Jump to content

Ptero

L28 Rebuild? Swap? Leave Alone?

Recommended Posts

I've got a spare engine which came with the Z that I purchased several years back.  The spare was an engine that was used for "racing" but there were no details on the internals or what kind of racing.  I'm looking for a project on the Z and an excuse to crack open an engine to get some hands on learning.

 

Looking for opinions on what to do. (slow day at work)

-swap it in and see how it runs

-open it up to see if it's bone stock or not

-tear it down for no reason besides putting it all back together for fun and learning

 

Side note, currently have a running L28 in the car now and have never pulled an engine apart.

Share this post


Link to post
Share on other sites

Ptero,

 

You seem to have an itch to learn about rebuilds. So..."just do it". My 2 cents is to tear the spare motor down, figure out what's what with it as far as a "racing engine" goes, and do a complete rebuild. These motors are not complicated, parts are readily available, and there are several publications to advise you along your journey...Tom Monroe's "How to Rebuild Your Nissan & Datsun OHC Engine", and Frank Honsowetz's "How to Modify Your Nissan & Datsun  OHC Engine". These publications are readily available. Also there several members here who are Canadians, eh, who can help you with hands-on help if needed. "Blue", and "Zcars" are two of several of the Canadian Zedders.

 

You say you've never done this. Short story: When I was a younger guy I had a VW beetle on which I needed to have some work done. I was introduced to a book called "How to Fix Your VW for the Complete Idiot". With that book in hand and a factory service manual I learned how to do all my maintenance even to the point of successfully, completely rebuilding my motor. I didn't know doodely about mechanical stuff then. Since then I have successfully maintained a blue-water cruising sailboat and a twin diesel powerboat. I have done all the work on my Zed with the exception of paint and seat upholstery. So, if I can do it, so can you. We here on this site can help keep your chin up when the going gets rough, all these things you contemplate have been done previously by our members here. It's not rocket science. Good luck and keep us informed as to your progress.

 

Cheers, Mike

  • Like 2

Share this post


Link to post
Share on other sites

If the engine is complete enough you could hook it up on the garage floor and start it to see how it sounds.  Might tell you something about condition.  As far as tear-down, there are different levels.  You can learn a lot just by looking at spark plugs and the cam shaft, and the crankshaft.  If things look in good shape, you might decide to leave it alone and swap it in.  

 

I like to take things apart too, but things almost always break in progress.  And, even the simple stuff will cost you substantial money.  Head gasket, head bolts, intake/exhaust gaskets, etc.  Just offering the "don't do it" view.  You might end up with a pile of parts.

Share this post


Link to post
Share on other sites

I'm on the side of "do it".  I bought that Tom Monroe book, read it about 3 times then rebuilt my 1st car motor all by myself and it turned out perfect.  One of the best feelings I've ever had, although there was a lot of anxiety and "while I'm this far why not do this...".  I could have easily done a good job for under $1,000 but I bought a new exhaust and header and a few other "while I'm this far why not do this...".

 

If you'll post some pictures you will get a lot more info/opinions.

 

Cliff

Share this post


Link to post
Share on other sites

my dad taught me some of the most important things about wrenching when i was a kid. i remember watching him work on an old automatic toaster to fix the little spring mechanism that makes the bread pop up when its done. he took it apart on the kitchen table, on the previous days newspaper and taught me that if you learn how to take something apart really carefully you can always put it back together correctly. 

  • go slowly, take your time, think as you go. it's easy to get excited and rip things apart and wind up with a dizzying pile of parts. never trust your memory - take notes, take pictures, label things, keep them in piles of associated components.
  • keep like fasteners together - in most cases they will serve the same purpose, and use an organizing system to keep track of where they came from (ziploc bags and a sharpie are perfect).
  • look carefully at wear marks where one part meets another - this will give you clues as to how the parts go back together.
  • think about what parts do - if you understand what a lock washer, compression washer, spacer, etc. does it makes it easier to know the order that these things go back on.
  • a motor seems complicated as a whole, but when you break it down into systems it gets very logical. think of charging system, electrical accessories, ignition system, fuel system, lubrication, valve train, timing, etc. and it will make sense.
  • ask questions, read up, get help when you feel that nagging doubt in your gut. when something doesn't seem right, it probably isn't. don't force parts together unless they're supposed to be, as in a press-fit component.
  • when you're done and you have an "extra" part or two, never, ever throw it away and assume it's not needed. don't ask how i know this...

the advantage you have with a spare engine is that you have no urgency since your car is currently running. if you don't rush you'll be fine.

looking forward to the build thread!

  • Like 1

Share this post


Link to post
Share on other sites

Wow, I wasn't expecting these well thought out responses.  Thanks everyone!  I'm leaning towards doing a tear down of the engine as I like learning new things.

 

I have both "How to Rebuild Your Nissan & Datsun OHC Engine", and Frank Honsowetz's "How to Modify Your Nissan & Datsun  OHC Engine".  I've flipped through them but at the time it was just theory as I wasn't working on an engine at the time.  I'll dig these out when I'm home.

