1. Hello Guest. You have limited privileges and you can't "SEARCH" the forums. Please "Log In" or "Sign Up" for additional functionality. Click HERE to proceed.

using a "used" head gasket?

Discussion in 'XJ Technical Chat' started by bensalf, Feb 23, 2021.

  1. bensalf

    bensalf Well-Known Member

    Messages:
    1,267
    Likes Received:
    254
    Trophy Points:
    83
    Location:
    yorkshire ,england
    hi all,
    so , after about 2 1/2 weeks of stripping and re-building my spare engine , and spending aprox £200 in the process.
    head barrels and pistons off and cleaned and measured, clutch stripped and cleaned and measured,
    sump off ,and checked everything i could see.
    rebuilt engine with new gaskets , timing chain , clutch springs, valve seals and shims.
    re-lapped all-valves in ( no 3 was low compression 10psi
    others were only about 80 psi)
    engine finished re-build yesterday,and now no2 has only 20psi other 3 are
    110 , 110, 120 psi.
    tried a leakdown test ( improvised from my air line) and i can hear air leaking from the no2 intake valve} so much it blows a paper towel, when its supposed to be closed.
    took head off again, couldnt find anything obvious , but poured some petrol in all 4 intakes, and no2 leaked through, others held fine.
    iv'e now re-lapped no2 intake,
    tried petrol in no2 intake and its been holding tight for a couple of hours now,
    will re-check in morning, if ok will rebuild headback on.

    so my question after all that is - i' intend re-using the head gasket, as its only been on for about 3 days
    and looks just as it did then, as new ones are about £40, and a week wait.
    would it be better to use some kind of sealant on it? if so ,what,
    cheers
    stu
     
    FJ111200 likes this.
  2. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

    Messages:
    19,613
    Likes Received:
    6,703
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    In the long-ago days it was (in certain circumstances, e.g. WW2) SOP to paint head gaskets with aluminum paint for reuse when new gaskets were unobtainable (let the paint dry).
    I have done that witth aircooled cast-iron engines, but not with an aluminum engine.
    Permatex makes an excellent copper spray-on gasket dressing, but I'm not sure that it's rated for head gaskets, and I have never used it for that.

    Another issue is whether or not the oil gallery oil seals are still going to do their job (likely they will, but be sure that they are still pliable and undamaged).
     
  3. JBurch

    JBurch Active Member

    Messages:
    210
    Likes Received:
    90
    Trophy Points:
    28
    Location:
    Owego, NY
    I'd re-use the gasket, it has not been thermal cycled
     
    Fuller56, FJ111200 and k-moe like this.
  4. FJ111200

    FJ111200 Active Member

    Messages:
    571
    Likes Received:
    112
    Trophy Points:
    43
    Location:
    Crewe, Cheshire, England
    I've just rebuilt the XJR engine i'm using in exactly the same way as bensalf describes.
    The XJR uses some sort of metal, three pieces on top of each other, pressed together. Only fired up a few times and taken a couple of times round the block but all seems good.
    I rebuilt an engine with new genuine Yamaha parts but wasn't quite happy so before i used it i took it all apart again and did it again. Was a bit dubious at first but all seems good.
    As JBurch says, not been thermal cycled.
     
  5. a100man

    a100man Well-Known Member

    Messages:
    1,597
    Likes Received:
    346
    Trophy Points:
    83
    Location:
    Bedford, UK
    I'm more curious about the valves not sealing.. Did any get mixed up during the head rebuild? Normally lapping gives a visual indicator on the valve edge that shows the process is working.

    I did a spare head sometime back (must have finished all the jobs around the house) and found a valve ever so slightly bent that wouldn't seal and lapping showed that up as an inconsistent band
    on the sealing edge..
     
  6. bensalf

    bensalf Well-Known Member

    Messages:
    1,267
    Likes Received:
    254
    Trophy Points:
    83
    Location:
    yorkshire ,england
    no ,all valves were put in marked tubs ,and the original lapping showed the dull grey band all way around on the valve and seat.
    i'm beginning to think something got stuck between the valve and seat, whilst dooing the shims, possibly by using the bent wire method ,between the valve and seat.
    because (something i didd'nt mention) , i blew compressed air in the intake , with the offending valve open, and compression went up to 80 psi then , but no further
    thats when i took the head back off.
    so this time when i do the shims, i'll make sure the wire is clean, its a piece of 1mm square flat twin and earth cable ,with both insulating sheaths on.

    re checked no2 intake this morning ,and its still holding the petrol after about 18 hours, so i think i'm good to go.
    still dont know if i ought to use some sealer on the head gasket?
     
  7. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

    Messages:
    19,613
    Likes Received:
    6,703
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    No heat cycles, so I wouldn't think you'd need to.
     
  8. JBurch

    JBurch Active Member

    Messages:
    210
    Likes Received:
    90
    Trophy Points:
    28
    Location:
    Owego, NY
    A quick question......what type of gasket is it? Composition or multi-layer steel shim?
    Generally speaking, you do not put sealers on head gaskets; I acknowledge that there are those people who have put sealers on gaskets for years/ decades and have had no problems so it's a matter of flipping your executive decision maker; I would not coat with sealer, I would however make sure surfaces are clean and oil free.
    Good luck.
     
  9. a100man

    a100man Well-Known Member

    Messages:
    1,597
    Likes Received:
    346
    Trophy Points:
    83
    Location:
    Bedford, UK
    Ah gotcha..

    Reuse - yes I would, mainly because I'm pathologically mean. Sometimes I win (mostly I hope) sometimes I don't. I wouldn't bother with sealant either, perhaps just a hint of a smear of oil on the composite elements
     
    Franz likes this.
  10. bensalf

    bensalf Well-Known Member

    Messages:
    1,267
    Likes Received:
    254
    Trophy Points:
    83
    Location:
    yorkshire ,england
    thanks all,
    got everything back together again ,without using any sealer, cleaned up all faces and gasket, and re-fitted.
    Gasket is the 3 layer, thin metal type ,riveted together .
    compression test now shows 110, 110, 110, 120 psi.
    yeh, it is a little low but i'm just using a replacement gauge from a tyre gauge. so i'm happy with that.
    going to re-check shims tomorrow , as they may have "settled" into the buckets , after spinning over.
    :)
     
    jayrodoh, Franz and k-moe like this.
  11. a100man

    a100man Well-Known Member

    Messages:
    1,597
    Likes Received:
    346
    Trophy Points:
    83
    Location:
    Bedford, UK
    Good Job! BTW does compression go up if you squirt some oil down the bores? If not it's a positive and its more likely your measuring system is reading low.
     
  12. bensalf

    bensalf Well-Known Member

    Messages:
    1,267
    Likes Received:
    254
    Trophy Points:
    83
    Location:
    yorkshire ,england
    not tried putting oil in the bores, bit reluctant to put anything in there after the first episode,
    on the plus side my cafe racer xj600 has loads of power ,with simular compression
     
    a100man and k-moe like this.
  13. jayrodoh

    jayrodoh YimYam Premium Member

    Messages:
    2,522
    Likes Received:
    1,102
    Trophy Points:
    113
    Location:
    Cleveland
    If the gauge is of unknown calibration, then the variance between cylinders is what you should pay attention too. Those numbers look good to me for something that hasn’t been run yet.
     
    k-moe likes this.
  14. bensalf

    bensalf Well-Known Member

    Messages:
    1,267
    Likes Received:
    254
    Trophy Points:
    83
    Location:
    yorkshire ,england
    :):)
     
  15. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

    Messages:
    19,613
    Likes Received:
    6,703
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    +1
    My girl only had 90 psi with 4 psi variance on a known-good gauge when I bought her. After valve adjustment and a good run-in she was back in the middle of the specified range.
     
    Franz likes this.
  16. bensalf

    bensalf Well-Known Member

    Messages:
    1,267
    Likes Received:
    254
    Trophy Points:
    83
    Location:
    yorkshire ,england
    thats good to know
    :):)
     
    k-moe likes this.

Share This Page