Hey Guys,

Encountered some butt puckering issues last night and looking for some ideas. So driving home last night, getting on the interstate on ramp. Have it in 3rd gear and do a little pull. RPM's get up to about 5500-6000 and the motor just shuts off ABRUPTLY and I'm coasting. I was able to pull over on the side of the road and attempted to restart, nothing. Seems like the motor is free spinning and only getting some pops and bang out of the exhaust, will not even catch on a couple cylinders. No visible engine damage, first thing I checked was for a new window in the block, nothing thankfully!. No smells, no leaks, and most importantly no noises. Oil is clean and appears to be free of any visible metal shavings. My first thought was piston to valve issues, thinking maybe the motor is spinning so fast it ate EVERY intake valve in a split second, but also think it would most likely kiss 1 valve and i'd lose a single cylinder, not all 8. It *sounded* like a motor with no/little compression, spinning quickly, but it was late and I was on another planet (for clarification, not trashed, but freaking out that I just blew up a very expensive motor) when this all happened so may be mistaken. For reference the car has milled PRC heads and a healthy cam motion cam, but I have driven over 10,000 miles on this setup and had a safe PTV clearance. Later today I am going to pop the valve covers off and crank the motor again and look for any signs of top end damage. Leaning towards possibly a crank sensor for the best case scenario, worst case PTV issues or even worse a snapped timing chain and ate every valve at one. I would assume in pretty much any scenario dealing with top end damage, I would be hearing something knocking/rattling around in the top end. Can also run a compression test once I run back to the shop and grab my tester.

So motor spins freely, no audible noises.
I smell fuel and get random pops and bangz out the exhaust, leading me to think fuel/spark are there and possible crank sensor issue giving ECM false readings. Not sure how cam sensors work on here, some vehicles can run with a failed cam but not crank sensor etc.

Just looking for some ideas to check, trying to avoid pulling the heads if it's something simple. Thanks in advance!

 

Quick update.

It's worst case scenario... Popped a valve cover off, all rockers in place, nothing looks wrong. Cranked it, no rocker movement whatsoever. Looks like timing chain failure... what are the chances that it miraculously did not hit any valves...

 

May or may not have. Probably need to turn the crank manually to see\hear anything before tearing into it. In my experience, if it did any internal damage, you would have heard a crunch coming from the engine.

Edit - My fault, didnt see the last line and looks like you have already checked this.

 

Thanks @schizcat Yea I spun the motor over a few times, spins freely and make's 0 unusual noises. This may be because the cam isn't spinning and moving any rockers and the bottom end is mostly fine. I would think that if a piston did hit a valve badly it would have broken some rockers off, but maybe not. I have spare 243 heads to throw on if the PRC got damaged, and along with those and a new timing chain setup I'm hoping to be back in action. Anyone have recommendations on a known bulletproof chain setup? I was always told LS2 chains were fantastic, it was nice and tight with no stiff links when I did the cam swap about 15k miles ago. Also any ideas on what could have caused the breakage? If I was able to put 10k miles on this exact setup I have to believe it wasn't installed or setup wrong. Also has a summit underdrive balancer, I've seen some reports of bad dampers causing crank wobble/chain fatigue but might just be hearsay.

 

wish you luck, but not sounding good.

 

Did you have it since new or did you buy it used? LS2's do not like underdrive pulley's make sure the HB is stock size, for the $ I use a power bond SFI unit, I could tell the engine got smoother after install. were are you? I can do a timing chain with you, if you help me with a torque tube job.

 

I was thinking timing chain as soon as you said it "spun over quickly, like there was no compression." Hoping at worst you've got bent valves, and at best you just need a timing chain and gears. May I suggest a Rollmaster chain, and gears? Never had any issues using them. Would also recommend a real close inspection of your harmonic balancer, because the OEM balancers aren't known for trouble free high mileage. It would suck to buy all new stuff, and reinstall the problem by using the old balancer. My .02.......

 

My Ls2 chain let go and I strongly believe it was the slp underdrive pulley. This was with a c5r chain as well. Go ati or another reputable pulley. I have also read of other chains breaking from underdrives with the Ls2. I ended up going with a crate Ls3.

 

Hey Guys, Still haven't had time to tear it apart. So no new updates there. I did install the summit 25% under drive pulley (SFI certified, assumed good to go, lots of good reviews) when I first did the cam install, roughly 15k miles ago. Motor felt plenty smooth, but that's not saying much. Car was bought used, but stock besides a cat back with roughly 80k miles on it. I did the cam/balancer at a little over 103k or so. And then did the PRC heads at about 110k miles, currently 120k on the motor. Stupidly I reused the OEM LS2 chain, everything I read said they are good to go, and it was nice and tight with no slack or tight links, not to mention seemed like a massive ordeal to tear the car down more to get the oil pump and chain out... learned my lesson there. I plan on dropping the entire drive train soon and doing a clutch job, as well as the oil pump and chain. Leaning towards a C7R chain and new gears and melling higher pressure oil pump.

 

Like said earlier Rollmaster with the Iwis chain, do a search of the Iwis chain! Precision you can feel in your hands

 

@grpweld Thanks for the tip. I've done a bunch of research on the IWIS chains, they also make the C7R chain I mentioned which is regarded as the best single roller available currently. I'm thinking I'd prefer to go single roller for easier install, they don't seem easily compatible with the melling pump I already have and require spacing and grinding on the timing cover. I'm assuming my chain failed for a reason, possibly the underdrive pulley and would rather put that money towards an ATI damper with a quality single row setup. Who knows, once I tear into it I may find the cam gear came off or something stupid besides the chain just breaking due to normal usage.

 

I popped the chain on my c5z ill give you the short version had 14 bent valve and the pistons was all marked up i now have a ls3 base 415 stroker in the car

hope you have better luck then I did!

 

Hey Guys,

Quick update. Yanked the heads, 8 bent exhaust valves, 4 intake. Guides are all fine, ordered new valves from Texas Speed and having them put in along with a valve job on every valve, and ordered a Rollmaster Billet Single timing chain set with IWIS seamless roller chain. Still haven't pulled the timing cover off yet, but all parts including oil pump and chain damper are getting replaced. Pistons have some small nicks in them, plan on smoothing them out with some 500 grit sandpaper and calling it a day. Worst piston damage barely catches my fingernail, seems like it mostly just knocked carbon off. Thinking the hollow stem valves just bent easier, maybe a plus lol. Had a long chat with Texas Speed's crew, they said they typically never see timing chains fail, but do NOT think the under drive pulley has anything to do with it, more so the mileage on the factory LS2 chain. They also said as long as there are no cracks on the pistons, sand them smooth and run them. Other odd thing, to me at least, not a single bent pushrod or broken rocker. Pushrods all rolled perfectly flat on glass, but will be replacing them regardless, along with upgraded trunion rockers. They also said not likely PTV issues due to cam or head milling, i'm running a similar combo they have set up multiple times with ample clearance. The As Cast 225 heads (62cc chamber stock) I am running have BETTER than factory valve clearance compared to 243 heads, and I had them milled to 60cc chambers, which is only a .014-.016 mill. Of the 4 bent intake, only 2 were even visibly bent. Seems like the chain snapped and ate up all the exhaust valves first before the valves were closed, and cam left at least 2 intake valves open at all times regardless. I will be double checking PTV anyway, and possibly a factory gasket as well, .051 thickness vs the .048 I was running. I will also be thoroughly cleaning/chasing all head bolts, lots of sand getting into all the crevices here in SW Florida. All in all, so far a 600$ or so repair, lots of labor but I'm handling that myself. I think I got off lucky!