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Im doing a refresh on a 5.3 LM7, changing all gaskets and bearings.
At the point Im at right now, its time for pistons. My old ones seem to have a bit more wear than Im comfortable with piston-to-wall clearance is too large.
I honed the bores myself to clean them up, and Im a bit concerned about the measurements I got. I dont have the possibility to let a machine shop bore and hone the block, as the price is very high where I live and all shops are very far away.
I have two choices: either buy used pistons in good condition and install them, or buy new Silvolite pistons. However, they recommend a 3.7808" bore for their standard size, and I have smaller measurements than that in some cylinders.
What do you think?
These are the measurements I got.
First row is thrust, second is side, measured from top middle bottom.
If I were you, I'd go for new pistons. You've gone to all that labor to get this far. I sure wouldn't install used pistons. Pistons wear in more areas than just the skirt. The pin bores, ring lands, etc., must also have wear. My .02.......
If I were you, I'd go for new pistons. You've gone to all that labor to get this far. I sure wouldn't install used pistons. Pistons wear in more areas than just the skirt. The pin bores, ring lands, etc., must also have wear. My .02.......
thanks for the answer!
the Question is silvolite recommend 3.7808 in bore for their std piston and i have 3.779 in one cylinder, not in the thrust angle tho. But its a little weird when stock bore is 3.78. Maybe because I dont measure with a torque plate
What tools are you using and how good is the resolution for the measurement? What are the temps you are measuring in and yest the torque plate could slightly change things in certain spots. I would have someone check your measurements with theirs to sort of calibrate yourself. Silvolite, Moresa and NPR are decent replacements. Check with the WS6 store for pricing also.
What tools are you using and how good is the resolution for the measurement? What are the temps you are measuring in and yest the torque plate could slightly change things in certain spots. I would have someone check your measurements with theirs to sort of calibrate yourself. Silvolite, Moresa and NPR are decent replacements. Check with the WS6 store for pricing also.
Im using a dial bore gauge and micrometer with calibrating block. The temp is 17-18 degrees Celsius.
You're probably fine measuring the way you are. However, some of the accuracy depends on how good the calibration block is, whatever a calbration block is. The most accurate way is to use gauge blocks to set up the bore gauge. Most of us don't own a set if gauge blocks. Next best thing would be to have a local machine shop set up your bore gauge to their gauge blocks. Since you're providing the bore gauge, if you'd buy them a dozen donuts, they would probably set your bore gauge up free. It wouldn't take more than 2 or 3 minutes, if that. Tell them the size you want to have the bore gauge set to, and you're good to go.....
You're probably fine measuring the way you are. However, some of the accuracy depends on how good the calibration block is, whatever a calbration block is. The most accurate way is to use gauge blocks to set up the bore gauge. Most of us don't own a set if gauge blocks. Next best thing would be to have a local machine shop set up your bore gauge to their gauge blocks. Since you're providing the bore gauge, if you'd buy them a dozen donuts, they would probably set your bore gauge up free. It wouldn't take more than 2 or 3 minutes, if that. Tell them the size you want to have the bore gauge set to, and you're good to go.....
it is indeed gauge block that I use to verify the micrometer, then setup the dial bore with the micrometer. I have all the tools on my work and everything is calibrated every year.
Dumb question, what did the old pistons measure at? Part of the issue is the pistons you may be looking at might be the harder compound hypereutectic which translates a lot of heat to the bores, which may be why they are asking for a lot of clearance. Look at a set of UEM or Mahle replacement pistons and see what they say for bore size.
Dumb question, what did the old pistons measure at? Part of the issue is the pistons you may be looking at might be the harder compound hypereutectic which translates a lot of heat to the bores, which may be why they are asking for a lot of clearance. Look at a set of UEM or Mahle replacement pistons and see what they say for bore size.
