L31 daily driver rebuild

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Hipster

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Block decking accomplishes multiple things, First it ensures a good head gasket seal, second it establishes compression height(how far in the hole) and quench distances and if you are able to get to a satisfactory quench number for detonation resistance. Most replacement pistons are further in the hole by .010 than an oem piston as stated. Most stock blocks with stock pistons measure between .023-.025 in the hole, add .010 for a new piston and you're at .035 + a .028 head gasket and building a non quench, lower compression, less efficient engine @.058 distance. I tend to stay away from shim gaskets, Not decking the decking the block is a step in the wrong direction. Most off the shelf gasket sets will come with .039 - .040 head gaskets which don't really work unless it's zero decked.

Almost every manufacture used to do it,and advertised CR ratios are not even close to measured values, A 10 to 1 piston .035 in the hole is probably closer to 9.5 to 1, maybe even a little less.
 
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Orpedcrow

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What are you asking the machine shop to do, and how much are they charging? If you're asking for "the works", you're going to spend way too much money. Do as much as you can yourself. Clean and sonic check your crank yourself. Pop out all your core plugs yourself and just ask them vat, magnaflux, and bore the block. Only ask them to deck the block if it's not straight. Have them recondition the rods and install your oversize pistons.

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The factory rods are pretty good, even better than the famed "pink" rods. If you aren't spinning them to the moon and don't need 6" rods, stick with the stockers. Same for the crankshaft. For a street use motor, I'd stick with the stock pistons, but since you already need an overbore, you might as well bump up the compression ratio a bit. If you're not going wild, there are plenty of "good enough" piston sets out there under $200.


I'm pretty sure Genuine OEM parts aren't tested mid-production by GM, other than via warranty returns. I'm also pretty sure GM isn't opening every pallet and sending one off to a lab for measurement. When I was a Nissan tech, Nissan's piston supplier dorked up and sent thousands of pistons with the wrong size marked on them. There were a couple of years of engines that developed piston slap and got replaced under warranty.


No, they're not. It's only "after the fact". You really don't want the FAA probing after your part fails, but up until it does there's pretty much no oversight. We have to trust that you haven't fraudulently filled out your paperwork.
Thanks for those videos. I learned new techniques from both!
 

Orpedcrow

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Ok I’ve got the bottom end mostly sorted, do y’all have a recommendation for a replacement harmonic balancer and Flexplate?
 

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Ok I’ve got the bottom end mostly sorted, do y’all have a recommendation for a replacement harmonic balancer and Flexplate?
What's wrong with the OEM parts? If there is something wrong with the OEM parts...visit a Treasure Yard and get different OEM parts.

You "can" spend a shipload of money on aftermarket SFI parts...but there's no real need unless the track requires SFI, or the RPM of the build is going up. That's not your need.

There's more than one version of the torsional damper. The timing mark can be in at least two positions, about 13 degrees apart the way I remember it. And the torsional damper is neutral-balanced, so it's not a "balancer".

As for the flexplate, the GM units are prone to cracking. Very common problem, although I have no idea why. They made flexplates for decades with decent reliability, then they go to the one-piece-rear-main small-blocks and the flexplates are shiit.

OTOH, the aftermarket flexplates have screwed-up balance. At least, the two aftermarket flexplates I bought, did. They both went to the balance shop, got matched to a Genuine GM flexplate. One had to be drilled to correct it, the other had to have weld-metal added to make it correct. In the end, they now match GM specs for the offset weight.

Even if you have the entire engine balanced, you want the damper and the flexplate to be "standard" with whatever is the proper amount of offset weight; all the custom work gets done on the crankshaft, NOT ON THE FLEXPLATE AND DAMPER. Balance shops that custom-drill the damper or drill/weld the flexplate are doing hack work. I had a boat 454 engine that was "balanced" by some doofus. Welded bigass lumps of metal to the flexplate. Then someone installed the flexplate BACKWARDS on the engine 'cause the bigass lumps hit the marine engine mounts if it was installed properly. Boat shook like a dog crapping razor blades.

There are OEM companies that screw-up the balance--Buick, for example. God help you if you try to balance a Buick engine.
 

Orpedcrow

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What's wrong with the OEM parts? If there is something wrong with the OEM parts...visit a Treasure Yard and get different OEM parts.
My OEM damper is oil saturated, treasure yard isn’t really an option for me. You’re correct, I don’t need SFI rated anything, but also don’t want any communist garbage. The rotating assembly will be balanced, was trying to get these together instead of asking the machine shop to supply them.
 

Orpedcrow

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I've heard good things about BHJ dampers. I don't know what to tell you about the flexplate. GM units crack, aftermarket units may not have the correct offset weight.
Thanks, my current Flexplate is not cracked but the one that was on the engine before this one was. I’ll see what I come up with.
 

Orpedcrow

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Looks to be an 8” according to my tape measure, with the timing mark just left of the 12:00 position, if the woodruff key is 12:00. The elestomer is swollen, cracked and gooey.
 

Orpedcrow

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