Bearing tolerance Type 4 engine

Discussion in 'Mech Tech' started by Deefer66, Nov 8, 2019.

  1. .. so just put the micrometer on the journals of the crank I picked up from a 0.25mm grind today.. first quick measure up puts them 0.003mm out apart from No.1 which is 0.013 too big (59.763) and big end journal no.1 could be 0.02mm too big 49.770mm.
    Going to clean up properly and double check and get the plastiguage out over the weekend in case saddles/ bearings have spare but in advance how much is too much with regard to being over?
    Will it just wear in or have too high oil pressure or seize...

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  2. I would give the journals a good polish if the shop didn’t do it. Then pop it in & plastigauge it. If you’re not happy with the plastigauge results take it back to them.
     
  3. 0.01mm is less than half a thou. I’d doubt if they’re going to be exactly the same. I’d have a look in your Bentley or similar to see what the max/mins are for a 0.25mm grind.
     
  4. Bentley gives you a 0.02mm band to aim for...if I'm ignoring the thousands of a mm most are good but I guess if a quick polish with 400-600 grit and wd40 doesn't clean off anything that might be affecting it it's back to the shop![​IMG]

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  5. When I had mine done . I gave them the bearings( NOS) and they looked up in their book what the journals had to be in relation to the bearings ...
     
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  6. I offered them bearings but they were happy with the Bentley page above printed fot them.... just make sure it's not me first these imperial vernier micrometers take a bit of getting used to..[​IMG]

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    Valveandy likes this.
  7. what bearings are you using ?
    The guy that did mine was Porsche specialist and wanted the bearings ...
    plastigauge is going to be your best bet
     
  8. Oh and they are not vernier micrometers ( sorry ) you should have a 1inch calibrated bar with micrometer to check it against ?
     
  9. Silvernine bearings,... yeah got the little bar got two of them as have a set of three micrometers.. 0.0001" ones.. the cheapo calipers measure them exactly right too.. not sure if that's good or otherwise. What should you call them? I thought as they were micrometers with a vernier scale on they'd be a vernier micrometer.. .. My engineering involves moving earth and concrete so a tape is usually good enough

    I'll be having another look tomorrow been off blacksmithing for the day today

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  10. ..
     
  11. Yep.. the dial guage has a vernier scale on it to get the 0.0001 part..

    [​IMG]


    Found this now too..


    [​IMG]


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    Last edited: Nov 9, 2019 at 10:46 PM
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  12. I use Silverline bearings; steel backed unlike some other manufacturers and usually good quality.

    It’s worth using plastigage on the bearings where it is possible but VW state a surprisingly large tolerance for bearing clearance and I wouldn’t be too concerned if measurements were not accurate to 0.0001” – however, I wouldn’t be happy with bearing clearances at the top end of the wear limit.
     
    Deefer66 likes this.
  13. I'm rounding to nearest .01mm.. the micrometers were just cheaper in imperial to that level than 0.01 metric!.

    t's the lower end I'm worried about more.. I think they've left a bit too much on there when they ground it down so it'll be too tight for a healthy oil flow

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  14. Can't find clearance for con rod bearings in Bentley but taking tightest from above table being 0.03 is ok on mains 0.038 should be ok on these

    [​IMG]

    Did 4 at quarters to make it balance and all pretty even

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    snotty likes this.
  15. If everything's within VW's limits, should be fine. Doesn't matter whether it's towards the top or bottom. Stick your bearings and crank back in with a bit of oil/lube, tighten the case up and see what it feels like. If the crank spins freely, it's fine.
     
  16. Re measured all big end journals to less than 0.01mm away from 49.75mm. Done all rod journals clearance at .038mm and only main you can plastiguage No 2 Main.. that's just under the 0.038mm so good to go.
    Run out on crank is 0.01mm max barely moves dial guage so. Main journals all to within 0.01sh after a clean up[​IMG]

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