KR/6A bottom end rebuild options?

Discussion in '16-valve' started by ambrose89, Dec 6, 2021.

  1. ambrose89

    ambrose89 Forum Member

    Joined:
    Mar 19, 2007
    Likes Received:
    21
    Location:
    on back,crap in eyes, beneath car
    Hi and TIA.

    I have an Audi 2.0 6A/ACE block 82.5mm bore that I suspect has low comp on P2/requires rebore.
    I also have the KR bottom end.
    I'd like to sort out low comp cheaply if possible as currently between jobs/car buying sprees.

    1. if taking the Audi bottom end apart what is recommended/prudent to carry out regards possible rebuild ..stroker crank/parts to replace/ballpark cost?

    2. buying new forged pistons is pricy. Looking at maybe getting 83mm pistons -is it wise to get these by buying an Audi A4/A5/A6 engine? will they have suitable pin holes in piston for my conrods?

    3. could I use the existing Audi 82.5mm pistons to rebuild into the KR block/would it take 81mm to 82.5mm bore out? is it worth doing on what is the original block sat in shed?

    Any steer towards things I need to consider/build threads appreciated.
     
  2. Sirguydo

    Sirguydo Fastest milkman in the West Paid Member

    Joined:
    Nov 7, 2012
    Likes Received:
    1,203
    Location:
    Bolton
    Ive a KR race engine that’s got an ABF crank and pistons in it . The KR rods need ABF rod bushes putting in for the bigger pin size but not sure about ACE piston pin size off the top of my head.
     
    ambrose89 likes this.
  3. Tristan

    Tristan Paid Member Paid Member

    Joined:
    Apr 25, 2006
    Likes Received:
    1,205
    Location:
    Southern IRELAND
    Tbh, it all depends on your budget and skills.
    What car has 83mm pistons that you were thinking of using?
    If it's a newer, tfsi engine, they'll be no good for you.


    Before you do anything though you need to properly assess what is the actual problem you have.
    It's unusual to have low comp in one cylinder due to wear on the bores. Remember, all pistons are doing the same amount of travelling! More usually it's a head related issue.
    If you do indeed have compression loss in just one bore, that's more likely to be a broken ring or similar.

    I've seen 1.8 blocks with a lot of wear on the bores, yet with decent compression.
     
    ambrose89 and Jon Olds like this.
  4. ambrose89

    ambrose89 Forum Member

    Joined:
    Mar 19, 2007
    Likes Received:
    21
    Location:
    on back,crap in eyes, beneath car
    Thanks both for the replies.
    skillswise I've got a 4 year trade apprenticship engineering sys maint. specialist machining, spanner bashing so am okish -not done full top/bottom eng rebuilds but the joy of golf ownership has seen me do most remaining stuff excluding body so I'd most likely do all work bar that requiring a machine shop.

    regards the piston rod, iirc the 6a/ACE are similar so think according to this sticky it may be 46mm and 19mm- but handy to know regards option of bushes to suit.
    https://clubgti.com/forums/index.ph...oke-combinations-max-bore-stroke-list.228971/

    Looking at carfolio advanced search quite a few Audi A4/a5/a6s have 83mm bore.
    https://www.carfolio.com/search/res...c&y1=2000&y2=2020&bore=83&bore2=83.5&offset=0
    my thinking is the rings and cyclinder walls may be sacrificial under normal use but pistons may be more likely useable
    I know at some point I need head off for a look, Bore micrometer is on the shopping list.
    I dont think the issue is top end related, comp test with oil in p2 brings up compression suggesting bottom end.
    Also the head was rebuilt/ported less than 7000m ago by the head in the head so I doubt its top end.

    This car isnt a daily, but has been used sporadically for a few months at a time whilst I'd forgotton about the low p2 comp. covered 9k in last 8 years.
    Interesting to hear about a cracked ring as a possible cause( that'd potentially make it a less costly fix)
    hopefully this wouldn't result in a bore issue if I've inadvertantly driven on it for a few 1000 miles ?
    any recommedations for bottom end rebuild parts suppliers ?
     
  5. Sirguydo

    Sirguydo Fastest milkman in the West Paid Member

    Joined:
    Nov 7, 2012
    Likes Received:
    1,203
    Location:
    Bolton
  6. Tristan

    Tristan Paid Member Paid Member

    Joined:
    Apr 25, 2006
    Likes Received:
    1,205
    Location:
    Southern IRELAND
    What engine codes are the 83mm pistons?
    If they're a tfsi type engine, they're not suitable for your head.

    Seriously, don't even look at new parts til you at least get the head off for a good study.
     
    ambrose89 likes this.
  7. ambrose89

    ambrose89 Forum Member

    Joined:
    Mar 19, 2007
    Likes Received:
    21
    Location:
    on back,crap in eyes, beneath car
    not sure engine codes - but this is an example -2004 A4 3.0 tdi
     
  8. Tristan

    Tristan Paid Member Paid Member

    Joined:
    Apr 25, 2006
    Likes Received:
    1,205
    Location:
    Southern IRELAND
    I very much doubt a piston from a common rail diesel will work!
     
    ambrose89 likes this.
  9. HPR

    HPR Administrator Admin

    Joined:
    Aug 11, 2009
    Likes Received:
    1,819
    You need 2.0 16V pistons from an engine with a low block ( 82.5 mm ) on condition the bores are good.

