Idle issues after pseudo rebuild

[Odisomus]

1985 Nissan 720 King cab 2.4L Manual 3rd owner for 5 years now

 

That's the resting beauty that I had accidentally (while distracted at night) driven sixty plus miles through a multi altitude section of interstate at thirty-five miles an hour since that was as fast as she would go.  A previous issue with the headlights and the instrument panel lights working at the same time and this drive being at night after a snow storm were only a few factors that lead to me overlooking the oil pressure gauge which was at half it's required operating level.  The low oil pressure was realized before catastrophic failure occurred and all issues relevant to it were fixed the following morning (or all relevant issues I was aware of at that time).

 

So a few weeks later on a different section of interstate at approximately 65 mph a loud sound that will be identified by the onomatopoeia "Clanking" with a clear pause after it.  The truck was then driven at a speed below 15 mph to a parked position, after that it was test driven once, started multiple times for a compression test and for two possible buyers.  Other than that it was towed on a trailer or as the brakes in tandem with a larger truck.  The compression test showed lower (still within acceptable limits for operation) compression on cylinder two, I'm unsure if both sides were treated for each cylinder but I'm fairly certain that both sides were tested of each cylinder and only cylinder two was different from factory specs.

 

I felt how I got to this point was important to show the amount of time and consideration this engine has been given getting to where it is today, less that 10k miles ago a new cylinder head was installed by a professional mechanic shop (whatever qualifies for that these days) when the timing chain guide had broken and the engine began to "jump" timing when it had advanced it's timing enough to only drive in reverse at less than 5 mph then would not start again.  That was when I had it towed to a reputable shop for the work and if the shop were still open I'd consider taking back there but that beginning to segway from the actual subject.

 

So a 1985 Nissan Z24 engine with the stock 5 speed manual transmission that had fused the rod bearings on cylinder two together and one of them had fused to the connecting rod.  Basically the rod bearings for so hot they started to act like metal being forged, they thinned out, after having probably spun one, it eventually took up all the extra space that the oil wasn't in on top of the other bearing.  Then the loud Clanking was the bearings, having changed shape only slightly as it spread out, then the top one fused causing resistance depending on the operation of that cylinder on the connecting rod and giving me one of the most hellacious piston slap symptoms.  It was thought to be the bearing, or maybe the wrist pin, check out the photos I didn't get any that really show what happened. 

 

After the application of heat and force I was able to remove the fused rod bearing from the connecting rod, I got the lobe machined and measured, (SUPER LUCKY) the lobe was still at factory spec (or after painfully measuring every component, close enough) so I replaced the bearings, assessed what other parts needed to be replaced like the rings, head bolts, gaskets, as well as cleaned up the pistons so there wasn't so much carbon build up because there have been home mechanic fixes that I have been fixing on this since I got it. It's a pseudo rebuild because I did not replace everything as would be considered a full rebuild; that considered I've gotten the engine to run for up to a minute if I control the throttle.

 

That's what brings us to the pseudo rebuild and the idling issues of today hope I didn't lose you before here......

 

I have set everything back to how it was before I started taking it apart in an attempt to start at stock so to say and go from there.  So with everything put how it ran before and adjustments being made first in the direction towards stock I can get it to start if I press the throttle, then I have to just barely press the throttle and it'll idle around 600 rpms. If I press the gas harder it seems to cut the fuel even though I have the throttle positive sensor disconnected, if I stop pressing the throttle it just dies out like it has no gas.  Before I had a copper ball valve inline right before my pressure regulator.  The vacuum system is sealed and there is sufficient pressure to the regulator which I was told was bad and that was why the ball valve had been placed there. 

The ball valve started leaking and spraying gas on my belt which then began to slip so I removed it and used to feather my gas before the Clanking began because it seemed to flood out and feathering worked until the rpms got higher. 

 

Here is the bearing still fused to the top.

So lucky only material from the bearings got transferred to the connecting rod and cap, here's a shout out to the company that I ordered due to reviews, price, availability, and a few other factors.  By far the lowest cost is anything I had to buy for this rebuild. 

 

Thank you all who have commented or started other subjects about this engine it helped me tremendously with this rebuild. I'm hoping there is something easy I'm not thinking about cause it's been months and there is no reason this motor shouldn't be running. 

 

I'll include pictures as requested beyond what I have just to not convolute the thread too early.

[DwayneOxford]

Check vacuum?

[datzenmike]

21 hours ago, Odisomus said:

1985 Nissan 720 King cab 2.4L Manual 3rd owner for 5 years now

 

... lead to me overlooking the oil pressure gauge which was at half it's required operating level.  The low oil pressure was realized before catastrophic failure occurred and all issues relevant to it were fixed the following morning (or all relevant issues I was aware of at that time).just to not convolute the thread too early.

