OzVMX Forum
Clubroom => Tech Talk => Topic started by: mainline on September 10, 2009, 06:40:31 pm
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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
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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
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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.
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I recommend and use Aero/Hylomar blue head gasket cement. Either the spray on type or paste in a tube.
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cool, thanks guys, always a wealth of knowledge.
looks like I've got sat mornings project organised ;D
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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.
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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
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hey paul when you anneal the gasket how soft does the copper go
cheers rusty ;D
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Try with some Wurth or copper silcone. Wurth leave for 20 min Copper RTV leave overnight.
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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?
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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.
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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.
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banging your head against the wall Lozza?
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Why would he be banging his head against the wall
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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.
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If after locking the two nuts together to the point of stripping the threads, and the stud will still not budge, try striking the top of the stud a nice blow with a hammer. This usually shocks the stud sufficiently to make it easy to wind out. the YZ's and IT's are notorious for stuffing the threads in the barrel, heli- coils are the way to go for a nice repair.
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Sometimes you need to tighten the stud slightly and then loosen the stud in aluminium as the thread grabs on aluminium.
Aluminium heads and barrels go soft over time and with heat.Yours maybe soft and stretching.
Also if your head has a recess where the gasket sits in,make sure its crushing on the gasket and not head to barrel.
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Because it feels fantastic when you stop mainline. Try it, it's S.O.P in all those expensive health retreats ;D
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thanks to all for the info and tips. I had actually got the cylinder off early in the piece and re-surfaced the top, after doing the same to the head only at first. The head and cylinder surfaces now seem to be spot on when I sit a straight edge on them.
As far as the annealing is concerned, I held the gasket over the gas stovetop burner till it was dull red and then quenched it in the kitchen sink. All done rather quickly while the better half was in the shower of course.
After reading Nathan's comment about the raised ridge in the gasket, I had a better look at it last night, and it has seen better days so a new one has been ordered. Hopefully it'll all hold together this time.
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As far as the annealing is concerned, I held the gasket over the gas stovetop burner till it was dull red and then quenched it in the kitchen sink. All done rather quickly while the better half was in the shower of course.
I'm no metalugist, but I'm pretty sure when you anneal metal to make it more ductile, the metal needs to cool of slowly. Quenching it makes the metal hard again.
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camP is right you let it cool down slowly
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Quenching doesn't adversley affect the annealing of copper. Cooling slowly causes oxidisation, but either way works. Quenching in oil works well.
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How are you tensioning the head down? I had the same prolem with an elsinore, found out it had nothing to do with the gasket or Head/Cylinder surfaces.
It was a simple case of using a tension wrench and the correct tightening pattern. Problem solved.
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The annealing thing has been discussed on here before, with a bit of to and fro between whether to quench or not, and apparently copper is different to other metals and the water quenching method is the way to go to anneal it.
http://ozvmx.com/community/index.php?topic=4358.0
From looking at the condition of the gasket, I'm thinking it's definately part of the problem. It's been used too many times on uneven/pitted surfaces by the looks of it. I'll see how I go with the new one.
Cheers again
suz125, any tech tips you'd like to add??