: 4.6 L NorthStar Engine Design Questions



Lonezuk
05-06-06, 12:32 PM
Engine questions, i have never taken a northstar apart.

1) Heads cooled by forcing water through passage ways in the units.
a) Water jacket near the combustion chamber to cool the head.

2) Does raw air flow into the cylinders on the compression stroke up to the point where the values close and the injectors pump into the cylinders after additional compression not at the start of compression.

3) Intake water cooled ?

4) Exhaust water cooled ?

5) Do water jackets surround cast in sleeves?

6) Cast sleeves with offset water jackets.



Reason for the questions:

a) Head failure (not gasket) and leak super heated vapor into the coolant.

b) A cracked liner below the maximum area of compression can leak air into the coolant on the compression stroke before TDC and the area of ignition and the fuel injection phase of the stroke.

c) Intake or exhause gaskets can fail and force pressurized air into the coolant chamber.

Basis:

1) Leak down test @ TDC does not find a problem.
2) Negative hydrocarbon readings
3) Coolant system holds pressure
4) Coolant system pressurized without hydrocarbon injection.


Strange questions for strange problems.

zonie77
05-06-06, 02:32 PM
There are water jackets through the heads and block. Intake and Exhaust are not water cooled.

The cyl leakdown test tested the Head Gaskets. They are above the top ot the pistons at TDC.

If the heads, cylinders, or head gaskets were leaking you should get a positive combustion byproduct test. Have that test redone.

At the beginning of failure they may hold pressure at low speeds and low load. So a cyl pressure test may not show the leak. A slightly warped head or unevenly torqued bolts may do the same.

If you are getting leakage from anywhere you should be getting a positive combustion byproduct test. You would get a false negative if you recently changed coolant, so make sure it's been run with the coolant that's tested.

Ranger
05-06-06, 03:43 PM
Engine questions, i have never taken a northstar apart.

1) Heads cooled by forcing water through passage ways in the units.
a) Water jacket near the combustion chamber to cool the head.

2) Does raw air flow into the cylinders on the compression stroke up to the point where the values close and the injectors pump into the cylinders after additional compression not at the start of compression.

3) Intake water cooled ?

4) Exhaust water cooled ?

5) Do water jackets surround cast in sleeves?

6) Cast sleeves with offset water jackets.


2) I believe the injectors are just upstream of the intake valve so they are injecting fuel into the intake manifold, not directly into the cylinder.

3) No

4) No

5) Yes

6) ?

zonie77
05-06-06, 10:28 PM
Look at Mikeay's headless thread if you havn't seen it already.

thu
05-08-06, 02:27 PM
2) Does raw air flow into the cylinders on the compression stroke up to the point where the values close and the injectors pump into the cylinders after additional compression not at the start of compression.


No. On the N*, the injectors 'squirt' fuel into the cylinder from outside the intake valve when the valve is open.

What you describe is a Direct Injection engine. This may be the wave of the future as some new engines from Audi and Nissan have this for some of their gasoline engines. This allows one to get rid of the throttle and the huge associated pumping losses this mechanism induces. This is one reason why Diesels give good economy - they don't have throttles. This also allows higher compression ratios, another reason for the power and economy of diesels.

chevelle
05-08-06, 02:46 PM
The heads have water jackets, yes....

Air and fuel flow into the cylinder during the intake stroke and the mixture is compressed. The Northstar engine has a conventional port fuel injected system. Direct Injection gasoline engines (and diesels) inject fuel directly into the combustion chamber....but not the Northstar.

The intake manifold has no coolant in it.

The exhaust manifolds do not have coolant in them.

Coolant surrounds the cylinders. The cylinder liners are cast into place in the block with a layer of aluminum around them. The coolant surrounds the cylinders but the liners themselves are "dry" as they are separated from the coolant by the layer of aluminum.


I suspect from what you have described (basically the cooling system is being pressurized by combustion gases causing overheating and "false boiling" of the system before it has actually warmed up) that the head gasket may have failed.

If you are running a typical "leakdown" test with an orificed leakdown tool then that will not show the problem. What you want to do is to use the spark plug port fitting to introduce 120 PSI shop air directly into the cylinder to pressurize it. Do not orifice the air feed to the cylinder. Pressurize each cylinder at TDC and watch the (full) cooling system for bubbling. Fill the system completely to the brim of the surge tank and hold each cylinder at 120 PSI for 5 or 10 minutes to see if any bubbles appear. THAT will tell you if there is a head gasket problem or not.

Lonezuk
05-08-06, 05:01 PM
Pulled the plugs and used shop air directly into the spark plug holes.

Did not use the astro leak down tester on this one.
Used a compression extension with the valve removed, connected to a pressure regulator to the main air line on my compressor.

Each one was tested a TDC and held at that position using a breaker bar by the second person. They were all held a min of 5 minutes.


Ran a driving test with the thermostat removed and the cap loose coolant tank full. The upper large hose to the inlet of the radiator was firm/hard when the engine heated up. Coolant was coming out of the tank with the cap off.

zonie77
05-08-06, 09:28 PM
Redo the combustion byproduct test. preferably at a radiator shop. They are usually cheaper and they do it more so they are experienced.

You could but the kit youself. It's about $50 at NAPA and it's good for a bunch of tests.

It sure acts like head gaskets but it's odd that you aren't getting bubbles when you pressurize it.

If you crank the engine with the cap off do you see coolant movement in the surge tank?

chevelle
05-08-06, 09:37 PM
You're sure the shop air was entering the cylinder?? Compression testers have a one way check valve in the fitting that would stop shop air from entering the cylinder. You mentioned "with the valve removed". I assume you mean the shraeder check valve that would keep shop air from entering the cylinder or did you mean the "fitting" that the gauge usually plugs into? Since you mention breaker bar it would sound like the engine was trying to turn when the air was applied so that would indicate some air pressure was entering the cylinder.

You're problem certainly sounds like a failed head gasket. If it is, it is the first time in history that pressurizing the cylinders with shop air like that didn't show the problem...!!

Is it possible to let the engine turn until the piston is down the bore aways (just before the exhaust valve starts to open) and lock it there and do the air pressure test. If a cylinder liner is cracked (very very unusual....happens but very very rarely and usually because of some other problem) that could allow combustion pressure to enter the cooling jacket as the piston moves away from TDC and give the symtoms you indicate which would be analygous to a blown head gasket. Usually, if a liner does crack it will crack at the top of the bore, not down the bore or from the bottom up. If the liner cracks there is still the aluminum "muff" surrounding the iron liner but combustion pressure will find it's way into the coolant jacket thru the crack and the cast interface between the liner and the block.

When the coolant is spewing out, etc...is the engine truely hot and overheating or is it doing this with the coolant somewhat normal in temperature? It isn't clear to me whether you are trying to find a pure overheating problem (that could be water pump drive slipping, plugged vapor vent line, etc.) or a head gasket failure that is pressurizing the cooling system. That SHOULD show up in the chamber pressurization test with shop air. If the problem only shows up when the engine overheats then the symptoms you state could simply be due to overheating. Have you checked the vapor vent line for flow and obstructions and the water pump drive/drive belt for slipping?