 

 

Just what was the reason for low oil pressure???? Was it 3 quarts low??? That will cause bearings to over heat and wear. Lack of oil is totally preventable.

 

21 hours ago, Odisomus said:

1985 Nissan 720 King cab 2.4L Manual 3rd owner for 5 years now

 

 I'm unsure if both sides were treated for each cylinder but I'm fairly certain that both sides were tested of each cylinder and only cylinder two was different from factory specs.

 

 

 

You only need do a compression test on one of the spark plug holes, usually the exhaust side as they are easier to get at.

 

22 hours ago, Odisomus said:

1when the timing chain guide had broken and the engine began to "jump" timing when it had advanced it's timing enough to only drive in reverse at less than 5 mph then would not start again.

 

The timing chain and anything to do with it, has zero connection to ignition timing. Only way the ignition timing can advance is if the distributor adjustment screw is loose.

 

FYI Z series head bolts do not need replacement unless damaged. They are totally reusable.

 

If you have to press on the gas to idel why not turn the idle speed screw up?

 

Did you replace the rings on #2? did you re-hone the cylinder?

 

Why do you have a fuel??? pressure regulator??????? Why a 'ball valve???????  I thought this was a stock set up. What are you not telling us?

[Odisomus]

I thought I had communicated more clearly so allow me to answer/address your posts because all the replying parties are ones I've listened to in other posts and found great success with all of your advice. 

It is a 1985 Nissan 720 4wd Kingcab with a 5 speed manual 2.4L TBI SOHC in line 4 or however you need to write that the motor is the electro-injection from 1985 Z24.  I recently put it back together after taking it apart and replacing the rod bearings on cylinder two only; all necessary gaskets and other parts that needed to be replaced after inspecting them were replaced, i.e. I didn't take the throttle off the intake manifold and took the motor apart in as few pieces as possible as to need to replace as few as possible.

 

The previous issue of the timing chain guide breaking(which is common on these motors) and then when in normal operation the timing chain had slack so it began to jump teeth of the top sprocket and advance the timing or maybe it was retarding it I'm not sure but I know that the crank and the sprocket were off by about 90° from each other and I replaced the cylinder head and it ran great until it needed the pseudo rebuild. 

 

Now rebuilt the only thing I didn't put back into the stock setup was a copper ball valve that the previous owner had put on the incoming fueline to the motor because before I parked it the ball valve had begun to leak and was causing my belt to squeal, after I removed it I could only put the accelerator pedal down a little ways before it seemed like the fuel want getting to the engine, it would bog down until it staled, if I waited and barely feathered the gas I could get it going and once at higher rpms could press the pedal down further, the other way was if I started it and took off right away it would drive normal but if I stopped it would idle but only go if I barely pressed the pedal.

 

The pressure regulator is attached to the throttle body and I was told the ball valve was there cause the pressure regulator was washed out but after a vacuum test it appears to be functioning fine except it won't hold it's idle. I've wondered if the person before me had difficulty finding or servicing or had emissions issues with the carburator so they put the injection on it but I don't have two adjustment screws that are in the book so setting the idle has been very difficult, I thought keeping everything close to how it was before I did the rebuild it would just be minor adjustments to get it running again.

 

So for all intensive purposes I've set it to stock and ask necessary measurements were taken to ensure the clearances and other areas were within factor specifications. I got very lucky cause I stopped driving it. Also I may be missing a fuel filter that helps regulate pressure in the engine compartment because I have an in tank pump then an electric one on the frame near the tank like some carburator models have, they didn't make many of these injected ones in 85 and they changed the layout in 86 so it's been unclear if it's originally the TBI from the factor and that's why its without two adjustment screws on the manifold or if it was installed later and that's why it seems to not fit any of the lay outs in the book.

 

I've got it running after disconnecting the throttle position sensor like it says to do when setting the idle and the ACC valve. It gets almost to idle speed if I pump the gas staying in the beginning half of the pedal travel distance and it seems like it dies out from no gas.  The fast idle screw for when it is warm, the screw on the side next to the float and the screw on the wheel for the throttle cable have all been adjusted to factory settings and I've got sufficient pressure at the manifold so for so intensive purposes all previously mentioned issues like low oil pressure have been resolved and the only issue is it won't hold it's own idle, and when I'm pressing the gas it's easier to control under the hood than to use the pedal but that's difficult to do since it only idles for the gas primed at the start.

 

Well let me know if I need to clarify any further sorry and thank you.