If the problem's the bore surface finish, then the only way to fix it is to tear the engine back down...

I know it sucks to hear that. I *really* didn't want to pull the car back down after I'd gotten it back together, but the fix requires rehoning the bores correctly.
Once you do that, your piston-bore clearance will be out of spec... There are no oversized pistons available...
It gets to be an expensive spiral quickly.
Northstars are NOT engines that can be torn down for a quick, easy overhaul like Chevies can be...

[This message has been edited by Will (edited 02-16-2008).]

quote Originally posted by Will: If the problem's the bore surface finish, then the only way to fix it is to tear the engine back down... I know it sucks to hear that. I *really* didn't want to pull the car back down after I'd gotten it back together, but the fix requires rehoning the bores correctly. Once you do that, your piston-bore clearance will be out of spec... There are no oversized pistons available... It gets to be an expensive spiral quickly. Northstars are NOT engines that can be torn down for a quick, easy overhaul like Chevies can be...

I think GM sells oversize pistons. I know they list that the 93 to 99 engines can be bored .050

[This message has been edited by AJxtcman (edited 02-16-2008).]

quote Originally posted by AJxtcman: I think GM sells oversize pistons. I know they list that the 93 to 99 engines can be bored .050

Sure that's not .005, the same as the initial overbore spec for the LS1? Liners don't like being overbored.
Last time I checked (admittedly ~4 years ago), a replacement piston from GM could only be had in kit that included the rings, locks and pin to go with the piston. ONE kit was for ONE cylinder and cost ~$200.

I've had 8 or 10 longblocks that were warranteed because GM would rather warrantee that engine than have dealership techs try to overhaul it. Read the threads on this board about overhauling Northstars and you'll see why...

quote Originally posted by Will: Sure that's not .005, the same as the initial overbore spec for the LS1? Liners don't like being overbored. Last time I checked (admittedly ~4 years ago), a replacement piston from GM could only be had in kit that included the rings, locks and pin to go with the piston. ONE kit was for ONE cylinder and cost ~$200. I've had 8 or 10 longblocks that were warranteed because GM would rather warrantee that engine than have dealership techs try to overhaul it. Read the threads on this board about overhauling Northstars and you'll see why...

I have installed over 50 sets of pistons in Northstars under warranty. All of them standard, but I know what it will take to bore and hone the 93 to 99. They even have stone specs

.5mm is .01968", or just under .020"

Man, as cool as N*s are, they sure do seem impossible to use!
I like how Will has referred to the SBC before... You can rebuild it with bubblegum and sand and it'll run just fine.

Good luck with your problems, that'll be one SWEET car when the bugs are worked out. It sounds great too!

I think that the Northstar gets cobbled together as well.

I put the intake back on today and ran it for a while with the PCV disconnected and it was still smoking, so i shut it off and pulled the intake again. This time there was definatly a pool of oil on the backs of some of the valves. Probably a teaspoons worth on the backs of the #7 valves. I might still do the leakdown test depending on how i feel but it looks like it's gotta come out again. The real question is: Is it worth it to try and rebuild it again and have it bored and honed with new pistons and whatnot, or should i just buy a new shortblock from the dealer?

quote Originally posted by AJxtcman: I think that the Northstar gets cobbled together as well.

I don't think its the engine, more the owner. The engine needs to redline now and then to get rid of carbon deposits. It doesn't seem to like lumbering along in an old man cadillac. Piston slap can be pretty much solved.

There is no reason the N* can't last 300k miles, but you have to do propper maintinance on it, like changing out the coolant every few years. Keep the anti corosion properties fresh in the coolant and 3/4 of the headgasket problems would go away.

Great motor, a big cadillac is a poor platform for a DOHC V-8. A new N* will probably last longer in a fiero with regular WOT runs than idling along in a cadillac.

[This message has been edited by crzyone (edited 02-17-2008).]

quote Originally posted by AJxtcman: I think that the Northstar gets cobbled together as well.

