I had a head off of my 5050 that I finished dyno testing two weeks ago after finding a leaky exhaust valve when doing a leak down test, that cylinder was 80/70, all the rest where between 80/78 and 80/79 After removing the head I saw witness marks on all four piston edges near the spark plug side of the cylinders, Eddy RPM heads. I used a set of H beam RPM rods and a set of Diamond pistons, the piston deck hieghts vary from -.0039 to -.0082, the head gasket is a Cometic .041 MLS so I assumed that I had plenty of clearances, the piston edges say no I don't see severe conatct, just some light contact on the pistons and a tiny bit on the head or the lack of carbon on the head maybe.I'm sure piston rock at TDC has something to do with this that I'm not understanding I should have taken pictures of them last night before putting the motor back together, but I didn't I saw this one other time on my 518 low deck stroker(this is a 400 block stroker also) when I switch cranks and made that motor a zero deck motor with a .042 head gasket with these same heads What say you guys that have seen this or not seen this with similar clearances

i think the piston can rock .015 + depending on clearence.

what was your compression height, cab? i know how you love those short short pistons. i've run .032 piston to head with taller pistons, 6500 rpm maximum, steel h beams, fairly loose clearances (.007 piston to cylinder). i've never gone less than that. compression height on that one was about ~1.5? no evidence of touchy the heads.

I have run as little as .027 on a 4.020 bore. Pistons don't make contact but there is a definitely a lack of carbon build up in that area. I'm currently running .032 on a 4.030 bore. I don't know what effect a larger bore would have though.

It sure doesnt sound right... with the pistons in
the hole .004 and a .041 gasket it shouldnt have hit
unless it was a dome style piston... if it was rock
then I would have thought it would show near the edge...
I wonder if its just that the burn is different and
there's no carbon there.... did ALL of the pistons
show the same... you had .004 difference in height
between them... just thinking out loud

the negative number is out of the hole. it's supposed to be, anyway.

if that is 3-8 thou out of the hole i am sure it did touch. probably only touched on the exhaust stroke.

I use + for above deck and - for below deck on the deck of the pistons. The pistons do have a small dome as this is a bracket motor, I used the measurement directly above the wrist pins, rocking them forward and back and then average the results for the blueprint sheet, IE -.010 low and .001 for the high for both front and back rocking = .0045 deck hieght These pistons are the loose alloys and ended up with .007 or slightly more piston to wall clearances, so it has .0035 minimum per side, maybe a little more when rocked over and back . I may end up taking those heads off of that motor and put a set of 440-1 that Jeff CNC ported for me, got them back last Friday Thanks for banging them out Jeff Those heads should be at least 60 CFM better and there 8 CC smaller combustion chamber than the Eddy RPM heads on the motor now The 440-1 also have a set of Jesel paired shaft rockers on them so that should raised peak HP rpm some as well as make a little more power out of this rascal I will diffentitly(SP?) try remeasuring the total piston rock deck hieghts from the cam side to the block side instead of just front to back like I did on this the first time I called Diamond pistons after posting this and they said I should have plenty of piston to head clearances time for dinner, got to go for now

i'm guessing by now you already know where you went wrong. first off, why so loose on the skirts? even a 4.5 bore Diamond piston usually only calls for .0055 wall clearance. what size bore is yours?
always measure piston rock from cam side to exhaust side without rings. what's the deal with having .004 difference in deck height, is that those 300.00 dollar rpm rods or the crank stroke?
in any case, glad you didn't hurt anything. you could always put a .045 or .051 gasket in there and screw it back together. i wouldn't expect any real longevity from the rings, but your probably not too worried about that. go have some fun with it.

This set of pistons are the 2618 race alloy, not the 4032 street alloy( I probally have the alloy numbers reversed ). Diamond wanted .0065 minimum piston to wall clearances on the 4.35 bore according to the instruction sheet so .0005 more is better than .0005 less, right Not all micrometers and people measure exactly the same on the same part also , right The machine shop I used on this motors is not as Hi Po oreintated as Pettis is so we shall see how it works in the car They have a DTS engine dyno and one of my stroker bracket motors(527) made the next to the most power they have seen on that dyno Maybe I can help them get better on machining procedures, cylinder wall finishes, time between honing each cylinder and which cylinders to hone first and then in which order Win, win maybe As far as the deck hieght difference reason may be one or both I'll have to look at the original build sheet on the 512 motor that this crank was in originally with a different set of rods and pistons. I'l try and measure the stroke of each cylinder, if and when I have the heads off of this motor the next time don't we love problems BTW, I have seen varinces in motors like this with Oliver rods and Bryant cranks No perfect motors yet

that's really odd on the piston clearance. i just finished a combo with 4.600 bore and those pistons only needed .0065 clearance. the 4.375 pistons i put in a combo last week only called for .0045 and the current combo with 4.625 bore only calls for .0065. not sure why a 4.350 bore would need that much clearance with 2618 pistons. i guess i'll take your word for it if that's what was on the spec sheet. just seems like a lot to me and i probably would've questioned Diamond on that one.