When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
This is my first build. My cylinders have recently been honed and now measure 3.781-3.783 inches. Do I need oversized rings? Is this within tolerance for using stock rings?
Depends on the rings. Although, there are some pretty reliable Rules Of Thumb.
Put one in the cyl; tamp it down with a piston turned upside-down to make sure it's absolutely square with the cyl; measure the gap with a feeler gauge.
"Nominal" for an otherwise typical "hot street" motor of that bore size would be around .020" - .022" on the top ring, and maybe .025" - .026" on the 2nd. A LITTLE "too much" is FAR LESS BAD than ANY "too little". Think of the "spec" as a minimum that you want to approach from above, NOT an "ideal" value that has a tolerance band around it. Remember, rings GROW when they get hot, and that gap closes up; if it closes to .000001", you're golden; but if it closes beyond zero AT ALL, you have A PILE OF SHRAPNEL. Tread on the thin ice carefully.
Add .003 - .005" if this is a turbo motor or the like. (doesn't sound like it)
For something like checking ring gap use a feeler gauge, place the rings inside the bores, and check to see if they are within tolerance; you can square up the ring with a piston. You may have to swap rings from one bore to another to get the ring gap you are looking for.
Thanks for the help everyone. Sounds like going for the next size up and working down (3.785) with feeler gauge and file is the way to go.
I have just taken delivery of the block from the machinist. And have a few questions it looks like it needs to go back to me. The cylinders now all have a ridge at the top of the cylinder. It's quite pronounced, these ridges weren't there before the honing process so I am a little worried this is going to need a rebore to put right now. I was planning on reusing stock pistons and con rods. Can I get your opinions? I worry that these ridges would interfere with the rings and cause a bit of a shrapnel situation
Those ridges WERE there before whatever work was done; you just couldn't see them. What they are is, at the top of the area that the rings run on, the bores are worn; but the honing process didn't touch the block there, so it's all as-is, unhoned, in those dark areas. Butt, that's THE MOST IMPORTANT PART of the bore to get a good seal on, since the pressure in the cyl is highest when the piston is at the top, just after ignition and before the pressure drives the piston downwards to do useful work. The places that NEED THE MOST to have been honed, aren't.
That block looks plenty worn enough to need to be bored.
"Shop" did what all too many shops will do... "we did exactly what the customer said" [in this case, hone the walls] regardless of whether it was the right thing to do or not. They wasted your money.
The little dirt or metal dust or whatever is trivial; since you'd be taking it to the car wash before assembly anyway, it would all get cleaned up at that point, regardless.
That block is too far gone to run the stock pistons in it. That plane has already left the gate. It needs new pistons of some slightly larger diameter, and to be bored out and honed (again) to match.
Those ridges WERE there before whatever work was done; you just couldn't see them. What they are is, at the top of the area that the rings run on, the bores are worn; but the honing process didn't touch the block there, so it's all as-is, unhoned, in those dark areas. Butt, that's THE MOST IMPORTANT PART of the bore to get a good seal on, since the pressure in the cyl is highest when the piston is at the top, just after ignition and before the pressure drives the piston downwards to do useful work. The places that NEED THE MOST to have been honed, aren't.
That block looks plenty worn enough to need to be bored.
"Shop" did what all too many shops will do... "we did exactly what the customer said" [in this case, hone the walls] regardless of whether it was the right thing to do or not. They wasted your money.
The little dirt or metal dust or whatever is trivial; since you'd be taking it to the car wash before assembly anyway, it would all get cleaned up at that point, regardless.
That block is too far gone to run the stock pistons in it. That plane has already left the gate. It needs new pistons of some slightly larger diameter, and to be bored out and honed (again) to match.
Right ok thanks for that. I'll take it back and talk to them about reboring it. The next size up for pistons seem to be 3.785 inches would your gut instinct be to go higher than that? What size would you go for? My new cam specifies a compression ratio of 9.5:1 which seems to be a little hard to guarantee with the larger size pistons. Any advice in that regard?
Mind you I only worked in a reman/performance machine shop for a year, but never saw a block that had ring wear so bad there that the hone did not clean up that particular part of the bore.
I'm sure it will run, but if you are going this deep into it time and money wise, you will probably want to correct that
The machine shop should be able to tell you how much over you need to go to true everything up. 3.810 may do it for you. Pistons are readily available in that size.
Even with the hone job, the bores look to have "acne".
I'd ask the shop to credit your cost of the "hone job" towards a bore and hone with plates.
No plates? Find another shop.
05-06-2022, 11:39 AM
5.3 LM7 Piston ring sizing after honing 
