enginenerd
enginenerd HalfDork
6/20/23 1:46 p.m.

Been a while since I've posted here since I've relocated across the country and been busy fixing up a garage (that came with an attached house!)

Have a couple projects going now but the most interesting lately has been the teardown and hopefully subsequent rebuild of an LS7 from a 2007 Z06. Quick back story: this car was purchased from a salvage auction with only 9k miles. It was repaired but kept bone stock. Since then, it has slowly accumulated about 10k more of mostly street driving mixed with some mild HPDE. At our last outing at Thunderhill, oil pressure tanked at the end of the session so I brought the car in and parked it. After cooling off, the car restarted with no audible noise but I was nervous enough to drive it onto the trailer where it has since been parked. We checked the oil and found some very pretty glitter as confirmation that the engine followed the same path as many of its LS7 brethren. 

Fast forward about 2 years and I finally have some time and space to evaluate things. Pulling the engine wasn't terribly difficult, but less fun than I anticipated. Rather than try to lift the body off the subframes, I elected to unbolt the torque tube, drop the front subframe, and yank the engine from above like any qualified backyard mechanic. 

Kendall Frederick
Kendall Frederick Reader
6/20/23 2:13 p.m.

Yeah, you probably needed more head room if you want to get the body off of both cradles.  It sure is a lot handier that way though.  You probably already know this, but check the rod coating to see if they are galled; if so it's almost easier to get steel rods and rebalance.  Calico will supposedly recoat the titanium rods.  I have a set to do this with but have other stuff in the way, so no personal experience.

enginenerd
enginenerd HalfDork
6/20/23 2:27 p.m.
Kendall Frederick said:

You probably already know this, but check the rod coating to see if they are galled; if so it's almost easier to get steel rods and rebalance.  Calico will supposedly recoat the titanium rods.  I have a set to do this with but have other stuff in the way, so no personal experience.

Yes I sent an oil sample out because I'm curious how much Ti is in the oil. I believe actual failure was due to either oil starvation or overheating but would not be the least surprised if con rod wear was a significant contributor. Getting a bit ahead of myself but the big end faces of the con rods are absolutely trashed. 

BTW: Have been absolutely fascinated by your DIY ZR1 thread!

enginenerd
enginenerd HalfDork
6/20/23 3:55 p.m.

So, somehow I've made it through life never having worked on an LS engine. I am amazed at how simple the design is and had it torn down within an hour or so. I can really appreciate not having 14 unique fasteners for a front cover or such like every BMW I've messed with. I tried my best to enjoy the process instead of tallying up the cost of everything to replace along the way. 

Pulled the heads off and had a look around. Everything seems perfectly normal other than some minor scoring of the lifter bores. Also, I can't remember the last time I'd seen a pushrod! These heads will likely get new guides and exhaust valves if reused but I found the factory porting impressive. 

Nothing catastrophic here compared to the YouTube videos I've watched:

I also ordered one of these engine stand trays after years of using towels, blankets, buckets, etc to attempt to catch the mess. Expensive but was so satisfying to not have to clean up after every step!

 

Around this time I was starting to wonder if I had been hasty in pulling the engine. Everything looked pretty clean so far, even the remaining oil I drained didn't look terrible. The oil pan was clear of debris and it really didn't look like other failed engines I had torn down. That is until I used a pick to scrape around the hidden sides of the oil pick up:

Ruh roh...looks like bearing material of the chunky variety!

enginenerd
enginenerd HalfDork
6/20/23 6:14 p.m.

After pulling the pan it was immediately obvious something got hot:

That's the cylinder 5 & 6 connecting rods looking a bit beyond well done. I pulled the rod caps to see how chewed up the bearings and crankshaft were. Neither bearing actually spun but the journal is somewhat scored. 

One interesting thing to note (as mentioned above) is that the LS7 uses titanium connecting rods. I was surprised at just how light the piston/rod combo felt when I dropped the first one out of the block. Titanium rods are very cool from a performance perspective, very uncool from a cost and reliability perspective for this particular engine. There are a lot of reports of the chromium nitrate coating wearing off and these engines developing friction issues between adjacent rods. You can kind of see in the picture above at just how worn the rods were. A quick search shows a new set of factory rods could be upwards of $4500 surprise

Next I removed the main caps. This is where the damage got excessive. The #4 main bearing was in terrible shape...even worse than the rod bearings. The other bearings were better but looked to have been scored up from bits of metal in the oil. Luckily the main caps seem to not be distorted and fit well on the block. 