And we're seeing the results of doing that.

quote Originally posted by Zac88GT: I put the intake back on today and ran it for a while with the PCV disconnected and it was still smoking, so i shut it off and pulled the intake again. This time there was definatly a pool of oil on the backs of some of the valves. Probably a teaspoons worth on the backs of the #7 valves. I might still do the leakdown test depending on how i feel but it looks like it's gotta come out again. The real question is: Is it worth it to try and rebuild it again and have it bored and honed with new pistons and whatnot, or should i just buy a new shortblock from the dealer?

Unless you can find oversized pistons (maybe they're out there now...), you'll need custom slugs if you get your block honed. Mine is ending up at 3.670 bore (3.662 is stock, so it's .008 over). Don't take it to a shop that does mostly Chevies, though, as they won't be able to hone the bores correctly. You'll have better luck with an import shop that does a lot of work on Hondas and Subarus.

Bump because knowledge is POWER!!!

What have you decided to do Zac ?

If it was me I would probably look for a low K used motor to replace but if money permits a brand new one would be sweet.

Re-sleeving is not an option?

quote Originally posted by Zac88GT: I put the intake back on today and ran it for a while with the PCV disconnected and it was still smoking, so i shut it off and pulled the intake again. This time there was definatly a pool of oil on the backs of some of the valves. Probably a teaspoons worth on the backs of the #7 valves. I might still do the leakdown test depending on how i feel but it looks like it's gotta come out again. The real question is: Is it worth it to try and rebuild it again and have it bored and honed with new pistons and whatnot, or should i just buy a new shortblock from the dealer?

Just so I understand You removed the oil from the intake manifold correct?
Then you ran the engine without the PCV system attached correct?
Just to double check that again. you had both PCV hoses pulled or just one when you ran it?
If it was a ring problem that was so bad it would deposit that much oil on the valves you would have had smoke billowing out of the PCV holes in the valve covers.
You have not mentioned that so I am going to assume that is not the case.
Think about it it the rings don't seal the gases have to leave the crank case some how.
Now we have kind of ruled out rings.
How can oil get to the back side of the valves? Hmmmmmmmmmmmmmmm.

The only way it is possible to get that much oil on the back side of the intake valves with the PCV disconnected is from the intake valve guides.
When I say the guides I mean the oil must run down from the top side. The can happen from to much Valve Stem to guide clearance, Bad or incorrect valve stem seals, or a leak from the outside of the guide. I have seen several valve guides that had been damaged in installation on Northstars.
Hand down it is a Valve train issue

I hope this is not something that repeats every single time (Will and now you). I too rebuilt my engine and although is not yet running yet I wouldn't want to go through this.

Zac I can almost feel your pain bro (money and time invested...). I wish you the best luck and hopefully it is something that can be fix without you loosing your whole investment.

JG

quote Originally posted by AJxtcman: Just so I understand You removed the oil from the intake manifold correct? Then you ran the engine without the PCV system attached correct? Just to double check that again. you had both PCV hoses pulled or just one when you ran it? If it was a ring problem that was so bad it would deposit that much oil on the valves you would have had smoke billowing out of the PCV holes in the valve covers. You have not mentioned that so I am going to assume that is not the case. Think about it it the rings don't seal the gases have to leave the crank case some how. Now we have kind of ruled out rings. How can oil get to the back side of the valves? Hmmmmmmmmmmmmmmm. The only way it is possible to get that much oil on the back side of the intake valves with the PCV disconnected is from the intake valve guides. When I say the guides I mean the oil must run down from the top side. The can happen from to much Valve Stem to guide clearance, Bad or incorrect valve stem seals, or a leak from the outside of the guide. I have seen several valve guides that had been damaged in installation on Northstars. Hand down it is a Valve train issue

You can't rule out ring sealing like that. What you say is not true.. Smoke does not have to billow out from the vent holes if he has a ring problem.
On decel the car billows smoke. This is true. There is vacuum in the cylinders because the throttle is closed. It's not generating blowby at this point. The cylinders are pulling up oil from the crankcase because the rings are not sealing..

quote Originally posted by Steven Snyder: You can't rule out ring sealing like that. What you say is not true.. Smoke does not have to billow out from the vent holes if he has a ring problem. On decel the car billows smoke. This is true. There is vacuum in the cylinders because the throttle is closed. It's not generating blowby at this point. The cylinders are pulling up oil from the crankcase because the rings are not sealing..

