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I bought a 5.3 LC9 from a junkyard as a long block, no info on the truck it came out of.
The plan was to gap the rings for boost, cam, springs, afm delete.
As I started taking it apart it became obvious that this motor had recently been rebuilt - new bearings, oil pump, timing set, possibly camshaft, rods are marked 1-8.
However there is a strange mark on one cylinder and some water marks on another. I'm wondering if I need it machined or if I can just put it back together as is. Photos are attached. Going over it with my finger or nail feels super smooth on both blemishes.
Depends on the intended use and budget. A simple cheap DIY ball hone would likely clean that up quick and easy in a few minutes. The cyl bore is likely fine and the least of your worries.
The rest of the motor is what would scare me. In my experience. If its been opened, chances are something was done incorrectly and likely why it was for sale. At minimum look at all the main/rod journals and measure them. I usually pass on engines I can tell someone else has been in. They often end up costing more than they are worth. Factory untouched gen4 small bore of any kind is super capable and a much better platform to start from if you are on a tight budget or just starting out. Even if its a 4.8.
If you aren’t on a budget and don’t care if its down a few months (or more). Drop it off at a good machine shop and go hog wild.
The last 2 look like it had water in it. The first 2 could have been water, but with out a closer look in person it's hard to be sure.
Is this a standard bore block?
Most likely you can run a 320 Ball hone with motor oil just to make sure there are no high spots from the etching.
I picked up an LH6 that someone had been inside.... As mentioned above. Other than the block everything else was scrap. I probably could have used 7 of the rods. But having them cleaned and checked for size was cost prohibitive especially sense I need to find another matching rod. It was actually cheaper to get another set of known good rods.
Take it to the machine shop, let them bolt a torque plate onto it and hone it with stones to restore the crosshatch marks. They can tell you if they think the rings will seal.
Ball hones are great for clean bores with no marks or wear, this ain't one.
Can’t see enough to tell IMO. Clean it up with a ball hone and get some T gauges if you want to be certain. I use the same rings that came out to put back in in most cases. Id source a new motor before taking it to a machine shop and going down that rabbit hole.
Thanks for all of the advice, I tried honing the cylinders, the big spot went away after 2-3 passes. Unfortunately the cylinder with what it looks like splatter/waterdrops wouldn't clean up even after 10 passes. They are definitely low spots.
I'll get bore/hone done and get the shop to measure all of the clearances and size new rings/bearings. Might as well get it done right.
Also this 5.3 is aluminum block(its going into 2200lb car), i got this for 500$ to buy another used one is 3000$ here in Canada. I think its cheaper/better to machine and build this engine rather than looking for another unknown condition one.
Can’t see enough to tell IMO. Clean it up with a ball hone and get some T gauges if you want to be certain. I use the same rings that came out to put back in in most cases. Id source a new motor before taking it to a machine shop and going down that rabbit hole.
I don't know what you're referring to exactly when you mention T gauges, unless its telescope gauges. If you are talking telescope gauges, I disagree. There are only 2 ways I know of to get a dead nuts reading, and that is with either an inside micrometer, or the best way is with a dial bore gauge set with gauge blocks. My .02......
I don't know what you're referring to exactly when you mention T gauges, unless its telescope gauges. If you are talking telescope gauges, I disagree. There are only 2 ways I know of to get a dead nuts reading, and that is with either an inside micrometer, or the best way is with a dial bore gauge set with gauge blocks. My .02......
Yes, telescoping gauges. Which are legit tools per the FAA for measuring and rebuilding aircraft engines. So IMO, good enough for my JY motor.
I’d argue that you don’t need “Dead nuts” measurements when playing with JY motors. You need “good enough” or “trash”. Can def get a good idea of roundness/damage with them.
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Cylinder wall condition question. 
