[FastRat]

Pls explain... what has to be done in order to line bore a block?...do u have to torque the caps down?...does it chng the bearing size on the mains of the crank?...is it absolutely necessary when changeing caps?...all info appreciated

thnx

FastRat

 

[gn7]

Pls explain... what has to be done in order to line bore a block?...do u have to torque the caps down?...does it chng the bearing size on the mains of the crank?...is it absolutely necessary when changeing caps?...all info appreciated

thnx

FastRat

First, yes it is absolutly necessary when any cap not originally on THAT block is changed. Period, no question!!! Yes the caps are torqued to spec with the EXACT same type of fastners you plan to use. Studs, ARP bolts, stock bolts, etc. First the face of the cap is ground a couple thousands (or more if needed) to get it FLAT and SQUARE to the bearing bore. Now the hole is no longer round due to this. Then he machines it round by honing it, or boringif it was way off or the bearing bores where damaged. If he does it right, he will make constent checks to see how the hone is cutting, and may loosen a cap alittle to adust the way the hone is cutting a peticular saddle. When done, your bore are perfectly inline and dead perpindicular to the cylinder bores and parrallel to the deck. And the diameter will hopefully be on the tight side of the stock specs and thery DO NOT require special bearings This is the over simplified explanation, but it no simple task, and for the bad news, 1 in maybe 5 machinists that perform align hone a block know what the flock they are doing.



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[ol guy]

First, yes it is absolutly necessary when any cap not originally on THAT block is changed. Period, no question!!! Yes the caps are torqued to spec with the EXACT same type of fastners you plan to use. Studs, ARP bolts, stock bolts, etc. First the face of the cap is ground a couple thousands (or more if needed) to get it FLAT and SQUARE to the bearing bore. Now the hole is no longer round due to this. Then he machines it round by honing it, or boringif it was way off or the bearing bores where damaged. If he does it right, he will make constent checks to see how the hone is cutting, and may loosen a cap alittle to adust the way the hone is cutting a peticular saddle. When done, your bore are perfectly inline and dead perpindicular to the cylinder bores and parrallel to the deck. And the diameter will hopefully be on the tight side of the stock specs and thery DO NOT require special bearings

X2! plus caps are matched from the factory and any change requires this.

 

[Fiat48]

"and for the bad news, 1 in maybe 5 machinists that perform align hone a block know what the flock they are doing."

Amen to that.

 

[sleekcrafter]

Why not bigger saddle dia. for the bearings, rather than cut the bore, and move everything north? I know how it's done, but the internals all get moved in the process.

 

[Infomaniac]

Why not bigger saddle dia. for the bearings, rather than cut the bore, and move everything north? I know how it's done, but the internals all get moved in the process.

You loose the bearing crush if you just open up the bore. And line "BORE" would remove a lot of material then you have to hone it afterwards The bore tooling is supported on each end. You can manipulate the center of the cut.The hone just follows the existing bore.

What you gain by moving the rotating assembly is worth it. It would be a lot of work to cut the caps and machine the registers to end up with the main bore in the same location when you are done.

We don't cut the caps when we do the high end aluminum blocks. It r,moves the anodiizing from them. We sand the registers to close up the hole before honing.

 

[scott foxwell]

BBig difference between align boring, and align honing...

 

[Hat]

Pls explain... what has to be done in order to line bore a block?...do u have to torque the caps down?...does it chng the bearing size on the mains of the crank?...is it absolutely necessary when changeing caps?...all info appreciated

thnx

FastRat

Line boring consists of cutting the main caps on a grinder (special) to ensure the ground surface is paralell to the bore about .005 and reboring the hole to the original size, the only times that process is usually used now is to size new caps to an old block, like aftermarket caps, then when a size around .002" small is achieved the block is then line honed to achieve much better finish, and results, a good hone operator can hold .0002" from end to end on a 7 main 6 cylinder, and the same tolerance with a 5 Main V8.

a good line bore tech should go for .000 at the block leave .002 to hone, thereby moving the crank up in the block a minimum amount

 

[scott foxwell]

I remember one team I worked for decided they were tired of taking the mains out of the blocks and instead, built replaceable inserts. They machined the block oversized and installed the inserts. (Alum block) I got the job of building the boring bar system so they could replace and machine new inserts in the block right at the track.

