Any problem boring 060" over?

I just bought a 360 off Craigslist. He sold it as a 318 (he's an import guy so he didn't know what he had) but once I scrubbed the dirt off the block I discovered it is a 1990 360 with a roller cam, that was run off propane. After opening it up I discovered it had been rebuilt at least once (as evidenced by the .040" Sealed Power pistons). All of the cylinders have a slight ridge at the top of the bores, barely enough to catch a fingernail, but one cylinder has a half inch long horizontal scratch that's deep enough to catch a fingernail. I also found the cause of the scratch, a piece of oil ring was in the oil pan. Since I'm looking at having it bored to the next size, is it really safe to go 060" over? I've heard these were thin walled and would run hot but I don't know.

I'm not looking for a street/strip warrior, just a daily driver engine to replace the aged slant six in my 84 D100.

Have your machine shop sonic check it, then no questions just what you are working with and what bore it will handle. It might be done as it is, but checking it should help know for sure.

Too bad it wasn't a 1971 Casting 360 block. They were cast based on the 4.04 340 casting. You can sometimes take them .100 over without trouble!

As stated, the machinist can tell you. The sonic testing determines cylinder wall thickness. There really is no clear answer on going .060 over safely. I've read some rare instances where casting flaws have occurred, resulting in some abnormally thin spots even in standard bore blocks.
***Another option: If it is just ONE hole that needs work, ask about sleeving the cylinder. A buddy of mine has 2 sleeves in a 340. No problems and he saved a bunch of $$$ as compared to the cost of a replacement date coded 340 block.

Thanks for the replies! I will have them sonic test the block. Sleeving the block sounds $$$. If it was a rare block though I could see spending the cash for that, but this is just an ordinary 360, nothing special. I was just worried that the cylinders might be thin and weakened by being overbored that much, but it's not going to be a high revving powerhouse, just a stock rebuild with a slightly hotter cam than stock.

On a positive note, the heads and crank are darn near perfect.

Keep in mind that half of the over bore comes off each side,.020 from all sides, not .040

Sleeves are ~$100 per hole. Don't be afraid of them. The final result is actually stronger than original casting


On the flip side, it's only a 5.9 magnum block that can be found for around $150 as a bare block or $250 as a full engine if you shop around n haggle

I'd return it because it is not what was advertised and look for another one. IMO a 5.9 is not worth putting sleeves in. Nothing wrong with a 318 either IMO. .060 over in not a good thing to do with any mopar block.

My Challenger has a 1976 360 that's .060" Street car driven everywhere for over 20 years, been 12.50@110.
Doug

I agree, hope you got it free. If you can't return it, sleeve it, hone the others then new rings. Finding another engine might put you in the same boat as now, crap shoot. Most all will need something done to it. Best bet is to find one running, hear it run for a least 20 minutes.

It wasn't free but pretty cheap. The heads and crank alone are worth what I paid for it, especially since it's already been turned and is beautiful. This engine shows signs it was rebuilt not too long ago but was an oil burner, and now I know why. Once the snow melts I'll get her to the machine shop for testing.

Can you post pictures of the bores and the damaged bore? From your first post it sounded like the 40 over bore had ridges at the top?

Maybe if the bores are not too bad the they could be rehoned and use the same pistons with new rings. If the damage is down low it may not effect how it runs.

I have done a half a dozen stock rebuilds with a hone job only and all of them ran for many more miles after my re ring and new bearings.

One motor had a gouged cylinder down low that I re used after just a hone. The cylinder sealed up fine and I even did a compression check on it years later and it was still good. We used that engine in a company van, 79 360 dodge van. Ran it 100K miles after a re ring job. Van had 200K + miles on it.
I always used moly rings, they are "soft?" and seal up easier than most others, good for re ring jobs and stock rebuilds.

I'll try to get pics soon. The ridges at the top of the cylinders could be just carbon. I'm hoping it is. I'm going to have the machine shop check the bores to make sure they are round and how much they are worn. I may be able to get by with just a hone. Or I may just be overly optimistic.

Scuff up the bores and put a ring/bearing/gasket kit in it. Might use a little more oil than a full rebuild but oil's cheaper than machine work.

A show of hands.

How many people here have actually seen a .060" over cylinder fail in a stock type build in ANY Mopar block?

