I have a forged bottom end tt ls6, I think they are diamond pistons. I don't have the "build specs" but this engine is making what to me sounds like an excessive amount of piston slap, and to me it seems to be getting a bit worse

the engine has a notable slap type rattle when cold, mostly between 1500-2000 rpms, but even noticeable at idle. as it warms up it gets a bit fainter, and cruise is quiet so I don't think it's a rod knock, good oil pressure, 30 psi at idle when hot.

might even be a rattle of the turbo pipes, but nothing I can find.

I'm thinking a few trips around the engine with a friend revving it up and me using a mechanics stethescope is the way to trace this down.

I also have a "direct valve cover" pipe to a puke tank and notice quite a bit of blow by smoke and crank case vapor smell. I'm thinking it might be that this engine was setup "loose" to allow for piston expansion, but I'd like to hear any thoughts on how to trouble shoot this.

car runs great, very strong, but I guess I should run a leak down test just to verify the overall cyl pressure health

thanks for any tips!!

 

I had the same noise, but the problem was the lifts were touchig the valve cover.

 

With the ambient temps so low I'm not surprised. I'd say it's normal as long as it goes away when warm.

 

It had a fair amount of piston slap when I play with it last year. Im sure by now it pretty loud, especially in the cold. I am not a fan of Diamond pistons "recommended" clearance specs and will rarely use them in FI applications anymore.

Phil

 

thanks Phil. not really sure they are diamond pistons, and I appreciate the feedback. I'm going to "stick with it" I have also noticed the #7 plug ground strap was shorter. didn't notice any alum flecks or other signs detonation. I changed the plugs when I got home and will check them again soon. car is running great and has STOOOOPID power.

the nitto drag radials are about gone, so some fresh 335 toyo proxy RA1s will be going on soon.

the other think is I think there is some excessive blow by in this engine, but since I'm broke, it's just fine!!!

 

I have pulled apart a couple motors with Diamond pistons that another shop had built which were not checked for clearance on the skirts to clear crank throws. All piston had marks on bottom of skirt.

 

I have used the same Diamond pistons "flat tops" twice now once for my original forged build then when I replaced the bearings and re-ringed while it was a part...you probably remember Phil.

But there is a lot of truth to the spec sheet that was sent out with both the Ross and Diamond pistons. Initially I used the Ross pistons (stock displacement) and the clearances were set per spec (piston) sheet. Well as a result it was blowing 1-2 qts of oil out every 400 miles or so..but had no blowby at idle...it was somewhat of a challenge when I had to challenge the engine shop on this...who had been in business (family owned) for 50+ years and built racing engines in some of the fastest "shoe box" chevys and Mopars in Cali.

However they listened and I pulled the motor and went with some flat tops from Diamond that were (.010 overbore). They called Ross about the issue then Diamond and after discussion it was determined that the pistons would not get hot enough (with an LSx FI build) to fully expand .006-.007" as suggested on the spec sheets. So they setup my ring clearances like a stock LSx (or close). if I remember correctly about .0025". On that first motor I burned zero oil or had zero oil consumption and so far on this motor I am experincing zero oil consuption.

So I understand what you are refering to and why you wouldn't want to use them..but my builder was able to fix the clearance issue.....beside a little sewing machine sound from he cam I have...my motor is quiet and burns no oil.