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Old 01-22-2004, 01:54 PM
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how important is measuring..

i am rebuiling a sbc 350 that i got out of a junk yard. it is a gm crate engine. it was in decent shape. this is my first rebuild ever.
after tear down, i found it was in good shape, except for one main bearing and some slight wear on one journal. i had that ground .10 under.
i am keeping the crank and 4 bolt caps. i am replacing cam, all bearings and gaskets, lifters, push rods, etc. the pistons, stock, are in good shape as well, except for carbon buildup on the top. i am keeping them. the bores barely had a ridge. my machinist said it looked good. i am also keeping the rods.

i am going to replace the heads w/ 2.02-1.67 and i got a street dominator aluminum manifold and a 650 holley carb.
i am going for 300-325 hp. i think i'll get it w/ what i'm doing. i dont want real high compression, the crank is going to give me fair lope at idle, etc.
my question is two fold.
one, does it seem i am on the right path for my goal and two, how important is it to measure everything before i put it back in w/ micrometers, etc?
anything i have to really be aware of?

thx

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Old 01-22-2004, 02:25 PM
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It is just good insurance to do it. I Don't and have gotten away with it all my life. I depend on my machine shop to do it right. I do gap my rings, feeler gauge my pistons in the bores, check deck and heads with straight-edge for flatness, and check all journals with Plasti-Gage but don't mike anything else.
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Old 01-22-2004, 02:28 PM
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Wow, willys I did not have you pegged for a gambler. I have always at least plastigauged the bearings. It is also a good idea to check side clearance on the rods and check the cylinders for roundness. I have never found anything so far out it needed work, but machinist make mistakes too. It is just insurance.

Chris
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Old 01-22-2004, 02:28 PM
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Since you are keeping the same crank, rods, pistons, there is not much for you to measure. You did have the crank turned so I would plasti-gauge the main and rod bearings (if you do not have mics). This will let you know if you are within an acceptable range.

You mentioned wanting "real high compression" How do you plan on getting there? What heads are you going to use? Keeping the same pistons and heads, your compression is not going to change.

When building an engine there are a LOT of things to be aware of and to check. Rod side clearance, crank end play, deck height, main and rod bearing clearance, degree the cam, etc... You are assuming everything was assembled right in the first place and if it wasn't you can/will have problems. If this is a high performance build you will want to check everything (and assume nothing). Sounds lioke this is your first build, if so go buy a good book like "How to Rebuild A Small Block Chevy" there are a few different books out there. You will need them for several reasons (torque specs is one reason), they will also have the required clearances of all components.

Royce
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Old 01-22-2004, 02:43 PM
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i said i DONT want real high compression. maybe 9-9.5 at the most. i am REPLACING the crank, the heads, the manifold and carb. i am keeping the pistons and rods because the bores were in such good shape, why spend the $$ for all the rebore and pistons...i want this baby to work well, first, then perform second.

on my next one, i'll go a little more wild.

i have the book "how to rebuild your sbc" which is great. i also have chiltons guide to sbc. i also have a video from a guy on the web. good guy-wayne partridge-knows his stuff.

i dont know much...but i know a hell of alot more thsn i did 6 months ago! i just want to make sure i'm keeping my chances for a screw up as small as possible.

if the crank has been turned .10 under and the bearings are new to match, do i still plastigage them?

any other tips as i plow ahead? order of assembly, little tricks, etc?

thx
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Old 01-22-2004, 03:02 PM
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It's kinda late now for your crank but, if I know the crank needs to be turned, I never get the work done before I get the new bearings. I will order the undersize bearings, put them in the block (no crank) and torque the mains to spec. I measure the bearing diameter in the main bore and THEN grind the crank to hit the correct clearances. I've worked with too many Pontiac motors where the crank clearance is critical and I just follow through when I build any other kind of motor. It's probably not necessary but I'm more comfortable knowing what I've got when I screw the motor together.
Mark
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Old 01-22-2004, 03:09 PM
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lucky for me, the guy who turned the crank has been doing it for 35 yrs and he already had the bearings to match 'em up!

he's a wonderful machinist and knows engines.

it was easy, more or less, to tear down. now the real fun begins and i want to double check everything i'm thinking, reading and hearing. i trust the info on here as well, so all or any advice is greatly appreciated.

by the way, is there any time limit once i start? i plan on taking my time
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Old 01-22-2004, 05:37 PM
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Quote:
any other tips as i plow ahead? order of assembly, little tricks, etc?
I would say that assembling the bottom end is trickiest.
Clean. Everything should be CLEAN.
I like to have a squirt can of clean oil and lots of lint free towels to keep my hands clean.
Regular rags will have lint if you start wiping out inside of block all sorts of it gets stuck to cast iron then comes off later and plugs oil pump screen.

