[Will]

Sorry to add another post on this, but the original post about the main bores in my new block got way off topic.

I believe I have a problem and need to find the CORRECT information so I know for sure. I got the block back from being align bored on Friday at Ed's, and Sunday morning had it checked at Roger's (the shop where most of the work is being done) with a dial-bore gauge. All the bores came out to 3.4395" Depending on what specs I look at, that's either .0005" or .001" over the max allowable size.

I helped Roger do the measuring and we recalibrated the dial-bore gauge three times just to make sure we weren't screwing something up. The specs we're going by at Roger's shop are published in a software program he has from the Automotive Engine Rebuilders Association. This program shows the allowable tolerance as 3.438" - 3.4385".

Someone else looked up the spec in a Sealed Power catalog and it shows there as 3.438" - 3.439".

None of these sources is a GM source, but regardless the bores are over the max spec of both sources.

Does anyone know what the allowable tolerance REALLY is? I've been unable to find this info in my '68 or '72 Service Manuals and don't know where else to look for the GM specs. I called a dealership service center and none of their books go back that far (1970 455).

Beyond wanting to verify that I'm working with ACCURATE information, I'm wondering what, if any problems would be caused if I have the main bores redone. Just how far can you move the crank centerline before you have to start worrying about alignment with the cylinder bore centerlines? How far can you go before you have to start worrying about timing chain length? I know shorter chains are available, but I was really hoping to re-use the chain from the previous engine which only had 1500 miles on it.

Help me out here guys. This may sound like worrying about minute details, but dangit, I already had one expensive engine go south on me because of problems with the main bearings and I do NOT want that to happen again. The real bummer of this is that
Ed's has a sterling reputation, holds a lot of championships and a couple of world records. Roger has been sending all the blocks that need line-boring to Ed's and this is the first one that's come back out of tolerance. Figures it would be mine...

[Will]

Sorry to add another post on this, but the original post about the main bores in my new block got way off topic.

I believe I have a problem and need to find the CORRECT information so I know for sure. I got the block back from being align bored on Friday at Ed's, and Sunday morning had it checked at Roger's (the shop where most of the work is being done) with a dial-bore gauge. All the bores came out to 3.4395" Depending on what specs I look at, that's either .0005" or .001" over the max allowable size.

I helped Roger do the measuring and we recalibrated the dial-bore gauge three times just to make sure we weren't screwing something up. The specs we're going by at Roger's shop are published in a software program he has from the Automotive Engine Rebuilders Association. This program shows the allowable tolerance as 3.438" - 3.4385".

Someone else looked up the spec in a Sealed Power catalog and it shows there as 3.438" - 3.439".

None of these sources is a GM source, but regardless the bores are over the max spec of both sources.

Does anyone know what the allowable tolerance REALLY is? I've been unable to find this info in my '68 or '72 Service Manuals and don't know where else to look for the GM specs. I called a dealership service center and none of their books go back that far (1970 455).

Beyond wanting to verify that I'm working with ACCURATE information, I'm wondering what, if any problems would be caused if I have the main bores redone. Just how far can you move the crank centerline before you have to start worrying about alignment with the cylinder bore centerlines? How far can you go before you have to start worrying about timing chain length? I know shorter chains are available, but I was really hoping to re-use the chain from the previous engine which only had 1500 miles on it.

Help me out here guys. This may sound like worrying about minute details, but dangit, I already had one expensive engine go south on me because of problems with the main bearings and I do NOT want that to happen again. The real bummer of this is that
Ed's has a sterling reputation, holds a lot of championships and a couple of world records. Roger has been sending all the blocks that need line-boring to Ed's and this is the first one that's come back out of tolerance. Figures it would be mine...

[PROBRD]

Will- The book I have says that the bore diameter for 3.2500" blocks should be 3.4385" + or - .0005". Same as you have found. H-O Racing blueprint specs.

