How to rebuild your motor through misdiagnosis and head scratching

[rockdog]

Rebuild.......no question.......your going to spend money on a different truck anyway.......and then throw money at it anyway. Like I said I bought my truck and put another 6 or 7 hundred dollars in it....

[rockdog]

Well...... rebuild or good used to swap hole engine.........you do have a nice new shiny carb to put on it....

[xsdg]

Maybe the carb problem dumped fuel into the cylinders, which got pushed past the rings and ended up diluting the oil?

 

I forget if your truck is a RWD or 4WD.  If RWD, I would pull the oil pan and look for heat discoloration.  It should be pretty straightforward, and you'll either find a smoking gun, or you should keep digging.  The bottom end is simple enough that "not rotating" should have a simple and obvious cause.

 

I don't know what your monetary situation is like.  If two vehicles is an option, at least temporarily, that's what I'd do.  Keeping this truck would be nice since you know what works (and what doesn't), and once everything is good enough again, you'll know what's been done to it.

 

If that's not an option, I'd probably start looking for something that runs and is in better shape than the current one.  Simultaneously, try to unload this one while you keep spending a little time figuring out what happened.

 

Since you're this far in, if it were me, I'd keep going at least until I had a definitive diagnosis about what's wrong.  e.g., you pull the oil pan cover, and things start turning again once you loosen the bolts on one of the rod bearing caps.

[xsdg]

One thing I was thinking: it's possible that even if you have some heat damage, you might be able to get it running again with some shade-tree mechanic work.  If so, that's the business.  That'll get you going, and even if you end up replacing the thing, the more time you have to scour CL, the less you're going to end up spending on a replacement.

 

This is the kind of thing that comes to mind:

[ggzilla]

Let's see...

 

* engine turns over when head is off

* does not turn over when head is on

 

Is that right? A new lower end won't fix that.

[ggzilla]

Ok, my Weber 32/36 is here, and mounted. I was wondering if anyone had a picture of their conversion, especially the throttle cable set-up on a 720 with an L20 (an Automatic would be even better). I think I have it figured, but I would love to see a working solution before I go wrong.

Get the throttle cable bracket from Weber. Then unbolt the throttle quadrant from the Hitachi and bolt it to the Weber.

[ggzilla]

what does everyone do with their EGR ports on the manifold? I saw a thread here, on a 510, where the guy basically cut off all the not needed pieces and sealed the holes, but I am thinking a plate is more proper. I built one out of some sheet metal, as the one from Weber, was for some other vehicle...I plan on having a machinist pal let me build a better one.

Most of use leave it alone. The EGR valve plugs the hole perfect and if the hose is not connected it will have no effect on the engine.

 

If the valve is removed, most guys remove the whole EGR plate, and hand-make a cover out of 1/4" aluminum.

[xsdg]

ggzilla: no, _head_ turns over when head is off.

 

"OK, head, as I said, is clean and clear.  Turns when not attached to the motor, and does what it is supposed to do.  I reattached it and tried to spin the motor again.  no go, not at all, not foreword, not backward, no movement."

[bananahamuck]

It is automagic yes? Sometimes the torque converter bolts in flexplate come loose and wedge themselves into ,,, well what ever ..  It should have plate between engine and trans at bottom jack her up and whip that off and shine a flashlight up in there.,, you never know.

[supererogator]

Head turns when not on the motor. Lower end doesn't turn at all. Other than the gas diluted oil, oil was clear when I drained the oil. I suspect either the year old oil pump diaphragm gave up or the carb issues dumped gas in the oil. This thinned it and now I have a seized bearing on the crank shaft. Rebuild/rebuilt short block is the fix.

I am trying to decide wether I keep this and get a driver, or sell this, whole or in parts, and get a driver. Honestly, I have a much better investment putting my 65 Mustang together than this. Both need tons of work. Either way, I am looking at a car loan for a reliable driver. With luck, I can consolidate some debt and get a roof on my home too.

[ggzilla]

More mis-diagnosis. Incomplete diagnosis.

[supererogator]

Just an update...I am about to buy a newer truck. I have my eye on a '95 XE with 104k on it. Anyone know about a factory purple?

 

I have also set the 720 on the back burner and have not decided if I am going to rebuild it or offer it to you fine folks, probably in pieces. Anyone really pining for a part? That might help my decision to sway.

[supererogator]

So, update. After working through my anger and disappointment, mostly at myself, I reassembled her top end today. Weather dependent, I plan on checking for the mystery bolt from the trany plate, as suggested above. Anything else my refreshed eyes should check to tell me why my short block is frozen both ways? I am heading for my oil pan next to look at the crankshaft and bearings.

[supererogator]

Well, I found a tiny amount of brass filings in the oil pan. Not enough to worry me much. Everything else looks to be correct, no noticeable damage to cylinders, pistons, or anything else I can see. All piston arms have a tiny bit of play on the crank, and move freely on the crank, back and forth, obviously not around and around or I wouldn't be here.  Oh, and the torque converter bolts are all four where they should be.  The teeth look a bit worn, but after 200k I figure they should be and the starter engages fine.

I really don't know what to diagnose/do next. I could pull the motor, but if I can fix the issue without doing that (not to mention the price of an engine stand and other things I do not have) I would be happier. Any other options you fine folks can recommend?

[wayno]

You don't want to see any brass in the oilpan, filings means something got or is being chewed up.

[supererogator]

My guess would be bearings, as they are the only things I know of down there that are brass.  Alas, it is only a guess.  How do I know?  Is there a way to tell without pulling the crankshaft and looking at the bearings, or is this a replace it and if it works, you solved it kind of thing?  This is farther than I have been in a motor, much less alone.

