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post #1 of (permalink) Old 11-30-2005, 10:48 PM Thread Starter
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rebuilding an engine

i have a spare engine for my jeep and i want to rebuild it and put MPI on it. I have all the stuff for the MPI i found the kit i want for the bottom end but how do i find out without pulling the bottom end apart yet to find out if i have over sized or under sized bearing rings pistons
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post #2 of (permalink) Old 11-30-2005, 11:09 PM
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Re: rebuilding an engine

if i remember correctly, they mark the crankshaft if it has been ground undersized

this is going back 15 years but i think it was just written on in grease pencil or something

mine was marked 10/10...indicating the main journals were ground .010 undersize/rod journals ground .010 under as well

i then pulled out standard main bearings and .025 oversize rod bearings......anyone want to guess how many miles on that motor when they spun?...explains why ill NEVER send anyone to motorworks for a rebuild

if id have owned it when the original died i would have done it myself....alas....
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post #3 of (permalink) Old 11-30-2005, 11:25 PM
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Re: rebuilding an engine

The only way to know for sure is to tear it down. Not everybody marks them. Generally the bearings themselves are factory marked though, and so are the pistons. "s" is for standard, and a number that looks like a size over or under generally is. You could pull the rod bearing caps and look for markings on the bearings (it's UNDER the bearing), and look at the skirts and tops of the pistons for markings without pulling anything else out. If the rod journals are all the same size, chances are the mains are turned the same amount.

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post #4 of (permalink) Old 12-01-2005, 01:26 AM
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Re: rebuilding an engine

You don't need to know....

Tear it apart...you then take the block, pistons and rods, crank, and heads to a good machine shop.
The machine shop will then measure the crank and cylinders for you. You then order the correct parts and take only the new pistons to the machinest. He does the rest....assuming he is a good one. The guy I used would actually bore each cyl to the correct size to match the piston. When I got it back from him, each piston and rod was marked as to which hole it went into.

If the crank has to be turned, then will turn it so it uses a standard size over stock, i.e., 20 over, 40 over, etc.

But, being the 'attention to detail' kind of guy you are (had better be), your going to use plasti-gauge to confirm the tolerances when you put it back together....right?
post #5 of (permalink) Old 12-01-2005, 05:34 PM Thread Starter
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Re: rebuilding an engine

im doing it all my self i dont want to bring it to a machine shop all be poping the crank out tommorow just didnt know if it was in part of the engine code some where to make it easyer for me insted of tearing the rest of it apart i have the head off and **** thanks
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post #6 of (permalink) Old 12-02-2005, 11:13 AM Thread Starter
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Re: rebuilding an engine

i took a look at my pisotons today and they all say 030 on them
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post #7 of (permalink) Old 12-02-2005, 12:50 PM
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Re: rebuilding an engine

Without knowing the extent of your mechanical abilities....and the fact that you had to ask the above questions in the first place....I would seriously reconsider trying to do it yourself....unless your not expecting the rebuild to last a long time.

There is a lot more that goes into a rebuild than just cleaning it up, putting in new bearings and piston rings. You need an accurate micromoter just to measure the pistons and cyl wall to make sure you are in tollerance. It does not make sense to put in new pistons if you already have more than .006-7 clearance....and don't forget, not all pistons marked 30 over are 30 over. Even on a new set, there will be .002-5" difference in diameter. The machine shop I used would actually measure each piston and then do the final hone to match that piston.

You also need to mic every journal to make sure it is in spec. It's kinda hard to buy a mixed box of new bearings. Your journals do not all wear the same. There is a good chance the crank will need to be turned....that is not something the emmery cloth on your workbench can do.

Your pistons say 030...that means the engine has been rebuilt once already....this adds even more uncertainty to the project.

Let me stress the phrase "We learn by our mistakes"......You can choose to learn from mine.....or learn by your own.
post #8 of (permalink) Old 12-02-2005, 01:17 PM
 
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Re: rebuilding an engine

i don't really post here but i read all the stuff here because i own a machine shop in idaho and we are all state of the art and a good machine shop is the whole key the crank needs to be ground, block cleaned and bored soft plugs rods recon head checked maged and maybe surfaced and valve ground, can you do installed heights on your head do you know the margin on your valves. I am not being mean but everything need to match and be to specs. If you have any question just ask. Jake
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post #9 of (permalink) Old 12-02-2005, 02:53 PM
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Re: rebuilding an engine

Well let's keep our heads about us here...

My very first car project was a 67 impala fastback, 327, 4 barrel. Ran when I got it, but it had a bad cam - flattened lobes. I wanted to learn how a motor worked, so.....

I got a ridge reamer, took it all apart, checked to make sure things weren't beat to crap, bought new parts, and put it back together. Sent the heads out to a machine shop for a valve job. I put new rings on the pistons (just ran them onto the pistons with my hands), ran one of those hones down the bores on the end of a hand drill, dipped the new bearings in motor oil, bought a cam and some cam lube, new lifters, and bolted it all together. Bought a typical "rebuild kit" from the local speed shop. Gaskets, oil pump, bearings, timing chain and gears, etc.

Thing ran great for years. Was a great car, too.

Things don't always have to be perfect. So, measure your parts - bores, crank - make sure you buy the right parts. If you can get an inside mic, measure the bores to see if they're egg shaped. If they're not bad (find a spec for the motor you're using) don't sweat it.

Obviously, if the crank is all scored, or you find a spun bearing, or obviously damaged parts, shouldn't be reused. If it all looks ok though when you take it apart, just worn, just put in fresh parts and go to town.

Now,
Is this the best? No.
Does it work? Sure.
How long will it last? Not as long as a perfectly built motor.
But it's only a jeep, and the 6 cyl jeep motor is no rev monster. It doesn't all need to be balanced and blueprinted.

I used to shift that 327 at 5000 rpm, ran great. Now, I was fortunate, I got to hear the motor run before taking it apart, so I knew it had no serious knocks, or that kind of thing. Still, it had like 130,000 on it when I "rebuilt" it.

Just my $0.02.
Pete
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post #10 of (permalink) Old 12-02-2005, 03:35 PM Thread Starter
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Re: rebuilding an engine

i have rebuilt engines befor this would be my 3rd one the other ones are still runing i know some manufactures put in the engine vin or the vehicles vin the bearing sizes piston sizes that is why i was asking if they did that with the 4.2
the block has 100k on it i pulled it out of my jeep so i dont know if it has been rebuilt but i dont think it has it does not have any rebuild tags or any thing on it
i am buying a full rebuild kit that comes with a crank pistons rings bearing that is why i was asking so i did not hafto tear into another project im sending the head out to have new valves put in and have the deck resurfaced its off of a 98tj
I heard the engine run befor i pulled it out i drove with the engine for 2 years it started to get really bad lifter knock so i pulled it got a good deal on a nother runing 4.2 so i swaped them the engine ran great didnt burn a drop of oil just bad lifters
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