The smallest measued 3.7748 and the biggest 3.7759. Will check with them too, thanks
I will make a suggestion here you may not want to hear, but here goes. What you're trying to do takes a lot of experience, money, and work. Im somewhat concerned you're taking a very cheap route with this. I'd hate to see you put all the time and money into this and have something go wrong. Anyway, FWIW, I've been doing this stuff for over 50 years. I do know how to check bearing clearances and piston to cylinder clearances. However, in all those years I have never attempted to finish hone my cylinders in any engine I've ever owned or worked on. If you get it wrong, the rings wont seat, you'll use oil, be down on power, etc. Your engine, your choice. Cylinder honing and finishing CORRECTLY is a pretty highly skilled operation, especially if you're doing it by hand with a drill motor!! It is one area I don't want to venture into, or learn. Best of luck to you......
Dumb question, what did the old pistons measure at? Part of the issue is the pistons you may be looking at might be the harder compound hypereutectic which translates a lot of heat to the bores, which may be why they are asking for a lot of clearance. Look at a set of UEM or Mahle replacement pistons and see what they say for bore size.
For giggles, I was just going to ask what the old pistons measured, but you beat me to it, Dave!
If this is a high performance build…you’re looking to make big power N/A or with boost, then you’re going to have to suck it up and have it honed to a .010 oversize etc. On the other hand, if it’s just a cruiser, throw a new set of rings on it and put it back together. As long as you ball honed it, which won’t take any metal, I’d clean it all up and send it. You’ll not gain anything with shiny new parts except for maybe a better night sleep. It might have a little piston slap with the ones you took out, but it goes away when up to temp. I see guys weekly pull junkyard, crusty, crispy, muddy, rusty, yucky, grimey, noisey, ready to be scrapped LS engines out of a wreck or clapped out truck, put an eBay turbo kit on it, and make 700 wheel, while bouncing it off the limiter….and some of these guys won’t even change the oil. I’m serious. Don’t overthink this. It’s a very robust platform that will last 300-400k with half decent maintenance. Fwiw, I’m a builder that’s had my hands in high end builds for decades, and I’m **** about doing things the right way…but I’ve also done quite a few sloppy clean it up, ball hone it, new bearings and rings and back together…and have them run great for years.
How did you hone the block? Dingleberry hone or one with stones? I've had many machinists tell me that the stone type should all be thrown right in the trash, they produce inconsistent results while creating the illusion that you're actually doing something right.
Unless you used a machine shop hone, I can promise you that your bores are NOT round and cylinder walls are NOT straight.
As Che70velle said, if it's a dailly driver shade tree build, clean it good, put new rings on it and let 'er rip. If it's a performance engine, take it to a machine shop and get it done right.
Parts are parts, one $1000 crank is just about as good as the next, same with rods. BUT...there is no substitute for spot-on quality machine work. The quality of the machine work willl determine the quality of the final product.
I cringe sometimes when I pick up a block from the machine shop when they hand me the bill... but I know that my bores are round and straight, my main saddles and caps are the correct dimension and all in alignment, my balance job is spot on. Valve job is perfect and valve springs are set at the correct height for my cam. I can beat the **** out of the engine when it's together and it's not going to self destruct from shitty machining.
its gonna go in an old bmw coupe, probably only a cam nothing more. I will have to think about this a bit and see what i do. I do already have all new bearings, rings, gaskets, lifter, rockers and some other stuff. Dont know if I want to put all those new parts in an engine thats gonna end up having piston slap and so on. Hmm
I guess I get too **** about doing things to umpteenth degree. That said, don't worry too much about piston slap. My 2000 C5 sounded like a diesel (not exaggerating!) when started under about 50°. A minute later, all was good. It was bad enough that I took it to the dealer, who refused to do anything unless it was using excessive amounts of oil, which, at 2,000 miles per qt., it wasn't. But quite a number of LS1s built by GM from around 1999-2001 had this issue. Did it slap before? My current engine, a built LS7, has one piston slapping. It has eaten 2 cams and at least 1 lifter, which has probably caused this. I don't like it, but it has been doing it for at least 15,000 miles now. A minute after it has started, it's gone......
Last edited by grinder11; Jan 10, 2026 at 10:05 AM.
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Piston to wall and what to to 