[banzai510(hainz)]

a guy told me at work his oil pump distr drive fell out and jammed on the crank. bnut this was a Pontiac motor(Pontiac= Poor old nergro thinks its a Cadillac)

[datzenmike]

-basic carb checks.  Secondary (lower) choke seems to not open correctly, as I can manually open it and revs up correctly, when I do not manually operate it, it revs 1/4 throttle and then any more throttle and it looses acts flooded and dies.  Both jets shoot clean, clear, and visible fuel.

Choke not working on old carb. Not opening, maybe the choke heater wire not connected. Explains the high idle and not being able to adjust the idle speed or mixture, explains the carboned head and low compression from washing the oil off the cylinder walls, also the gas thinned oil.

 

Ignition timing can't be set with the engine revved to 2-3K, has to be down around 750. And set to 12 degrees. Assume the weber idles properly now???????

 

AN valve connect and disconnect and plug the small vacuum signal hose from the intake to it.

 

EGR eave alone.... you could pull the small hose off it that goes to the carb/dizzy advance and plug.

 

 

If all rods have some movement move on to the main bearings. You can unbolt them and pop the bottom caps off one at a time and inspect them. Have a torque wrench to tighten them properly. If they are oily and 'loose' them something happened to the timing chain/guides/tensioner you changed.

 

 

You never said what was done to the transmission to fix it. Low on fluid???

[supererogator]

Yup, it was low on fluid (the tranny). Yes, once the Webber was on, it idled correctly.  Soon after, it froze all together.  I will pull the caps off the bearings and reset if they are fine.  I looked closely at the chain, tensioner, and guides.  All seem to be fine.  I checked when I had the head off, and again today, looking both down through the head and up from the bottom.  I am thinking the bearings, especially since I found the brass bits.

Thanks for the suggestions.

Can I change the bearings with the motor in the truck?  I have never known anyone who has, but they were all deep into a full rebuild/resto anyway.

[xsdg]

supererogator: nice to see you back

 

If you're looking for bearing problems in the bottom end, the first think you should do is get a bright flashlight and look for discoloration, which will be a signal of excess heat.  You've got four cylinders, and the parts on each of them should look the same.  If anything is noticeably darker than the other three, that's a definite place to investigate.

It's difficult to see here (and this is an extreme case), but if you look in the block, you can see how the #4 and #3 rod bearing caps are a tan color.  #2 rod bearing cap was removed, and the journal is bright and shiny.  Again, difficult to see, but the #1 rod bearing journal is pitch black.  Our oil pickup got blocked while on the race track, so we had severe oil starvation at high RPMs.  "Oops":

(from http://blog.doppler-photo.net/2012/04/can-you-hear-me-now.html)

 

That said, banzai510 has a point.  The crank only has so many points of contact with things that could keep it from spinning:
1) rod bearings
2) main bearings

3) Tranny / torque converter

4) Dizzy

5) Oil pump

Given that you saw brass shavings, that definitely implicates the plain bearings, #1 and #2 in the list.  datzenmike already told you how to check those.

It is far from ideal, but definitely possible to replace the bearings in the vehicle.  That said if there was enough heat building to damage the crank (warp the journals or something like that), then you're boned.  Here are two videos of in-vehicle bearing replacements:
https://www.youtube.com/watch?v=yPzaspB-bBc (Note: tons of profanity :o)

https://www.youtube.com/watch?v=-3qLhx4dh5U (note that he says in the comments that the crank was damaged, so he didn't actually finish)

[supererogator]

One question. I do not know enough to know what "journals" are.

 

Other than that, this sounds like an, "invest in an engine stand, you dumby" kind of thing. Not what I wanted, but I am this far in, right?

 

Thanks folks. Back at it.

[xsdg]

Wikipedia's got ya covered
http://en.wikipedia.org/wiki/Plain_bearing

 

But basically, it's the polished part of the crank where the bearing sits.

[datzenmike]

If it was idling when it seized it might be ok. It just gets tight and stalls. The rods get their oil through holes drilled in the crankshaft. The crankshaft gets oil from two block passages that line up with holes in the main bearings.  If the rod bearings were loose then they were getting oil, presumably. This leaves the very front, rear and the center main bearings which are fed oil from the block and don't pass it on to any rods. If a main is seized it's again, presumably, one of these three. Of these three the center one is the front to rear thrust bearing and holds and supports the crank from lateral movement when the clutch is depressed. When you see the thrust bearing you'll see why it and most likely source of the metal filings.

[supererogator]

So I went on a research mission.  Not under the truck, so I have not confirmed that it is the main crankshaft bearings yet.  From your words, it sounds like a very strong possibility.  I figured I should find out what they are going to cost me.  My normal parts store has no part number.  I put in a call to the local Nissan dealership, but it IS Sunday.  I left  message.  I did a few different google searches, to minimal avail.  I did find some, but I had to purchase a minimum of 100 of them… Where do I look to learn what I am going to need to pay?  How do I decide what ones are best?  It looks like I need to invest in a micrometer so I can find out if I need something oversized, need to have parts ground, etc.  WHat else should I know IF I decide to tackle this?

Edit:  Found this: http://www.ebay.com/itm/NISSAN-2-0-2-2-L20B-Z20-Z24-MAIN-BEARINGS-7139M-50MM-/310381431854

 Will this do the trick, IF the mains are the issue?

[datzenmike]

Yes, all 6 bolt flywheel cranks take the same mains. If the crank needs to be ground down to the next oversize bearing it will likely not be shiny smooth but dull and worn looking.