Rick

[KS circutguy]

Yo Will,I looked up the blue print specs. that Bruce Fulper aka;(Rock@Roll- fulperformance) they are;

"On a 3.250 main bore,(421/428/455) the main factory says; 3.4380-3.4390."
"Again,we use 3.3480-3.3485."

"And note that the checking clearance is taken from the twelve-to-six o'clock position
using a calibrated dial bore gauge."

"Using his specs. maintains good crush on the bearings,THIS IS CRUCIAL...The same theory applies to the rod bores"..

"And all Pontiac rod bores are 2.3745-2.3750.Again we use the small to the middle 2.3745 to 2.3748.Always preferring the smaller dimension."
And as you know these specs.are the size of the hole without the bearings in place.


Hope that helps, Steve.

[This message has been edited by KS circutguy (edited 11-13-2000).]

[Phil69GTO]

Will, sounds like you're taking a smart approach to this possible problem. The tolerance simply HAS to be correct. Even good machine shops make mistakes....better find it now rather than later.

[Half-Inch Stud]

Will, My Poncho Motor notes show the large mains at 3.4385 +/- .0005" and small mains at 3.1885 +/-.0005" at room temperature. Measured at 6:00. So, you 'need' a 1/2mil filler..

Perhaps going +.001 on the crank undersize to make up for the main bore. [.009 under crank with .010 under bearings.] Never made use of the allegedly available by GM .001 and .002 undersize Main bearings.

Or the Sandbox approach:
Several ways to add .0005" of durable material between bearing back and iron saddle. Let's first establish that you only need to close the tolerance in the middle of the U on the Cap and the Block Journal.

A shot of Copper paint onto the Bearing backsides may prove to be a durable film. Could arrange the Bearings frown-down on a flat surface and run a paint strip alone the back U. This way there is no paint film scraped during installation.
Practice spraying the exact Can angle and distance for fanout pattern, and spatter-free distribution. Let dry. Could heat-cure [cook] the paint too. This approach should get .003" thick film that will crush down.

IMOP: Uniform Coating application and adhesion onto the Block and Caps would be more difficult.

I suggest the thickness will compress: Install the bearings dry-back & oil-wetted fronts, and crank, and torque to 45ft-lbs. Check spin 1-2 turns. If good then torque to spec [100ftLbs and Rear Main 120ftLbs] and
Check for free crank rotation.

I wouldn't But: You could remove crank and bearings to check the paint crush.

You could: remove caps and check clearance with Plastigauge on journal bottom. May be on the tight side of .0002 to .002. High-Perf loading may open it up +.001.

Just don't tell anyone you did this, as they would think it was goofy and unusual. Nobody has to know. This idea may lead to some controversey, so let's see and here what a better [and equally ECONOMICAL] solution looks like.

H.I. Stud.

Fun with numbers:
Rod Big End hole: 2.3745 -2.3750
Rod Little End hole: .9789 +/- .0004" [.0012 +/-.0004 pressfit with pin.]
Rod Little End hole : .9810 +/- .0002" [Full Floating]
Piston Pin fit into piston : .0005 - .0007"

[Hot Rod]

Half-Inch,
Nice to meet you and ScottM, and all of the other guys as well!
Now let me understand this, you just gave this guy advise and then said don't let anyone know about it? You just told over 900 people that you recommemded for this guy to do this! DOLP! LOL!!!!!!!! And as for the plastic guage they only use that stuff in High School when the Teacher is looking for a WAG ( Wild Ass Guess ) from there students! [img]/infopop/emoticons/icon_biggrin.gif[/img] [img]/infopop/emoticons/icon_biggrin.gif[/img] [img]/infopop/emoticons/icon_biggrin.gif[/img]
It was great meeting you guys have a good winter and see next Race season!!!!!

