Draker Posted February 18, 2023 Report Share Posted February 18, 2023 I’ve dropped an L20b at the machine shop to find out what needs done. I know at a minimum it’ll need pistons due to a ring ridge at the top of all cylinders. I’m guessing 40 over? The problem is the machine shop is unable to locate replacements. I’ve done some digging (Jason grey post) and found some potential options from an L28 at 86mm. Maybe something from a z20. My problem is really sourcing the pistons.. seems like everything has dried up, including rock auto. eBay is looking promising, but quality seems like a big question mark?? The goal for this motor is to just be reliable. minor performance gains are appreciated, but not looking for a high compression build. More displacement is good, slightly higher compression is also fine. Not looking to be a race fuel build. any recommendations, or parts sources? Quote Link to comment
datzenmike Posted February 18, 2023 Report Share Posted February 18, 2023 40 over is 1mm or 86mm or same as the L28 pistons. You could use used L28 if in good shape. L28 from the 280z and '79 and '80 280zx were almost the same dish as the L20B. '81-'83 280zx were flattop. On an over bored L20B that's 10.11 compression Z20 pistons are the wrong pin height. Too short. There are 2 Z20 pistons the least worse would produce a 7.8 compression and worse if dished. However.... Z20E 1mm over size and Z20E rods would work perfectly and produce just over 10 compression. 1 Quote Link to comment
Draker Posted February 18, 2023 Author Report Share Posted February 18, 2023 Thanks Mike! yeah, I know with the z pistons I’d also need the rods. I guess I could try to source used l28 pistons. Always a bit of a gamble though. Quote Link to comment
Danalive Posted February 19, 2023 Report Share Posted February 19, 2023 i was going to ask the same question as im rebuilding my l20b. rock auto have these https://www.rockauto.com/en/moreinfo.php?pk=4811769&cc=1209338&pt=14008&jsn=605 listed for a 81 280zx, they're dished like the l20b pistons not flat tops, does anyone know if these would work? Quote Link to comment
datzenmike Posted February 19, 2023 Report Share Posted February 19, 2023 Those with the dish might be for the turbo 280zx. I think the regular zx L28 are flattop. The dished ones would be closer to the L20B piston. All 4 and 6 cylinder L series have the same distance from the center of the piston pin to the top of the piston. All you need is the correct bore diameter to match your L20B. Standard L20B bore is 85mm so if going over size get 1mm larger (86mm) L20B or standard L28 six cylinder pistons also 86mm. I suppose you could even go to 1mm over size L28 (87mm) if you want. Yes over size often come in smaller 0.5mm (85.5mm) but if having the block machined might as well go to the max. Quote Link to comment
Stoffregen Motorsports Posted February 19, 2023 Report Share Posted February 19, 2023 Really, the machine shop couldn't find pistons? Wow! Quote Link to comment
Draker Posted February 19, 2023 Author Report Share Posted February 19, 2023 2 hours ago, Stoffregen Motorsports said: Really, the machine shop couldn't find pistons? Wow! Yeah.. and I’m struggling as well. Looks like the either they are no longer being made or it’s a supply chain issue. 1 Quote Link to comment
toylet Posted February 19, 2023 Report Share Posted February 19, 2023 Dont make this harder then it needs to be...made in Japan https://www.ebay.com/itm/284365641332?hash=item4235835674:g:D3kAAOSwRrBg6GQF&amdata=enc%3AAQAHAAAA4F9Wc5PuPikUdWeoLHn8lHf9%2FUvxxzxUAKRJzaLvFwRuDDOErlVMe15i5Wg8v67xHCNXo2BouAd5eojzrnY8XhdJ2nYHLHyOVA9%2BEYHrc8rfkNRhvYGSghBQLQok3W9ZDj4Vc8OpGkG5xetzyp%2FWlN1wNIPO%2BM4NjiucsFCQY1z6NJnQZJQCaJ9UyZ4xESIqgb4o9lxBav8BMNtkzVG9fvmFipX2a15iQ2%2BWcimEWWcDpH0wqKheqVRPi0G46PfOVv82aroY3j5saHIHEiaK4vgvtLuztfk2o45ugMYXxnEd|tkp%3ABFBMxpD7s81h 1 Quote Link to comment
