Engine locked up, what could it be?

[xsdg]

So, on Monday, I went to start my truck.  It turned a little bit and then stopped.  In the past, there was a point where it'd slow down, but then it got past it, the engine fired, and everything was dandy.  This time, though, no go.  When I hit the ignition, I can hear the starter solenoid click, but that's all that happens.

 

Moreover, the engine is locked good and solid.  Tonight, I tried pulling the truck with another vehicle.  I stuck the truck in 5th gear (so the ground has maximum leverage against the engine), and the back tires skidded before the engine would turn.  I realize that I could tow the truck backward to keep it from skidding, but I feel like that's just asking for something to break.

 

So, what could it be?  The starter itself is obviously the place to begin, since it has so much leverage compared to the flywheel.  There's also the possibility that something is broken and jammed inside the engine itself.  An easy way to check that would be to see if the motor will turn backwards at all.  Any other big things to check?  The truck will roll fine in neutral or with the clutch in, so it's definitely something with the engine.

 

Another possibility is obviously that something in the bottom end got warped.  That seems unlikely in part because I don't want it to be true, but more importantly, there was no rod knock or anything.  I drove the truck on Sunday and it was fine.  I left it sitting for multiple hours in the evening, and then fired it up and drove it home at 11:00 pm.  12 hours later, nothing spins.  Having thrown out multiple engines from our race car due to oil starvation, those issues came on gradually and it just became increasingly difficult to turn the engine over, but it was never impossible.

 

 

Given the long weekend coming up in the US, I'm planning to spend one day and throw myself at this problem, so if y'all have ideas of other things to check, fire away.

[xsdg]

FTR, I've got this thread in mind, so I'm hoping it's something like that:

http://community.ratsun.net/topic/62252-i-picked-up-another-720awd/

[Guest Rick-rat]

pull out the plugs and see if it will turn over

[metalmonkey47]

Broken timing chain? Valves wedged into pistons? Huh..

[datsunaholic]

Pull the plugs first.  I had a NAPS-Z totally locked up- pulled plugs, hit starter and it turned over and sprayed the roof eaves with antifreeze.  Intake Manifold gasket had been "Chevy sealed" with multiple tubes of orange goo, and that didn't seal at all.

[ggzilla]

Yes Id start there

[datzenmike]

Do you start with the clutch pedal up, in neutral? or down?

 

You should be able to tow forward or backwards if in neutral.

[Nuclear Water Boy]

Hydrolock is not your friend= Bent push rods, broken piston skirt unless you're really lucky in which case I'm pullin for ya.

[xsdg]

datzenmike: I always depress the clutch pedal while starting, usually with the vehicle also in neutral.

 

Rick-rat, datsunaholic: I'll definitely pull the plugs, but coolant in the cylinders seems unlikely.  Radiator was filled to the top when I checked yesterday, and I've checked the oil recently and didn't see any signs of coolant mixing.

[ggzilla]

Locking up seems unlikely. It was running before Monday?

 

You have an unlikely scenario, so why rule out unlikely causes?

[xsdg]

*phew* I finally had some time to work on this.  It looks like it was the starter.

I pulled the plugs and shined a bright flashlight into the cylinders.  Plug tops were all dry and mostly-reasonable colors.  No fluid in the cylinders, and it behaved identically when I tried to crank with the plugs out (and both ignition coils disconnected).

 

Next step, pull the starter.  I got it removed, dropped the truck in reverse, pulled the wheel chocks, and when I pushed the front, I could see the flywheel spin.  Thank goodness.

 

I'm taking the starter to get checked now.  One thing I did notice is that the lower mount bolt on the starter seemed considerably looser than the top bolt.  So one thing that comes to mind is that maybe the starter was able to wiggle just enough for the drive gear to bind on the flywheel.  At the same time, there's tons of oil on the connections from my big oil pressure sender leak (since fixed), so some of that probably worked its way into the connections there to drop the voltage a bit at the starter itself.  Combination of the two might have meant that the starter was misaligned, and also had less torque than normal.

 

Whatever the cause, I know that the engine turns without too much trouble, so that's a load off my back.

[datzenmike]

An electrical circuit is a closed loop. Battery to cable, cable to starter lug, starter windings to ground on case, case to transmission, transmission to block, block to head, head to intake, intake to negative cable, neg. cable to battery. Any poor connection will cause poor cranking. 

 

Get a set of jumper cables and a vehicle with a know good battery. Connect to your battery posts... does this solve the problem?

 

Yes.. your battery is bad or both the posts are dirty.

No... connect positive jumper to the starter lug. Is problem gone now?

