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 Post subject: Line bore?
PostPosted: Fri Oct 29, 2010 11:44 am 
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Joined: Fri Oct 15, 2010 12:20 pm
Posts: 9
Location: Concord, Ca
What is the purpose for line boring, at least as far a s a new long block? Would a standard case be ok, or do I have to bore it?


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 Post subject: Re: Line bore?
PostPosted: Fri Oct 29, 2010 1:29 pm 
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Joined: Thu May 23, 2002 2:01 am
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Line boring should not be needed on a new case.


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 Post subject: Re: Line bore?
PostPosted: Fri Oct 29, 2010 2:12 pm 
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Joined: Tue Nov 14, 2006 1:17 am
Posts: 9559
Location: Just north of Seattle
Marc is correct on a properly machined engine, align boring shouldn’t be necessary unless you are going to blueprint.

Align boring is to ensure that the crank bearing seats in the case and the crank are to (in alignment) specifications. On an a/c VW engine, I don’t know just what is done other than ensuring that the crank bearing seats or cam bearing seats are in a straight line and parallel to each other but they can match several surfaces during the machining processes (you also need to have your crankshaft and cam shaft checked to make sure that they are straight too). With new cases (green cases, never been heated up since machining), especially with performance engines where keeping things to specification/tolerance (e.g., blueprinting) is more important than it might be for a stock (re-) build, the cases are often checked and align bored if necessary. Rebuilding a used (seasoned block), checks will be made on the crankshaft seats, bearing seats and the faces that the barrels sit on; further machining may be necessary if they are out too much. Align boring can/will also (re-) set the thrust surfaces for the crank shaft bearings.

(Generally speaking now) Align boring can also be done to fix minimal damage to the case; say if the case had over heated so that minimal movement of the crank’s or cam’s bearing seats (over sized bearings) may have shifted some or in the case of a spun bearing, may have done some damage to the bearing seat. With V-8 engines, they often align the crank head mounting surfaces are in alignment to ensure that the crank and the heads would be in alignment (consistent compression for example). Also, they can align the crank to the cylinder bore but I am not sure it they do that anymore.

I hope this does not muddy the water up any more than it is.

Lee


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 Post subject: Re: Line bore?
PostPosted: Sun Oct 31, 2010 12:05 pm 
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Joined: Fri Oct 15, 2010 12:20 pm
Posts: 9
Location: Concord, Ca
Nope, no mud. This makes perfect sense. I saw case builders with options of standard or boring over between .020 and .060 and I wanted to make sure that it meant what I thought it meant, my experience is all non-VW.

Thanks, great info!


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 Post subject: Re: Line bore?
PostPosted: Sun Oct 31, 2010 2:21 pm 
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Joined: Tue Nov 14, 2006 1:17 am
Posts: 9559
Location: Just north of Seattle
I was watching one of the Spike shows this morning and they brought up align honing which I had forgot about. It is similar to align boring but not so radical.

There are several books you might want to have in your library for handy reference on the subject:

If you can find one, look for a Hot VWs special printing: 'All About Performance VW Engines II' which I under stand may be hard to get or find. It covers several engine builds from a stock 1600 to: 1776, 2007, 2165, 2813, 2853 cc engines.

'How to Hot Rod Volkswagen Engines' by Bill Fisher, which was published by HP books. Among other things it covers tear down and inspection; what to look for and where to look for them (I liked the checking for cracks in the case best)

How to rebuild Your Volkswagen Air-Cooled Engine' by Tom Wilson, again published by HP Books. A good book quite a few things worth looking at and it includes a interchange section.

As I remember one of the books (may) shows an old trick for when you are not sure about a case and you want to do a quick check to see if you really need to have it professionally looked at (I hope I remember this correctly. I've only done a couple of ta/c VW engines and it was a long time ago too): lay each case half down flat, inside up, and block/brace it so it is level and won’t tip as you work around it. Using a known accurate straight edge, lay it in the main bearing saddles the full length of the engine unless there are places higher (like the seal area) than the bearing seals. If all things were perfect, you should be able to shine a flash light from the back side and not see light coming through. If you can see too much light, you need to get a feeler gauge out and see what the gap is. Do that to both case halves and check the cam bearing saddles the same way.

How accurate is this test; close enough that if you are not comfortable with what you see, you should have the case properly checked by someone who knows what they are doing (the key here is that they know, not think they know). The case then needs to be put together (let them do it) and the saddles need to be properly checked for alignment, concentricity plus the cam needs to be parallel to the crankshaft; within tolerance.

Lee


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 Post subject: Re: Line bore?
PostPosted: Tue Nov 02, 2010 7:54 pm 
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Joined: Fri Oct 15, 2010 12:20 pm
Posts: 9
Location: Concord, Ca
Wow, thanks for the info! As it turns out I 'How to Hot Rod Volkswagen Engines' is on it's way to me already. ;)

I'm a machinist by trade, so I am familiar with the scale/flashlight check you're talking about. It can be really accurate, I do it at work with feeler gauges. I'm glad to know it's something I should check.

Thanks a bunch!


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