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Old 09-16-2007, 11:05 PM   #1
shade tree305
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1985 chevy truck 305 crankshaft specifications help please

Im CURRENTLY REBUILDING AN 1985 305 CHEVY TRUCK ENGINEAND ALL WAS GOING WELL WHEN I ORDERED AN ENGINE KIT I ASKED FOR STANDARD PARTS.WHEN I PUT THE ROD BEARINGS IN AND TOURQUED THEM I HAD WHAT SEEMED LIKE TOO MUCH SLOP,GOING JUST BY FEEL.I MEASURED THE CRANK JOURNAL DIAMETER TO BE 2.0750 INCHES.IS THIS STANDARD ?I FOUND IN AN OLD MANUAL ON REBUILDS THAT IT SHOUD BE 2.0988 GIVE OR TAKE ASMALL AMOUNT.CAN ANYONE TELL ME THE CORRECT ROD BEARING SIZE FOR THIS.I MEASURED THE NEW BEARINGS TO BE .0625 THICK AS WERE THE OLD ONES I TOOK OUT.THIS HAS ME PUZZLED AS THE MOTOR WAS IN USE BEFORE I BOUGHT IT....ANY HELP WOULD BE APPRECIATED MY MY SELF MY DAD AND MY SON.....THANKS
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Old 09-17-2007, 12:34 AM   #2
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Re: 1985 chevy truck 305 crankshaft specifications help please

Sounds like its not the first time the engine has been rebuilt.

Also, there is a key on the left hand side of your keyboard, with "caps lock" printed on it.
Please use it, typing in Caps is considered yelling and there some older coots around here who don't like to be yelled at.
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Old 09-17-2007, 02:18 AM   #3
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Re: 1985 chevy truck 305 crankshaft specifications help please

You have to find out what the crank journals sizes are before you can just put new bearings in. The only time (realisitically) standard bearings can be used is on a brand new crank. After its been used and the journals have worn they have to be reground which is why there is the need for 10-under and 20-under bearings.
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Old 09-17-2007, 08:01 PM   #4
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Re: 1985 chevy truck 305 crankshaft specifications help please

Take a look at the back of the old bearing shells that you took out (assuming you did not throw them away) They should tell you the size in terms of thousands of an inch undersize.
ie: if they say .020 it means the crank was ground 2/100 ths of an inch smaller than stock to remove previous signs of wear, taper, etc.

Unless you are sure of the crank journal's condition, it may be reasonable to send it to a machine shop to be reground, to remove wear etc. They can fit it for new bearings so you are sure the correct parts are in place.
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Old 09-17-2007, 08:07 PM   #5
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Re: 1985 chevy truck 305 crankshaft specifications help please

sorry about the caps.and it isnt the first time the engine has been rebuilt.ive went with .020 over on rod bearings and .010 over on mains,which on closer inspection turned out to be what was in the engine when i broke it down.i found a website that made the claim that some cranks are undersized from the factory and are marked with paint or numbers.anyone now if this is true?just curious.i would really love to know some websites where i can find chevy small block specifications and tech data if anyone knows of any.also thanks for the help,this is a project 72 chevy pickup my 13 year old son and 71 year old dad and my self are working on and enjoying,so any help appreciated in the way of information and idea's thanks again.
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Old 09-17-2007, 08:48 PM   #6
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Re: 1985 chevy truck 305 crankshaft specifications help please

Many new aftermarket cranks are out of spec and should be taken 10-under before being installed. Not sure about factory cranks.
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Old 09-18-2007, 11:22 AM   #7
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Re: 1985 chevy truck 305 crankshaft specifications help please

I've seen a few "factory" undersized .001 or .002 (they are very few and far between)

All Chevy cranks (not the 2" ones) use a 2.099/2.1 crank pin size. (deduct multiples of .o1 for undersize)

2.075 is a dud and not a standard size. It is probably the 20 under "worn out" and may or may not clean up at 30 under. .005" is considered by many to be a go-no-gage when deciding which size to grind next.

In otherwords set the mic to 2.075 and if it slides over any of the rod pins in any spot then assume it may not clean up at .03" under and figure .04" as your next size.
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Old 09-20-2007, 09:49 PM   #8
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Re: 1985 chevy truck 305 crankshaft specifications help please

hey thanks ,the knowledge about cranks really help.whew this has really been an adventure on this motor .my dad and son and i are enjoying the process of learning and appreciate all tips and help.this motor has obviously had a lot of work and lol...probably is going to need alot more.i took the heads to have the valves ground,and was informed that the heads are off of a 350 instead of a305.my question's now are which head gasket is correct(305 or 350)and what does this do to the motors preformance?i think the intake may also be from a 350,any extra knowledge on this subjectwould be greatly appreciated.thanks again shade tree305
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Old 09-21-2007, 04:31 PM   #9
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Re: 1985 chevy truck 305 crankshaft specifications help please

Not too sure about the intake, but the heads probably just have a smaller bore on the gaskets. The correct ones should be used, but using the 350 bore in 305 is acceptable. Not the other way around if the gasket hangs into the cylinder.

The intake may have smaller ports on the 305, and may be acceptable to use either gasket.
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Old 09-21-2007, 11:13 PM   #10
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Re: 1985 chevy truck 305 crankshaft specifications help please

hey thanks again you were right on the money on the gaskets and i appreciate the info...probably saved me quite a bit of trouble.we are almost reassembled now with the main components...turned out my machine shop guy says the heads are off a 76 chevy ...lol...think my block is 85 and im pretty sure my bell housing and clutch are from the 68 ...lol...can i pick -em or what?my next dilemma is setting the valve....lash? i think it is... we have aprocedure in a manual .any info on this subject would be great and i thank you for any help....although this motor isnt exactly ideal...we are having a great time with it and taking pride in doing it ourselves...with help from a lot of friends im sure hoping to hear it rumble to life soon.....shade tree305
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