So...I'm not 100% on the story here. The failure occurred on a hot track day with the car on new 100 tw tires. There is a known issue with oil starvation on early C6z cars on sustained left hand turns w/ high lateral accels. My best guess is either oil starvation or oil temps got too high leading to the main bearing failure. Once that damage occurred, excessive heat from friction in that area and/or oiling issues wiped out the cyl 5 & 6 rod bearings. There is also the question of the connecting rod wear which seems premature even by the posts I've seen on Corvette forums.

Regardless, I think my next step is to have a machine shop check the block for distortion. None of the cylinder sleeves cracked but cylinder 4 has some scuffing in the bore. While an overbore is possible, I don't think there is that much material that can be removed if the bore is too tapered. Basically, my quick preliminary research is showing two options:

1) Use factory block w/ aftermarket forged crank, rods, and likely pistons (I don't think it's worth repairing the crank and trying to rebalance for heavier rods.) Re-use everything I can including cam and cylinder heads, likely with the valve guides replaced and new exhaust valves. 

2) If the block is too far gone, it may be time to start shopping for an LS3 to build. I'd prefer to keep this car close to stock so it can be registered (CA smog) but probably can't justify the price tag of an LS7 short block assembly. 

Kendall Frederick
Kendall Frederick Reader
6/20/23 8:50 p.m.

You can get a Darton sleeved block like mine from Thompson, Texas Speed, and others, so you can keep the bore size and the heads.  If you went to an LS3 block you'd have to change the heads, intake, yada yada.  I think Texas Speed has the option to start with a new factory 5.3 block.  Freshen the heads, put a decent rotating assembly in it, and you'll have something stronger than the LS7 without swapping too many ancillary parts.  Make sure they don't send you one with a crack in an oil galley like mine.. LOL

Mine is sitting right now while I work on my new shop, which will probably take most of the rest of this year.  I'm still trying to get down to work on it but I have a lot going on right now.  That's my excuse anyway and I'm sticking to it!

Edit: you could add some oil capacity to the dry sump while it's out.. I haven't done it but I don't think it'd be too hard.  The 2009+ factory setup is just another tank strapped to the side of the original one, it looks fairly rudimentary.

 

enginenerd
enginenerd HalfDork
6/20/23 10:48 p.m.

In reply to Kendall Frederick :

Great suggestions, I dropped the block off at a machine shop this afternoon so we'll see what they say. I am hopeful that it will be salvageable as the main caps fit well, none of the lifters seemed to get stuck in their bores, etc. I think most LS7 failures I've seen left some pretty spectacular windows.

I was planning on sending out the oil tank to get it modified for additional capacity, as well as adding some baffles. I'm sure there are probably some other related upgrades to consider. Will need to replace the oil cooler anyway and I'd like to see what's out there for oil pumps as well. 

myf16n
myf16n New Reader
6/21/23 12:39 a.m.

My LS7 also seized at Thunderhill. I was time limited and bought a crate LS7 from GM. On the new motor I installed the enlarged dry sump from Lingenfelter, and also installed the ARE air/oil separator in the sump and their baffles in the 'oil pan'.

Where in NorCal are you? I'm in Santa Cruz.

enginenerd
enginenerd HalfDork
6/21/23 2:14 a.m.

In reply to myf16n :

Ouch, guess I'm joining the club. I keep wondering if turns 1 & 2 had a hand in this engine's demise. 
 

That was pretty much my plan for the dry sump. Are you happy with that setup? Home base is currently in the Central Valley near Fresno but frequently am up around the Monterey area. Hope to get back to Thunderhill once this thing gets put back together. 

myf16n
myf16n New Reader
6/21/23 2:28 a.m.

In reply to enginenerd :

I haven't tracked the car since installing the parts.

Spearfishin
Spearfishin New Reader
6/21/23 7:01 a.m.

Just wanted to comment that I too removed a C6 lump (ls3) out the top for rebuild. When I put it back in, I had installed a tick remote bleeder on the clutch, and managed to tweak the little 22.5deg adapter fitting that comes out of the bellhousing on the firewall at some point in the reinstall/realign wrestling match hard enough that I cracked it.

Know when I found it? When we'd buttoned everything up and I was under the lift doing my final "which grounds did I forget to hook back up" walk with the flashlight and felt something drip on my bald head. Tasted like Dot4, and the rest was history. Got the pleasure of pulling the whole thing again. 

enginenerd
enginenerd HalfDork
6/21/23 11:27 a.m.

In reply to Spearfishin :

Ugh...I feel this more than you know. I think the only upside is that the 2nd time around I usually work twice as fast...not only cause I know how to do the job but I'm fueled by a bit of rage.

The remote clutch bleeder is a good idea...will add it to my list. 

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