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Tractor Talk Discussion Forum

line boring

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Big hunter

01-02-2008 06:51:38




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When, why, is an engine line bored? Is it when the bearings wore completely through and then wore into the block? Is it done to re-inline the journals (is that what they are called) from being egged? No the journals are on the crank, I mean, the part of the block the bearing sit in, whatever you call them. Maybe I better do a google search and get educated.




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Walt Davies

01-02-2008 11:48:56




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 Re: line boring in reply to Big hunter, 01-02-2008 06:51:38  
Line boring is an old system used to get the poured babbitt bearings lined up when renewed. Its pretty much obsolete now with modern engines as they as far better made than the old ones were. But If you are putting new Babbitt bearings in an old tractor then of course you will need to have them line bored. I wouldn't waste a dime doing it on any newer engine with new style bearings. Walt



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trucker40

01-02-2008 11:10:28




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 Re: line boring in reply to Big hunter, 01-02-2008 06:51:38  
Lots of reasons allready that are right,warping,spun bearing.When a bearing spins it pulls the metal to the center making the inside of the journal too small.You might think it makes it bigger,but it doesnt.I guess if it spun in there long enough to make it too big,line boring wouldnt fix it,and you would need a new block,or do something different.I guess if it was only a little too big they could grind off the end of the main cap.I dont know what all machinists do,but it allways worked whenever it came back from them.

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Bill in Colo

01-02-2008 09:16:06




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 Re: line boring in reply to Big hunter, 01-02-2008 06:51:38  
Early 70,s Case 504,s almost always needed a line bore job with the first rebuild , something to do with the way the casting was done at the factory, most of these engines seldom made 2000 hours on the first rebuild,but after a line bore they were good for several thousand hours.
I lined bore an engine in witch the main caps were loose once.



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37 chief

01-02-2008 08:23:36




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 Re: line boring in reply to Big hunter, 01-02-2008 06:51:38  
One thing to think about when a block is line bored (honed) is the cam, and crank gear might become too tight, when this is finished. This process moves the crankshaft gear closer to the cam gear, and may bind if too much material is taken out. I could think a good machine shop cam measure the block to be sure the repair is really necessary. I would have the rods resized if anything as Allan mentioned, this is the thing most likely to become distorted. I had a block with poured main bearings on my AC M, and had to have the main bearings repoured, and line bored was the only way to resize the bearings. I don't want to do that too many times($$$).I did save a block on my JD where a main bearing spun in the block, and had it honed back to size. Just my 2 cents worth. stan

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J Schwiebert

01-02-2008 07:47:35




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 Re: line boring in reply to Big hunter, 01-02-2008 06:51:38  
There is also equipment to line hone a block. A block is also line bored (or honed) if a bearing cap(s) needs to be replaced.



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baa

01-02-2008 07:44:13




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 Re: line boring in reply to Big hunter, 01-02-2008 06:51:38  
this procedure also insures that the land that the bearing rest in is in correct alignment and of proper size. We had a man boring blocks for us and the engines were droppin oil pressure down to 5psi almost immediately after startup. After much head scrachin it was found that the center cutter was a few thousanths larger than the others but the same over size bearings were being used. If your engin man recommends align-borin I would have it done. Everyone have a good new year.

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Ron in Nebr

01-02-2008 07:29:51




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 Re: line boring in reply to Big hunter, 01-02-2008 06:51:38  
Like mentioned below, it's usually done in a "blueprinting" situation to ensure everything is up to specs.

It isn't usually done in a regular rebuild/overhaul. If the old bearings weren't badly burned/spun on teardown, then with the new main bearings at the proper clearances and lightly lubed, with the caps tourqed down, if the crank spins freely(no rods attached yet) by hand, it probably isn't neccassary.

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supergrumpy

01-02-2008 07:12:15




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 Re: line boring in reply to Big hunter, 01-02-2008 06:51:38  
sometimes the holes bored in cast iron engine block drift out of alignment from overheating or just plain cussedness

other posters said it well



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steve from mo - dangit!

01-02-2008 07:08:38




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 Re: line boring in reply to Big hunter, 01-02-2008 06:51:38  
Some blocks don"t come out exactly right in the machining process, and some blocks will warp a little over time. Like Allan said, it is to make certain that everything lines up. Lubrication is improved, stress is reduced, and life is extended.



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Allan In NE

01-02-2008 07:02:20




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 Re: line boring in reply to Big hunter, 01-02-2008 06:51:38  
Line boring is done to make absolutely certain that the crank and/or camshaft is running dead center true thru the block/head/whatever.

I always have the rods and wrist pins aligned at the same time also.

Allan



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Big Hunter

01-02-2008 07:16:07




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 Re: line boring in reply to Allan In NE, 01-02-2008 07:02:20  
yeah that makes sense. thanks



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