Hot Rod

------------------
Outlaw Pontiac Racers Association
"For Those Who Live the Legend"

[Bracket Racer]

Take the block back to the shop that did the work and ask them to touch the caps and line hone it again, not as involved as the line bore, this should already be straight so they just need to take out that oversize condition. They will likely think your nuts but who cares, what I mean is .0005 is tough to accurately measure even with good tools, temperature can probably make it vary that much alone. I wouldn't put anything on the backs of the bearings as this could interfere with proper heat transfer and that creates it's own set of problems. When I install bearings, they get cleaned on the backsides to ensure that not even the oils from my skin is on them for this reason. This is something I remember reading in one of Smokey's books, about the importance of clean, dry bearing backs. Good luck!

[KS circutguy]

That is too funney bracket guy [img]/infopop/emoticons/icon_biggrin.gif[/img]
Bruce Fulper Quote:"Under NO circumstances will you use plasti-gage to measure ANYTHING.
Maybe the space between aunt Edna's teeth. [img]/infopop/emoticons/icon_biggrin.gif[/img] Its totally unreliable and worthless".

Hey 1/2 inch,maybe you could just STACK 2 sets of bearings to tighten the clearance up. [img]/infopop/emoticons/icon_biggrin.gif[/img]
Or fill er up with a little silicon. [img]/infopop/emoticons/icon_biggrin.gif[/img]

[This message has been edited by KS circutguy (edited 11-15-2000).]

[This message has been edited by KS circutguy (edited 11-15-2000).]

[Will]

BracketRacer, I hope you're right. The mains are oversized by .001" according to most of the references I have, maybe only by .0005" if we use the 3.4385 +/- .0005". The thing is, when we measured the mains the block was cold, it had been sitting in the back of my blazer for two days and it's getting down below freezing here at night.

I'll be taking it back on Friday and talking to the shop about it. My machinist just got another Chevy Big Block from them and it was dead-on right in the middle of the tolerance, which is the way he says every other block he's gotten has been. Just my luck to get the one block they screw up on.

1/2" - your idea about the paint isn't too far from my last-resort approach. One of the things my machinist showed me is pure copper sheets in .001" thicknesses. He said we could shim the bearings with this stuff if it came down to it as a last resort. I wouldn't think pure copper would hurt heat transfer characteristics in any way, it's a better conductor of heat than cast iron.

[Half-Inch Stud]

Yup. B-Racer, that's a fine solution.
Yup. Hot Rod, I'm not proud.
Yup. KC; I used Plastigague once, happened to be on main clearances. and your solution was?

I have a roll of 3M Aluminum tape that is .002thick...for other uses. Roll of .001thick Kapton in 1/4"wide and 1/2"wide for other uses too. But, you got the point.

If the machine shop balks at the cap mountsurface fine trim, then I'd let the mains ride as-is and see what the crank is measured at. Even with +.001, Bearing crush will occur.

[GTO Karl]

Hi Will:

You probably should at least take it back to the shop and see if they will take care of it, however, I don't think you have a problem to worry about.

What is the crush of your bearings? Is it the same as the ones that were on the shelf next the ones you bought? Is it more or less than the last production run out of that company? Is it more or less than the production bearings from the 70's or 60's? Is it more or less than the various production runs from that time? Is it better or worse than another brand of bearing?

In other words, you have no way of knowing one way or the other, and, although I think it is, in a perfect world, nice to have your tolerance on the tight side, if you keep good clean oil on your bearings, and a good tuneup on the motor, your bearings will have no particular reason to spin. In fact, I've never heard of a bearing that spun before catastrophic damage wasn't already done to get the bearings damaged enough to spin.(at least in low rpm(under 7000) street strip type applications.

In fact, the crankshaft is under constant distortion and twisting back and forth, unwinding and winding up, bending and unbending, four times per revolution. And I've often wondered just whether a straight main line makes any difference at all. I have yet to take a crank out of a used motor, including all my own motors upon freshening, and not found them to be bent by at least .001". I've seen good running motors with no bearing problems with cranks that were bent .0025"! I don't do line honing or line boring unless the main line is out more than .001" or changing caps or such. However, round bearing bores are important! Trusting machinists, is, I think, much more dangerous, in many cases, than just running the parts as they are. I do remember that you had to line bore in this case though.

