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Tax Return = Engine Rebuild


Pir0San

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I filled out my taxes a few days ago, and I'm getting back $360, so I decided I'm finally going to pull my engine and have it rebuilt. For anyone who hasn't read my engine story, I spun a rod bearing in my original numbers matching engine which I figured out was due to a cracked head sometime later, and the sucker was seized. I couldn't afford to get the crank fixed, so the car sat until I found a guy on ebay that was giving away a L24 block. I jumped on the deal, bought a new head, and slapped the engine together. She ran once again, but the ebay block had bad oil control rings that the PO failed to tell me about, so she burns oil like crazy. After doing some thinking, I have decided that I want to rebuild the numbers matching block, and once again have my Z as reliable as possible. I want to pull the crank and rods out of the ebay engine, put the numbers matching pistons onto the ebay rods, and piece together the original block with the crank and rods. From what I understand, this shouldn't be too much of a problem. I am going to do some machine work, which I will list below.

So, I have a plan, but I need parts. With my tax return, I plan on buying:

  • Standard piston rings
  • Main bearings
  • Rod bearings
  • Rear main oil seal
  • Timing cover gasket and front crankshaft seal
  • Head gasket
  • Oil pan gasket
  • Valve cover gasket
  • Oil pressure sensor
  • Assembly lube
  • Distributor

I also need some machine work:

  • Measurement of pistons and cylinder bore to check for need of oversize pistons/rings
  • Measurement of crank and rods to check for bearing type
  • Cylinder honing
  • Crank and rod micropolish
  • Block hot tank
  • Flywheel resurface

I also have some literature to help me with the engine rebuild, such as a trusty Haynes manual, and "How to rebuild your Nissan & Datsun OHC Engine" by Tom Monroe, which was very kindly given to me by one of the members from this forum (I forget who it was, but I do appreciate it greatly! You know who you are, speak up! :biggrin: ).

I do have a few concerns though. On the original block, one of my spark plug ceramics fell out of the plug and nicked away at the piston face. I'll get pictures of the damage, but I'm not sure if this will affect the operation of the engine at all. If it will, can the matching piston from the ebay block be used in the original block? I seem to remember reading somewhere that it's a bad idea to mix pistons between blocks. I also had water and oil mix on the ebay block before I realized the original head was cracked, but didn't drive the car once I saw it mixed, so I'm afraid the crankshaft may be scored. If so, I can have the crank machined for oversize bearings.

I feel like I'm forgetting something, so if you guys have any ideas, post them here!

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I'd replace the rod bolts. http://www.thezstore.com/page/TZS/PROD/PEM08/10-1311

If you are going to have the front cover off, I'd do the timing chain and leave the distributor till later as its an easy engine in swap. I've broken the timing cover bolts before, so having two motors will help. I bought new bolts for mine.

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It's only a bad idea to mix pistons when you use only one or two pistons from a different engine and not balance them. If you use all 6 pistons you will not have a problem. This is because the pistons are balanced to be similar to the others in the set.

You should pick your six best pistons and rods (from both engines). The crank, crankshaft pulley, flywheel, and pressure plate. Have the entire rotating assembly balanced.

Also inspect your original block to make sure that the seized bearing didn't spin in the bearing seat. Otherwise your looking at either using oversized bearings or having the block welded and allign honed.

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I've already replaced the timing chain and tensioners around 1500 miles ago, and they are still in good shape.

Rod bolts are a good idea, I think I'll look into those. Anyone have a set they want to sell? Those are a little too rich for my blood, but we'll see.

The only damage I saw due to the spun bearing was on the rod for the first piston. I'll take a look at the bearing seats tomorrow to verify, but the bearings weren't bad when I dismantled the engine.

As for the pistons: if I understand you right, it's okay to swap pistons, as long as I swap all six at the same time. So if the piston from the original block is bad, then swap all six and I'll be in good shape?

I'm going to get a new clutch and pressure plate assembly, so I should be good, right? I'll have the machine shop check out my crankshaft pulley when doing the work.

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Something else I was also concerned about was the installation of the rod and main bearings. I know you have to get certain size bearings and they have to be installed correctly, but the installation doesn't sound too complicated. If the machine shop does the measurements for the bearings, then it should be a simple task of installing them in the right places and lubing them up for the first startup, right?

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The center bearing is also a thrust bearing, so has to fit properly in the crank journal. The set I bought was a bit too thick, so I had to sand it down. Used a sanding block with wet/dry paper (400 I think), WD40, and lot's of patience. The process is described in "How to Rebuild your Nissan & Datsun OHC Engine".

