Years and years and yes, years ago, I was at a guys place and he had a 396 rebuilt sitting in a tri5 Chevy, and no heads on it. He pulled the cover off the engine and I recall a taper cut at the top of the cylinder into the deck. I should have asked him why, but we were talking about something else I guess, but I recalled that image of that shortblock recently, and wondered why that was done? Has anyone done/seen this before?
You put a little bevel around the top to keep from breaking the rings during install. At least most people I know do.
That never occurred to me! Mercy. I’ve always used the “sleeve” thing you snug up and tap the piston down. But that makes sense. Thanks! Edit: Begs a question, would one ask the shop to do it, or is there some type of ridge cutter used at home with a taper?
The tool we have to chamfer the top of the cylinder is a hard rubber cone with sandpaper that you run with a drill. As said above the chamfer is so the rings don’t catch on the way in.
Budget - A "taper" ? Do you mean a small, .03" to .04" "chamfer" ? Yes this is to break the sharp edge off of the top of the cylinder, It can also aids slightly in piston ring installation when done incorrectly. It should NOT be a large "taper". This is NOT good for proper combustion. The 409 did "NOT" have a taper !! The "W" engines had a slightly larger diameter bore cut into the top of the bore. I have no idea why is is/was there. Possibly for a reduction in compression ratio, as there is no combustion chamber in the heads for altering the combustion ratio. This is a perfect way, and acts similarly to a change in a cylinder head chamber size change. I say this because a .060" overbore will REMOVE this overbore ! And there is NO harm or degradation in the cylinder when not...using this overbore. Mike
396 had a chamfer for unshrouding valves also. Back when building dirt track small bore engines we used to do the same to help smooth flow. 348/409 decks are not square with bore. Combustion chamber is in the block. Step in bore was to facilitate ring install.
The counter bore in the 348/409 is for honing the cylinder. If the counter bore is not there the hone will not have support across from the combustion chamber in the block and will cause the hone to want to rock over at the top of the bore.
Mike, it’s been years, but as I recall it was a very pronounced taper. Something I noticed immediately when he pulled the cover back on the engine. I’m pretty sure it was much larger than .03, etc. in my mind now, I’d think/remember/etc it was in the 1/4 inch range and like 45 degrees. Now 30 plus years can play tricks on your mind, but I’m sure I wouldn’t be able to spot/see or even notice such a small amount you mentioned.
@TA DAD , do you put a pronounced taper, or more of a debur? Also your tool doesn’t look as severe as the chamfer I recall. Mike might be on track, maybe he was dialing in to a compression ratio and running a larger bore gasket. But the chamfer was all the way around the hole. Man I should have asked the fella!
Lol. That was maybe around the time of my first cell phone, a Motorola DP 550? As I recall. Place calls and take calls. “Texting” wasn’t even a thing then.
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