labrat Posted May 2, 2001 Share Posted May 2, 2001 What is the most accurate way to measure main bearing clearance? i've heard some people say that plastigage is not very accurate. Also, while i have the oilpan off and it's on a stand, is there anything i need to look for as far as indicators of wear? I know it was rebuilt (the rods are stamped w/cylinder number), but not how long ago. Thanks for all the input! Bill Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted May 3, 2001 Share Posted May 3, 2001 Well, do you want a $5 answer or a $100 answer. Mic'g an engine (the crank specifically) is more involved than just putting a mic on the journals. You will also want to know if it is bent & if so-how many thousanth's out of tolerance or w/in tolerance is it. To state the obvious-as you're tearing your engine down you should be looking for scars, gouges, discolored bearings or metal parts. As far as how to mic the journals; you'll need the appropriate outside mic's, inside mic's & slide calipers (I prefer dial slide calipers). You put the 2-3" mic on the journal being measured until its snug...not too lose but not so tight that you scar the journal. Slide it off "GENTLY" & measure w/your calipers. Write down which journal you just measured & its measurement. You'ld then want the measurement for the bearing it was riding in; obtaining that measurement is the same process for the main as it would be for a rod journal; it takes the inside mic's. You torque down the main caps w/the bearings installed (w/out the crank in it) & put your inside mic inside that particular main; set the inside mic (lock it) & after removing it you take your reading. For a rod journal-you'll need a vice for torquing the rod cap down...measurement for it is obtained the same way as the mains were. The difference between the actual journal & the measurement of the main cap or rod's (w/the bearing in it) will be your tolerance. Once you've obtained that tolerance-you can check your measurement w/a performance book which will have "Blueprinting" measurements for the street build & measurements for the race build. If you're not up on how to read calipers/mic's, keep in mind-the machine shop you choose will mic your engine for you. I always like to know what my engine is before dropping it off at the machine shop-that way I know if the machinest is yanking my chain or being up front/honest w/me! Remember-not everyone is looking out for your best interest! Hope this helped/maybe someone else might have something to add! Kevin, (Yea,Still an Inliner) [ May 02, 2001: Message edited by: Kevin Shasteen ] Quote Link to comment Share on other sites More sharing options...
labrat Posted May 3, 2001 Author Share Posted May 3, 2001 Thanks for the info, kevin, but i think i will take the cheap way and plastigage it. I got the crank out today, and didn't notice any discolorations and the pistons cleaned up really well. There are a couple of scratches on the crank journals, but barely big enough to feel with a fingernail. Will this case a problem? Should i have the crank machined? I started out just freshening up a running engine, but now it's gone way beyond that... Bill Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted May 3, 2001 Share Posted May 3, 2001 If you can see a scratch but cant feel it-that usually translates into about .001"; I wouldnt have a crank turned just for that. If you're gonna plasitgage it-do so; once you've obtained your spec's from that you can check it against your tolerances. If your tolerances check out-I'ld grab some of the proper grit paper...you can buy it by the foot from your local machine shop & fine/polish the crank journals by hand till they look nice & pretty/shining nice like. When you put it all back together-just make sure you use assembly lube & that the crank turns smoothly w/each piston & rod assembly you install. Turn it slowly at first confirming there isnt any binding. Make sure you put the pistons/rods in facing the correct way! Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
labrat Posted May 4, 2001 Author Share Posted May 4, 2001 Thanks kevin, I intend to do that. I just wanted to make sure the crank was okay to use again. Didn't think it would be a problem. Is there any way to put the pistons in the bores without scratching the cyl wall with the rods? Or is this a problem? I havne't gotten that far yet, the parts store ordered the wrong mains for me. The retaining boss is on the aft side of the bearing instead of the fore. They cross referenced to my donor car, but does anyone know what model/make car these bearing came out of? small journal with the boss on the front side of the bearing. Thanks! Bill Bill Quote Link to comment Share on other sites More sharing options...
Guest Locutus Posted May 4, 2001 Share Posted May 4, 2001 I don't know about any of you other guys but there is this channel on Direct TV called DIY, and they had a kit car build up, a 427 Shelby Cobra. They talked about building a performance engine, and what is involved in blue printing and balancing an engine. The good thing is that for those that missed the series they can go to www.diynet.com and they have all the information they presented in the shows. It might be a good place for alot of begining engine builders to learn the basics. Mike Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted May 4, 2001 Share Posted May 4, 2001 Yea Mike, I would definately tell anyone to read all you can about an engine...the more you read the more you learn. Bill, I'm not sure anyone can help you about which bearings you have-that's kind of something one would have to have in front of them; what you can do is get the engine block numbers off of your engine-perhaps if you had those numbers someone here could cross reference them w/info they had at home; still the size bearings you need is totally dependant upon your tolerances. I would not put your pistons/rods in your engine w/out bearings; I'ld store them; soak them w/oil-wrap them in news paper & ziplock them in a gallon ziplock back out of the sunlight; make sure they're in a cool/shaded area as any sunlight will cause condensation which could cause things to rust. Or if you have a tub of some kind-fill it up w/oil & drop those puppies in it. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 4, 2001 Share Posted May 4, 2001 I saw the DIY cobra buildup, that was pretty cool. The definately showed the steps needed to do it RIGHT. They're attention to detail was pretty intense and it was interesting to see the things you normally don't in the machining of the block, and the balancing of the rods (for example they're weighed on each end on a scale, and not just setting the rod on the scale as I supposed it was done.) Many things they did assuredly produced a engine far superior to the cobra originals, like the epoxy (?) paint they used to seal the block and such, and the better heads than original. The motor was supposed to put out about 450-500 hp, which doesn't sound like alot considering the small blocks, but where that old FE shines is in torque, I'm not sure of the numbers, but it wouldn't surpise me if it was close to 600 ft/lbs, but this wasn't no boat motor, this dude would rev too. Anyway, like Mike said, have a look on they're site and use the net, put in the phrases you want to know about, its out there and free to access. To do it right takes much time, thats why performance engines can be so expensive, your paying for the knowledge of the builder. Any monkey can throw a engine together, but to put out all it can and live, well thats what separates the primates from the pro's. Lone Ps: And no I'm not calling anyone a monkey, just a analogy.. Quote Link to comment Share on other sites More sharing options...
labrat Posted May 4, 2001 Author Share Posted May 4, 2001 Turns out the bearings were for a 350, not a 327 after all. They were for a large journal crank, not my 327. So they are on order again. Sorry i'm flooding the board with all these posts, but pearls of wisdom dropped around here are much more valuable than my chevy smallblock rebuild book. I just don't have the experience, Thanks for the help, guys! Bill Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted May 4, 2001 Share Posted May 4, 2001 About performance books; dont limit yourself to just one. I've discovered that the write up of most books are about the same; yet each book will have its own {tasty morsal} of wisdom or {graph} which will turn a few light bulbs on. Even if you dont buy the book-take a pen/notebook w/you to the bookstore & scour thru their books; when you come to something that catches your eyes-write down their thoughts in your own words on your notebook...now you have it for your own records for as long as you wish. A book on the SBC I came across that claims to be a "STEP-BY-STEP" guide as well as {Picture Guide} is: "How to Build the SBC" by Larry Atherton & Larry Schreib; published by SA Design w/a 1993 Copywrite. I already had multiple SBC perf.books when I found this one-what caught my eyes was the fact that they claim it is a "Step-By-Step" build & includes step-bystep "Photos". So I thought why not; add it to my collection. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
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