 

[Moneypit]

Block material

If done correctly, the block will not lose any material. (assuming it was straight before you started). As mentioned, finding someone with the knowledge and equipment to line hone a block is tough. 4 out of 5 will make it worse. IMO, the shorter timing chain sets are proof some body screwed up and moved the main bore too close to the camshaft. This can't be a good thing if the bore was moved that far unless the crank C/L to cylinder perpendicularity was way off to begin with............Original stock caps on a block are usually damn close and IMO, better left alone unless there is an obvious problem. Replacement caps must be bored/honed to size and alignment, and held to .XXX to camshaft C/L parallelism and location....Ray

 

[sleekcrafter]

So you spin a main, just toss the motor? Just thinking...why not bigger o.d. bearing shells, same I.D. not cost effective?

 

[Moneypit]

Spun main?

So you spin a main, just toss the motor? Just thinking...why not bigger o.d. bearing shells, same I.D. not cost effective?

I don't know. I've never spun A main bearing. I've wiped out all of them, but never just one. I didn't spin any, but the block saddles got so hot I was afraid of it......

I imagine there is a "fix" to save the block, but all I've seen were scraped because like you said, "cost effective" vs starting over with another block.....

Ray

 

[lbhsbz]

Crap like this is why I always seem to go through 3 or 4 core blocks before I find one I'm happy with.

I've had 2 blocks that one of the main caps twisted on and locked up the crank when studs were used...problem wasn't there with the stock bolts. Both of them are already bored and honed when I find this out.

I'm getting kinda tired of it, but I'm not happy with the solution either...becuase line boring involves an interupted cut with very little material removal and no room for error, which means more likely than not, it'll get screwed up. Seems the price you pay to fix a block right any more...you could by a new dart block instead, but are they even straight?

 

[Moneypit]

Straight?

Crap like this is why I always seem to go through 3 or 4 core blocks before I find one I'm happy with.

I've had 2 blocks that one of the main caps twisted on and locked up the crank when studs were used...problem wasn't there with the stock bolts. Both of them are already bored and honed when I find this out.

I'm getting kinda tired of it, but I'm not happy with the solution either...becuase line boring involves an interupted cut with very little material removal and no room for error, which means more likely than not, it'll get screwed up. Seems the price you pay to fix a block right any more...you could by a new dart block instead, but are they even straight?

I worked in a shop that measured down to Millionths. Our stuff wasn't "perfect" even at that, but we called it "Adequate" for the task it was made for. Good word, Adequate........hand What I mean is, how straight is straight enough?...........Ray

 

[scott foxwell]

Crap like this is why I always seem to go through 3 or 4 core blocks before I find one I'm happy with.

I've had 2 blocks that one of the main caps twisted on and locked up the crank when studs were used...problem wasn't there with the stock bolts. Both of them are already bored and honed when I find this out.

I'm getting kinda tired of it, but I'm not happy with the solution either...becuase line boring involves an interupted cut with very little material removal and no room for error, which means more likely than not, it'll get screwed up. Seems the price you pay to fix a block right any more...you could by a new dart block instead, but are they even straight?

That's odd. Did you re-size the main bores after installing the studs?

 

[lbhsbz]

That's odd. Did you re-size the main bores after installing the studs?

My machinist sent the the block out to get the mains worked on....but they clearly took material off of the block side, and as soon as I got the crank in I threw a cam in and put on the timing chain...lots of slop....so now my cylinders weren't square with the crank. The mains need to be the first operation, not the last, since the rest of the work references off of the mains. My guy had "never seen that before" ... LOL.

I finally gave up on the motor that I've got in it now, and just used the stock bolts.

I don't mind shortening the deck height a couple thousandths and using a shorter timing chain for the kind of duty most of my engines see, but I have a problem when everything isn't square. Not sure why...it just seems fairly simple to make it right so why go and make it not right.

