2019 Nationals in Bathurst are 8-10 November, just over three months away! Make sure to register at ozvolvo.org/nationals!

What would cause welch plugs to blow out continually on a rebuilt engine?

ab1Alex (@ab1) Melbourne
edited June 2018 in General
im battling an infuriating problem at the moment with a rebuilt b30 that will not stop blowing new welch plugs.

I really have no idea what the issue is that could be causing that much pressure to build up that would pop them out
«1

Comments

  • Combustion getting into the cooling system.
  • Installed imprpperly is a common issue as well
  • Blown 5 out all on the same side under the exhaust manifold. If it was combustion gases wouldn't a hose blow first?
  • maybe get some english plugs?

    I will see myself out.
    tbrojamesincgoodenoughSpacbgpzfm142ab1
  • Blown 5 out all on the same side under the exhaust manifold. If it was combustion gases wouldn't a hose blow first?

    Would need to have the block fluxed and look with a bore scope to see if there was a crack
    But yes... easily blow out plugs long before hoses with a cracked block

    Otherwise could be that they were installed wrong or the wrong plug used or defective batch of plugs or any of a dozen other things
    tbrobgpzfm142
  • Could also be the type of sealant if any is used, I've always used paint, throw the plugs in the freezer for 1/2 hr, use circlip pliers to grip the inside of the plug so you don't warm them up, apply daggy old paint or whatever you use, run a ring around the sealing area, allow it to skin up, for a couple of mins and then tap them in.
    Also, please tell me your using mild steel units or at worse brass plugs and not the " the best stainless plugs"
  • maybe get some english plugs?

    I will see myself out.

    I must be tired, I had to read that 3 times before a big bell went ding-a-ling................very good bigal
  • Vee_QueVee_Que (@Vee_Que) South Eastern suburbs Melbourne.
    edited September 2017
    I think maybe the incorrect plugs may be used. They are 35mm not imperial. They need to be tight and to flare them out. They need to be a flat/dome plug not a dish plug. I have spares the correct size.

    That is one theory. Otherwise they are not being installed correctly.
  • Mistake we made on dome type was not to hit them hard enough to take the dome to flat. Learned this the hard way with 3 to get it right. 1 causing an engine loss due to overheating.

    We also used a two pack epoxy on advice from a Jaguar engine rebuilder as that's what they use.
    Vee_Que
  • can't say for sure as Im not the one who's installing but if it happens again these points will be raised. unfortunately its ruled my 164 out of benella :(
  • can't say for sure as Im not the one who's installing but if it happens again these points will be raised. unfortunately its ruled my 164 out of benella :(

    Sorry to hear that. (Hope you'll be there to collect your sway bars though).

    Use of genuine welsh plugs from Mother Volvo herself is highly recommended.

    Also
    http://www.turbobricks.com/forums/showpost.php?p=5275730&postcount=5

    Plus - US experience has shown the blocks squirm at high RPM, which will pop the plugs. The big six has a lower rev limit than the four potters. Plug retainers are recommended, e.g. the screw and washer method by John V., as shown by an example of some other gadget here.

    2009051711362049982DSC00779.JPG
    See the washers overhanging the freeze plugs?

    Probably easier to drill and tap some little holes than all the other genius stuff folks here are suggesting.
    The a little allen screw and the right size washer and I'll betcha a nickle the freeze plugs won't walk out...
  • Vee_QueVee_Que (@Vee_Que) South Eastern suburbs Melbourne.
    That's different on a b230 being a cup not a dish plug to the b20/30 block. The motor is being bedded in and not revved out to my understanding too. The retainers are too extreme for this purpose.
  • ab1Alex (@ab1) Melbourne
    edited September 2017
    Sorry to hear that. (Hope you'll be there to collect your sway bars though).

    I should be there otherwise ill have someone to collect them and the radiator :)



    I would have to agree with veeque it is being treated delicately until it has reached the end of break in procedure

    is it possible that corrosion could have expanded the slots where the plugs sit?
  • geniune welch plugs were used as replacements. faith in them has been eroded after blowing one 5 minutes after driving. wouldve been revved out to maybe 3.5k-4 so by no means full throttle. engine has 10,000km

    going to put these retaining plates in. anyone got any suggestions for a source of these. otherwise these will be tacked in place.
  • 1971_144GL1971_144GL (@1971_144GL) Launceston, Tasmania
    https://www.itwpf.com.au/devcon/wet-surface-repair-putty-uw/

    The engine builder I used always put a smear of this on Volvo Welch plugs block rim when installing to stop this problem. I think that the blocks corrode a bit in this location. He said he never had a customer come back in 20 years after he started this. On performance engines he also used a high quality clear epoxy arround the rim after installation, but not five minutes aryldite. My cars and several other 164s he built, including Vince harmers race engines, have been used in anger for many years without leaking. Might be worth a try. Not that expensive, try blackwood's or another engineering company. It is very different stuff to supercheap epoxy.
  • 242GT242GT (@242GT) Wollongong NSW
    Many years ago when I was an apprentice we used Stag Jointing paste, a thick maroon substance to seal Welch plugs and hit them in the middle with a ball pain hammer to make to expand and stay in position.
    Ex850R
  • 242GT242GT (@242GT) Wollongong NSW
    P3rXwpWh.jpg
  • We had same issue and used either stag or epoxy. Old Jag owners swear by epoxy.

    We found the biggest issue was being too soft on them. Need to get that sweet spot between concave and convex and we found we were not getting “flat” enough for want of a better description.

    Cost us an engine
  • Stag has been used on every part/ seal on this engine by the builder .

    Might try jbweld
  • I was also taught to use stag in my apprenticeship days. The product Stag has been around for longer than I can remember (and these days it is not that long) and to my knowledge the the formula has not changed so it must work. It is primarily used for water and steam jointing by plumbers and boiler attendants and does not cost a fortune.
Sign In or Register to comment.