Low / no compression

Discussion in 'Mech Tech' started by jason meadows, Feb 22, 2019.

  1. Hi all , I have done a compression test on my 1600 twin port engine and cylinder 3 is low and cylinder 4 has no compression at all . What would be the main causes of this and can i remove the cyclinder head with the engine in situ .

    thanks in advance
     
  2. davidoft

    davidoft Sponsor

    Cracked head I would say, but double check the compression tester is sealing properly
     
  3. Check the rocker shaft hasnt come loose, then check valve clearances, if they are ok its head off time
     
    snotty likes this.
  4. I compression tested 3/4 times and nothing on cylinder number 4 , all other showed a reading 1 and 2 were fine whilst 3 was slightly down . can i remove in situ or would it be easier to remove engine
     
  5. You'll not known until its out and it needs to come out for head removal.
    Presuming tappets are set properly ??
    Always worth asking ...

    Could be a knackered valve / seat or piston rings . Whatever , you'll need to drop the engine out ...

    Sent from my SM-A320FL using Tapatalk
     
    jason meadows likes this.
  6. Rocker shaft is fine as I only readjusted the clearances last week , i think it has been running out of time for quite a while
     
  7. also forgot to say that when i took it for a run before doing the compression test , oil was P***ing out of the oil filler cap
     
  8. Probably rings then ...

    Sent from my SM-A320FL using Tapatalk
     
  9. mikedjames

    mikedjames Supporter

    You will need to pull the engine.
    You cannot remove the cylinder head without taking off the fan housing and tinware as the nuts are covered.


    Gas is leaking past the piston or though it and pushing the oil out of the filler.

    Maybe its like my engine .... this was a dropped valve...the head of the valve is at the bottom of the pile in the cylinder.
    20180907_150411.jpg
     
  10. Is your crankcase breather clear? May be rings, just seems odd it's only on one cylinder. I'd pop the rocker covers off again and just make sure that all valves are closing properly. Zero compression might imply a stuck valve.
     
  11. If you have access to compressed air you could do a leakdown to help identify where the leak is, but sounds like it's rings or a holed piston due to crankcase pressure. Have you drained the oil and checked the strainer for bits?
     
  12. davidoft

    davidoft Sponsor

    Double check the valve clearances are correct too
     
    Lasty likes this.

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