How to rebuild your motor through misdiagnosis and head scratching

[banzai510(hainz)]

since your car runs at full trottle I bet the main jet is plugged.

I lay money on if you can get it running enough block the main side of carb with your hand so all the air goes thru the vacuum 2ndarys. then put you finger to open the vaccum plate I bet you can control it better. this will show its a carb proplem.

 

Unfortunalty people rebuild things all at once and introduce a proplem . always change things one at a time time and use the orginal stuff first when rebuilding a motor then upgrade later as to know your part you get are good.

 

your motor is fine im 98% sure

[supererogator]

So, there is a link to all the pictures I took during the carb rebuild. https://www.flickr.com/photos/33594589@N08/sets/72157644250173282/

 

 

  To be clear, this is a hitachi DHC340-113.  Stock on my '80 720.  I followed similar directions to what were given in this post ( http://community.ratsun.net/topic/33847-diy-hitachi-carb-rebuild-pic-heavy/ )

Hopefully this will help others see what *I* saw.

[banzai510(hainz)]

So is it fixed?

I could never rebuild a stock carb myself.

[supererogator]

There is a compound gremlin in there. I have a few more things to fiddle with and a stripped hole in the timing chain cover to repair. So, kind of, but not on the road again yet.

 

Thanks for all your help.

[xsdg]

Holy smokes, that thing was nasty.  Did you make sure to hit all the holes and ports with carb cleaner and compressed air during the rebuild?
  When I rebuild mine (6-wire carb for a Z24, but it looks like the design is really similar), I did a general cleaning with Simple Green in an ultrasonic cleaner, but then extra tarnished fuel came out when I sprayed carb cleaner through all the little ports and passageways.  It also showed me that all the different passageways were free and clear.

[supererogator]

Chem-dip and an air compressor.  We cleaned the thing.  And, yup, in my breakfast nook.  No wife, no problem.

[hang_510]

No wife, no problem.

simple. like a datsun.

[supererogator]

Ok folks....I am at my wit's end here.  Six weeks since my freeway breakdown, and I am still not running. New timing chain (and kit), rebuilt carb, new coil and plugs, fuel filter is less than 3 months old and clear, carb jets show fuel going through, choke opens and closes correctly, vac lines are solid, timing is close enough to run...I am just stuck.  Three days ago, she started up pretty well revved and idled on her own.  Today I cannot get her to start at all, not even a sputter.  I have done NOTHING other than re-instal the radiator and fan shroud, put gas in her, and remove some of the long ago disabled AC unit.  Nothing I touched has anything to do with running.

I am about to take her to a mechanic, which in my family is near a sin.  But I am blinded by this issue and do not know where else to go.  Seriously, ran three days ago, and not now.  I did put gas in her, as she was out, the carb shows gas in the window at the dot, there is spark at the plugs, the plugs smell of gas, ignition is on...it has GOT to be something simple that I am missing.

Color me frustrated.  If you have any ideas, I am glad to hear them.  If not, then, thanks for letting me vent to understanding folks.

[datzenmike]

How are you checking for spark??? Because there appears to be gas and the only other thing needed to run an engine is spark.

[izzo]

suck bang blow (bang includes compression)  Gotta time it juuuuuuus right to make the magic happens.

[ggzilla]

If you have any ideas, I am glad to hear them.

Perform a Basic Spark Test

 

1. Disconnect a spark plug wire and position the terminal within 1/4 inch of bare metal. For example a nut on the strut tower. Stick a screwdriver in it as an extension to the terminal.

 

2. Have an assistant turn the key to START and crank the engine a few seconds

 

3. Check that the spark, if any, jumps the gap to the metal.

 

Is there is no spark?

 

Is the spark is weak or yellow?

 

Is the spark big, fat, and blue?

[datzenmike]

suck bang blow (bang includes compression)  Gotta time it juuuuuuus right to make the magic happens.

 

Well he said it runs fine when it runs so I assume the compression is working, timing close. Oh, hey Tim.