toylet Posted February 19, 2023 Report Share Posted February 19, 2023 https://www.ebay.com/itm/313742099982?fits=Make%3ADatsun&hash=item490c7c860e:g:9N0AAOSwmc9geKFg 1 Quote Link to comment
toylet Posted February 19, 2023 Report Share Posted February 19, 2023 https://www.ebay.com/itm/353198979508?fits=Make%3ADatsun&hash=item523c4cb9b4:g:KiQAAOSwBslgeQUl 1 Quote Link to comment
toylet Posted February 19, 2023 Report Share Posted February 19, 2023 3 Different sizes..pick your poison 1 Quote Link to comment
datzenmike Posted February 19, 2023 Report Share Posted February 19, 2023 4 hours ago, Stoffregen Motorsports said: Really, the machine shop couldn't find pistons? Wow! 2 hours ago, Draker said: Yeah.. and I’m struggling as well. Looks like the either they are no longer being made or it’s a supply chain issue. Maybe it's the machine shop. 1 Quote Link to comment
Draker Posted February 20, 2023 Author Report Share Posted February 20, 2023 On 2/18/2023 at 10:08 AM, Draker said: ebay is looking promising, but quality seems like a big question mark?? 6 hours ago, toylet said: Dont make this harder then it needs to be...made in Japan Yep Quote Link to comment
Draker Posted February 20, 2023 Author Report Share Posted February 20, 2023 5 hours ago, datzenmike said: Maybe it's the machine shop. Anything’s possible. If rockauto is out of stock, most places are out. eBay is probably the best bet. Quote Link to comment
SWFL Posted February 20, 2023 Report Share Posted February 20, 2023 A competent machine shop can press in new cylinder liners to get back to the standard bore size. Quote Link to comment
Stoffregen Motorsports Posted February 20, 2023 Report Share Posted February 20, 2023 20 hours ago, toylet said: Dont make this harder then it needs to be...made in Japan https://www.ebay.com/itm/284365641332?hash=item4235835674:g:D3kAAOSwRrBg6GQF&amdata=enc%3AAQAHAAAA4F9Wc5PuPikUdWeoLHn8lHf9%2FUvxxzxUAKRJzaLvFwRuDDOErlVMe15i5Wg8v67xHCNXo2BouAd5eojzrnY8XhdJ2nYHLHyOVA9%2BEYHrc8rfkNRhvYGSghBQLQok3W9ZDj4Vc8OpGkG5xetzyp%2FWlN1wNIPO%2BM4NjiucsFCQY1z6NJnQZJQCaJ9UyZ4xESIqgb4o9lxBav8BMNtkzVG9fvmFipX2a15iQ2%2BWcimEWWcDpH0wqKheqVRPi0G46PfOVv82aroY3j5saHIHEiaK4vgvtLuztfk2o45ugMYXxnEd|tkp%3ABFBMxpD7s81h Those are Lazorlite too. Not a bad name brand. Quote Link to comment
Draker Posted February 20, 2023 Author Report Share Posted February 20, 2023 53 minutes ago, Stoffregen Motorsports said: Those are Lazorlite too. Not a bad name brand. Good to know. I've never heard of it, but this is the feedback I'm looking for. Thank you! 1 Quote Link to comment
RetroRocket Posted February 24, 2023 Report Share Posted February 24, 2023 Draker, I use L18 pistons 85 mm dia. 4.36 cc dish, same pin ht, bore diameter and configuration as your L20B pistons (11.36 cc dish); but with 7 cc less dish volume. Your choice over overbore diameters. Raises the compression ratio in an amount in accordance with which head you use. Crunch the numbers and you'll see what I am talking about. I built this configuration in my RWD 721 about 15 yrs ago. SU's, header with L20B stock cam. It ran strong as my utility/daily run-around truck. It would haul a bed-full of dirt without trying. I had tuned the SU needles using my drill press and fine sandpaper to configure the mixture control. It was a painstaking process and I used various tensions of damper springs and fluids to get the throttle response and mixture optimal for the rpm I needed to use the engine at. I got it pretty close. But that would have been a lot easier if wide-band O2 sensors had been readily available back then. One of my kids totaled the truck and I sold it as-is. The intake