He has oil on top of the VALVES

How can the oil get on top of the valves from a ring not seating? Remember he pulled the PCV

OK, i've ordered new pistons and rings, 0.25mm oversize. The ring gaps were a little on the large side at .022" top and 2nd compression rings. And the stock pistons rocked a little in the bores so it needed new ones anyway. I checked the valve guides by feel and they felt good but i didn't take any measurements. I compared them to my friends lotus esprit head and his valve stems are larger and have more play, therefore more room for oil to leak past. The lotus head doesn't use valve stem seals at all, of any kind, for intake or for exhaust, and it doesn't smoke at all. This makes me believe that it's impossible for this much oil to leak past the valves, especially when i have the pcv connected. It's definatly not the pcv sucking in oil either, because when i disconected it (both hoses) and cleaned out the intake the problem still continued. I'm pretty sure the rings are the only place where this amount of oil transfer can happen. Because they're a low tension ring and may not have seated properly, during high vacuum situations the oil and crankcase air can be sucked into the cylinder quite easily. During combustion the increase in cylinder pressure forces the rings against the cylinder wall creating a half decent seal. This is why i'm not seeing much blowby. The oil on the backs of the intake valves must be comming from the cylinders caused by reversion in the intake. Since the intake valve doesn't close until 73* after bottom dead center there would be lots of time for some of the oil to be blown back out into the intake. I didn't think it was the rings at first because i was in denial and didn't want to redo everything, but the more i think about the symptoms and the amount of consumption and all the factors the more i'm convinced it's the rings. Good news is that i was finally able to find a set of pistons for it for a reasonable price. Forged pistons from CHRFab were like $1220 with rings and all i want were some oversized stock replacements. I work part time at a parts store so I called Mahle, Sealed Power, and Silvolite. All three of these companies make the pistons and offer them in an oversize but they are all on factory back order and have no idea when they'll be available. I called engine tech, (thanks AJ) and they refered me to their canadian branch called Ontario Reman. Ontario Reman had a set of pistons and rings in stock in the states so they are just doing an interstore transfer and then shipping them to me. They'll probably be cheaper than i could have gotten through work anyway, and i'm pretty sure they're made by Mahle. The pistons were $280 and the rings were $70. It's only $150 for boring and honing, $200 for rod bolts and $25 for some more engine sealant. I thought about just getting another used engine but this will much cheaper in the end (all the wreckers here think northstars are worth their weight in gold).

here are some pistons in case you are interested on ebay ..apparently they offer them oversize

They have a # you can call to find out what manufacture

http://cgi.ebay.com/ebaymot...ksid=p3756.m20.l1116

quote Originally posted by AJxtcman: He has oil on top of the VALVES How can the oil get on top of the valves from a ring not seating? Remember he pulled the PCV

Because the valves open and there's oil getting whipped up around the combustion chamber.

Obviously it could still be the valve guides, I'm just saying you can't at all rule out rings..

