Hondanx250 Posted April 7, 2015 Report Share Posted April 7, 2015 Hey Guys, I have made a few post on this engine. Its a Napz Z20s Engine block. Alright, So i ran into a Dilemma with a broken bolt. But Had a Welding shop Get it out and re-tap it. So i kinda been put off on building it back up. Well anyways. This is my First Engine Rebuild and I am a Newbie at it. I want to do it right the first time. So here are my questions. I want to get the Freeze plugs, Cylinders Bored and Hot Tanked. 2 of the 3 i know you can do at home. But I have never done it before. My Friend was telling me just take a pressure washer to the block. But i don't want it to instantly rust. He was also telling me i didn't need to change the freeze plugs. But i said why not? I already have them and the engine already taken apart. I want a Fresh new engine when i am done. The cylinders have some Deep Scratching from what i was told broken rings. (Pictures Attached) Should i have the Machine Shop do the work? On Replacing the Freeze Plugs, Hot Tanking it and boreing it(to size needed)? Also, On Timing the Engine, How do you go about doing that? Setting the timing chain? So the Valves open and close are the right time? I forgot to mark the chain when i took it apart. Also one of my connecting rods is shorter then the others. Not sure if i should be to worried about that? because it was running fine before i took it out? Or try to find one? Open to All Information and Advice, Criticism... Whatever you want to toss at me. Not sure what this was? But its broken in half. Quote Link to comment
ggzilla Posted April 7, 2015 Report Share Posted April 7, 2015 You won't have a new engine. It'll be a good rebuilt engine. No need to hot tank it. That is for engines which have been left out in the rain. Yes, replace the core plugs. Yes, replace the Rod that differs. One short rod may run fine, but will lower the HP output. Quote Link to comment
datzenmike Posted April 8, 2015 Report Share Posted April 8, 2015 Yes, replace the core plugs. Finally someone who knows they are core plugs... for removing the casting sand after casting the block. Yes they may pop out if you are stupid enough to let your block freeze. The term 'freeze plug' assumes this is to protect the block from cracking if it freezes... it isn't and it does not! You can replace them or not. As you have them you might as well. Several cylinders are badly scored. Decide on an over size like 0.5mm or 1.0mm (to be safe go 1mm) and buy new pistons. Have the machinist bore the block to match the new pistons. Buy new chrome rings to match the over size pistons. Chrome work best in brand new perfectly milled and honed bores so take advantage of their long life properties. If one rod is wrong, then this has been apart for a hillbilly rebuild before and probably why the rings broke and scored the cylinders. Z20 rods should be 152.5mm center to center so find one. The Nissan part number is 12100-N8500 about $100 if still available or use number to cross reference another source. Better to try a wrecking yard. '80-'81 A10 HL510 or '83-'86 Mileage option 720 trucks have them. The broken thing on the block is likely the oil jet for lubing the chain. Part number 13081-21000 about $2 get one! This is a sign the timing chain or guides are loose or worn out. Chain slap probably sheared the oil jet off. Get a timing chain kit with new chain, new guides and new chain tensioner. Do it! Quote Link to comment
Stoffregen Motorsports Posted April 8, 2015 Report Share Posted April 8, 2015 If you're replacing one rod you will need to balance the whole set. This requires the pistons to be removed, but then you probably need pistons anyway if one of them had a shorter rod. Quote Link to comment
Doctor510 Posted April 8, 2015 Report Share Posted April 8, 2015 I have a set if you need them, i'm in Arizona Quote Link to comment
datzenmike Posted April 9, 2015 Report Share Posted April 9, 2015 A shorter rod worked and it must have been way way lighter. They are close enough from the factory. Won't hurt though. Quote Link to comment
Hondanx250 Posted April 9, 2015 Author Report Share Posted April 9, 2015 I ordered a New Connecting Rod. But they Discounted the Oil Jet. Quote Link to comment
datzenmike Posted April 9, 2015 Report Share Posted April 9, 2015 It will work without it. I imagine the hole is quite large? Only needs to be the size of a large needle. Quote Link to comment
Hondanx250 Posted April 9, 2015 Author Report Share Posted April 9, 2015 I can try another place or check rock auto. Should i have them bore to the size first and then order the pistons? Quote Link to comment
datzenmike Posted April 9, 2015 Report Share Posted April 9, 2015 Preferably get the pistons first. No two pistons are exactly the same diameter. The machinist can measure them and bore accordingly to get the correct clearance. 1 Quote Link to comment
Stoffregen Motorsports Posted April 9, 2015 Report Share Posted April 9, 2015 A shorter rod worked and it must have been way way lighter. They are close enough from the factory. Won't hurt though. Is that what we're striving for here? If he just wants the engine to work, put it back together with the short rod. If it's a mismatched set, I would balance them. I have seen them off quite a bit between sets. Enough to notice. Quote Link to comment
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