Well I just bought this car. It's a 1970 240z with a P79 head and a F54 block out of a 81-83 280zx non turbo. The complete engine was rebuilt less than 6000 miles ago by a very reputable Datsun engine builder, Eiji Hosomi, out of Datsun Spirit. When I bought it the PCV was capped with a freeze plug and there was a breather hose coming off the valve cover. This was smokey and stinky since I've had it. The previous owner said that it had always smoked a little but recently had smoked more. Doing a lot of reading I figured I would uncork the PCV hoping to reduce the blow by coming out of the crankcase and setup a catch can with a breather filter on top. I did just that this morning and this thing is smoking even more now it seems. There is white gray stinky gas smelling smoke almost billowing out of the catch can breather filter. I drove it around the block and she runs SOLID. She just smokes a lot out of the catch can to where it's coming into the cab and it's unbearable. I've read and read. Rings are shot? Compression test? Leak Down? The car runs just fine I would think the compression is fine....I'm bumming. I have money left over from buying the car to cover fixing stuff, that I was hoping to break at the track, not to get it ready for the track! Any insight is appreciated. I need to hit the sac. Night shift sucks. I've been up since 3pm yesterday and I am beat!

13 hours ago, zmanoside said:

Got a call this morning bright and early. Rings from #6 were broken and in oil pan. #6 piston has a cracked skirt. #5 piston skirt is also cracked with damaged, but still in place rings. Mechanic called to ask if he could proceed to remove the rest of the pistons to inspect the remaining pistons and cylinders. Obviously I said yes. He said the #6 cylinder didn't actually look too bad, and will most likely be fine with a good honing, and the rods and bearings looked good too. So I think at this point its looking like a new set of pistons and rings. Hopefully all of the cylinders will be good with just a hone....

I have a question. How do these rings get into an oil pan even if broken?

There is a small gap, very small, between the piston and the cylinder wall, but made bigger with a broken ring. The gap is probably bigger when the car is cold too. The broken ring fragments get wedged in between the the piston and the cylinder wall until it falls down below into the depths of the oil pan? It's probably more likely forced down through that gap on combustion. Just trying to answer your question with my limited knowledge of internals! I think I must be close to right!

8 hours ago, Lumens said:

I have a question. How do these rings get into an oil pan even if broken?

 The cracked and or broken piston skirts explain how the pieces of the ring got onto the pan. My question is, was did the destruction caused by a bad tune-up (preignition and detonation) or did the replacement head raise the compression to the point of preignition and or detonation?. Low octane gas would have made either scenario worse.

Get us a photo of that piston if you can.

I and others too may like to see what it looks like.

I have heard of this before on Z turbo builds but nothing that bad on a NA engine.

Will do. I called the mechanic today just to ask him not to throw the Pistons away and that I wanted them.....he says, oh ya, the Pistons I ordered are not the flat top Pistons you wanted, I can't find them anywhere, so, you get me some Pistons and I'll put them in for you.....so I got online and ordered some standard size 81-83 flat tops from zcar source of Arizona. The gent, Jeff that helped me on the phone was awesome and they will ship the Pistons to the shop, should be there Monday.....which takes me to, what is the PROPER way to break these new Pistons in guys...I have an hour drive home on the freeway...to do 65mph in this car will take me to around 35/3600 rpm...hopefully that is not too much for them...do I just need to stay below 5k? Or...

Interesting that you got Standard.  Eiji didn't bore a size over?  Might check bore size with your guy.

Break-in depends more on the rings I think.  But most products come with instructions.  Follow those.

4 hours ago, Zed Head said:

Interesting that you got Standard.  Eiji didn't bore a size over?  Might check bore size with your guy.

Break-in depends more on the rings I think.  But most products come with instructions.  Follow those.

You know that is what I was thinking too. Just put rings on some standard (new or old) pistons, some bearings and reassemble?

Not that there is anything wrong with that. Anyone can do that.

Why spend extra money to have that work sent to Eiji? Does not compute. Must be more to the story.

Edited April 29, 20168 yr by Lumens

Previous owner sent me specs on his order with Eiji. 86mm flat top Pistons. Maybe he wanted Eiji to do the work because he's familiar with datsuns. That's the first thing I did when I knew that I didn't want to do it myself, I wanted a Datsun mechanic to do the work. The previous owner has been nothing but honest on every single thing from the beginning with this car and at this point I have absolutely zero reasons to not believe what he is telling me.

The skirts weren't cracked they were straight sheared off of 3 of the Pistons. The mechanic said he's been working on Datsuns for 40 years and never seen anything like it

More questions...

What's the brand of the pistons?  Is it possible that the skirts were too long and actually touched the crankshaft?  Still not seeing how bits of ring got past the oil scraper and the piston structure.  Yes, there's an indentation but it closes up at the bottom.  No obvious path for the top ring fragments.

Kind of looks like somebody opened it up, maybe when they changed the head, and really hacked a bunch of stuff up.  Maybe cracked the piston skirts when they were in there.  Or had the pistons and rods out and cracked the skirts then, playing with them like rattles.

Hosomi said they were ITB pistons 

11 minutes ago, zmanoside said:

Hosomi said they were ITB pistons 

But are they?  Should be marked.  If they're not then it's not the engine Hosomi put together.

Is this the ITB mark?  Don't know much myself.  Edit - did you mean ITM?

Edited May 4, 20168 yr by Zed Head