manifold was broken and one of the SU's was hanging there. The engine block/head were probably still salvageable. That engine may still be running in something up here in WA. The L18 SSS pistons were flat top 85 mm with valve pockets iirc. But with the longer stroke (86 v. 78) of the L20B the flat top c.r. would be too high for the street. But the stock configuration L18 US engines had a mild dish and are useful in a street L20B engine. I'm working on a completely different approach with piston head shape/closed combustion chamber head configuration for L4 and L6 engine builds. It will be a while before I put it together but it has potential. Best of luck. 2 Quote Link to comment
datzenmike Posted February 24, 2023 Report Share Posted February 24, 2023 I thought L18 piston sources dried up. 2 Quote Link to comment
Draker Posted February 24, 2023 Author Report Share Posted February 24, 2023 56 minutes ago, RetroRocket said: Draker, I use L18 pistons 85 mm dia. 4.36 cc dish, same pin ht, bore diameter and configuration as your L20B pistons (11.36 cc dish); but with 7 cc less dish volume. Your choice over overbore diameters. Raises the compression ratio in an amount in accordance with which head you use. Crunch the numbers and you'll see what I am talking about. I built this configuration in my RWD 721 about 15 yrs ago. SU's, header with L20B stock cam. It ran strong as my utility/daily run-around truck. It would haul a bed-full of dirt without trying. I had tuned the SU needles using my drill press and fine sandpaper to configure the mixture control. It was a painstaking process and I used various tensions of damper springs and fluids to get the throttle response and mixture optimal for the rpm I needed to use the engine at. I got it pretty close. But that would have been a lot easier if wide-band O2 sensors had been readily available back then. One of my kids totaled the truck and I sold it as-is. The intake manifold was broken and one of the SU's was hanging there. The engine block/head were probably still salvageable. That engine may still be running in something up here in WA. The L18 SSS pistons were flat top 85 mm with valve pockets iirc. But with the longer stroke (86 v. 78) of the L20B the flat top c.r. would be too high for the street. But the stock configuration L18 US engines had a mild dish and are useful in a street L20B engine. I'm working on a completely different approach with piston head shape/closed combustion chamber head configuration for L4 and L6 engine builds. It will be a while before I put it together but it has potential. Best of luck. yeah I would consider going this route but l18 pistons are hard to come by these days. They’re a good option! 2 Quote Link to comment
sick620 Posted February 24, 2023 Report Share Posted February 24, 2023 rock auto has l28 pistons in standard or oversize variety in stock, 1 Quote Link to comment
datzenmike Posted February 24, 2023 Report Share Posted February 24, 2023 Dished and flattop? Also need 1mm over bore on an L20B Quote Link to comment
sick620 Posted February 24, 2023 Report Share Posted February 24, 2023 just dished. Flat tops getting very hard to find. They have 40 over dished ones currently in stock. That's 1mm over Quote Link to comment
john510 Posted February 25, 2023 Report Share Posted February 25, 2023 22 hours ago, datzenmike said: I thought L18 piston sources dried up. They did.I think I got the last set there was a few years back.86 mm for my L20b. Quote Link to comment
datzenmike Posted February 25, 2023 Report Share Posted February 25, 2023 Standard L28 are 1mm over size for an L20B bore so 2mm for an over size L28 piston. Still if going over, go all the way. Quote Link to comment
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