Barrel shape in #1 cylinder (sbc)

[Ada88]

I have a 400 small block Chevy that has a .0029 barrel taper in the middle of #1 cylinder. This motor will not see any more than 350-375 hp and rev to 5000-5200 Max rpm. It will be a weekend driver and maybe only see 70 miles a week. I’m not worried about a little smoke or it lasting 50,000 miles.
Will I have other problems though like piston slap? (I’ll be using hypereutectic pistons) Or will it be fine and not even smoke? Can I get by without having it sleeved as it has already been bored to the max?

Thanks in advance,
Adam

Also I’ve heard of using special rings in a similar situation. If so what are they?
I’m still new to all of this as this is my first build, so any help would be greatly appreciated.

[Racer97]

I say try it .some guys have had luck with worse .

[BillK]

Any idea why the taper is there ? Did the engine hydrolock and possibly push the cylinder wall out ? If so I would not feel good about using it as is.

Not sure what to tell you otherwise. The way my luck goes I know I certainly would not use it

[dannobee]

Any idea why the taper is there ? Did the engine hydrolock and possibly push the cylinder wall out ? If so I would not feel good about using it as is.

Not sure what to tell you otherwise. The way my luck goes I know I certainly would not use it

^^^^ This ^^^^

Might be wise to sonic check it, especially since it's on the last overbore anyway. I've seen some scary sonic checking results over the years.

[rebelrouser]

I agree with the sonic check, every block I have seen with a barrel shaped cylinder had cracks or was about ready to let go somewhere. An engine bore wears 90% in the top 1/2 inch of the bore, if it has .002 wear in the middle of the cylinder something is not right with the block. Just my experience, others may vary.

[Ada88]

Any idea why the taper is there ? Did the engine hydrolock and possibly push the cylinder wall out ? If so I would not feel good about using it as is.

Not sure what to tell you otherwise. The way my luck goes I know I certainly would not use it

I purchased engine from a guy who had just built it and ran it for about two hours before One of the Pistons failed. I Checked the failed piston with a micrometer and it was a .040 over piston labeled as an .060 over so my guess it was a factory mix up and the prev owner did not mic all the pistons before installing. I made a DUMB rookie mistake of honing out a couple of scratches and ended up with this problem. So the taper is caused from honing not hydro lock. Lesson learned the hard way and I will be leaving honing up to the machinist on any future projects.

[Schurkey]

You managed to hone .003 out of a cylinder creating a barrel taper, to clean up a "scratch"?

Thousands of years ago, when I was in Trade School, we were told that maximum cylinder taper--for a "Grandma going to Church" engine--was .007. But that assumed typical bellmouth taper, not middle-of-the-cylinder barrel taper. Middle of the cylinder taper means the rings are flexing--expanding and contracting--twice per stroke instead of once per stroke.

"I" would sonic-test all the cylinders, if possible. Best case, I'd likely have that one hole sleeved. Worst case, you're sleeving multiple cylinders, or even looking for a new block.

[rustbucket79]

Either close your eyes and run it, or toss the block. Yes some 400 blocks have been successfully sleeved over the years but my feeling is you have a high probability of cracking a head bolt hole due to the extremely thin casting remaining around the head bolts.

There is no ring that fixes oddly shaped cylinders. If you are spending any more money than the single replacement piston and maybe a set of cheap rings, move on to another project.

[rebelrouser]

This is how I explain taper wear, if a cylinder is straight and true the rings slide up and down the cylinder and do not expand or contract as they seal the cylinder. If the cylinder has wear the rings have to expand and contract to maintain contact with the wall. So take a piece of wire and start to bend it back and forth, after a while the wire will break, so will your rings, just a question of time. Years ago when I started fixing cars, we called them farmer rebuilds, ridge ream the bore throw in a set of rings. I took scores of them apart, shook the pistons and the rings fell off in pieces.

[novafornow]

There are things that can be done. Either one cylinder or all of them. Hone round, coat piston. Heck, I have even knurled an old set of pistons years ago. Not a world record holder, but ran fine for brackets.

[Ada88]

Thanks for the input guys. I have another 400 that is still at 4.125 bore. I’m going to send it to the machine shop have it checked and if all is good then have it decked and bored .030 over

I bought the short block that was .060 over for the crank, and rods because it was a steal. I only paid $100.00 for it, and the crank checked out perfect on my mic as it should because it only had a couple hours on it, or so I was told, so I’m not at a loss. I’m just going to have to stick to my original plan and pay to have the virgin block machined as I’m not going to risk any problems that could arise like broken rings shortly after build or crack at head bolt like stated above. Again, thanks for everyone’s input,
Adam

[rfoll]

A sonic check will give you plenty of information. I have run 2 400 blocksat +.060, 412 cid. One was bracket engine that survived for years. Your results may vary. A sleeve in a 400 block is more risky than an overbore. The bolt holes are very close to the edge of the cylinder.

[1972ho]

Are you can send that one piston to line to line and have the abradable coating applied and it will seek its on clearance to that bore.

[rustbucket79]

The 400 blocks I’ve sonic tested are quite thick for a factory block on the major and minor thrust sides however they are sculpted every place there’s a head bolt hole, so invariably those areas are the thin spots.

The OP starting with a virgin block is the right idea for a decent build.

[rebelyell]

Thanks for the input guys. I have another 400 that is still at 4.125 bore. I’m going to send it to the machine shop have it checked and if all is good then have it decked and bored .030 over .......Adam

Why +30 ? ... if you're gonna buy good pistons, they're usually available in +20, +25 etc. Why bore an OE 400 more than necessary ? JME