[supererogator]

Spark checks. From coil to ground and from plug to ground. Motor is timed to TDC As/per spec. Not runnig, so I cannot get 12 below...but it should run at 0. Compression is better than 100 on all cylinders. Any other ideas?

[supererogator]

Spark checks. From coil to ground and from plug to ground. Motor is timed to TDC As/per spec. Not runnig, so I cannot get 12 below...but it should run at 0. Compression is better than 100 on all cylinders. Any other ideas?

[ggzilla]

Set the timing to spec. It doesn't need to be running.

 

hard to start with retarded timing.

 

 

1. turn engine off. Set parking brake. Put transmission in neutral

 

2. turn engine by carefully turning fan clockwise, until the timing marks line up (12 degrees BDTC or whatever the under hood sticker says)

 

3. Pull cap off distributor. Is the rotor pointing at the Number 1 spark plug wire OR #4 wire? Good.

 

4. Are the teeth aligned? Good, timing is correct.

Blue lines

 

 

If the timing needs adjusting:

 

A. Loosen the distributor hold down bolt slightly. Be careful not to rotate the distributor while doing this

 

B. Rotate housing slightly until the teeth align

 

C. Tighten distributor hold-down bolt

 

D. Put cap back on (ensure rotor still points to #1 or #4)

[supererogator]

All of those things check out, and BTW, that dizzy pic is from an earlier model, as on an 80 720, the rotor cap points toward the rear of the motor when everything is lined up correctly.  This caused me much frustration way earlier in this game.

 

Thanks for trying guys.  I will get there eventually, but this may have to become a pet project, as it is no longer serving me as a daily driver.

[ggzilla]

Motor is timed to TDC As/per spec. Not runnig, so I cannot get 12 below...but it should run at 0. Compression is better than 100 on all cylinders. Any other ideas?

Set the timing to 12 below before you try to start the engine.

[xsdg]

If it were me, I would go all the way back to first principles and triple-check all the basics.  I would try to make sure things should work, even assuming that some physical aspect of the engine is damaged or misconfigured.

 

1) Use the straw-in-spark-plug-hole trick to verify that the crank pulley is clocked correctly against the actual orientation of the crank shaft.

 

2) Pull the cam cover.  Turn the engine over to #1 tdc compression stroke.  Make sure that both valves are closed (cam lobes pointing up), and use ggzilla's method to verify that the dizzy is configured to send spark to the #1 plug (or is just past that point).

 

3) Keep turning the engine over and make sure that valves are opening and closing as expected.  L20b firing order is 1342.  In particular, make sure that the intake valve is open prior to the intake stroke, and that the exhaust valve is open prior to the exhaust stroke.

 

4) A timing light should work while you're running the starter.  Use a timing light to verify that you're getting a spark when you expect it.  If you're bold and don't mind getting oil on things, hit the starter with the cam cover removed, point the timing light at the valves for the #1 cylinder, and verify that the valves are closed when the timing light (and hence, the spark) fires.  You'll probably need a strong light and/or low ambient light level for this to work.

 

5) A really bad vacuum leak (or carb issue) could mean that you're not getting a good A/F ratio.  Do you smell raw fuel coming out of the tailpipe?  If you put your hand (or a towel) over the carb ports while a buddy hits the starter, do you feel/see suction?  Have you played with the starter fluid recently?

 

6) Stick a paper towel down the carb port and hit the accelerator pump a couple times to catch some of the fuel.  Presumably it smells like gas.  Does it burn like gas?  How old was the fuel you put in the truck?

 

 

If all of those checks fail, then I'm at a loss, especially since you mentioned that you're getting at least some compression on all cylinders (are those numbers consistent?)

[ggzilla]

If it were me, I would go all the way back to first principles and triple-check all the basics.

One of the basics is setting the timing, which he haint done yet.

[supererogator]

Oh, set the timing I have....over and over.  Last night, I set it while not running as suggested. Nothing.  I am going to try to drain the fuel and put new in, as that might get any sediment out of the tank, but after that, I have pretty much given up.  I may take one more run at here before taking her to someone with all new eyes, but I think wrench blindness is a large part of my issue at this point.

