leaky head gasket

[mainline]

I found a bit of info when I did a search for the above, but just wanted to check a couple of things.

The YZ's head gasket leaks, so I took the head off and flattened it on a piece of emery paper over a flat surface. Annealed the head gasket, put it all back together and it leaked.

So I took it off again and used some VHT head gasket copper spray/cement on the (once more) annealed gasket and put it all together again and it held. Went up to Cooroy with QVMX and then it started leaking again.

I'm assuming the only option left is to pull the barrel off and resurface the top of that?

If so what is the easiest way of getting the studs out of the top of it, and what should I be using sealant-wise on the base gasket when I stick it all back together again?

Cheers

[oldfart]

Put 2 nuts on the stud and tighten them up against each other and away ya go
 
Some are put on dry others I've used loctite 515 master gasket

[pmc57]

You could also be getting stud pull where one or more of the head stud threads are slowly stripping. You'll know for sure when you remove the studs to lap the top surface.  If you unscrew the studs and find some of the female threads come out with the studs, this will tell the story.
Easist way to get the studs out is tighten two nuts together then un screw it by working the bottom nut.
As for the base gasket, preparation is always the key to good sealing face. Ensure ALL old gasket material is removed, no burs or rough edges are present, if the faces are in good nik all that's needed is a slight smear of grease or vasiline. If the faces are damaged or scoured, some Loctite 518 Master Gasket or similar may be used to ensure a good seal.

[LWC82PE]

I recommend and use Aero/Hylomar blue head gasket cement. Either the spray on type or paste in a tube.

[mainline]

cool, thanks guys, always a wealth of knowledge.

looks like I've got sat mornings project organised

[Lozza]

Will most certainly be the top of the cylinder collapsed a bit near the exhaust port(usually) I use a Wurth 210 silcone , don't even need the gasket, good to go in 15min.

[mainline]

bloody, bloody,  bloody!

it's leaking again. Not as bad as before, when it was leaking all the way round, this time it's only on one side.

I took the cylinder off, spent half an hour doing some figure 8 work on a piece off 180 wet and dry to clean up and flatten the surface, then put it all back together. Seemed all right, then off it goes again.

After re-reading your replies I got to my first enquiry, were you guys saying to use the Aero/Hylomar/wurth/Loctite gasket stuff on the head gasket or the base gasket? I used some of the loctite gear on the base gasket which is fine, no leaks, but re-annealed the head gasket and used the VHT gasket spray on it.

Am i looking at repeating the process? should I have used something else on the head gasket? Should I take the cylinder and head to a machinist to be surfaced? Will timmy be able to get out of the mine shaft before the flood waters rise?

Cheers once more

[holeshot buddy]

hey paul when you anneal the gasket how soft does the copper go

cheers rusty

[Lozza]

Try with some Wurth or copper silcone. Wurth leave for 20 min Copper RTV leave overnight.

[Nathan S]

How have you been annealling the copper?

A new gasket has a raised ring that's pressed in, which would have to help seal. Is a new one out of the question?

[JohnnyO]

There must be another problem causing the head gasket to keep leaking. Possibly a stud is pulling loose in the cylinder or the head is warped and needs machining or the top of the cylinder is not flat.

[pmc57]

Also check to make sure the head is not holding off on something, not allowing it to tighten down properly.
I'm not sure if the Yamaha studs are similar to some Suzuki studs where they have a flange on the stud that locates in a counterbore in the head, but if the head has been faced a few times the counterbores becomes too shallow and stops the head from sitting down or being able to be torqued down on the cylinder proper. Also check the head nuts are not running out of thread on the studs, again stopping proper torqueing down of the head.
I'd also go back to my earlier input and check one or more of the studs aren't pulling out.

[suz125]

banging your head against the wall Lozza?

[mainline]

Why would he be banging his head against the wall

[yamaico]

Hi Mainline,
I don't know what you are using to flatten the gasket surface but rubbing the head in a circular motion on a piece of glass lubricated with valve grinding paste and a splash of WD-40 usually does the job. Takes quite a while, particularly if the head is warped, but it'll get it dead flat with minimal removal of material and it's easy to gauge the progress with the flat areas being a dull grey colour. It would be good to remove the head studs and do the same with the cylinder if you can. If the head studs are tight try spraying a 50/50 mix of ATF and acetone on them and let them sit for a while. If they are still tight put the cylinder in the oven for a half hour or so on a couple of hundred degrees and then try.
Hope this is of some help to you,
Pete.