buy 1 under bearings from king bearing
or take crank to machine shop
or take engine to machinest
all of wich cost money

I know this topic has been beaten to death around here, and now i am the next victim, and quite frankly frustrated to no end! whats the next step...today i spent most of the day with yes plastigauge and trying the 2 sets of bearings i had in my possesion...i am happy with the rear main at .0028, but 1-4 are a consistent .002  so i never even gave the rods a chance! what's my next step...the new motor i believe will be turning around 5500, and i think that is just way to tight! i would really like to see .003, and the rods a little loser, but i am at a loss for words, and summer isnt waiting on me!

oh yeah the money tree has shriveled up and died

Nordie 

Plastigauge is worthless...I once saw ,001" clearance on plastigauge with .010 bearings on a standard crank...


If you'd like, pay shipping, and I'll gladly loan you a bore guage and some mics so you can accurately measure things up.

I'd say if you're over .002 and only plan on spinning this thing to 5500, run it and use a good Group 4 base stock 5W-30 oil.

I'd still like to see you accurately measure the clearances though.

im going to jump on the hater train and also suggest throwing away that plastigauge. i would use it to check stuff in a bind, but to determine what bearing size you need, no way in hell. you will just make this project longer and longer because you will get a reading, buy bearings, then get a whole different reading with those bearings....then repeat.

borrow pats stuff and do it right the first time.....oh wait, the first time was 20 times ago 

agreed, just want it to be right! dont need something questionable...

Why so loose Nordie?

Just a question.  I have always used .00025" for every inch of journal, that number will vary given certain info. such as; engine RPM, crank material, block material, preferred oil temp and viscosity, actual estimated torque and stroke (which almost always falls under RPM) among others but you get the idea...

I would love to hear some other input also...(BTW, don't forget the cam bearing clearances, not as important, but comes in to play)......

GT

So...by that, a motor with a 2.1" crank pin (like a SBC) would run about a half thou clearance?  That seems tight.  I suppose it might work on rods if you could find an oil that was up to the task (which I don't think you can) but you'd have to do some work to get most mains lined up perfectly enough for 0.00075 to fly.  I'm thinking more like 0.001 per inch of journal diameter...but even then, diameter has very little bearing on surface velocity...you'd have to calc circumfrence, which grows quite a bit for a small change in diameter.

Have you assembled engines using this formula?  On a BBC, that would give you less than .00055 on the rods and about .0006 on the mains?  How long did it run?  What oil did you use?

Ya I know, Dave already called me on that..My bad...What I meant to say is .00025" in addition to the OEM clearances...For instance, 2" journal at .002" would be .0025", hope that makes sense...

I was getting my new laptop dialed in when I posted and may have been a bit scattered.

Sorry if i confused.....

GT

OK, that makes sense.  

The problem I have with bearings is this:...you can only get them so close without a crazy investment.  What if the target is 0.003 - .0035".  Say I've got 0.0027 w/ a standard ACL race bearing.  I can go to 0.001 under bearings and arrive at 0.0037, which is out of my target.  What do we do in these situations?...start buying bearings from different manufacturers until we find some that are a little off and get us where we want to be?  At $85 or so for a set of race bearings (for use with a steel radiused crank)..that can add up pretty quick.  Or, should I stick with my 0.0027  or settle for 0.0037?

There's no crank grinder out there I don't think that can come in and knock the crank down 0.0003 - 0.0005" with any kind of accuracy.  Sometimes with a coated bearing you can hit it with scotchbrite, removing the coating which will get you another 0.0002 or so I guess.  I've heard some people mix the a 0.001 under shell with a std shell to arrive at .0005", but it seems like that would have kind of a screwed up parting line...there would be a 0.00025 step, which I'm not sure will have an affect on anything.  So, out of all the different ways to skin the cat...what's the prefered method of hitting the mark?

OK, Now my head hurts......But all great info! Granted, I used the plasiguage when I set up Moo's engine last year. But that's really all we had out in the sticks 25 years ago, and it's been that long since I've built an engine! We all know where THAT got me!

This is VERY educational! Kinda why I'm posting every nuance of what went wrong on mine. All my fault, somewhere, to be sure!

I disagree that a crank grinder cannot knock down those numbers accurately and consistently even on less than modern equipment. I beleive the problem is with the operator of the lathe, setup, tools and dedication to perfection. Also depends on the accuracy of the line hone and squareness of the bore/hone to that same line.

My brother owns his own machine shop and routinely gets accuracy to under 2 millionths of an inch, consistently, when he needs to (He does a lot of intricate EDM Electrodes and injection mold cavities for another shop, next to impossible to get him to work on my $hit).  I think we substitute the word Cannot with Will Not in this case, or the cost would be a huge factor. Just my .02.

Pat makes a lot of excellent points though. I'm not one to go out and buy 4 or more sets of top shelf bearings to make this work, when the rest will probably never be used again.....Or.....I WILL pay a good machine shop what it's worth to do it right to begin with......I dunno. Some of the numbers I see so far seem to be splitting hairs, to a certain extent, but I also see Nordie's frustration. I'll be balls deep into this 460 of mine with the same frustrations very soon, I think, but I'm gonna do what Pat, Dave and Glenn said this time, measure, measure, measure, then torque. Repeat, repeat, repeat. Not gonna be afraid to take a part back to the shop that is wrong.

Ray

It is all do-able ..but at a price ..tolerances can be set to customer's spec's ..no problem, the problem is always the pocket book.

i saw you do just this

now keep this in mind, nordies deal is just a lake motor not a race deal sooooo. yes he wants it rite,but when he measures then brad measures and some one else measures they more than likely will all get a different measurement because they dont do this on a daily basis.

set up of the mic's will be critical

wow i love this thread thanks to everyone for your input! i definately see this as a critical part to the build, and cant see me continuing on until i like where it is at! i just got home from work so this was an awesome read! hope it keeps going, but i love that most of you are all on the same page

Plastigauge is for the shade tree mechanic tearing down his neighbors truck for a back yard overhaul, basically for checking if he needs to put the crank in the back of his wife's' Civic and head to the machine shop...It does sort of work, but the human error element is huge (the rotating assy. simply cannot move, or the measurement is worthless, should be around 75* too...it melts).

Dave,

I would have to say I like the thinking....But need to add, align hone first and base everything from OEM numbers, it removes a little of the math for me...In other words, you say middle, I like middle to be OEM spec and the over/under the clearance....Do you try to equal it up? or does it really matter that much? In other words (again) if over .0005 on the block, the under .0005" on the crank?

I am a simple minded guy.....

I had an Eagle crank that I swear was made by a dyslexic third grader using a wooden ruler to measure with and was machined with a snow shovel with a broken handle....I thought I was losing my mind....

GT

Guys... I am working off "OEM " numbers.

WAIT!! If you are looking for a measurement smaller than .0005 and you are using plastigage, just do it over and over until it gives you the number that you want. It will vary atleast .0005.

Problem solved! Next.