[This message has been edited by Steven Snyder (edited 03-05-2008).]

quote Originally posted by AJxtcman: If it was a ring problem that was so bad it would deposit that much oil on the valves you would have had smoke billowing out of the PCV holes in the valve covers. Think about it it the rings don't seal the gases have to leave the crank case some how. How can oil get to the back side of the valves? Hmmmmmmmmmmmmmmm. The only way it is possible to get that much oil on the back side of the intake valves with the PCV disconnected is from the intake valve guides. Hand down it is a Valve train issue

This is not correct.
My engine smoked like a chimney out the exhaust pipes and had oil on the backs of the valves, but nothing coming out of the PCV openings.
The problem was the hone job and the bore surface finish.
Rings will still seal compression pressure, but during the intake stroke the oil will be drawn into the cylinder past the rings.
Intake resonance will loft it out of the cylinder past the intake valves, even at part throttle. When the engine is shurt down, it comes out of suspension and pools on the backs of the intake valves. PCV and valvetrain have nothing to do with it.

quote Originally posted by Zac88GT: I put the intake back on today and ran it for a while with the PCV disconnected and it was still smoking, so i shut it off and pulled the intake again. This time there was definatly a pool of oil on the backs of some of the valves. ******* Probably a teaspoons worth on the backs of the #7 valves. *******

That just seem like more than the amount that is sneezed up into the runners.

quote Originally posted by AJxtcman: That just seem like more than the amount that is sneezed up into the runners.

It's certainly more than the regular amount because the rings weren't properly seated. That volume of oil is probably 10 times larger than the valve guides could possibly flow in 2 revolutions of the engine. The valve stems can only leak around a few mm valve stem and the clearance isn't all that much, plus there is a positive valve seal, and crankcase vacuum helping prevent flow down the stem. The pistons are trying to draw in air and oil past the rings, they're over 90mm in diameter and have way more clearance. This volume of oil has to be comming from the rings.

This is all valve guide.


I will look for a better picture of this at home

I just installed a set of updated GM pistons into this car. #8 piston had a piece of metal embeded into it. It wore/scored a groove into the cylinder. I honed .0015 out of that cylinder. Guess what no smoke. Well from the exhaust
hmmmmmmmm

[This message has been edited by AJxtcman (edited 03-26-2008).]

quote Originally posted by AJxtcman: I honed .0015 out of that cylinder.

Now your bore clearance is twice what it should be.

quote Originally posted by Will: Now your bore clearance is twice what it should be.

Specs
Bore---------------------------------------------- 3.6611-3.6617 in
Cylinder Bore Out-of-Round ------------ 0.0039 in
Cylinder Bore Taper ----------------------- 0.0039 in
Piston Diameter ---------------------------- 3.6597-3.6603 in
Piston to Bore Clearance --------------- 0.0008-0.0020 in

Hmmmm I did not hone the scratch out all the way. The bore is still in spec. The new pistons are coated. They are GM replacement pistons. I would have to guess that they are slightly larger than the originals and the Piston to core clearance is still in spec. I did not hone all the wave out of the block.

Bottom line I honed the block and it is not blowing blue smoke.

So if the bore clearance was .0015 like it's supposed to be, and you honed the bore .0015, your bore clearance is now .003... with a cast piston.

Take measurements instead of copying and pasting out of the shop manual. You'll build better engines for it.

quote Originally posted by Will: So if the bore clearance was .0015 like it's supposed to be, and you honed the bore .0015, your bore clearance is now .003... with a cast piston. Take measurements instead of copying and pasting out of the shop manual. You'll build better engines for it.

If the spec for taper is .0039" how can the Piston to cylinder spec be .0015? The Spec is listed as .002" correct?
I said I installed the replacement OE coated pistons. Since this is a repair piston could it be .001 larger?

Sorry for hijacking your thread Zac.
I find myself apologizing a lot recently for getting into pissing matches. Sorry again.

[This message has been edited by AJxtcman (edited 03-31-2008).]

quote Originally posted by AJxtcman: If the spec for taper is .0039" how can the Piston to cylinder spec be .0015? The Spec is listed as .002" correct? I said I installed the replacement OE coated pistons. Since this is a repair piston could it be .001 larger? Sorry for hijacking your thread Zac. I find myself apologizing a lot recently for getting into pissing matches. Sorry again.

one is a mechanic with common sence - one is an engineer without - one builds engines that smoke - one doesn't - huummmmm

[This message has been edited by Russ544 (edited 03-31-2008).]