 

Yes... positive cable is bad

No... connect negative cable to intake or the block. Problem gone?

 

Yes... the ground cable is bad

No...  connect ground cable to the starter case. Problem gone?

 

Yes... bad connection between starter and transmission/engine block

No... starter is bad.

 

 

 

Costs nothing to solve the problem... don't throw a starter at it.

[xsdg]

Checked resistances.  Ground is good (<1Ω from starter housing to ground lead).  Resistance from the battery hot terminal, through the windings, and out to the starter housing is 4 kΩ.  When I short the solenoid switch terminal to ground, I hear the solenoid go but the motor doesn't even try to turn.  And finally, I took the entire motor starter to AutoZone, and it tested fine.

 

I'm taking a break for lunch now.  I forgot to check the battery voltage while I had everything hooked up, but I'll check that when I get back.  That said, at this point, signs are pointing towards either a bad battery, or something wrong with the power transmission from the solenoid to the starter motor itself.

[datzenmike]

The solenoid terminal needs 12 volts to energize, not ground

 

The first check on my list would have saved you taking the starter out if this proves to be a low or bad battery.

 

The red highlight would show a bad solenoid .

 

An electrical circuit is a closed loop. Battery to cable, cable to starter lug, starter windings to ground on case, case to transmission, transmission to block, block to head, head to intake, intake to negative cable, neg. cable to battery. Any poor connection will cause poor cranking. 

 

Get a set of jumper cables and a vehicle with a known good battery. Connect to your battery posts... does this solve the problem?

 

Yes.. your battery is bad or both the posts are dirty.

No... connect positive jumper to the starter lug. Is problem gone now?

 

Yes... positive cable is bad

No... connect negative cable to intake or the block. Problem gone?

 

Yes... the ground cable is bad

No...  connect ground cable to the starter case. Problem gone?

 

Yes... bad connection between starter and transmission/engine block

No... starter is bad.

 

 

 

Costs nothing to solve the problem... don't throw a starter at it.

[xsdg]

Automotive diagnosis 101:

 

1) It's always the battery

2) If you rule out the battery, sometimes it's the battery terminal lugs.  Corrosion is a thing.

3) It's always the battery

 

In my case, the answer was #2.  Everything became a lot clearer when I realized that the solenoid actuation line was powering the solenoid, rather than just signalling it at low voltage.  Prior to that, I had believed that the power (for the solenoid as well as the starter) came from the large cable connected to battery positive, which would have meant that that cable was good.  I was also somewhat confused, since I had tried to jump-start the truck and that didn't seem to help.

 

Prior to that, I saw the voltage across the battery drop to ~11V when the starter solenoid was engaged, which convinced me that the battery was good.  I independently measured the resistance along the positive wire to the starter at under 1Ω, and the resistance from negative to the starter housing also at under 1Ω.  In hindsight, I most likely measured from the terminal lugs rather than from the terminals themselves, which masked the actual problem.

 

So there were two compounding problems here.  1) I fundamentally misunderstood how the starter assembly was wired, and 2) I didn't pay close enough attention to the interfaces between the different components in the system.  #2 meant that when I tested things, I failed to test the interfaces.

 

Once I realized #1, I tested and verified that all pieces of the starter assembly were working properly (both independently and in aggregate).  The only remaining possibility was the power transmission from the battery terminals to the battery terminal lugs.  The positive terminal lug was corroded to the terminal so badly that I broke the battery housing trying to pry the lug off the terminal (after having tapped it a couple times with a hammer).  I eventually cut the lug in half to get it off.

 

Because I had broken the battery casing, I replaced the battery.  I then proceeded to cut off the cable ends for the ground (filled with corrosion) as well as the positive (somewhat corroded, although not as badly), and replace them with new lugs using freshly-exposed cable.  Finally, I covered everything with a good bit of dielectric grease to hopefully protect a little against future corrosion.

 

Anyway, Truckula is back in business after all that.  Thanks for all the help.  Hopefully y'all can learn from my mistakes.

[ggzilla]

Now you've learned what the rest of us have gone through.

 

Another Datsun truck back on the road!

[JoeCool]

Good to see you figured it out and got it up and running again!

Last time (two years ago) I replaced the battery on mine I had to replace the positive terminal cable and end due to corrosion. I just bought a two pack of the color coded terminal ends, it was only a dollar more from Advance Auto, figured may as well replace both. This year my starter crapped out. Had it tested at Autozone just to be safe, as a rule, it is always best to be sure the part is bad before replacing it. I know Autozone, O'Rielly's,  and Advance both test batteries, and bench test starters and alternators for FREE. If they test the parts for free, it's a "no brainer."