11:31 AM, datzenmike said:

Nissan pistons come in 0.5 and 1.0 mm over sizes. A 1mm oversize is about 0.5mm removed from the cylinder wall. About 0.020".

 

The Z20 pistons appear to be 85mm bore, 31.75 pin height and 13cc dish.

 

The Z22 in the later* S110 200sx was '87 mm bore and 32.1mm pin height. The dish is unknown but the early Z22 was 9.32 so it can't be much different. This is a 2mm bore increase which is only 1mm or 0.040" removed from the walls.

 

While the Z22 piston will sit slightly above the deck it's only 0.15mm or 0.006" nothing. If you bore your Z20 block to 87mm and run these Z22 pistons you would have a 2,042 displacement engine. If the Z22 pistons are 9.32cc dish the compression would be 9.411. 

 

* January 1982 and on, S110 200sx Nissan Part number 12010-D8101 in standard bore 87mm.

If you want these they come in 1mm over size also. You can keep boring to 88mm or 1.5mm removed from the walls, about 0.060" This would increase the displacement by another 49cc. The 1mm oversize Z22 pistons are 12010-D8103.  Just sayin'.... 

 

 

 

But these pistons would be too far out of deck correct? Would Different rods be needed? 

[datzenmike]

10 hours ago, Stoffregen Motorsports said:

Pistons can be up to .015" out of deck. I'm not sure what the deck height of the L20B/Z20 piston is, but the Z22 piston would be .013" taller, and could easily be machined to fit or left un-cut to be at or under the .015" out of deck rule.

 

Per Jason Gray you can be .3mm above the deck. More and a super high revs the rods can stretch. Unlikely though as you have 1.2mm of crushed head gasket of space available between the top of block and the bottom of the head.

 

L20B/Z20 and Z22 have 227.45mm between the center of the crankshaft and the deck. Thus 227.75mm of crank stroke + rod length + piston pin height will fit.

 

The L16 is 0.1mm above the deck. The Z22 in the 200sx is 0.15mm above the deck. There's tons of room above the piston.

 

 

[Stoffregen Motorsports]

14 hours ago, sick620 said:

But these pistons would be too far out of deck correct? Would Different rods be needed? 

Much easier and cheaper to machine pistons to fit. Machining the tops of flat top (or dished) pistons can be done in a lathe in minutes.

[datzenmike]

But they are flat enough. 0.15mm is basically nothing.

 

Or coarse sandpaper on glass for those without a lathe. But the only build using stock pistons is a rare 2.1 using VG30 pistons that need almost 3mm removed.

[Stoffregen Motorsports]

Right, I was just making the point.