Author Topic: mk 4 keeps blowing headgaskets  (Read 2182 times)

0 Members and 1 Guest are viewing this topic.

Offline Evanc

  • Member
  • *
  • Join Date: Dec 2013
  • Posts: 18
  • Location: Australia
mk 4 keeps blowing headgaskets
« on: 05 May 2014 at 12:33 »
I rebuilt my engine and overhauled the magneto a month ago. Since reassembling the motor I have blown the right hand headgasket twice in about 150 miles. I'm sure the ignition timing is right. The valves were machined but I did not touch the surfaces of the head or barrel. I have replaced the rings. I had no problems before the rebuild. I will obviously have to check the surfaces of the head/ barrel, but is there anything else I should look out for? thanks a lot, Evan

Offline Vermont-Ian

  • Member
  • *
  • Join Date: May 2008
  • Posts: 15
  • Location: Vermont, USA
Re: mk 4 keeps blowing headgaskets
« Reply #1 on: 05 May 2014 at 14:57 »
G'Day Evan
You probably have now read the previous thread that raises the possibility of gummed up threads in the head nuts and/or studs.
Also, I assume you are using composite head gaskets.  The originals were copper, and you can anneal them and re-use several times.  I still use copper - made my own by cutting from a sheet of copper plate.  Never had a problem with them.  Does anyone else recommend copper?

Ian
Ian Stokes
Richmond, Vermont, USA
1948 Mk III
1936 Citroen 'Traction' 7C

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1654
  • Location: Hampshire, UK
Re: mk 4 keeps blowing headgaskets
« Reply #2 on: 05 May 2014 at 17:16 »
Evan,
         As Ian says, make sure the nuts spin freely onto the studs - and make sure they go up far enough to pinch up on the barrels before becoming thread bound. Also, make sure you grease up the threads - preferably with Copperslip or Molyslip grease - there's no point in applying a lot of torque to the nuts if most of it is consumed dragging a dry nut around the thread!

  Regards,
                Eddie.

Offline tck

  • Senior Member
  • ***
  • Join Date: Jul 2004
  • Posts: 343
    • old racer
Re: mk 4 keeps blowing headgaskets
« Reply #3 on: 05 May 2014 at 19:37 »
Having recently had a batch of footrest plates cut with a water jet  from 8mm alloy using a CAD profile pattern taken from one drawn on paper by tracing round an initial thin metal master I am supprised that the club spares do not get a batch  of copper head gaskets done, the cost was very low with my batch size of 5. So for 50-100  even in copper I guess well within budget

Offline Evanc

  • Member
  • *
  • Join Date: Dec 2013
  • Posts: 18
  • Location: Australia
Re: mk 4 keeps blowing headgaskets
« Reply #4 on: 06 May 2014 at 12:14 »
Thanks for the input guys, the gaskets are composite ones supplied by the club. The studs are fine. When I blew the first gasket I had left the spring washers off the head studs. Naturally when I replaced the gasket I fitted the spring washers. When the first gasket went it cracked in the front top corner. The last gasket blew the whole top section out. I pulled the head off tonight, but there is no obvious problem. I will check the head for straightness tomorrow but it looks fine. The nuts run all the way up the studs no problems. I will keep you posted, Evan

 

motorcycle