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

The casting looks like ITM's. Here is a couple pics of an ITM flat top before it went in one of my F54 blocks. Amazing.....I've never seen anything like those broken skirts. Good luck in finding the cause.

.......on second examination, mine don't have the markings you are showing in your pics.

I probably did mean ITM. I knew it was IT something...I looked at Datsun spirit website and saw a picture of there flat top Pistons they have for sale. The is a mark on top of the piston that say STD. This same mark is on each of the Pistons I have in the box.

STD is stamped on the top of almost all standard size pistons, of any brand.  The shape of the letters and stamp depth might be a clue though.

I found a picture of what are purported to be ITM pistons, on the CaliforniaDatsun site.  Salt grain.  They don't show that odd trademark.  It looks like a T and a K to me, with maybe an odd-shaped "i" in between.

But here's the ITM pictures.  from here - https://www.californiadatsun.com/cylinder-head-parts/flat-engine-piston-set.html

Found it.  Taiwan Piston.  https://www.google.com/#q=tik+pistons

http://www.tik.com.tw/

You have a mystery here.

 

Edited May 4, 20168 yr by Zed Head

Really nice work Zed Head.......you should be a detective! Those aren't ITM pistons and therefore is a mystery block from a mystery builder. I wonder what brand of pistons California Datsun uses?

Well, thanks for providing the puzzle.  Beat's the heck out of a crossword.

You might have your builder compare dimensions of the new pistons to those.  People often pick a piston to swap in based on pin diameter and height and just make it work.  Honda 500 pistons for example, seem to be popular.  Maybe they missed skirt length, or overall piston height, and it banged off of the crankshaft.  Do you have the skirt pieces?  Look for impact marks.

That Taiwan site does have some Nissan pistons if you use the drop-down menus on the left, on the Products page.  More of a curiosity at this point, but might offer a clue.

http://www.tikparts.com/index.php?option=product&lang=en

Were the skirts all broken on the same side? A measurement from the top to the pin center and from the pin center to the bottom of the skirt would be interesting to compare with stock pistons.

Are there marks or damage of some sort on the crankshaft? Hopefully the mechanic in S.D. is checking dimensions between the sets. Can't wait to hear what he says about it.

Zed Head, I couldn't make out what it said (the markings) on those pistons until you posted it. I can see it now that I know what I'm looking at.

 

Is ITM it's own manufacturer or are they made by someone else?