 

[IMPATIENT 1]

just make sure whoever does it knows wtf he's doin, we've gotta brand new forged eagle crank with less than 30minutes on it that's bent due to a machinist phucked up line boring and honing :|err took 10/10 to straighten the crank, now its just a spare

 

[Morg]

BBC lives & dies on the mains. You have to have clearance, the crank needs to be straight & the mains need to be align perfectly.

The more power you get out of a motor the more import this becomes.

 

[wagspe208]

Christ....let's reinvent the wheel.

Align honing is done with a long mandrel. It goes through all the mains at once. Align boring is done with a tool bit. It does one main at a time. Generally align boring is done when caps are replaced. Generally align honing is done to correct diameters, straighten, when studs are installed, etc.
Align honing... the caps are cut about .005". (machinist preferences here). Align boring, caps need to be cut more than that.
Align honing... let's say you cut your caps .005". Let's assume you had minimal issues... this will move the mains up .0025 (based on average material removal). If anyone on here running a damn boat thinks this makes 2 hoots in hell regarding their mains to cylinder relationship, they are fools. Hell, 1/2 of the shops out there cannot get the cylinders to .002 round and straight. Hacks!
Align hone/ bore/ deck/ assemble.
It is not rocket science.
Wags

Oh, and BTW, sunnen recommends if a cap is getting bigger than the others, that cap is removed and recut. This will help the mandrel to straighten up. Loosening the cap every time magnifies the issue.

 

[Fiat48]

The BBC is a POS and always has been. The foundation can't accept the power that can be produced. When the factory line bored the blocks they did it with a tool coming in each end. To "correct" this they used "select fit" bearings...special bearings not available to the public. That is how they got away with it.
Next thing you know some rebuilder puts a set of "standard" bearings in the thing and the clearances are all over the map. Main saddles were never straight in the first place.
Block is continually flexing and changing these clearances plus the weak crank is always flexing. One day things flex a little much and the crank grabs hold of a main bearing. The heat from this contact shrinks the main bearing.....it tries to wrap itself around the crank. Now there is no place for the oil wedge and a spun bearing is the result.
The heat created by this "shrinks" the main cap....it doesn't enlarge it.

Now the cap does not index in the block as it should...it's too "small". Some guys will try to weld the cap near the index line, get it to index "straight"(?) and then cut the cap faces and try to line hone the block.
Other guys will grab a collection of main caps they have saved (from other blocks that have met their death) and try to find one that will line up close enough to where they can cut the cap and then line hone it.
Out comes the dull chisel and the rest of the block is "staked" to try to expand the block indexes which were too damn small in the first place (it's a production truck motor...remember that always) to try to tighten the locations of the caps back up.
We weren't straight in the first place thanks to the factory and we are crooked as Hell now.

So the rest of the caps are cut .001-.002 and now we have a series of crooked holes to try to make straight with a line hone bar....that naturally tries to follow the crooked path.
Most guys don't load the stones correctly...they just make light passes in and out of the block trying to achieve the proper dimensions (2.937 to 2.938).

The block never cuts each main cap the same. You are honing and #2 is approaching 2.9372 and yet #3 is "behind" and she's at 2.9363.
So Main cap #2 is loosened slightly so that it doesn't cut......taking it out of the picture so the others can catch up.
But then #1 is cutting too much....what to do.....pick the block up out of the machine....turn the block around and hone from the other end.
Ok....somehow you got them all at 2.9375....right in the middle of spec. Damn your good.
Are you?
Odds are it isn't straight. It's to dimensions but is it straight?

How to tell?
A precision ground bar needs to be inserted in the mains. If she is straight then the bar will pass through nicely. If it isn't the bar will stop sliding through at some point.
But you thought the line hone bar....which is straight....was gonna make your main saddles straight? Right? Nothing can be further from the truth. I've line honed many that the bar dead stops when inserted for checking. You gotta cut the caps another.001.....then load the stones hard and pray she straightens.

But nobody has this ground bar. So...you pays your money and you takes your chances.
Or you buy Dart. Every one of those have been straight that I have seen. Or if you don't make much power you get by. Doesn't mean it's right but you get by. Maybe next time you can blame it on oiling like most guys do. Or the machine shop can use his famous detonation word and explain it all away.