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Another smoking L20b


loungin112

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Nothing was done to the pistons, the stock ones were replaced with others. Looks like they have domes on them? Or is that a reflection??? Don't use photobucket. Terrible viewing.

 

Once apart any warranty would be void anyway. Head may have been warped. Get a straight edge and check. You're allowed no more than a 0.004" feeler gauge under.

 

Blown head gaskets do not mix oil with coolant. The only place this might happen is the oil jet where it passes through the gasket from the block to the head between #3 and #4 directly above the oil pressure sender. Gaskets can blow into the water jacket, between cylinders and even out to the side of the block. If water is involved, compression will force it past the rings, if enough water and time. This will mix with the oil and make it milky. Most obvious is the steam blowing out the exhaust pipe. Steam will clean the bad cylinder... so if the combustion chamber, valves or a piston top is shiny clean this is the place to check the old gasket. Looks like cylinder 2 is cleaner than the others although all are strangely black????.

 

If those are flattops or more, the head gasket should have held. Maybe not torqued properly, warped, or overheated and caused a warp. If dowel missing the gasket won't line up properly too.

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I should add the following:

 

dual 38mm SU's

Stock Exhaust mani

U67 head

p68 pistons

AmeriCam

Mallory distributor

Stock radiator

 

Regarding the mechanic...seems to be a good mechanic but a crook.

...how can he be good and a crook at the same time?
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I should add the following:

dual 38mm SU's
Stock Exhaust mani
U67 head
p68 pistons
AmeriCam
Mallory distributor
Stock radiator

Regarding the mechanic...seems to be a good mechanic but a crook.

 

 

Good and crook are not mutually exclusive.

 

That is not a stock exhaust manifold. Definitely not from a U67 head. Does look like an L16/18 though so... KEEP IT

 

 

WTF are P68 pistons??????

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Good and crook are not mutually exclusive.

 

That is not a stock exhaust manifold. Definitely not from a U67 head. Does look like an L16/18 though so... KEEP IT

 

 

WTF are P68 pistons??????

 

Interesting note about the manifold.  i have no plans to go with headers...actually have a set hanging on the wall, which is where they are going to stay. 

 

P68std pistons: from my research, they were pistons used in the NA 280zx.  They do have a dome to them to increase compression.  Prior to the rebuild, they did not have any grinding on the dome...that was done by the mechanic.  I found a set of 4 for sale at $400, so I guess they are rare??  Doesn't really matter though...I'm running what I've got.

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Warped head is my guess.

Also check very close on the block between 2&3. Every block I checked was bad. Coolant flows through there.

 

Also what ex Mani gasket? If head not drilled for coolant flow, use a tiny amount of rtv there.

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Alright. Got the head to a reputable shop and learned some things. First, it looks like what stoff noted about a rotary grinder was found by the mechanic.

 

Leaky intake/exhaust manifold gasket? Check the torque on those fasteners first, then remove the intake if it persists.

 

Did you install the intake? Did you surface the manifold with a Roloc disc on a 20000 rpm grinder? If so, that's bad and could be the cause.

It will have to be resurfaced, but this was not the cause of the coolant leak. A pressure test showed that the PO had enlarged the intake and exhaust ports. This caused a hole into a coolant channel that finally give way. Not sure why it finally gave way, but it did.

 

We're going to see if the hole can be repaired...not sure if this is a good idea or not. Anyone know the stock height of a u67...trying to find one that hasn't been resurfaced before.

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  • 1 month later...

Two of the head bolt holes in the block (on the left side) and the head have a wider hole. A small sleeve or dowel fits into the block holes and sticks up. When the head is aligned it drops down over the dowels

 

fel-es74007_w_ml.jpg

 

Anyone know where I can find a set of these?  I only have one...so I need another.  If you have one, let me know how much to drop it into an envelope and USPS mail it.  (I've checked the usual sources...ebay, amazon, autoparts stores, etc...)

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Funny how nobody ever thinks to try the Nissan parts department.

Because i never have any luck with local nissan dept. The furthest back they could, or would, check is back to 1983. They found a part number for a 280z...figured i would give it a shot since it is still an l series engine and they were only $1.25 each. Will report back on whether they are the same as an l20b.

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Because i never have any luck with local nissan dept. The furthest back they could, or would, check is back to 1983. They found a part number for a 280z...figured i would give it a shot since it is still an l series engine and they were only $1.25 each. Will report back on whether they are the same as an l20b.

You should be ok with that part.....

This is the part # I found for my L16 which also fit the L20b.... should be what you bought... #11053-73400

I found at the dealer they don't know how to access the old info.... they have it but even where I go there is only one guy who even knew how to use it even if I gave him the part number.....

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Too much work for the little princesses.

 

 

Take this Nissan part number in and give to them. 11053-73400

 

It was later, and last used, in the

 

'79-'83 280zx with L28 engine.

'88-'90 KA24E in the 240sx

'86-'89 Pathfinder with Z24i engine

'82-'84 Maxima with L24E engine

'89-'93 D21 Hardbody with KA24E engine

'86-'89 D21 Hardbody with Z24i engine

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You should be ok with that part.....

This is the part # I found for my L16 which also fit the L20b.... should be what you bought... #11053-73400

I found at the dealer they don't know how to access the old info.... they have it but even where I go there is only one guy who even knew how to use it even if I gave him the part number.....

That is the part number i ordered. I get them today and will compare with the one i have on hand.

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Part number I ordered look to be the part needed....got 5 in my possession now.

 

The welds on the head didn't take, so I'm having to try an rebuild another one.  Thought the one I bought was a solid head, but it turns out it was shaved a bit before....shaved unevenly unfortunately.  The guy rebuilding the head thinks it will work though.  Keeping my fingers crossed.  Not quite sure what to do with the old head...any suggestions?

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Welding a head is tricky. Porosity needs to be completely ground out before any welding can happen, and sometimes that means removing quite a lot of material.

 

I remember back when our go-to machine shop started charging extra for a "squared surface", meaning that they would cut both ends of the head the same amount. Most machine shops will cut corners anywhere they can and it doesn't surprise me to hear that your head was cut unevenly.

 

What casting is it? If it's a good one, don't throw it away as you might be able to find someone in the future who can repair it.

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