Thank you again for all the help and suggestions.

[dr.feltersnatch]

Where are you located maybe a member can swing by and take a look. Sonetimes a new set of eyes can spot sonething your missing.

[supererogator]

I am in Eugene, and I would gladly pay in beer and gratitude if anyone is close.

[supererogator]

Moral of this story is....do not borrow a gas can from your mother, or any other non-mechanic, and assume the gas is good.  I have my dear little truck running again.  She still is not perfect.  She runs at high revs at an idle, the choke seems to not work quite right, I lost the send/sensor for my temp gauge (anyone know what that thing is called so I can source one?  It mounts just under the thermostat and is basically a wire and plate that bolts into the head housing just under the thermostat), and have a terrible leak in my water system somewhere.  I suspect radiator AND poor hoses.

To think I drove this thing for three years without knowing all these little things were wrong.  Of course, after all those years of grease build up I think the grease and grime may have been what was holding her together.  Only after starting to clean her up did this stuff start happening.  Now I am proudly to a point where I can wrench AND use my phone without destroying my phone.  All it took was one misdiagnoses and I am fixing all kinds of stuff.  So, also on that note, does anyone know if the radiator from an 82 will fit an 80?  I know of a local yard with an 82 that I plan on harvesting from.  The radiator might be a good thing to get rather than having mine repaired.  Besides, then I will have 2, and that is always better right?

 

Thanks again for all your help.  I am now trying to dole it out in return.  Most of you are better at wrenching than I, but I am glad to help if you think I can.  I have learned one hell of a lot about the last of the L20b motors during this adventure, and am only learning more.

And, BTW, I would also like to thank all of you, and the infiniverse for keeping me optimistic about this whole thing.....mostly.

[supererogator]

So, I may as well have called this thread, "Help some out of practice wrencher rebuild his engine in 2 million head scratching steps".  If a site mod felt like changing it, I would not mind. *wink wink*

I have a runner!  Starts pretty consistently*, runs smoothly*, leaks are solved (yet another small oil leak has appeared, this time it seems near the head gasket above cyl 1...worrisome), carb is very close to adjusted so the truck runs.  All of this is better than I have had in what is now two months.  I even figured out that the thing that was broken, under the thermostat, was the "water temp sender unit".  They are getting harder to find, as it took three stores in town to find one that could get it.  Luckily, they had it too. *win*.  When warm, and it does run long enough to get warm, temp gauge at dash reads dead on the center line.

BUT, and here is the explanation of the "*"...she idles at about 3k, in neutral.  When in gear (auto tranny), she drops to a pretty normal 1k.  She also does not rev correctly.  She takes about 3-5 seconds to catch up to herself.  I suspect this is incorrect carb setting.  The difference in RPMs is too much.  Now, I removed the large canister near the cab,, and behind the carb, which connects to the air filter which I believe is an EGR.  That hose is moving TONS of air. I assume this is good.  In fact, the only way to stall kill the motor is to plug this AND the carb with your hands.  If I plug only the hose for the EGR, I may stall out, and I may keep running although poorly.  All of this is done in neutral, as I cannot reach the cab from the front of the engine.  However, if I partially close this hose with my fingers the idle drops to almost normal (1500-1750ish by ear.  Cannot see the gauge either).  AM I chasing the wrong demon?  It really seems like an air issue at this point.  Gas is good, timing is good (although I really want a friend to do the cab work while I put a light on it correctly), spark is beautiful...the only other thing I suspect is that the compression is low, but even.  All cylinders are near 100psi. Datsun factory manual says 130psi is perfect.  Now, the truck has 200k on it, and I expect this is wear that I want to cure, but for now, I need a truck as it is my daily driver...currently NOT driving.  Could that be the issue?  Also, I have not set the valves yet, as she just started running long enough to get warm, so I plan on doing that tomorrow.

What think ye, oh wise Datsun wrenchers?  Keep chasing a possible vac issue, or am I fishing in the wrong pond?

[ggzilla]

You can change the title. Go to the first post and click edit.