Another two cents out of my pocket!

I don't think you have anything to worry about.

Karl

[Steve C.]

With extra honing will the crank centerline be moved close enough to the cam to require the use of a "plus" size timing set? Or is their use always the norm?

[PONTIAC DUDE]

Why would you measure the main bores at that temp. No wonder it's not coming out!!!!!!!! Room temp!!!!!!!! Your builder should know better. How did you torque the mains, sequence and steps? Did you ask the shop anything or just do it your way? You can have anywhere from .002 to zero with temp change. Did you put the crank in? check for drag, bearing scuffing? I don't bore, hone, or mic until temps are reached. Besides the crank can still go south as problems lie elsewhere. Pontiac lubrication can be a problem in the block for higher HP applications. Later.

[Will]

P-dude, I appreciate your concern. I have no way of controlling what the machinist who did the line boring did. I do not know how he torqued the main caps or at what temperatures the boring/honing operations were performed at.

What I do know is that I picked up the block from him after the work was finished and drove home. The block sat in the back of my Blazer for two days and then I took it to the shop where the rest of the work is being done. We unloaded it from the Blazer and measured the bores. We didn't touch the nuts on the main studs, just wiped off the oil and measured. If anything, wouldn't the block being cold have caused it to come in undersized? Metal contracts when it's cold. The fact that it's oversized even when it's cold is really scary to me. The fact that this is the only block my machinist has ever had come back from this shop out of tolerance is scary. I realize I may not have anything to worry about (thanks Karl) but why take chances? I didn't pay for out of tolerance work. The factory specified a very specific diameter of the main journals for a reason. It's the only clearance in the whole engine that I know of that is so exacting. Considering how hard it is to find 428 cranks and 455 blocks around here, I do NOT want to risk anything. I want to do this engine once, and have it run for at least 50,000 miles of street and regular strip use before I have to think about opening it up again. Having lost one expensive engine already, if it happens again I'm sunk and have nothing to look forward to but driving my 6-cylinder Nova for the foreseeable future... (though I might be able to get a Pontiac 350 into it if I get desperate enough).

Thanks!
-Will

[PONTIAC DUDE]

Simple enough. Load it up. Take it back. Be nice and explain your concern after checking it at you assembly shop, with out loosening the caps. Have him check it with you there. And he should show you with his tools. Also take your gauges along and compare notes, as he will explain any differences and should work with you. But remember. "Everybody likes some a$$, but nobody likes a smarta$$." LOL.
I know my attitude is "ALWAYS" a reflection of the customers attitude and will explain, talk tech, joke and talk to anyone. Good luck, dude.

[Will]

Dude,

Did exactly as you suggested today and the guy offered to redo it for me before I even asked. I just told him that it appeared it was out of tolerance and I was real concerned about it. He said "would you like me to redo it? I can set it up on the tight side of the tolerance if you want." Well, sure! He'll definitely get my business again. Cool shop, wish I had one like it. Dyno room, flowbench room, and the machines to do every conceivable operation short of crank grinding.

Now the only concern will be if the crank centerline has moved significantly. Measured a couple of virgin blocks over the weekend so have something to compare this one to.

-Will

[Half-Inch Stud]

..you'll never see it in the timing chains.

[Will]

Hope you're right Half-Inch. I really wanna reuse the timing chain from my last engine as it's a good quality unit with only 1500 miles on it.

Also, the shop that's doing the boring/honing jigs the block so that all the bore centerlines are done perpendicular to the crank centerline. If the crank centerline has moved far enough, it could cause problems near the bottom of the bores. Guess it would have to move quite a bit for that to be an issue on a .035" overbore.