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).
Erik
MAR 05, 02:35 AM
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
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).]
Will
MAR 05, 01:33 PM
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.
Will
MAR 05, 01:34 PM
quote
Originally posted by Steven Snyder:
Re-sleeving is not an option?
Resleeving costs about $2500...
Will
MAR 05, 01:36 PM
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
I've corresponded with Allen Cline (one of the engineers who DEVELOPED the Northstar) and he told me that YES, the dynamic environment in the intake tract during even part throttle operation can lift oil out of a cylinder and into the intake manifold.
AJxtcman
MAR 05, 01:45 PM
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.
Zac88GT
MAR 05, 04:01 PM
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.
AJxtcman
MAR 05, 04:54 PM
This is all valve guide.
I will look for a better picture of this at home
AJxtcman
MAR 26, 07:13 PM
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).]
