cylinder overbore

[JackFish]

I have a block that we've discovered is already over bored to .030.
Is it possible to bore it out to .040 to freshen it up?
Or, does it have to go to .060, as the machine shop suggested?
It's at the shop and I am picking it up today after a cleaning and can take a few measurements later.
What I noticed is that there was no ridge on the top of the cylinders, and there was still a bit of crosshatch on the walls, but just a minimal amount.
Oh yah, it's a 302.

 

[rbohm]

8) pistons do come in .040 oversize. that said you need to check the taper and out of round in the bores first to determine how much of an overbore is required, if any.

 

[JackFish]

Assuming the block is within spec to be @ .040, I guess my question is, to be more specific, are there any machining issues that arise with going only .010 larger bore size? Is that a problem for a machine shop, or no?

 

[StrangeRanger]

No problem whatsoever. I wouldn't be real comfortable taking a 302 to .060 over (unless it was a race block with siamesed bores )

 

[JackFish]

Yeah, I'm a bit uncomfortable with it too, which is why I'm asking.
This is a Mexican block (courtesy StorminNorman ) and it has larger main caps and webbing than regular blocks, so they say, and it would appear to be so to my inexperienced eye.
I don't have a vehicle for it, but I'm thinking that I'd like to put it in an aluminum hull boat with a jet drive. So if that's the case, it will spend most of it's final life @ 3/4 throttle scooting around on Lake of the Woods.
On another note, I've gleaned info from some of the threads on sleeving here. Perhaps this would be a good candidate?

 

[StrangeRanger]

Those Mexican blocks are high-nickle content and will take a ton of abuse. If you're going to go .060 over, you should probably get it sonic checked. Sleeving sounds like a plan if you can make it work financially. Take it back down to stock bore and have meat for several more rebuilds

 

[JackFish]

Those Mexican blocks are high-nickle content and will take a ton of abuse. If you're going to go .060 over, you should probably get it sonic checked. Sleeving sounds like a plan if you can make it work financially. Take it back down to stock bore and have meat for several more rebuilds

Is sonic-checking magnafluxing? If so they did it and said it had no cracks.
I read in a book (George Reid, How to Rebuild the SBF) that the higher nickle content is a myth, that said they compared the weight of the blocks.
Perhaps this method isn't conclusive?

 

[StrangeRanger]

Sonic (actually ultra-sonic testing) determines the thickness of the cylinder walls. It looks for a core shift and keeps you from getting too thin a wall on a large overbore. It's obviously irrelevant if you sleeve.

 

[Lazy JW]

.... the higher nickle content is a myth, that said they compared the weight of the blocks.
Perhaps this method isn't conclusive?

There are ways to scientifically test for element content but I seriously question this method. The first doubt that comes to my mind is how does one acurately determine the total VOLUME of material in something so complex as an engine block?

Comparing by weight is an attempt to compare density. To do this in a meaningful manner one must first know the EXACT cubic volume of said material.

If we were starting with a relatively simple geometric shape that could be accurately measured I would have more confidence in this method. Count me as sceptical.
Joe

 

[Thad]

Eight sleeves will cost more than a rebuildable core.

0.40 is no problem, a good machine shop can measure out of round and bore centering on that. I have bored with one of the four centering pins setting in the worst part of the "eyebrow" this slightly offsets bore but not enough to be any problem. Often times able to used a smaller O/S piston than centering less worn area. Definately saved some blocks.

 

[JackFish]

Eight sleeves will cost more than a rebuildable core.

Heh, try and find a Mexican block up here in the Great White North
So how much more? How much does a liner cost?

 

[rbohm]

Eight sleeves will cost more than a rebuildable core.

Heh, try and find a Mexican block up here in the Great White North
So how much more? How much does a liner cost?

8) about 10,000 years ago or so, when i was in college, i asked one of my instructors who also owned a machine shop, and his reply was $8 per cylinder for boring, and $40 per for sleeving.

 

[JackFish]

Saw this on another forum, the thread was about 289vs302, but the info on the chamfering of the bore caught my eye:

I have set several 289 and 302 blocks side by side and measured the cylinder length.
the difference in cylinder length is irrelavent because the factory puts a chamfer on the lower end that varies as much as .070 in depth from block to block. A deeply chamfered 302 block is as short as a 289 block. Boring the cylinders reduces the chamfer. .060 over usually eliminates it completely.

Is it possible that if the machinist I saw was not aware of this (mebbe more of a chebbie guy?), that he could have interpreted a reading down in the bore as out of spec in his recommendation to go to .060?

Can someone confirm this taper? How far down would this chamfer start?

 

[addo]

I think it's just referring to a small bevel cut (45°).