quote Originally posted by AJxtcman: If the spec for taper is .0039" how can the Piston to cylinder spec be .0015? The Spec is listed as .002" correct? I said I installed the replacement OE coated pistons. Since this is a repair piston could it be .001 larger? Sorry for hijacking your thread Zac. I find myself apologizing a lot recently for getting into pissing matches. Sorry again.

quote Originally posted by AJxtcman: Specs Bore---------------------------------------------- 3.6611-3.6617 in Cylinder Bore Out-of-Round ------------ 0.0039 in Cylinder Bore Taper ----------------------- 0.0039 in Piston Diameter ---------------------------- 3.6597-3.6603 in Piston to Bore Clearance --------------- 0.0008-0.0020 in Hmmmm I did not hone the scratch out all the way. The bore is still in spec. The new pistons are coated. They are GM replacement pistons. I would have to guess that they are slightly larger than the originals and the Piston to core clearance is still in spec. I did not hone all the wave out of the block. Bottom line I honed the block and it is not blowing blue smoke.

The bore clearance is listed as .0008 to .002. A typical blue printing spec for cast pistons is .0015, which falls within the quoted range.

As for how the piston to bore clearance can have a max of .002 while the taper and out of round specs are .0039... that's a question for YOU to answer, if you're going to be using these specs.

What did you use to hone it?

quote Originally posted by Russ544: one is a mechanic with common sence - one is an engineer without - one builds engines that smoke - one doesn't - huummmmm

You think the first engine I ever tried to overhaul is the only one I've ever built? I thought you had common sense too, Russ.

My Sunnen hone with 500 stones
I had been using the dealerships Central Tools Bore Gauge, But about a month ago I bought a very nice Mac Tools bore gauge for only $436.98. Wow is it nice. sooooooo much easier to use.
CBG280
Range: 2"-8". Graduation: .0001". Measures cylinder wear. Measuring depth: 12". Self-centering, jeweled indicator. In durable case. Meets JIS B7515 specification.


I have been doing so many 3.6L engines it is unreal

[This message has been edited by AJxtcman (edited 03-31-2008).]

Well, I just took the heads apart and measured the valve guide clearance and they are perfect. With the valves in the head I siliconed a plate with a barb over the intake and exhaust ports of the cylinders that were burning the most oil. Hooked up my vacuum bleeder and there were no signs what so ever of any leakage past the valve seals or guides. I did find out why #6 had low compression duing my compression tests though. One of the exhaust valves wasn't sealing very well. I had ground the valves and seats so it shouldn't have leaked but i'll relap them and test them before i put it back together. I had ordered a set of pistons from Ontario Reman because they had said that they were in stock in their state side branch. It turns out they were wrong so now they're factory back ordered. I have no idea when i'll get them but hopefully they'll come before the summer is over. If the oil burning isn't the rings than i'm completely stumped. The only places where the engine can really burn oil is either through the rings, the valves, and the PCV system. The valve guides are right in spec and the seals are brand new and sealing great. After pulling the PCV valve out of the valve cover and looking down into the baffle while the engine was running it was totally dry, so it's not the PCV. The only thing left is the rings. The pistons were pretty sloppy, i could rock them back and forth, so it needed new ones anyway. The ring gaps on the new rings were .025 which is double the spec but i've never seen large ring gaps burn oil like this. I'm still stumped but i just hope it's fine when it goes back together this time with new pistons and rings.

I've had no experience on this with the Northstar specifically, but on some engines, if there is not a vaccum in the crankcase, oil will go past even a new and proper sealing set of rings. it's too late to check now, but it might have been enlightening to know if you had a vaccum, or presure, in the crankcase when it was running and pumping oil. but then again, with as much oil as you discribe behind the valves, it sure sounds like it also could have come in via a manifold vaccum port of some kind. pvc or otherwise.

hope you get it worked out,
Russ544

Can you roll the engine over and get a good look at (or even pictures of) the bore surface finish, especially in cylinders that were burning oil?