BTW, you should definitely have that book if you're doing the rebuild yourself and aren't already a trained mechanic.

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I do have the book, but I'm still a bit shy on doing the lower end work. I spoke to the machine shop a while ago, and I asked if they'd be able to help me out with measurements and whatnot, and they said they'd have no problem with it. I will probably read up and see how comfortable I feel, and if not, I'll get the shop to help me.

I don't think I'll get the whole engine rebuilt for $360, but that will at least pay for all of my machine work, and I've priced out parts for around the $200 range. When I called the shop last, they quoted me $200 for all machine work I want done, so I'll have to pay some money out of pocket, but it's worth it!

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If you are going to spend all the money on the bottom end, why are you ignoring the top end (head)? The head is where the power is made, the bottom end has to take the power.

It would be a shame to do all this work and bolt on a high mileage head.

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One more thing you will have to decide on once you have the block back from the hot tank: can you get away with just honing the bores and staying with stock pistons? When I rebuilt my L28, the clearances were "ok", but more than I wanted (I forget what the actual numbers were). After speaking with a few people who rebuild engines more often than I, it came down to my intentions for the engine. If it was going to be driven moderately, then there was no need to bore to the next size and go with new pistons. That would have saved me a few hundred dollars. But I wanted to go with a bigger cam and knew that would mean high revs and hard driving. For that use, my clearances were on the high side, and I decided to bite the bullet and go oversize.

The point here, just as for almost every aspect of working on your Z, is to have a plan for what you intend to do with the car, and make your decisions based on it.

BTW, having given that great advice, my "plan" has changed quite a few times (always in the direction of more performance) and that has caused me to go back and redo things again. The result is wasted time and $$$. That's not a huge issue for me as I want to experiment and learn - and that's the price to be paid. But nonetheless, knowing where you are going is bound to save you $$$.:)

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The head I have on the car is a rebuilt one, that has less than 1000 miles on it since I bought it. It has a new cam, new valves, valve seats, valve seals, and a 3 angle valve job (might have been a 5, I don't remember).

240Zman, I appreciate the comment about the tolerances. I was going to get the machine shop to measure the clearances for me, and then let me know what exactly I should be doing in terms of parts. I've still got a little bit of time in front of me, so I'll do some more research and see what I can do. I do know that before the rod bearing spun, the engine made great power and never burned oil, so I'm hoping this is a good indication of a good block.

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Jeremy, a few more things I learned when rebuilding mine:

- When I told my shop I had plans for a bigger cam that revs to 7k and some track days, they felt that MORE tolerance between the pistons and bore was good. This was to allow for the aluminum pistons to expand and not bind.

- BUT, my shop works primarily on chevy V8s, and mostly the older ones at that for 1/4 mile racing. Apparently they prefer more tolerance than Datsun L6s.

- When I spoke with people more experienced with L6s, they felt my tolerances were a bit on the high side for my intentions, but still nothing to be too concerned about. In other words, I really didn't have to go to the next size pistons.

- In the end, as this was already my 2nd time rebuilding, I decided to spend the extra to be SURE I wasn't going to have issues, and have been very happy with the results.

What I found interesting (and a bit frustrating as well) was even though the measurements are very precise (down to 1/2 thousandth inch), the process/rules used to make decisions from those measurements was much more "gray" and imprecise. Also, the shop I used is very honest and does good work, but doesn't have experience with L6s.

In the end, it all seems to go back to classic phrase "How fast do you want to spend?".

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Thanks for the advice. I'll see what my measurements are, and compare them to those found in my haynes manual and my "How to Rebuild..." book. I hope that we're in good shape. Now I'm getting eager to work on it.

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As for the pistons: if I understand you right, it's okay to swap pistons, as long as I swap all six at the same time. So if the piston from the original block is bad, then swap all six and I'll be in good shape?

Nope, you can use a single piston from a different engine. But before you use it, it must be measured, weighed, and balanced along with the other pistons. So that all 6 pistons are the same weight and have the same dimentions.

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Nope, you can use a single piston from a different engine. But before you use it, it must be measured, weighed, and balanced along with the other pistons. So that all 6 pistons are the same weight and have the same dimentions.

Ah, okay! I get it. If I use all six pistons I'm in good shape because they are balanced as a set, but if I mix and match, I have to get them all balanced. Sounds good!

I'm working overtime these past few weeks so that I can spend more on the engine rebuild. I'm hoping for a hefty paycheck!

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