    ABF Pistons in a low block can be done... but need the piston crown machined as it will be about 2 mm above deck
    that also means the valve pockets need machined... as the are now 1.4 mm closer to the valves
    and the piston pin is 21 mm so low blocks have 20 mm piston pin ... so the conrods smal end bush need modified to accept a 21 mm pin

    To use the existing pistons... its hard to say... it depend much on their condition... altough not the prefered choice
     
    ambrose89 and erreesse like this.
  10. ambrose89

    ambrose89 Forum Member

    Joined:
    Mar 19, 2007
    Likes Received:
    21
    Location:
    on back,crap in eyes, beneath car
    Thanks all, the responses give me a better understanding. Looks like I'll have to prep for stripdown when it gets a bit warmer.
    ingers crossed it's a cracked ring.
     
  11. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    148
    Location:
    Southwest
    The simple solution if the ACE block is damaged is the swap all the 2ltr internals into the KR block. No problem at all boring from 81 to 82.5 and fitting the ACE crank/rods/pistons. There maybe some relief needed to clear the rods which will be evident during a dummy build.

    You may yet find there's no bottom end issue with the ACE. If it's 1 cylinder that's drastically low I'd suspect a burnt out valve, unless you have a damaged piston from det damage perhaps. How low exactly is number 2 compared with the other 3?
     
    ambrose89 likes this.
  12. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

    Joined:
    Jul 26, 2006
    Likes Received:
    3,320
    Location:
    Creating Pfredstarke
    6A=ACE=9A=3A(8v)
    All the same blocks with minor updates.

    Remove the cylinder head and inspect bores, before thinking about short engine rebuilds.
    83 mm is just a 20 thou increase, which will be for a deep scratch. But we got no idea what is the problem, until you give it a through inspection.
     
    ambrose89 likes this.
  13. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Its gonna have to come to bits to find out what's needed, anything else is guesswork
    Jon
     
    ambrose89 likes this.
  14. ambrose89

    ambrose89 Forum Member

    Joined:
    Mar 19, 2007
    Likes Received:
    21
    Location:
    on back,crap in eyes, beneath car
    Thanks all, and I know -I'm asking questions without providing hard evidence obtaine from head removal.
    Mr Hill Climber-"You may yet find there's no bottom end issue with the ACE. If it's 1 cylinder that's drastically low I'd suspect a burnt out valve, unless you have a damaged piston from det damage perhaps. How low exactly is number 2 compared with the other 3?"

    Looking at an old post of mine
    https://clubgti.com/forums/index.ph...-starts-once-engine-warm.282257/#post-2425854 (the issue I had then was oil coooler(white smoke) when I was fitting a rebuilt head in shed head) less than 10,000 since then. I dont think its valve related as oil in bore/comp test brings up pressure, Dave rebuilt the head, I haven't wragged it.
    I didn't see issues with bore (though tbh I was prob focussed on smoke/head gasket suspicions)
    Ambrose89- "torque was 40, 60 nm
    did wet test today, throttle open, engine temp 90degress, outside temp mild (10degrees)
    1-14
    2-12.5
    3-14
    4-14
    noticed the water level is down a bit and its clouds of white smoke (not just a wisp) when i give a bit of pedal.
    head is now off, cant see anything obvious, its down the engine place in the morning for pressure test/skim."
    then a bit later on : "having recently done comp test on warm engine, cranked 5 secs, fully open acc my results iirc were 17,15,17,17 (P2 was 17 when tested with oil in it) these are higher than those a couple of years ago which were 14,12.5,14,14."


    It's most likely any potential rebore (i reqd) will not immediately follow (due to cost/sourcing) head removal.
    Original KR was swapped out in 2007 -since then it has lost itermediate shaft( I've a vague recollection of selling it) and a tarp I had it stored under[:$] outside didn't protect the bores as well as I naively hoped[:[].
    Local Engine machininsts (old boys/decent) have quoted me £120 for 4pot rebore. £30 a piston liner if reqd.
    At some point I'm guessing its prudent( to aid any further sale/ allow retrofit) to get the KR block rebuilt and moth balled PROPERLY given what OEM 16Vs are commmanding. - So atm an internal ACE swap into KR block might be a none starter.
    I will update once I've bore pics.
    If I need oversize pistons will I need to buy forged due to availabilty ?
     
  15. ambrose89

    ambrose89 Forum Member

    Joined:
    Mar 19, 2007
    Likes Received:
    21
    Location:
    on back,crap in eyes, beneath car
    P.s -apoligies for typos my keyboard has sticky F & Ds
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice