Before I installed my Northstar in my 88GT it was sugessted that I have it torn appart and clean it up. I agreed as it seemed like a good idea at the time. Now I know better.
The intent of this thread is to overview what I had done with what results, and to receive opinions as to what the best action might be for me now.
To summarize:
The engine: 97 4.6 from a Deville (VIN Y)
Prior to being worked on: ran well enough, 105,000 miles, small puff on startup or after long idle, plugs a bit black
Work done for "warm over":
-heads reworked including valve grind, new valve guides and seals
-new cam chain tensioner and guide
-hone and new rings (old rings were stuck in the piston grooves)
Errors made that I learned about later:
1) Shop did not timesert the block as they had never heard of them. They only chased the threads with a tap. When I learned about timeserts and complained about it the heads were already on, and I was told all the bolts took the torque.
2) Head bolts were reused. The shop did not know about the lube/thread lock coating. They thought the bolts were stretch bolts and measured them to see they were not stretched, so re-used them.
3) They did not use anerobic sealant on the case reassembly. The engine leaked before it even ran. I had to pull it out and seal the case. A waste of my time.
4)Old style rear main seal was used and leaked. I changed this to the newer speedy sleeve seal style but had to pull the tranny and clutch off the engine first. Another waste of my time.
5)Hone stones were likely way too fine. As far as I know, a hand hone was used. The rings did not ever seat and the engine horks oil like a pig. It was suggested by en actual engine shop to run 4 or 5 tablespoons of Commet cleaner through at about 2000 rpm and then drive it like I stole it. I did this since I had nothing to loose anyway, and the oil consumption is now about half. The Commet scrubbed in the rings a bit, but it still horks oil.
The engine shop loaned me their borehole scope to look at the top of the pistons. If the engine was burning oil past the rings, the outer circumference of the piston top would be shiny where the oil was washing the piston. I took some pictures by holding the camera on the scope eyepiece and the pics are not quite what your eye sees, but get idea of what's there. I only did the rear bank as the front bank would need a longer scope.

The borehole scope:


A typical piston top in my engine:


A zoomed in view of another cylinder:


The shiny bits in the center are reflection from the scope light. The edge of the piston was shiny for about 1/8" and the eyebrows for the valves were also shiny on the edge. So this seems to confirm my rings are blowing by.
These pics were taken before the "Commet Treatment".

I am undecided as to where to go from here. Nothstars are not common in the shops where I live so there is not a good base knowledge of them.
Can the cylinders be honed again? One shop has said they can power hone and remove a small out of roundness.
If they are found to be out of round can the block be bored? I have read much about the sleeves being Nitrided for surface hardness but I have not seen this confirmed by a ruputable source. So are the cylinders boreable a bit? How much? Are oversize pistons available?

I would appreciate your informed thoughts......

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Daviero - 88 N* GT

You might try Design 1 systems - I THINK that's where curly got his NorthStar conversion and they might be a reliable source of info. "Contact Design 1" is a block on the left side of the page.

http://www.design1systems.com/northstar/index.html

[This message has been edited by PaulJK (edited 10-22-2008).]

Your experience sounds a lot like mine... I went through 2 qt's of oil in 100 miles of test driving.
The engine will NOT fix itself.
At this point, your only credible option is to tear it down and start over. BTDT. There's no such thing as a cheap Northstar build.

My engine always tested with very high compression... over 220 psi. This was because the rings were bathed in oil and that helped them seal. It also always had puddles of oil on the backs of the intake valves. Since pulling the intake isn't very hard, you should check this out.


The first shop I went to was locally reputable, but worked very little with anything but domestic iron V8's. The hone job they did was piss-poor and I didn't know enough at the time to pick that out. Also, honing the block and then using cast pistons opens the bore clearance up a lot. IIRC, the stock pistons are fit at .001 to .0015. Honing even .001 out doubles the factory bore clearance. You won't get a good hone unless you take at least .005 out.

NEVER pay an engine shop to assemble your engine. They almost never use procedures or build sheets, so they're almost certain to screw up an engine they haven't done before. Not only will they likely not do it right, NOBODY cares more about your engine than you do.

As long as all the bolts take torque and the aluminum in the holes isn't corroded, there isn't a strict *need* to timesert. I did my block as a safety measure.

As far as shops go, you're best off trying to find a shop that specializes in import engines, especially Subarus and Hondas as those are open-deck die cast blocks like the Northstar.

On a basic Chevy, the entire block is iron, so GM used a cheap soft grade of iron. On old Cadillac big blocks, GM used a high-nickel iron and paid much more attention to core shift, with predictably better results. For the Northstar, not only is it a Cadillac and thus worthy of a few more dollars, the amount of iron is MUCH smaller. I conjecture that this means that GM used a VERY high grade of iron in the bore liners. The GM Powertrain lists them as cast grey iron, vice nodular iron for cranks and truck blocks. The high grade of iron is MUCH harder than older domestic iron blocks and takes very different honing methods to get a good bore finish. Kevin at Total Seal recommends aluminum oxide stones instead of silicon carbide. SiC is the stone usually used with a SBC. If you use SiC stones to hone a Northstar, the hard iron of the Northstar bores and the hard silicon carbide stones just polish each other and you end up with a bore finish that's *worse* than what you started with. A hand/drill/dingleberry hone is a complete waste of time on these engines. They NEED a proper machine hone with the proper stones.

I bought my own set of honing stones and took them with my block to a shop that builds high end import engines. The second hone job looks great, but my block is .008 over at 3.670. That's what it took to get the bores round and fully finished. I made my own torque plate and had the shop use it. You can borrow the torque plate if you'd like. I had a set of custom pistons cut by CP for that bore size. I think they're fit at .0025-.003 or so.

Total Seal can set you up with gapless rings in that size, but the quality control of the third party ring that they have to start with for that bore size is pretty poor, so you're not going to get great results from them unless you pay a lot more money to have the rings lapped. If you do that, you have to get the rings first so the piston MFG can cut grooves for that specific set of rings.

Sealed Power rings have the best quality control and tolerancing right out of the box of any set of rings I've seen for a Northstar. Thickness variation was .0005 on any given ring and .0010 across the whole set. They should function well with an overbore/overhone of less than .010.

Piston coatings and block porting are each worth a couple of ponies. Block porting is basically free and piston coating isn't that expensive compared to the rest of a good build.

Anything else you want to know?

[This message has been edited by Will (edited 10-22-2008).]

Forum members Will and AJxctman should be able to help you with your situation.

I'm an automotive machinist by trade, and have done a few Northstars, but If I was doing one in my Fiero, instead of the LS V8 I am doing, I'd pay whatever it took to get a cherry Northstar from a low-mileage car. Better to never open them up.

quote Originally posted by Isolde: Better to never open them up.

Absolutely.

What do you mean you've "done" Northstars? Stock rebuilds? What's your experience with them?

quote Originally posted by Will: Your experience sounds a lot like mine... I went through 2 qt's of oil in 100 miles of test driving. The engine will NOT fix itself. At this point, your only credible option is to tear it down and start over. BTDT. There's no such thing as a cheap Northstar build. My engine always tested with very high compression... over 220 psi. This was because the rings were bathed in oil and that helped them seal. It also always had puddles of oil on the backs of the intake valves. Since pulling the intake isn't very hard, you should check this out. The first shop I went to was locally reputable, but worked very little with anything but domestic iron V8's. The hone job they did was piss-poor and I didn't know enough at the time to pick that out. Also, honing the block and then using cast pistons opens the bore clearance up a lot. IIRC, the stock pistons are fit at .001 to .0015. Honing even .001 out doubles the factory bore clearance. You won't get a good hone unless you take at least .005 out. NEVER pay an engine shop to assemble your engine. They almost never use procedures or build sheets, so they're almost certain to screw up an engine they haven't done before. Not only will they likely not do it right, NOBODY cares more about your engine than you do. As long as all the bolts take torque and the aluminum in the holes isn't corroded, there isn't a strict *need* to timesert. I did my block as a safety measure. As far as shops go, you're best off trying to find a shop that specializes in import engines, especially Subarus and Hondas as those are open-deck die cast blocks like the Northstar. On a basic Chevy, the entire block is iron, so GM used a cheap soft grade of iron. On old Cadillac big blocks, GM used a high-nickel iron and paid much more attention to core shift, with predictably better results. For the Northstar, not only is it a Cadillac and thus worthy of a few more dollars, the amount of iron is MUCH smaller. I conjecture that this means that GM used a VERY high grade of iron in the bore liners. The GM Powertrain lists them as cast grey iron, vice nodular iron for cranks and truck blocks. The high grade of iron is MUCH harder than older domestic iron blocks and takes very different honing methods to get a good bore finish. Kevin at Total Seal recommends aluminum oxide stones instead of silicon carbide. SiC is the stone usually used with a SBC. If you use SiC stones to hone a Northstar, the hard iron of the Northstar bores and the hard silicon carbide stones just polish each other and you end up with a bore finish that's *worse* than what you started with. A hand/drill/dingleberry hone is a complete waste of time on these engines. They NEED a proper machine hone with the proper stones. I bought my own set of honing stones and took them with my block to a shop that builds high end import engines. The second hone job looks great, but my block is .008 over at 3.670. That's what it took to get the bores round and fully finished. I made my own torque plate and had the shop use it. You can borrow the torque plate if you'd like. I had a set of custom pistons cut by CP for that bore size. I think they're fit at .0025-.003 or so. Total Seal can set you up with gapless rings in that size, but the quality control of the third party ring that they have to start with for that bore size is pretty poor, so you're not going to get great results from them unless you pay a lot more money to have the rings lapped. If you do that, you have to get the rings first so the piston MFG can cut grooves for that specific set of rings. Sealed Power rings have the best quality control and tolerancing right out of the box of any set of rings I've seen for a Northstar. Thickness variation was .0005 on any given ring and .0010 across the whole set. They should function well with an overbore/overhone of less than .010. Piston coatings and block porting are each worth a couple of ponies. Block porting is basically free and piston coating isn't that expensive compared to the rest of a good build. Anything else you want to know?

I have read your engine thread Will at the suggestion of Ryan Hess. I am also struggling withe a stumble and idle problem that he has tried to help me source.This is a separate issue (I think?) that I need to resolve before the engine comes out. I have changed the intake to try and correct this and noted then that my valves were oil laden like yours have been. My compression is also 220 plus psi too.
Your assertion about using the same pistons in overbore/overhone sleeves is what I was worried about.
One thing I forgot to mention - when I had the case apart to seal it up with aerobic sealant I found that the 10 or 12 small (6mm?) bolts that tighten the oil gallery plate down near the perimeter of the oil pan were loose! The guy actually forgot to torque them before putting on the pan. I'm glad I found that before running it.
This shop too was a small block shop. They and I did not know any better at the time. I know now, not too sure if they do yet.
So how is yours now? Is there light at the end of this tunnel? Another option I have not ruled out is the purchase of another engine, either a low mileage jewel as you suggest or a warranted rebuild from a reputable rebuilder if there is such a place.

------------------
Daviero - 88 N* GT

I'm coming to the light at the end of the tunnel and hope it's not an oncoming train.

The crank counterweights have been cut. It should go in for journal cut to .010 under and final balance this week. After that it'll be the weekend of the 1st before I'll be able to make it out to the shop to pick everything up. Once I do that, I'll have to spend another entire weekend cleaning everything before assembly the next weekend. Even once it's assembled, it'll be a couple of months before it runs because I've got a lot of other things to do... clean the garage, get the current (failed head gasket) temporary engine out of the car, change the trans FD to 3.94, put together my crazy oil system, re-engineer the accessory drive, re-route the harness, etc. etc. etc.

I have a friend with a 4.6 northstar and from the hassle he went through with them leaking into the cylinders. Here is the know problems with the 4.6 Northstar as quoted on aa1car.com:

Northstar Problems & Recalls
As well-engineered as Northstar V8s are, like other engines they've had some problems. According to various sources, head gasket failures are not uncommon. Nor is oil burning or oil leaks.

Cadillac service bulletin 01-06-01-011 deals with oil burning on 1996-'99 Northstar V8s. The cure, says Cadillac, is to do a ring cleaning procedure (seems those long oil change intervals weren't such a good idea after all). Cadillac recommends using GM cleaning kit (P/N 12378545) and Kent-Moore J-45076 induction/evacuation tool to do the job. The cleaner is added into the cylinders through the spark plug holes and allowed to soak the rings for two hours. The cleaner and dissolved crud is then vacuumed out of the cylinders through the spark plug holes, followed by an oil change. Cleaning the throttle body and EGR valve is also recommended.

The cylinders have cast-in-place iron cylinder liners that are not replaceable. Compression up to model year 2000 was a relatively high 10.3:1. It was lowered to 10:1 in 2000. Each head has two camshafts (one intake, one exhaust) and four valves per cylinder (33mm intakes and 29mm exhausts). Direct-acting hydraulic lash adjusters are positioned over each valve. The overhead cams are all chain-driven, and use an intermediate chain sprocket under the front cover to connect to the crankshaft. Three separate hydraulic tensioners are used to keep the cam chains tight.

The Northstar V8 is an interference engine, which means if a chain fails or is disconnected when the engine is cranked over, the valves will hit the pistons. That's something you don't want to happen with an expensive engine like this!

The intake manifold is Nylon 66 thermoplastic, which helps cool intake air by conducting less heat from the engine. Fuel delivery is by sequential fuel injection with separate injectors mounted under the engine's top cover. Under the top cover you'll also find the MAP sensor, intake air temperature sensor and fuel pressure regulator.

If the fuel pump relay fails on a Northstar V8, the engine should still run because the fuel pump also can be energized through the oil pressure sending unit.

A four-coil distributorless ignition with a waste spark set up provides spark to the plugs. Two crankshaft position sensors are used (A and B) plus a camshaft position sensor to provide timing inputs. Both crank sensors are mounted in the block and the cam sensor is located on the rear head in front of the exhaust cam. There's also a knock sensor on the rear head between cylinders 1 and 3 to retard timing if detonation becomes a problem under load.

The ignition system has two modes of operation: "module mode" and "ignition control mode." In ignition control mode, the PCM controls ignition timing using sensor inputs. If there's a problem in the PCM or with its sensor inputs, the module mode takes over and runs the engine with a fixed 10 degrees of advance. The engine continues to run (essentially a limp-in mode) but with reduced performance.

In model year 2000, the DIS ignition system was changed to a coil-on-plug design, which eliminates the spark plug wires and waste spark. Each head has its own ignition module that fits in the middle of the valve cover.

Another feature of the Northstar engines is a "limp home" mode that allows the engine to continue running if all the coolant is lost. If the PCM senses an overheating condition, it temporarily disables up to half of the cylinders. This pumps enough air though the engine to keep temperatures from getting hot enough to cause any damage. Even so, GM says the vehicle should not be driven more than 50 miles in the limp-home mode.

Another unusual feature you may see is a liquid-cooled alternator on the DeVille and Seville. Cadillacs are crammed with electrical accessories that put quite a load on the charging system, so using liquid cooling helps prolong the life of the alternator. In 2001, GM went back to an air-cooled alternator to "eliminate the coolant tubes and potential leak points."

Engine Maintenance
As for maintenance, there isn't much. One of GM's goals with the Northstar program was to reduce maintenance to a minimum. The engines are factory-equipped with 100,000-mile platinum-tipped spark plugs and five-year/150,000-mile Dex-Cool antifreeze, and use chain-driven cams to eliminate the need to replace timing belts. Except for oil and filter changes, there isn't much to maintain - unless something breaks.

The newer Northstar V8s use an "oil life monitor" light rather than a specific mileage interval or service schedule to indicate when oil changes are needed. The PCM tracks engine rpm, operating temperature, load, running time and ambient temperature to calculate oil life. Up until 1999, the maximum oil change interval under ideal conditions was 7,500 miles. In 2000, GM bumped the upper limit to 10,000 miles. In 2002, they did away with the upper limit altogether stretching the oil change interval to 12,000 miles or more, depending on operating conditions. However, GM does say the oil should be changed at least once a year regardless of mileage.

Note: When changing oil on a 4.6L Northstar V8, keep in mind that this engine holds 7.5 quarts instead of the more common 4 or 5 quarts.

Hope that helps on some aspects

Shelby