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Just opened up my replacement engine. I'm not looking for a bunch of extra horsepower. I'm looking for advice on whether to just hone this engine or have it bored. The attached picture shows the existing bore sizes.
At what point of the cylinders did you measure the bore?
How many miles on the engine? Are the pistons cast or forged?
Measured about 2" down. I don't know the history of the engine. I'm told it was out of a 70 Toronado. Mounts and a few other things indicate that as well. I haven't rolled it over yet to inspect the bottom side. Guessing from the oil sludge nobody has been into the engine before.
Glazing looks very shiny. It is what happens with use, the walls are slightly rough after boring and honing which helps the rings scuff and seat, at this time the crosshatch pattern is most visible. As the engine runs and gets hot the walls get polished and oil can burn onto the walls. In order for new rings to scuff and seat properly the walls must be de-glazed.
Glazing looks very shiny. It is what happens with use, the walls are slightly rough after boring and honing which helps the rings scuff and seat, at this time the crosshatch pattern is most visible. As the engine runs and gets hot the walls get polished and oil can burn onto the walls. In order for new rings to scuff and seat properly the walls must be de-glazed.
Glazing looks very shiny. It is what happens with use, the walls are slightly rough after boring and honing which helps the rings scuff and seat, at this time the crosshatch pattern is most visible. As the engine runs and gets hot the walls get polished and oil can burn onto the walls. In order for new rings to scuff and seat properly the walls must be de-glazed.
If your machinist buddy says the clearances look good with just a hone, then just hone it.
You can just do a quick dingle berry run. Worst case you might get a bit of extra piston slap so it'll be a slight bit noisier.
You need to measure at the TOP OF THE RING TRAVEL because that's typically the most-worn part of the bore. But that's not the only place you'd need to measure. If you have a ridge of just a few thousandths, you need to bore rather than hone. They used to say that up to seven thousandths (0.007) was acceptable cylinder wear for a Grandma-car. Seven thousandths taper means a ridge at the top of three and a half thousandths (0.0035). Current service limits are ONE thousandth (0.001) or even less taper. If you can feel a ridge...you're probably going to have to bore it.
You also need to check the cylinder for roundness, as well as straightness. Cylinders usually wear "bellmouth", (larger at the top) but not always.
MAYBE you could dingle-berry hone the cylinder with 280- or 320-grit and be OK. Last Chevy I rebuilt had .001 to .0015 taper, I brushed it and "so far, so good".
Last edited by Schurkey; Oct 18, 2020 at 10:35 PM.
You need to measure at the TOP OF THE RING TRAVEL because that's typically the most-worn part of the bore. But that's not the only place you'd need to measure. If you have a ridge of just a few thousandths, you need to bore rather than hone. They used to say that up to seven thousandths (0.007) was acceptable cylinder wear for a Grandma-car. Seven thousandths taper means a ridge at the top of three and a half thousandths (0.0035). Current service limits are ONE thousandth (0.001) or even less taper. If you can feel a ridge...you're probably going to have to bore it.
You also need to check the cylinder for roundness, as well as straightness. Cylinders usually wear "bellmouth", (larger at the top) but not always.
MAYBE you could dingle-berry hone the cylinder with 280- or 320-grit and be OK. Last Chevy I rebuilt had .001 to .0015 taper, I brushed it and "so far, so good".
Thanks for what sounds like excellent advice. After discussion with my local machine shop I'm going to bore it. Only want to open this engine one time.
Thanks for what sounds like excellent advice. After discussion with my local machine shop I'm going to bore it. Only want to open this engine one time.
1. Figure out what you're using for pistons BEFORE you bore. The TRW forged pistons are battleship-heavy, and have 1950-style rings. You can do WAY better in terms of lightness, strength, friction with a modern piston/ring package. It used to be a "thing" that the bores would be final-honed to the individual pistons going into them. This isn't such a concern any more as pistons are sized more accurately now, and the better ones are packaged as weight-matched, size-matched groups.
2. Make sure that machine shop can hone the bores with a torque plate in place, main caps attached, and if they're going to align-hone the main saddles, hand them an old oil pump to torque in place during the align-honing process.
