Correct technique for applying RTV sealant

Discussion in 'Lounge & Gossip' started by SpeedyGee, Tuesday 31st Mar, 2015.

  1. SpeedyGee Administrator Staff Team

    England Speedy Birmingham
    My technique for applying RTV (liquid gasket) between two surfaces (say gearbox casings or oil sump or timing cover) is to run a bead all the way round about 4-5mm high and then flatten it down so it's uniform and about 1-2mm high. I know some people wouldn't flatten the bead but the only time I didn't do that recently actually led to a leak.

    The other thing I've realised that what I don't do is leave time between putting the two surfaces together and torquing up the bolts. I should wait for sometime for the sealant to start to cure before torquing. But again I've never had an issue with anything leaking.

    So I'm interested in hearing how other people apply liquid sealant, to see if I can improve upon the technique.

    @Beefy would be good to hear how you do apply it also.
  2. RogerH69 Premium Member Club Supporter

    South Africa Roger Oxford, UK
    Please excuse the noob question, but if it's liquid sealant and you flatten it, won't some of it go inside whatever it is you are sealing and possibly cause issues ?
  3. SpeedyGee Administrator Staff Team

    England Speedy Birmingham
    The trick is to just put enough so the when it flattens its just about cover the surface that it needs to.

    Some will inevitably go inside but when it's dry it will not detach away.

    The trick is to use the right type of RTV sealant for the application.

    Liquid sealant is used extensively on the engine and gearbox.
    RogerH69 likes this.
  4. Ichiban Founder Staff Team

    England CJ Leeds
    A small bead of 2mm following the counters of the casting and getting close to the thread pitch and when both casings are matched it's squishes the bead equally for a good seal.However prep is the key both matching surfaces have to be ultra clean and free for oil,old gaskets for this work.

    I wipe down with IPA prior to sealant application is a must.
  5. Nels Moderator Staff Team

    Dad used to put a blob of liquid gasket on an old spanner. He could then tell when it had gone off enough and therefore when to tighten everything up. It didn't take long in the summer, but a fair bit longer in the winter.
    SpeedyGee likes this.
  6. Bones126 Club Veteran ★ ★ ★ ★ ★

    England Dave Birmingham
    I clean both surfaces free of old gasket etc, I then clean both surfaces with brake part cleaner on a clean rag. Then apply a thin, approx 2-3 mm bead all the way around the contour, assemble the parts together and then torque in a criss cross pattern.
    Never had any issues of leakage on the motor bike engine cases doing it this way.
    Nels and Ichiban like this.
  7. Zebster Guest

    The Honda type suggested for the sump and chain cover on the I-CTDI should be done up within 4 minutes of application, according to the Honda e-manual. So really no time for coating both surfaces or fiddling about!

    However, I used Loctite 5920 and only applied it to the sump/chain cover mating surface, not the engine mating surface, as a 2-3mm wiggly bead. There have been no leaks in the 6 months since.

    Yes, it does squeeze inside the engine very slightly, but this over-spill is firmly attached and doesn't look like it might come off (in any case, it would fall into the sump and be caught in the gauze of the oil pick-up pipe).
  8. Beefy Club Veteran ★ ★ ★ ★ ★

    United Kingdom Stoke
    its not exact science. good prep is key so there is two clean mating surfaces, not essential but a light rubbing over with abrasive paper (nothing aggressive just enough to key the surfaces) final spray of brake cleaner and allow to flash dry. apply a small bead approx. 2mm any more and its just wasted and looks messy. just ensure the bead covers all the mating surface inc around bolt threads. I've never waited for sealant to cure off before building up, the time it takes to apply the sealant and place item in place and tight is plenty enough. just ensure the engine is not run for a few hours in order for the sealer to cure.
  9. SpeedyGee Administrator Staff Team

    England Speedy Birmingham
    Thanks for all the reply guys, all points duly noted.
  10. PeteMM Premium Member Club Supporter

    Northern Ireland Pete Belfast, UK
    Method doesn't make much difference. Leaks are down to prep and prep alone.

    I didnt thoroughly clean the rocker cover gasket area last time it was off before putting a bead on and now the Accord leaves puddles everywhere. Will rectify this soon though.

    The K20/24 have a tendency to leak from the rocker covers either out the back where it then dribbles into a pocket in the casting or between the inner of the head and the cam gears. Both areas need to be thoroughly cleaned and a bead of rtv thrown round it every time the cover is off.