Thought so.

Kevin

How high in the bore is the scratch from the broken ring?

A few years ago one of the members bored a 383 out to 0.060 over and had it sonic checked. Thrust face was right at 0.090 and he asked if he could run at that. I replied that he could, he believed me and did, ended up with a cylinder wall crack. So yes, Virginia, it does happen.

I did worse with another make. However, I was not aware of the problem when I bought the block. It was only +.030" but was a 700HP, high RPM motor. Had all the good stuff, light weight JE pistons, Al rods, roller cam etc. Previous owner never sonic checked block when they made into race motor. Thrust wall was .080", other side .300". It had core shift.

Fate caught up with it. Finally at top of 2nd gear around 7,200 it let go. Everything that moved in the motor was junk. I mean everything.

I would never do a performance motor ever again without sonic checking.

Low po DD, the odds are well in your favor. What Nanket said, more info on the scratch. EDIT with more thought (& rereading your OP) I would NOT rebore it but just rering it with some file fit plasma moly rings with dingleberry honing it with a their 320 grit. I dont think that scratch will be any problem & I would bet my last dollar that you will be fine & end up with more power & plenty of longevity (plus you're gaining almost 40 cubes) & you could spend some of that cash on milling the heads.

Agree with this ^^^^ for a street motor.

Yes, Blazin' Bob has the answer. Don't worry about it. The ridge is probably carbon and can come off with a pocket knife.

It's a cheap block and not worth sonic checking. I'd sleeve it first if 0you must, leave it at 40 over.
BTW, a '9 360 block is NOT a 5.9 Mag block.

R.

The scratch is in the upper third of the cylinder, not on the thrust side. I was going to go grab a pic of it but it snowed and these old bones don't like being cold, so walking to the garage wasn't on my list of things to do.

I'm going to a ceremony tonight (my son won officer of the year) but I'll definitely get pics tomorrow. Supposed to be significantly warmer than 17 degrees tomorrow too. I'm really hoping I can just get by with a good hone and new pistons and gasket set. The cam looks great, just a little discolored where the lifters rolled over it. No scratches.

Yes I have had 2 340s crack cylinders and they were both stock bores. They both sat with coolant in them for 20 years or so and caused rust that weakened the bores.

The direct connection performance bible used to only recommend a max .010" over bore. Now we know that is extreme and for performance builds and the OP wants a DD motor.

Like I said earlier I would not bore any moper .060 over personally.

If you can just hone, then why do you need new pistons? Are they damaged?

I have a hand held sunnen hone that I use with a bigazz 1/2" drill and have honed many motors with it successfully and re used the pistons with fresh rings. You would be surprised how some junky bores can be cleaned up and ran for another 100K miles. I have done it numerous times.

Too many people have bored engines when they did not need it and now there are not that many left that are standard bore.

I still have 2 spare 340 blocks that are standard bore and 2 340s with cracked bores that might get sleeves some day if I ever need them.

So yes I have seen more than one engine go bad from cracked bores in small block mopars

Yes, one piston is damaged where the oil ring came apart. Even if I hone out the scratch, I'll need to buy one piston and new rings. Pics of the cylinder coming soon.

I wiped out the cylinder and got some of the "ridge" to come off; apparently it's mostly just carbon. But after magnifying the image I can see what looks like chatter marks on the cylinder wall. After wiping out the cylinder and taking a closer look I don't know if this'll hone out.

I'm wondering if those are crosshatch (normal) or actual damage from the mishap?

Is that pitting down low? Might be what broke the oil ring?

Yes it is. Very shallow, but there's lots of little pits. This is the cylinder that had the oily spark plug.

It's much deeper than the crosshatch, plus there are chatter marks in the metal there.

.060 is as far as I go unless a hemi block

I looked at another 360 for sale from a 1985 D350. It didn't seem to be in any better shape. People around here think that any V8 is worth its weight in platinum, running or not, and even junk is $400.

My plan at this point is to get it sonic tested, and if it's good enough I'm just going to do a low performance stock rebuild and bore it to .060" and call it good. Thanks everybody for the responses!

or a slant six, most any /6 block can go .100

I've heard that as well. But it costs about as much to rebuild a slant six as it does a 360, and the slant would be pushing 150 horsepower unless you spend $$$ porting the head.