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!

From Hasting Rings;

STARTING PROCEDURE

1. Set tappets, adjust carburetor and ignition timing as accurately as possible before starting engine.

2. Start engine and set throttle to an engine speed of approximately 25 miles per hour (trucks, tractors and stationary engines one-third throttle) until the engine coolant reaches normal operating temperature. Then shut down engine and retorque cylinder head bolts, recheck carburetor adjustments, ignition timing and valve tappet clearance. (Run engine at fast idle during warm-up period to assure adequate initial lubrication for piston rings, pistons and cylinders.)

BREAK-IN PROCEDURE

                  1. Make a test run at 30 miles per hour and accelerate at full throttle to 50 miles per hour. Repeat the acceleration cycle from 30 to 50 miles per hour at least ten times. No further break-in is necessary. If traffic conditions will not permit this procedure, accelerate the engine rapidly several times through the intermediate gears during the check run. The object is to apply a load to the engine for short periods of time and in rapid succession soon after engine warm up. This action thrusts the piston rings against the cylinder wall with increased pressure and results in accelerated ring seating.

Where I live we have some pretty good mountains not too far away from home.  I have always read and been told to pull the hills and not get over 3,000 rpms then go back down the hill letting the gears slow the car, not using the breaks.  Don't hold a steady RPM, run it up and then let the gears slow it down.  The engine decelerating itself forces the rings out against the cylinder walls, I was told that on my first rebuild and followed that and have good compression.  

 

I believe in the "break it in like you're going to drive it".  Don't baby it. 

Ok, well just got off the phone with Eiji Hosomi. He confirmed that ITM Pistons were used when he built the bottom end. ITM Pistons were not in the car when I bought it. In the eBay ad, it clearly states "Engine block builder, Eiji Hosomi" so I'm obviously upset. Someone is lying here. The good thing is, as mad as I am about this, it doesn't bother me as much as it should. I got the car for a ridiculous price. Even with the money spent on labor and parts to get this fixed the car is worth almost 2x what I paid for it. Now if I paid a lot more money than I did when I bought it then I might pursue getting reimbursed from the seller..At this point it's not worth it. However, I did text the seller with ALL of the info uncovered.....The car is fixed, ITM Pistons are singing nicely in it. Here are more pics of the Pistons and broken skirts. Yes, the skirts were broken on the same side on each piston. I don't know what marks to look for, but the break in these are about as identical as you could get as you can see.

I dont understand, there is no damage, that I can see, on those skirt pieces. If it made contact with the crank shouldn't there be noticeable damage of some sort?

I wonder if the ring issue and the skirt issue are related. In other words did one cause the other? Or two separate fitment problems.

Definitely does not look like a Datsun Spirit build at all. May be he means California Datsun. That would make more sense.

I would say that motor must have been very noisy with that damage. Good to hear you bought it at the right price.

 

Those wrist pins don't look in very good shape either.  Not 5000 miles of wear.  Overall, it looks like a set of used high-mile pistons.  Maybe the skirts and ring lands got damaged/cracked when the pistons were removed from the old engine.

4 minutes ago, Zed Head said:

Those wrist pins don't look in very good shape either.

Was noticing the same thing. I was questioning; how old are those pistons, really?

I wonder if those pistons were in a properly sized hole? Maybe too tight, maybe too small...got jambed up or tight and cracked off the ear on the skirt. Anyway mystery solved. For what its worth, cracked piston skirts and rings will make your Datsun smoke...

I have read improper wrist pin fit/install can crack piston skirts.

I will see if the retired Datsun mechanic I know has an opinion.

47 minutes ago, Patcon said:

I wonder if those pistons were in a properly sized hole? Maybe too tight, maybe too small...got jambed up or tight and cracked off the ear on the skirt. Anyway mystery solved. For what its worth, cracked piston skirts and rings will make your Datsun smoke...

Cracked skirts would make ME smoke!  A crack up in a skirt would make me smile though.  8^)

5 hours ago, rcb280z said:

I dont understand, there is no damage, that I can see, on those skirt pieces. If it made contact with the crank shouldn't there be noticeable damage of some sort?

 Exactly. I expected to see something that would indicate the cause. Kind of a long shot but is it possible the pistons were loose in the bore and were rocking?

 Let the guessing game begin.

On 4/29/2016 at 0:33 AM, zmanoside said:

Previous owner sent me specs on his order with Eiji. 86mm flat top Pistons. 

I hope the mechanic checked bore size and didn't just assume that STD was correct.  There are some breaks in the assumed sequence of events, like the assumption that this is a Datsun Spirit engine.  STD of the ITK pistons could be STD for a different engine.  Or they are STD for an L28 but the bore isn't STD.  Apparently loose pistons can slap and break.  There's a bunch of Jeep forum comments on skirt breakage.

Whatever the cause, the dimensions should be checked before reassembly.  I don't see any numbers in previous posts.

I don't know if he checked bore size. He probably didn't. I told him the previous owner had standard bore 86mm Pistons in it and that's what I ordered and that's what he put in. But now that I'm finding out after the fact that and the car is already back together and in my garage that the Pistons that we took out aren't the Pistons that Hosomi put in it would have made sense to check the bore on it....too late now... I guess I'll be big time SOL if the whole thing happens all over again and I'll have to get the RB25det early......and my wife will be SUPER PISSED. I'll call the mechanic that did the work and see if he measured bore size before he honed.