Jump to content
HybridZ

Lost oil pressure on new motor


Recommended Posts

Hey All,

 

I just put in my built motor and all was well for the break in.  I changed the oil and drove to work and back once.  On the second trip to work, I lost oil pressure.  I checked the oil level, just fine, and drove home (I know, should have towed it) coasting with engine off as much as I could. 

 

The cam was chirping and dry, hopefully salvageable.  I pulled the oil pan and didn't see anything disastrous.  I'll be pulling the oil pump tomorrow to check for blockage.  

 

In thinking about causes for the loss of oil pressure, I can only think that the oil pump (brand new) failed or there was some crap left in the engine from the build that caused blockage. 

 

The only other possibility is (that I can think of)...   I removed the distributor when I put in my hall sensor ignition.  I know the distributor shares the shaft with the oil pump.  Does the distributor hold the shaft to the oil pump?  Is it possible that without the distributor in place that the cog is not held to the oil pump?

 

Thanks for any input!

Link to post
Share on other sites

No - if the shaft is in there, then it is held in place by the timing cover and that keeps it riding on the gear on the crank. Did you see any trash in the oil pan when you pulled it? On my racecar, I'm running a diesel Maxima pump shaft - which is a 4" long stubby shaft - distributor has nothing to do with the holding/placement thereof. So - you had pressure initially on the break in?

Link to post
Share on other sites

That is really unfortunate. I was hoping that you just lost the sending unit or something of that nature, but if the cam is chipping then you may have a problem.

 

Taking the oil filter apart as well will reveal if you hurt the motor any.

 

Possibilites are pretty much what you state:

Bad oil pump (seized etc etc etc)

Blockage

Insufficient oil

Filter failure

Broken oil pump shaft

Link to post
Share on other sites

Ok, oil pan has just a touch of metallic dust in the oil.  I don't think it's catastrophic.  Oil filter is clean as can be- possibly because no oil was circulating...  The oil pump has no obstructions, nor does the pickup (which was tight). 

 

The one thing I did notice is: the tang that drives the pump only seats 1.08mm...  There is a half inch alotted on both the male side of the shaft and female side of the pump receiver, but it's only seating 1.08mm.  This seems wrong to me, like the shaft should sit deeper in the pump.  Could a different model year pump have a different size housing which would cause this???

 

Thanks for all the input, I do appreciate the help!

Link to post
Share on other sites

That's a calibrated distance... If your. Oil pump is so far out the shaft is not engaging, then the oil feed and suction ports are also misaligned by that 1/2" you reference! The pickup gun drilling in the block is only 10 or 12 mm to begin with...

 

Start measuring, and find another pump to compare!

Edited by Tony D
Link to post
Share on other sites

I haven't looked at the bearings yet...  Wouldn't they have had a problem from the get go?  Or am I looking for a spun bearing?  I did notice the bearing caps didn't all have the Nissan logo on the same side- not sure if that matters, but if I had built it, they would be.  I've got a new oil pump on order for comparison.  I've read each of your posts for a long time and respect your input. 


Link to post
Share on other sites

I think that he's saying that if there was no oil at the cam then there was probably no oil at the bearings.  No oil > no lubrication > metal to metal contact > damage.

 

Your first instinct was right - (I know, should have towed it).  You saved $75 and will probably spend hundreds.  For as cheap as it is, oil is probably the most important thing in an engine.

post-8864-0-08797700-1408679517_thumb.jpg

Link to post
Share on other sites

Your main bearing caps have an arrow on them. The arrows should all point forward. Don't recall seeing the Nissan logo on any of the main caps. There is a 'badge' on the rod caps if that's what you're referring to - and in that case - yes - they should all be uniform in their orientation.

Link to post
Share on other sites

Yeah, I'll check the bearings for damage.  The logo is on the rod caps, but I forgot about the arrows on the mains- will check them too (and take lots of pictures for the shop that built it).  The cost of towing wasn't an issue, things being rocky at work and being 2 hours late might have been...

Link to post
Share on other sites

Got the new oil pump and it measures exactly the same.  The shaft still only engages that same 1.08mm.  The distance from the end of the shaft to the drive gear is 30mm.  On the other side of the drive gear is 5mm, then a notch.  Is the gear permanently mounted on the shaft or could it have moved 5mm over the past  38 years?  Does anyone have one that they can measure?  Thanks!

 

post-12144-0-43951000-1408845727_thumb.jpg

Link to post
Share on other sites

They have been known to spin, there are few axial forces and it's pinned on either end between oil pump and distributor drive.

 

If the gear "moved" axial lay enough to disengage with the oil pump drive shaft---what did it do to the distributor drive end? It's virtually captive between those two points.

 

If the gear slips, and was to be axially displaced (for the sake of argument, let's say the helical engagement moved the gear axially 5mm....

 

You would have a huge timing shift from that spinning. I can't imagine what forces would act on the shaft once installed to move the gear position axially on the shaft, save for gear drive helical angle ... And we know thy have spun countless times without ever changing that axial position--so why would yours?

 

I'd check your measurements off the front cover again, and on the oil pump. At worst, assemble it all off car in an old front cover to see what is happening (is the thrust surface in the front cover eaten away letting it move? Again--it can only go so far with the distributor on the other end!)

 

I think this will be found elsewhere. What does the oil pump look like internally? Signs of running dry?

Edited by Tony D
Link to post
Share on other sites

This picture look likes 5mm of possible difference.  Looking at your 5mm to notch marking.  I don't see a notch in the eBay picture.

 

 http://www.ebay.com/itm/Datsun-Nissan-240Z-280ZX-Rare-Turbo-L28-L24-Oil-Pump-Gear-Drive-OEM-/151384028550?pt=Motors_Car_Truck_Parts_Accessories&hash=item233f30f586&vxp=mtr

post-8864-0-15785400-1408849339_thumb.png

Edited by NewZed
Link to post
Share on other sites

I have removed the distributor, running a hall sensor DIS... I'm thinking the thrust force of the crank spinning the drive gear without the distributor in place must have forced the shaft sprocket downwards reducing the mating area.  I'm also a few beers deep, does that sound accurate/possible?

Link to post
Share on other sites

Tony D added a bunch to his post.  This could be a red herring, wild goose chase.  

 

If you lost drive because the tang slipped out of the notch you should see spin/wear marks on the end of the shaft from where it slipped out.  How do the ends of the tang and notch look?

Link to post
Share on other sites

Remember the front cover has the bearing surface in it...

 

The axial forces from the helical gear would press the gear into the front cover bearing...and there it stops. That was what I was trying to get at by "where would it go?"... Unless the distributor was preloading the shaft INTO the oil pump, I don't see any way any axial force could move the gear on the shaft in that axial direction?

 

The whole assembly could move should the front cover bearing be damaged...but again, and axial displacement away from the oil pump would be seen in the distributor end being pinched. If you have nothing there, then nothing would show.

 

Install the shaft in the front cover.

 

Measure it's protrusion from the front cover.

 

Measure relative position of the tang in the oil pump relative to front cover mounting surface....I strongly doubt there is an engagement mismatch unless the front cover is damaged.

 

 

More likely there is a suction break letting the oil pump suck air on the suction side of the equation: oil pump to front cover gasket, front cover to block gasket, oil pickup to block...

 

Blockage in that same circuit.

 

Stuck relief valve In pump allowing 100% bypass.

 

Pump failed...

 

 

I mean, if it wasn't pumping oil, it's gotta be torn up inside. Started without prime? No grease preluding the gerotor to make suction?

 

I seriously doubt the "engagement" is only 1mm, but that's the information we gets so that's the rabbit hole we run down.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...