Wipe off the bearings before you install them, wipe out the bearing bores before you install the bearings. Squirt some oil in cylinders wipe it around, squirt some oil into ring grooves and orient them so they're not lined up.

Get some 3/8 vacuum hose to make protectors to put on rod bolts, gas engine cranks are like butter one little bump and you have a little nick that could wipe out the bearing.

Get a good torque wrench. Be sure to put oil on bolt threads, also on rocker studs before you install the nuts. Seen where a guy forgot ended up having to replace them all because they galled up threads. Use sealer on head bolts though.

Lets hear somebody else tricks.
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Old 01-22-2004, 06:39 PM
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Your thread title "How important to measure" can be answered with. "It's very important to measure.". Most of the answers were basically somebody should do it. We have the correct mics in the shop and my Bud, the master tool and die maker is and expert. We measure every thing after tear down, then take what needs work to the machine shop and tell them what we want done. We trust our shop to order the needed engine kit to complete the job and we do some spot checking when we assemble the motor. All machine work we have spot checked over the last 11 years has been extremely well done. Our only problem we had with a machine shop was not vatting the blocks properly after the work. We no longer use them. One note, on any cylinder that has a noticeable ring grove has required boring and new pistons.

Trees
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Old 01-23-2004, 07:16 AM
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Measurment

From your post it sounds like you may be doing this more then once. If you are thinking about rebuilding more motors i would spend the time and money to do it right the first time. I would at least get the micrometers to do the bearing sizes. It is a pain in the butt to use plasti-gage to check out-of round and taper on a crank. I have been a machinist for almost 20 years and i still make mistakes. If you double check what the machine shop has done it will reduce a chance for failure. About a year ago a customer gave me a crank that a shop gound(this shop has been in business for like 15 years) Anyway this crank had .001" taper on every rod and main journal. The chances of finding that with plasti-gage is kinda slim.

look at msc ( www.mscdirect.com) they have some good priced measuring tools that will work in your application.

keith
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Old 01-23-2004, 07:40 AM
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Good point Trees. I let my machinist do the heavy lifting for me on my measuring my engines. Then all I need to do is a quick Plastigage on the bearings, feeler gage on the pistons & fit the rings & I/m done!
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Old 01-23-2004, 08:08 AM
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what am i looking for with plastigage and when feeler guaging the pistons?

what is my purpose for doing this?
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Old 01-23-2004, 08:27 AM
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Plastigage is a wax thread that is precisely sized. You break off a 1/2" long piece and place it on a dry crank main or rod journal and bolt on the cap, with bearings, torque to spec, then take the cap off. The wax thread will be squashed out to a thin layer on the journal. Finally you take the paper envelope that the Plastigage comes in and hold it next to the wax streak. There is a calibrated scale on the edge of the envelope that corresponds to the bearing clearance. When the width of a dash on the envelope matches the width of the wax smear, yo read the clearance number printed on the envelope and compare that to the spec in your rebuild manual. Very accurate. You can get Plastigage at any parts store.

Your rebuild manual will list a spec for the piston/cylinder clearance. Shove a piston half way down the cylinder and insert larger feeler gage leaves in until there is resistance. Compare the thickness of the feeler gage to the spec in the book. If too tight, you must hone the bore until it meets minimum clearance spec. If too loose you need larger pistons. I have never had a problem here but if I did, I would take the whole mess back to my machinist and tell him to make it good at no charge to me. He would have screwed up.

Finally, fitting rings is the one thing the home mechanic must do himself. Place a ring in the cylinder bore and shove it down an inch or so with the top of an upside down piston so it is square with the bore. Measure the gap of the ring with a feeler gage and compare that reading with the spec in the manual. If it is too tight, you must file the end of the ring until it is large enough. If it is too big, take the rings back to your auto parts store and get a set for larger bore.
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Old 01-23-2004, 08:54 AM
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willy's, that was immensely helpful!

i marked each cap and rod with a punch to correspond to the cylinder it goes in.
if i screw up and put the wrong one in the wrong cylinder, what is the result?

this is great!
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Old 01-23-2004, 09:21 AM
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Measure

All things being said, always measure. However, kids have been building these things for years. Problem is they grow up to be old men. We have honed the cylinders to remove the top ridge for years and STOCK rebuilt the engine. Sounds like that is about what you are doing. Crank excepted. Build a racer and you dam well better mic everything. Once you build one, you can not wait until the second one. As much as measuring is important, remember that a VERY clean area is equally important in a good build. Time is not a real factor. However once you clean things, you don't want to wait to long for dust and things to get into your project. Let us know when the hook is set and how your project turns out. No Fear.

hr41pearl
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