Camshaft Oil Spray Bar Redesign and Rebuild

[Zed Head]

I got the impression from somewhere that the front one is not really necessary.  It might even be discontinued in the later engines.  Might have read it in the Rebuild book.

You could pull them out, do some work on them, and replace them without introducing swarf in to the engine.  Looks like they're still available.  Could probably make your own also.

12 and 13

https://www.carpartsmanual.com/datsun/Z-1969-1978/engine-280z/cylinder-block

https://www.nissanpartsdeal.com/parts/nissan-jet-oil-cyl~11047-e3000.html

[jonbill]

The oil jet on the front of the block is actually a supply (from the head) to the chain tensioner, so you only need consider opening up the side one.

AIUI, the jet is there to ensure adequate pressure to the bearings. The flow should be enough for a std cam.

I opened the jet up on mine by 1mm I think it was, and set it to idle at 1000rpm to ensure adequate flow.

[Zed Head]

Did you mean timing chain?  Nissan removed the description of the front oiler in the 1976 FSM.  They mention chain lubrication but not the specific oil jet.

Here's 72 -

Here's 76 -

[grannyknot]

1 hour ago, jonbill said:

The oil jet on the front of the block is actually a supply (from the head) to the chain tensioner, so you only need consider opening up the side one.

AIUI, the jet is there to ensure adequate pressure to the bearings. The flow should be enough for a std cam.

I opened the jet up on mine by 1mm I think it was, and set it to idle at 1000rpm to ensure adequate flow.

You're talking about adequate pressure to the cam bearings?  I'm not sure I understand how forcing oil through a 1mm dia hole at the top of the block that then opens up to a 6mm hole in the head creates pressure.  The oil passages in the 5 cam towers for the cam bearings and oil spray bar are, I believe, 4mm holes. It seems to be the opposite of pressure

I know these engines have driven millions of miles in the past 50 years with this system but still can't see a reason for that 1mm restrictor in the middle of the block. 

I've got to do something, I can't run the engine for more than half a minute the way it is.  I'm thinking about ordering one of these, https://www.yoesheadporting.com/product-page/datsun-240z-260z-280z-cam-oiler

What is nice about his design is he is using the oil supply from 3 towers for the spray bar instead of 2 the way it came stock.

[Yarb]

Friend that’s cheap insurance! The you can rule that variable out. Personally I wouldn’t crank that engine again.

[Zed Head]

17 minutes ago, grannyknot said:

You're talking about adequate pressure to the cam bearings?  I'm not sure I understand how forcing oil through a 1mm dia hole at the top of the block that then opens up to a 6mm hole in the head creates pressure.  The oil passages in the 5 cam towers for the cam bearings and oil spray bar are, I believe, 4mm holes. It seems to be the opposite of pressure

I know these engines have driven millions of miles in the past 50 years with this system but still can't see a reason for that 1mm restrictor in the middle of the block. 

I've got to do something, I can't run the engine for more than half a minute the way it is.  I'm thinking about ordering one of these, https://www.yoesheadporting.com/product-page/datsun-240z-260z-280z-cam-oiler

What is nice about his design is he is using the oil supply from 3 towers for the spray bar instead of 2 the way it came stock.

The oil jets (restrictors) are designed to maintain pressure to the lower end.  It's a balance between top and bottom.  If everything is to spec. it might be that the bottom end clearances are too loose and bleeding off the pressure.  Maybe you're looking at the wrong parts.  Maybe the low flow at the top is a sign of too much at the bottom.

Could also be that you have a restriction from the jet to the spray bar.  Through the head, in to the towers, and then to the bar.  A new spray bar wouldn't fix that.

[jonbill]

1 hour ago, Zed Head said:

Did you mean timing chain?  Nissan removed the description of the front oiler in the 1976 FSM.  They mention chain lubrication but not the specific oil jet.

Here's 72 -

Here's 76 -

Yes, it comes out behind the chain tensioner - I've assumed for pressuring the tensioner shoe, but it might also oil the chain.

[grannyknot]

1 hour ago, Zed Head said:

The oil jets (restrictors) are designed to maintain pressure to the lower end.  It's a balance between top and bottom.  If everything is to spec. it might be that the bottom end clearances are too loose and bleeding off the pressure.  Maybe you're looking at the wrong parts.  Maybe the low flow at the top is a sign of too much at the bottom.

Could also be that you have a restriction from the jet to the spray bar.  Through the head, in to the towers, and then to the bar.  A new spray bar wouldn't fix that.

Ok, I see what you and Jonbill are saying now, never thought of the low end like that.  I did a plastigage test on 3 conrod and 3 crank journals and the gap was bang on so I guess I'm looking at an obstruction in one of the passages.

Thanks guys

[Captain Obvious]

Yeah, I wouldn't open up those oil restricter orifices at all. If everything is working as intended, there should be plenty of oil delivered to the cam lobes.

Did you put a mechanical oil pressure gauge in the block and see what kind of oil pressure you're getting?

[Yarb]

With the cost of rebuilding/repairing these engines this day and age, putting a “T” in the system and being able to monitor the oil pressure at the engine is a life saver IMO. It’s inexpensive and just a piece of mind.

[grannyknot]

9 hours ago, Captain Obvious said:

Yeah, I wouldn't open up those oil restricter orifices at all. If everything is working as intended, there should be plenty of oil delivered to the cam lobes.

Did you put a mechanical oil pressure gauge in the block and see what kind of oil pressure you're getting?

I have 5-6 mechanical pressure gauges but all of them are 1/8th-28BSP instead of 1/8th-27NPT, need to pick one up.

I was told that the oil pump is the upgraded high flow variety but I think I should do some measuring while everything is apart, does anyone know what the internal differences are between the stock pump and the high flow?

Thanks

[jonbill]

My recollection is that the high flow pump rotor is 40mm tall compared to stock 35mm.