 

The spare engine also has a 4 speed attached to it so I suppose I could pull the starter off my running car and do a compression test on this engine before I pull it apart.  I'd do a leak down test but I don't have the tool.

Share this post


Link to post
Share on other sites

Good thought on putting the starter on. It's about impossible to turn over by hand fast enough to do a good test . You should be able to tell somewhat the condition with a compression test. Might take note of the cam timing also.

Share this post


Link to post
Share on other sites

if that lump has been sitting for a while, be sure to pull the valve cover and pour some fresh oil over the cam & rockers to avoid damage from cranking dry...

Share this post


Link to post
Share on other sites

Took a bit of a closer look at the engine last night.  It's an L28 with an N42 head.  I managed to run a dry and wet compression test but the results were inconsistent at times.  I could test a cylinder 3 times in a row and each test would be a little higher than the last.

 

Ran a dry test twice.  Tested all cylinders and then tested them all again because I was seeing inconsistencies.

 

Cylinder #

1 - 105 dry, 120 dry, 130 wet

2 - 140 dry, 143 dry, 157 wet

3 - 122 dry, 120 dry, 145 wet

4 - 98 dry, 123 dry, 135 wet

5 - 40 dry, 60 dry, 75 wet

6 - 90 dry, 92 dry, 110 wet

 

Given the numbers I'm getting, I would say there are some issues that need to be looked at.

 

Any because everyone likes pictures...

 

IMG_3556.JPG

 

IMG_3603.JPG

 

IMG_3615.JPG

 

IMG_3613.JPG

 

IMG_3617.JPG

Share this post


Link to post
Share on other sites

you could loosen all valve lashes quick and dirty (just back off the adjusters a full turn in ). This will make sure the valves seat at maximum and break off any carbon when you do another compression test. It will give you a better idea of what is going on.

Share this post


Link to post
Share on other sites

You could have surface rust in the cylinders also, hindering sealing.  I was thinking that a spin would reveal any clanking or crunching, not really useful for a compression test on an old cold engine.  Plus that looks like newer reduction geared starter, they turn slow.  Did you prop the carbs open?  That can affect pressure readings.  Makes it harder to draw air in.

 

Also, you have a picture of the notch and groove but the damper marks aren't at zero.  And which block is it, N42 or F54?  Won't tell you for sure, but if it's F54 the PO might have left the flat-top pistons in (assuming it's an NA F54).  That would raise the CR.  

 

And, that looks like an L24 damper (multiple timing marks) with an L28 timing tab.  So the damper's not stock.  And it has a mechanical fuel pump, not stock for a US market L28.

 

You're going to take it apart anyway, I can tell.  Just a few things to think about.

Share this post


Link to post
Share on other sites

you could loosen all valve lashes quick and dirty (just back off the adjusters a full turn in ). This will make sure the valves seat at maximum and break off any carbon when you do another compression test. It will give you a better idea of what is going on.

 

I'll give that a shot and see if there is any change.

 

You could have surface rust in the cylinders also, hindering sealing.  I was thinking that a spin would reveal any clanking or crunching, not really useful for a compression test on an old cold engine.  Plus that looks like newer reduction geared starter, they turn slow.  Did you prop the carbs open?  That can affect pressure readings.  Makes it harder to draw air in.

 

Also, you have a picture of the notch and groove but the damper marks aren't at zero.  And which block is it, N42 or F54?  Won't tell you for sure, but if it's F54 the PO might have left the flat-top pistons in (assuming it's an NA F54).  That would raise the CR.  

 

And, that looks like an L24 damper (multiple timing marks) with an L28 timing tab.  So the damper's not stock.  And it has a mechanical fuel pump, not stock for a US market L28.

 

You're going to take it apart anyway, I can tell.  Just a few things to think about.

 

The intake is barely even attached so I'm pretty sure it has sufficient air but I'll double check.

 

The block is also N42.

 

Haha, yeah I'll probably take it apart but opinions and suggestions are always welcome from people who have done this all before.  Thanks for the extra info about the other parts!  I would have never known.

  • Like 1

Share this post


Link to post
Share on other sites

Amazing what adjusting the valves can do!  It seemed the clearances were way off initially.  Couldn't even fit a .006 for some of the intake lobes.  I adjusted the valves to .010 for intake and .012 for exhaust.  Yes, I know those are what they're supposed to be hot but, I was trying to loosen them as Blue suggested.

 

Here are the new numbers after the valve adjustment:

 

1 - 146

2 - 165

3 - 157

4 - 147

5 - 132

6 - 137

 

Things are looking a lot more even than when I first started but, still not ideal.

  • Like 1

Share this post


Link to post
Share on other sites

I don't think that you'll get good pressure numbers from an engine that's been sitting, turning it with that gear reduction starter. 

 

 

Some other things you might examine are the backs of the valves, for carbon deposits, and the tops of the pistons, what you can see through the plug holes.  If they're all crusty and caked, the engine has some miles on it, if they're shiny and look good, maybe somebody just put it back together and ran it for a few miles.

