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Hey guys, coming off the failure of my first engine build and was hoping to get answers as to why I ran into failure to avoid making the same mistakes twice. Long story short I was running a ls6 block with factory rotating assembly, ported 243 heads, an A&A supercharger kit running 10psi with 60lb injectors, LPE pump and bap along with methanol. I was making 650whp.
I did a freshen up 6k ago replacing bearings and rings along with getting the block honed, crank polished and the block cleaned. I tore down because I had no compression and could hold no pressure on cylinder leakdown in piston 7. However on piston 3 compression was down to 150psi versus 180 on the rest of the cylinders.
I discovered that I trashed the ringlands on piston 7 and had a crack on piston 3 ringland. There was no pitting on the cylinder tops or in the heads of the combustion chamber.
Major mistake I know I made was not gapping the rings for boost and going with stock gaps. Would that alone have been the cause or should I be looking at other issues? I had a 6100rpm fuel cutoff trigger in place because I was out of fuel on the dyno beyond and was starting to go lean. The failure occurred during last winter when temps were cool. Thanks in advance for schooling a newb.
Did you measure the rings gaps? If so, what were they set at?
I just went through a 383ci LT1 a buddy bought from a guy on Facebook. The builder didn't bother to gap the rings either and the top and second rings were at about .010" out of the box.
Major mistake I know I made was not gapping the rings for boost and going with stock gaps. Would that alone have been the cause or should I be looking at other issues?
Not enough ring gap, I'd go way on big side next time if you want number 7 to stay alive. I lost number 7 on a stock engine with just a tune, Ring gets too hot expands too much and breaks the land and piston. Ring gotta go someplace, piston loses every time. Big gap isn't going to hurt anything....think .030 or so. Everyone learns the hard way with this.
yea ringlands butted and popped top off piston. Ive had a few diff 5.3/6.0 turbo setups anywhere from 10-24psi boost. never popped a piston (knock on wood!).
But I have bent rods and spun rod bearings after a while.
I always open rings gaps. I usually run .28 and .30
I found the sheet where I documented all the measurements I took. I went with sealed performance rings for more information. I definitely screwed up on my piston ring gaps but don't quote me, I believe I found the tolerances for stock pistons rings.
Should have called sealed performance and told them I was running boost and got their tolerances. Should have made sure the ring gaps were uniform. I literally took the rings out of the box, found they met the spec I found and called it good without feeling the need to make them uniform or increase the gap. I at least staggered them just overlooked how critical gapping them was, pretty inexplicable looking back now.
On piston #3 that has a cracked ring land I ran .011 on top ring and .018 on the bottom ring.
On piston #7 it had .0145 on top ring and .0175 on the second ring. Here are pictures of piston #7 and #3 for reference and my sheet where I recorded gaps.
On the positive side I found a local that has a gen 4 L33 long block in good shape with 122k on it. It allegedly was pulled because of a failed lifter. I'm going to trade my lq4 bare block with no crank just mains and pistons for his short block including covers and sensors + 400$.
Will then disassemble the shortblock, and replace bearings and rings, get the crank polished, cylinders hone and block cleaned and decked. Then get my 243 ported heads decked and cleaned as well, I have a set of 317 heads sitting my garage that are filthy and may not be in good condition. Could get them checked and cleaned, swap my valve train over to it. More thoughts on next steps or previous failure? Thanks guys.
One last thing the block I'm looking at trading for is a gen 4 block with dod and a sensor for vvt. How can I bypass both running my Gen 3 electronics? I was planning on swapping my cam and ls7 lifters over. Do I need a non dod valley cover? Was planning on grabbing a lingenfelter converter box. Thanks again. Here is a picture of the engine I'm looking to trade for.
That’s not an l33. My l33 does not have dod, or VVT either.
Be careful here. DOD lifter failures often hurt the lifter bore bad enough to warrant a lifter bore sleeve.
The GEN 4 guts are stronger than the GEN 3 stuff so I would do what you need to convert it. The LPE box you mentioned is the main thing other than the valley plate that will need the blockoffs for the DOD. Its really not that hard and much stronger. How much timing were you running on the LS6? 93 pump?
I would have to pull the map up in hptuners, I was running 91 octane and boost juice meth via cooling mist kit.
I talked to the owner again of the gen 4 block I'm looking at he said the lifter bores are good and he will be pulling the heads for me to look at them. It sounds like all is needed is for me to take my ls7 lifters and existing cam/cam gear and swap it over in addition to picking up an ls2 valley plate or tapping the holes and blocking them with a screw and loctite.
From a machine shop perspective if I pick up this block and the internals look good. I was going to replace rings and bearings and get the following done...
From a machine shop perspective if I pick up this block and the internals look good. I was going to replace rings and bearings
The only thing done to the newly established SBE 5.3 record (7.16@190)
were ARP rod bolts and they opened up the already worn factory rings.
There's a funny reason why this "JUNK" was able to make over five per cube
I would not tear yours down, polish the crank, or hone the cylinders
Remove the pistons and rods, open the compression ring gaps to .028" primary and .032" secondary......re-install and use........freshly honing the block will only loosen the piston to wall clearance which will promote ring flutter and bleed off the compression you're trying to keep on the north side of the piston
Putting new moly faced rings in is also a bad idea as the boost can easily overheat the moly facing causing it to flake off and weld to the cylinder walls.......then it wreaks havoc on the skirts and everything
Also while the rods are out, get new ARP bolts, wire wheel the black oxide coating off the threads, apply the special lube, install with EPL under the bolt shoulder, torque and have the big ends measured. most times the machine shop can just stroke them on the Sunnen hone a few passes and they'll size right in....I'd just leave the crank right in the block
If you insist on tearing it down....and I wouldn't unless you have a reason to, ring and bearing it and leave all else alone. I would not cam bearing especially.
Found a better alternative locally. The seller wants my LQ4 bare block and 317 heads in trade + 500$ on my end for his clean, honed lm7 with gen 4 floating rods and dish pistons. It has had the crank polished with new bearings and rings installed. He's also throwing in a set of ARP head studs. I'm going to have gap the rings and do preassembly to measure tolerances on bearings but this short block should be ready to drop in. Anything I should be weary of? Can't express how much I appreciate all the advice! Here is a picture of his block.
Last edited by tommypenguin; 01-17-2018 at 09:59 PM.
Shouldn't be sketchy if the guy wants to build something with cubes instead of stock cube. I would ask why he wants to trade though. I am a little fuzzy though, you said its got new rings and bearings, but youre going to measure....meaning tear it apart? Why not just get the tolerances from whomever put it together?
He said he has gapped the rings to. 016 and. 018. I would call mahle to find out what gap I should run but should be at least another. 010 off. He had his short block for sale for a 1k but I told him I had an Lq4 block that was magnafluxed I could trade + cash. He said he wants to go Lq4 and a 4.8 Crank in hopes of spinning the motor to 8000rpm. I had a set of 317 heads sitting in my garage and he a set of arp headstuds so I offered to trade my old heads for the studs as well. Hoping it's not a sketchy deal will post back later today.
01-15-2018, 04:08 PM
2 pistons with cracked ringlands post mortem 
Sounds like you know exactly why it failed 
