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Does align honing the main journals usually make them oversized or does this demension need to stay at the standard measurement? Also does micropolishing a crankshaft usually take a few ten thousandths off the journals? I would like to do my first motor this summer and am a little confused about setting this measurement correctly. I plan on purchasing a new crank and using a used block. the goal is 400 hp. it is a SBC and I plan on buying a 3.75 stroke crank.
 

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brian12c said:
Does align honing the main journals usually make them oversized or does this demension need to stay at the standard measurement? Also does micropolishing a crankshaft usually take a few ten thousandths off the journals? I would like to do my first motor this summer and am a little confused about setting this measurement correctly. I plan on purchasing a new crank and using a used block. the goal is 400 hp. it is a SBC and I plan on buying a 3.75 stroke crank.
K I S S
Align honing crankshaft main saddles in block:

The mounting surfaces of the main caps themselves are usually cut .004 which makes the hole eggshaped, reinstalled, and then the hole is honed to the specified size in a "line hone" which does all 5 mains at the same time. This cap alteration moves the crankshaft .002 toward the cam. If a timing chain is too loose afterward, Cloyes makes timing chains for this purpose, but people rarely buy them.

Crankshaft micro-polishing does in fact remove a couple ten thousandths. Insignificant if done correctly. When a crankshaft is ground undersize the grinder operator knows this and works to a final dimension for specific clearances.

A solid 400 hp 383 cube is easy, very streetable, and is fun to drive. Need good heads to avoid radical cams. At least factory Vortecs or better, and all the usual stuff.


http://www.chevyhiperformance.com/t...e/photo_14.html

http://www.eqcylinderheads.com/flow.html
 

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Discussion Starter #3
so I would tell my machinisht what size I would like the main journals honed to?and then I would subtract the bearing thickness from that then subtract the crank journal diameter to find the bearing clearance?
 

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brian12c said:
so I would tell my machinisht what size I would like the main journals honed to?and then I would subtract the bearing thickness from that then subtract the crank journal diameter to find the bearing clearance?
The crankshaft machinist will micrometer measure it and regrind it, if necessary, in the largest size possible, -.010, -.020, -.030 and polish it. He knows the specified bearing sizes/ clearances, so when he is done it is ready to install "as-is". It is the installers job to clean it inside and out thoroughly. :thumbup:

Same rules apply to the block main bearing honing. They are all brought back to specified standard size as explained in previous post.
 

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Align honing is used to resize and align the main bearing bores. They are brought back to their correct std size. If they were too big the bearing wouldnt stay in place.

Some engines have oversized main bearings available but if they are being used block would be align bored not honed. Honing is used when only small amounts of metal are required to get sizes back to normal size.

This is because the hone is going to take metal off equally from block and cap until its size you want. If caps were cut say .005 then .0025 would come out of block & .0025 would come from cap.

When align boring the machinist would set block in machine so that almost all metal would come from bearing cap.

All this is important because as crank gets moved up farther in block timing chain gets looser & looser. Or if engine is gear driven timing gear even a couple thousandths and all sudden theres no backlash in gear train.



Crankshaft micro polish is a term used for how crank is polished. On cast cranks when they are ground tiny fragments of metal stand up on journal surface these little "hairs" will wipe out the bearings asap if not removed.
Steel cranks get polished too.

Micro polishing is polishing in 2 directions to cause them to break off.
A std polish would be polish in 1 direction to lay then down so they dont tear up bearings. If done correctly there wont be any change in size of journal.

Everything has a procedure, grind in correct direction based on engine rotation, polish in correct direction based on how it was ground. In marine applications std or reverse rotation becomes important.
Im not a crank grinder so I cant answer all this just off cuff.
 

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brian12c said:
so I would tell my machinisht what size I would like the main journals honed to?and then I would subtract the bearing thickness from that then subtract the crank journal diameter to find the bearing clearance?

If he's a competent machinist you shouldn't have to tell him what size to hone the mains to. He'll have a standard range that he'll work to. The clearance will be determined by the sizes of the journals on the crankshaft. If the crank journals are standard you order standard size bearings. If the crank has been cut the machinist usually will cut the journal either .010 or .020 under and you would order either .010 or .020 under bearings to match. There are other sizes available such as .001 over or .001 under if you're shooting for certain clearances with stock journal sizes as well.
 
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