Cracked block deck = expensive paper weight or mach up block?
12-20-2016, 05:09 PM
#1
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Cracked block deck = expensive paper weight or mach up block? I had some machine work done to my LS1 about 3 years ago. My # 7 cyl was cracked and had to be replaced. I had a local machinist do the work , the machinist suggested boring the the other cylinders because of small amount of block distortion from re sleeving that cylinder there was also some amount of welding involved. So I went ahead and had it done . They bored it out to 3.915 which I think is past minimum thickness for these ls blocks. Had to have custom auto tech pistons made for that particular bore size, they weren't cheap. This block has been shelved for three years while i had other projects. I recently pulled it out and put the block on a stand got the new main bearings installed and caps torqued then I turn it over to start installing pistons and rods and I find a crack in the block deck and down the aluminum that was welded on that #7 cyl. I since took it back and the machinist and he says no problem because the head gasket covers the crack, it'll be ok keep going with the build . I have a feeling that its not ok ,and I don't want to waste money on a doomed block. Is it scrap now?
Last edited by WideGlide; 12-20-2016 at 05:15 PM.
12-20-2016, 10:22 PM
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This was just gonna be a stock build , N/A, stock cam , heads. Was gonna drop it in my 1968 Firebird do the restomod thing that seems to be real popular.
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12-21-2016, 06:25 PM
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Talked to 3 different machine shops in my area Vancouver, Washington, The original place where I had the work done and two others . Loaded it up in the truck and drove it down and had it inspected, they all say run it. All three asked if I planned on turbo or super charging I told them just going to stock form besides the oversize bore . So still undecided on my next move, but any way I go its gonna undoubtedly be expensive. Thanks for the input people, next question should a machine shop guarantee a weld ? The only place the cracks are at is in the weld itself, the block did nothing but sit covered in a warm dry place for three years. Should I be bitching about this? or because I waited so long do I just let it go? I've read on other threads here on this site that when these ls1 block crack just give up and buy another block. That thought makes me f&%$^n physically ill
12-21-2016, 08:06 PM
#9
The time period is killing yiu as far as getting anything done about it I would think. With that being said on a sleeved block that portion is usually milled out anyways. Since the money is already spent you can bet your *** I'd be at least trying to run it. Put a couple GM coolant tabs in the antifreeze for good measure and see what happens.
12-21-2016, 08:11 PM
#10
I mean, if you offer a service and get paid for it, there is an implied warranty---but I think the statute might have run out on that.
It was probably a bad weld, that failed with some aging..aluminum is a funny duck like that.
It's probably not the weld filler material that cracked out, but where the weld meets the parent material. Crystalline grain structures and yadda yadda like that.
Personally, I would not run it. The risk of damaging the rotating assembly is high. I would pressure the original shop to go halfsies on machining a new block to put that assembly in.
It was probably a bad weld, that failed with some aging..aluminum is a funny duck like that.
It's probably not the weld filler material that cracked out, but where the weld meets the parent material. Crystalline grain structures and yadda yadda like that.
Personally, I would not run it. The risk of damaging the rotating assembly is high. I would pressure the original shop to go halfsies on machining a new block to put that assembly in.
12-22-2016, 12:32 PM
#11
The clamping force of the head bolts will effect that crack and thermal expansion will work to only make it bigger. Also since the crack is in the water jacket coolant will seep between the block and the sleeve and probably wind up in other places you don't want. Running that block will cause it to fail and I'd bet large amounts of money it'll take the rotating assembly with it. Don't waste any more money on that block unless you're gonna have wet sleeves installed.
12-23-2016, 07:45 AM
#13
Far from expert, I wouldn't run that block. I would worry too much about it having issues and taking my rotating assembly & other expensive parts out when it failed. Its a milk shake maker in the making. The crack will expand in time with use and heat cycling.
In 2010 I had a similar experience with a badly machined and built 383 SBC stroker for my 72 vette. The cylinder walls were to thin, the main caps loose etc so we learned on tear down. While many would have said the block was ok to re-use and it might have been for a little while, it would have had issues down the road. It hurt dropping $1400 for a Dart SHP with a 4.125 bore but the new engine has been perfect for 6 years and many hard miles. It was really a chance to upgrade.
For $600 or so you can probably find a good LS1 or LS6 block.
For $1000 or so a new LS2 block and get a 4.0+ bore and make more power with better oiling system.
For $1400 or so a new LS3 with 4.06+ bore
With any of these you can have a trouble free engine and not worry about land mines later down the road.
I would write off the current block its a poor canidate for an ERL resleeve, I talked with ERL about doing Darton wet MID sleeves on my spare LS6 block. ERL didnt want to use the LS6 block. The newer LS2 and LS3 blocks are just better starting points.
In 2010 I had a similar experience with a badly machined and built 383 SBC stroker for my 72 vette. The cylinder walls were to thin, the main caps loose etc so we learned on tear down. While many would have said the block was ok to re-use and it might have been for a little while, it would have had issues down the road. It hurt dropping $1400 for a Dart SHP with a 4.125 bore but the new engine has been perfect for 6 years and many hard miles. It was really a chance to upgrade.
For $600 or so you can probably find a good LS1 or LS6 block.
For $1000 or so a new LS2 block and get a 4.0+ bore and make more power with better oiling system.
For $1400 or so a new LS3 with 4.06+ bore
With any of these you can have a trouble free engine and not worry about land mines later down the road.
I would write off the current block its a poor canidate for an ERL resleeve, I talked with ERL about doing Darton wet MID sleeves on my spare LS6 block. ERL didnt want to use the LS6 block. The newer LS2 and LS3 blocks are just better starting points.
Last edited by 99 Black Bird T/A; 12-23-2016 at 08:16 PM.
12-23-2016, 04:25 PM
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Agreed this block is officially a mach up block now.
Next question I'm thinking about the LM7 5.3 Iron block . They seem to be plentiful, my 05 Tahoe has one. Can it be bored to 3.915? is the bore spacing same? I just got off phone with machine shop he said that would almost be an 1/8'' of the cylinder seems unlikely to safely remove that much . Has anyone here done this with any success ?
Next question I'm thinking about the LM7 5.3 Iron block . They seem to be plentiful, my 05 Tahoe has one. Can it be bored to 3.915? is the bore spacing same? I just got off phone with machine shop he said that would almost be an 1/8'' of the cylinder seems unlikely to safely remove that much . Has anyone here done this with any success ?
12-23-2016, 07:37 PM
#16
well I haven't personally done it, but there are many folks who've built an "iron LS1" by taking the 3.78 stock 5.3 block out to 3.905. 3.915" is only five thousandths more per side---not much.
Your machinist (hopefully a new one) will want to sonic check the block to make sure the core shift from casting doesnt create any problem areas.
Your machinist (hopefully a new one) will want to sonic check the block to make sure the core shift from casting doesnt create any problem areas.
