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How to measure bores accurately/maximum measurements?

VAG-Slag Feb 5, 2015

  1. VAG-Slag

    VAG-Slag Registered User

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    I'm just in the midst of stripping an AGU lump ready for building up, although the bores look great (can still see original honing marks) I'd like to give the bores a light honing.

    What's the best tool and technique for measuring bores? When I went up to see Bill he showed me some sort of T-shaped tool to accurately measure the bores, but I can't seem to find them anywhere.

    Also, what are believed to be the maximum bore sizes for dealing with hybrid power while still using a standard AGU piston?.. I know what the Audi tolerances state, but obviously that's not quite good enough!

    Thanks chaps

    Lewis
     
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  3. aragorn

    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    I dont think i've seen a block where those "honing marks" arent visible. Even when the bores are worn oval, they're still visible. So its no guarantee that the bores are good or not.

    You need a "bore micrometer". they usually come in a 25mm size range, so you'll get one which will measure 75 to 100mm.

    Why do you think the Audi tolerances arent good enough?
     
  4. Andrew@A.L.D

    Andrew@A.L.D May add NOS to 600+bhp S3.

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    Stacey did measure his bores in his build thread with lots of info with where he measured it etc
     
  5. beachbuggy

    beachbuggy Registered User

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    To do it accurately or more accurately you should use a torque plate bolted to block to replicate the stress the head would give once bolted up..
     
  6. VAG-Slag

    VAG-Slag Registered User

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    Oh, ok... Well I was going to take some measurements anyway!

    Yea, I was kindo hoping for a tool that doesn't cost too much... Otherwise I'm best off just giving the block to my engineering guys to have a look at. Bill had a quite a basic looking tool he showed me...

    Also, I say Audi tolerances aren't good enough based on 2 things:

    1, I recall a conversation (on here I think) where Bill was saying how an engine was down on power and on further inspection the bore size was xxx. Someone pointed out that's within Audi tolerances and bill then went onto explain how those tolerances were no good for the big turbo build in question

    and 2, I'm currently suffering from a slight loss of compression. Compression is still within Audi tolerances, which is probably fine on standard boost, but when Bill was mapping he got so a certain point and the cylinder basically wasn't able to hold that extra boost/combustion and I didn't make the numbers I was aiming for...
     
  7. Rrobson

    Rrobson Registered User

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    You could use an internal micrometer. Having had a quick look on eBay they don't fetch much (buy a good brand like Moore and Wright, will last a lifetime) but if you've never used one they can be difficult to get the hang of when measuring bores.
     
  8. <tuffty/>

    <tuffty/> Badger 5 Edition...Its all about the flow... Staff Member Moderator

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  9. Rrobson

    Rrobson Registered User

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    As above, you could use a bore comparator but these can also be tricky to use if your new to them, and you'll also need an external mic to check it against but much easier to use then an internal mic
     
  10. badger5

    badger5 www.badger5.co.uk Site Sponsor

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    bore mic and or comparitor with external mic i have
     
  11. VAG-Slag

    VAG-Slag Registered User

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    Thanks for your input guys, I've just been reading through staceys build thread for the past couple of hours... I managed to find out what the tool I think Bill showed me was:

    http://www.ebay.co.uk/itm/6pc-Teles...UK_Measuring_Tools_Levels&hash=item5d50f0dfeb

    Much more within my budget! . . From what I read though perhaps not the best way of measuring bores.

    Also, I've found where he measured his bores, but he never said what maximum tolerances are though...

    To be fair, overall I'm starting think I'll just be best for me to get someone else to do the honing/measuring... Still it'd be good to know what the maximum acceptable bore size for a build like this would be!?
     
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  13. superkarl

    superkarl MAN OF STEEL

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    You know the size of th Pistons, and a quick Google will yield a lot of very close tolerances for piston-wall clearances, thus giving you an idea of bore size.
     
  14. Rrobson

    Rrobson Registered User

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    Even with those measuring tools (Ive always known them snap gauges) you still need an external micrometer and there's a higher chance of making a mistake because you've got to be really careful not to push them in when measuring. Also you may be slightly out as you've got to measure the bore with the snap gauge, then measure the snap gauge.

    With measuring if there's any doubt it is always better to getsoneone who is more used to doing it. That way you can be sure there are no mistakes. Also, get them to show you how to do it while your there :)
     

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