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i'll start by saying this is my ls6 engine, last week timing chain let go (ls2 upgrade chain when cam swap less then 10k miles)
so i got a bunch of bent valves but what i noticed is a couple of the pistons have a circle in them like there clean almost? engine when cold has a knock that would start making noise about 5 seconds after start up then go away some where around 60 seconds maybe piston slap or at least i thought? looking at the pics it looks like the valve was bearly touching the pistons from it having those rings on them and the valves in those cilynders are also cleanish
heads are PRC cnc's 243's ls7 lifters 7.425 pushrods stock MLS gaskets was used
what do you guys thing? the pistons have little moon shapes from that valves hit when the chain let go but those two have circles
That sucks. Same thing happened on my bike. The chain tensioner let go, timing chain skipped a few teeth......custom valve reliefs. How long was it running before the timing chain let go?
Did you assemble the motor? Just curious, because of the push rod thength you’re running. I know when I assemble my motor I used the Ls7 lifters with bone stock 243 heads, when I check pushrod length I got 0 lash at 7.350, so I went with 7.350 length pushrods.... 7.450 seems to be way to long of a pushrod for your setup!
Probably happened when the chain broke. Have the heads cleaned up, knock the sharp spots off the surface of the piston with a little air grinder and light disk and run it. Check p2v when it all goes back together.
Normally they will just leave the little eye brow when they create their own valve relief, the full circle is where the valve bent and flattened out on the piston. When the valve bent it smacked the carbon build up off. Not to mention, that sound wouldnt go away after 60 seconds.
Last edited by TXsilverado; 10-08-2017 at 07:38 AM.
the pushrods are 7.425 not 7.450 they was used since the ls7 lifter cups are .025 deeper then the ls1
the cam is BTR ls1 stg2 227/234 .614/.576 113+2 so its not really a big cam, after talking with brian tooley him self and PRC to find out how much was removed when they surfaced the heads (.005) i was told i didnt need to check valve clearances its not a issue with this cam so i never did actually check to be honest
the pushrods are 7.425 not 7.450 they was used since the ls7 lifter cups are .025 deeper then the ls1
the cam is BTR ls1 stg2 227/234 .614/.576 113+2 so its not really a big cam, after talking with brian tooley him self and PRC to find out how much was removed when they surfaced the heads (.005) i was told i didnt need to check valve clearances its not a issue with this cam so i never did actually check to be honest
thats strange, because with my bone stock 243 heads and Ls7 lifters, I had to run a 7.350 length pushrod to get my pre-load at 3/4 of a turn before the rocker bolt torqued to 22ftlbs. Strange yours used a 7.425?
you guys with the 7.350's you using 5.3's or ls6's?
mine is a ly6/l96 iron block geniv. And from what I’ve heard/read, the aluminum blocks have a shorter deck height compared to the iron blocks. Not sure if there’s much truth to that, but if that is right, then I’m willing to bet your pushrods are wayyyy to long for your setup! Did you test pushrod length when assembling it, or just go with what someone said? I’m really curious to know how much preload is on your lifters! I’ve always set mine anywhere between 1/2-1 full turn, max, after zero lash point on the rocker arm and pushrod.
Last edited by B00sted2007; 10-08-2017 at 08:03 PM.
10-07-2017, 02:20 PM
valve hitting the pistons?
