Line boring your block, worth it?

Reign_Maker

Reign_Maker

Has cheezberger
Aug 31, 2005
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About to drop my block off tomorrow for machine work... Im having everything done, honing, boring, lapping, vat the block, polish crank.... Im debating having one thing done: a line bore... If you dont know what that is, you dont need to answer this question... If you do know what that is, should I do it? Do I NEED to do it?

I'll be dropping my head off to this shop later when I get my springs and retainers... I feel REALLY confident about this shop... I've had 5 people locally recommend them, and when I talked to the guy today, he said something very important: How much boost will you be running through this motor? *the guy knows about tight ass tolerances when it comes to high boost* Also, the shop was not too clean and not too dirty, lol... You know what Im talkin about... You dont wanna walk into a dump, but you dont wanna walk into a shop you could eat off the floor on, lol...
 
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bluepearl

New Member
Jul 21, 2005
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IMHO, you're machinest should be the best judge of that decision. He will be the guy that is taking the proper measuments to warrant if it is needed or not. Does he know about the previous condition of you're motor, did he see the bearings? Measure them? Are the cylinders scored, out of round ? These are things that should be talked about with him after he takes a good look at the block.
 
antman

antman

Supramania Contributor
Apr 6, 2005
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did you really think people who don't know what it means would answer?(rhytorical)
 
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malloynx

Member
Mar 30, 2005
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it take 5mins to spec it with a straight edge and feeler gauge. just check it and see.

don't line bore or hone if you don't need it.

also for the head make sure to pay close attention to the valve margin. it must be in spec and if oyu get a valve job, you don't want ot loose it.. gotta keep those valves cool ;)
 
ToyoHabu

ToyoHabu

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Jun 25, 2005
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On the old VW Air cooled engines, the two case halves would walk under normal conditions. this caused uneven wear on the journels. It always was advisable to line bore them. you would need thicker bearings as a result. The crank on the 7M is supported very well and I would not anticipate unusual wearing. It is best to avoid it if possible. On a side note are they going to check for bore alignment ?
 
Reign_Maker

Reign_Maker

Has cheezberger
Aug 31, 2005
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Malloy I have a t-square and a ruler, will that work for a straight edge? eh? eh? eh? LOL... I dont THINK I need a line bore, because it looks really good and all my bearings were in top notch shape... I also dont think hge'll do it if it doesnt NEED it... The guy is good at what he does, and I feel confident he'll take care of me on that...

As for the head, Im sure it'll be in spec... Goin with the 1mm oversized Farrea SS valves, and all ferrea valve train... Im also having new brass valve guides installed... And a nice P&P...

Thanks for the input on the line bore...
 
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boltz

New Member
Jun 17, 2005
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My shop calls it an allign bore :icon_razz They check everything, but that is to be expected with a performance shop.

You only do it if you need it done. Your shop will have to check it as the people above have already explained.

The one thing you should look into tho is to have your OEM used piston rods resized and re bushed. what this does is almost like a line bore of the rods big end except it stays at a factory diameter spec. The Rebush part just replaces the wrist pin bushing on the small end.
 
Reign_Maker

Reign_Maker

Has cheezberger
Aug 31, 2005
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Boltz, wont be needed, getting all new rods and pistons...

Thanks for the input guys, I'll just have him check for me and only do it if needed...
 
rakkasan

rakkasan

Currahee!!
Mar 31, 2005
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Jake, tell the machinist to go over your block thoroughly & let him tell you what work your block needs. If he asked you what kind of boost you plan on running, that's a good sign that he knows what he's doing.
 
Reign_Maker

Reign_Maker

Has cheezberger
Aug 31, 2005
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He actually did ask what boost and turbo I was going to be using because "when you start boosting these motors, you need to have extremely tight toerances, you dont wanna build this motor and the first time you crank the boost, you blow your motor apart: and I've seen that happen"... I'll let you guys know how it turns out when I drop it off...
 
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88turboma71

el3men2
Mar 30, 2005
115
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nyc
Well il see if i can find it but i read somewhere that it is recommended that u get your block line bored when using main studs, i got my block line bored, i would have even if i would not have had main studs, it only costs a few more bucks, think about how much money you are going to be putting in this motor and i know u are going to want everything to be perfect, and since the block is out y not do it anyway. Dont take any chances.
 
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IJ.

Grumpy Old Man
Mar 30, 2005
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I come from a land down under
boltz said:
Translation? LOL
Click to expand...
I'll have a go ;)

I think what Nash means is you'd end up with thicker bearings but it doesn't work that way.

They take a cut off the mating face of the caps to close up the diameter first then line bore till they just touch the block so most of the material comes out of the cap.

You need X Size on the OD of the bearing to get the correct crush or it will spin.

The "Bad side" is if it's not needed you run the risk of the machist getting it wrong and trashing the block, it's not like good condition 7M blocks are plentiful as most are shagged though years of abuse and not being looked after.
 
miggles

miggles

i wasnt speeding officer
Jun 3, 2005
526
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perth West Australia
There seems like only one size under on the crank you can machine to. 0.25 undersize.Thats the size i got mine machined down to as i had spun a bearing on rod #1 and parts of he bearing had welded itself to the crank.The caps had these X hatchings on the inside similar to the hone hatchings.
 
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