Weird deal, have my motor down waiting for a new block and machine work,
cleaning up parts and noticed all my even number cylinder pistons are cracked in the exact same place, where the inside of the pin meets the inside of the skirt.

I have two other sets from the same motor (each time I would clean up the bore and get new custom CP pistons made, pistons are identical except bore… 4.50, 4.52, 4.535) and every even number piston in all 3 sets is cracked in the exact same place. I just never noticed it when taking them apart.

The only thing that has been constant between all three builds is the block. They were 3 different sets of rods (Callie’s steal then two sets of MGP aluminum), three different cranks (Callie’s magnum and two Brian’s billet). I suppose heads/cam/blower the same but not sure that would effect anything.

No Witness marks on pistons, never pinched a ringland (#1 cylender did on set 2, no cracks on it), never melted a plug, so don’t see a tune up issue. Hit rev limiter in two of those sets a time or two but wierd it would only crack even numbers when all Cylinders see that.

Any thoughts on cause?

I have shelf full of pistons cracked under wrist pinn just off center. All very fine but still a crack. Mine are out of blown alky Hemi and pretty sure Venolia pistons.

can you post a pic

I would call a couple of good piston companies and ask them what could cause that.

My first thought would have been deck height on that side wrong and pistons hitting but you said there were no marks on top of pistons.

Three different sets of pistons with three different sets of rods and cranks, the constant being the block that is where I would look. My suspicion is that there is an issue with the cylinders on that side. I’m assuming the cylinders aren’t completely straight in the view from the side. I’m thinking they are tilted front to back. Top leaning to timing cover bottom to bell housing. I just ran into a Merlin bbc that came from California that is that way. Bad deal because without four sleeves it can’t be fixed.

Call CP. ask for Ed Urcis. If he is still there. Used to work @ JE

Keith when I was cracking pistons in the pin area it was tune up related due to lean conditions. Once I fattened up the fuel system the cracking stopped. This was with Diamond pistons and MGP rods

quote:

Keith when I was cracking pistons in the pin area it was tune up related due to lean conditions. Once I fattened up the fuel system the cracking stopped. This was with Diamond pistons and MGP rods

steve were yours cracking in same spot as his

im going out on a limb here it looks like a stress built into the casting.
would like to here steves response

Yes Rusty pretty much the same spot. Also broke the crankshaft at the 1-2 pin. Had 4 crack pistons when that happened. The next tear down I had 2 cracked pistons. After that I never had another because the tune up was finally happy

quote:

Originally posted by TD3550:
Call CP. ask for Ed Urcis. If he is still there. Used to work @ JE

He is at Ross pistons....

I'd like to see what the pins look like.
Detonation usually leaves tracks there first.

Pin flex? Pin dimensions?

quote:

Originally posted by BP758:
Pin flex? Pin dimensions?

My pins were .250 wall, no way they were flexing and looked perfect.

quote:

Originally posted by Big Steve:

quote:

Originally posted by BP758:
Pin flex? Pin dimensions?

My pins were .250 wall, no way they were flexing and looked perfect.

Nemo963?

quote:

Originally posted by NEMO963:
https://ibb.co/TBZYxL8
https://ibb.co/x7GJ33r
https://ibb.co/HFQVMW7

I sent your pics to Dave C he’s retired from CP but still has his head there..He asked to see the skirt but recommended sending a piston to CP.
Dave designed those pistons.
Piston to wall clearance?

Sorry, off grid a few days.

Yes .250 pins, they always looked great as well.

I can send some pics of the skirts. Can also send to CP. I’ll need to ask my machine shop what they did for piston to wall, I can’t remember where he was setting it.

Pm sent

Couple of thoughts about all this.....

Since it's one side of the block only, obviously get the block to a shop that has a block-tru fixture and have them check it....OR, just do up another block all together....

Change brand of pistons....CP may just not be happy in your combination..although I don't know why only one side..

Check compression ratio on that side of the engine....maybe you're going into detionation on that side....

Just throwing my 2cents out there