 

Look at the chain guides from the top, see how much plastic is left.  High mile engines will wear the guides down.  Check the notch and groove for alignment and hole number, that will give an idea of chain wear.  The valve train area looks pretty clean, no signs of sludge.  That's a sign.

Share this post


Link to post
Share on other sites

Valves & pistons look pretty dirty but I'm not sure what's a normal amount of carbon build up.  Whatever was on the pistons was pretty soft so I'm wondering if that would just burn off or get blown out once it was started.

 

IMG_3679.JPG

 

IMG_3681.JPG

 

Pics are not great but I was just using what I had kicking around.  First piston picture is the cleanest one and the 2nd pic is what most of the others look like.

 

IMG_3672.JPG

 

IMG_3673.JPG

 

 

What's normal wear on the timing chain guides?

 

IMG_3688.JPG

 

IMG_3689.JPG

 

 

Can't see that well from this picture but the notch is slightly to the left of the marking on the cam when at TDC.  About half of the notch was to the left of the marking.  I don't fully understand these numbers and markings yet.

 

IMG_3695.JPG

 

This is where the timing marks are on the damper but which notch is the one that is supposed to be used?

 

IMG_3698.JPG

 

 

I'm starting to think I might toss this engine in the car to see how it runs and end up rebuilding my other engine that's in the car right now.  It's been leaking oil from a number of places for a while and could use some refreshing.

Share this post


Link to post
Share on other sites

Your chain guides actually look in really good shape.  The used ones I've seen all have grooves worn in them from the links rubbing.  

 

The damper pulley looks like a problem.  I don't know if Nissan put zero at the same spot on both styles or started from scratch with each design.  I think that you could get a 240Z pointer and be right, assuming the damper is in good shape.  But it's always good to confirm the TDC mark is correct.

Share this post


Link to post
Share on other sites

The engine was at TDC for both the damper & cam marker pics.  I'll grab the 240z marker from my other engine to see where it lines up here.  Or would this mean that the 2nd notch from the right is the correct one as the engine is at TDC in that photo?

Edited by Ptero

Share this post


Link to post
Share on other sites

How do you know it was at TDC?  The piston barely moves up or down over a pretty wide range of crankshaft rotation.

 

Just saying, that's why they use "dead center" to describe it.  It's a very specific location.

Edited by Zed Head

Share this post


Link to post
Share on other sites

How do you know it was at TDC?  The piston barely moves up or down over a pretty wide range of crankshaft rotation.

 

Just saying, that's why they use "dead center" to describe it.  It's a very specific location.

 

I put a pencil in #1 spark plug hole and slowly moved the crank until the pencil didn't move up any further.  Super scientific!  I know!

Share this post


Link to post
Share on other sites
The biggest notch at the far left is 0 on the 240 damper, then 5 degrees for each smaller notch moving up clockwise.  It looks about right compared to mine but like Zed said there is a "perfect spot" for TDC.  I'm thinking with the keyway on the crank it would put any damper at the same position, a 240 or a 280 damper.

The white spot in this picture is past TDC, my timing chain was advanced a tooth or two from the previous owner.  Caused me a big ole headache, never could get the timing adjusted right.  Now I'm rebuilding it.

 post-23570-0-32350000-1420908714_thumb.j
Edited by siteunseen

Share this post


Link to post
Share on other sites

I'm gonna try this method later to get a more precise TDC.  

 

"Now pull the oil dip stick out and put it in the # 1 spark plug hole. Put a 27 mm socket on the crankshaft damper pulley bolt and turn the engine clockwise with a ratchet until the dip stick just starts to go down. Put a chalk mark on the damper pulley where 0 TDC pointer is.

Now turn the crank the other direction (counter-clockwise) until the dip stick starts to go down again. Mark the damper pulley one more time. Exactly half way between the two chalk marks is true TDC."

Share this post


Link to post
Share on other sites

I used a drinking straw cut in half.  I think a dipstick would be too long and fall out.  Maybe a short screwdriver but metal on top of the piston getting bound up would suck.  But I'm a little too cautious, it causes me to drink a lot.  :D

  • Like 1

Share this post


Link to post
Share on other sites

haha, yeah I wasn't actually planning on using the dipstick either.  It's just a comment I found elsewhere but I liked the idea of finding TDC using that method.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

  • Who's Online   7 Members, 1 Anonymous, 43 Guests (See full list)

  • Search Engine Meta Tags:
    classic, z, datsun, 240z, 260z, 280z, zcar, zed, s30, classiczcars.com, 240z.org, fairlady, 240, 260, 280, nissan, 240 z, 260 z, 280 z, zx, turbo, classic z, 280z cars, cars 240z, car forums, datsun, nissan, cars datsun, car club, 280zx, car, nissan zcar, classic z car,performance,300zx, car years, car raced, texas 350z, 300z, 350z, nissan racing , clubs car, zcca, club datsun
×

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.