|
|
Post by magoconnor on May 30, 2018 16:57:14 GMT -5
Hello.
I have been running with a bigger cylinder head.
I'm currently have a 72cc cylinder installed.
Im thinking about putting the stock size head back on, but I only have a stock head gasket 39mm.
I have to wait a week and a half for a 47mm gasket.
Can I just cut the stock one to fit?
Head gasket = thin aluminium.
|
|
|
|
Post by magoconnor on May 30, 2018 17:10:43 GMT -5
Could I use a high heat resistent paper gaasket? Or does it have to be alu?
If so what thickness should I use? ( paper gasket)
the easiest way would be, if I just could use the stock gasket and open it up a little.
Would this be advisable
|
|
|
|
Post by magoconnor on May 30, 2018 17:13:17 GMT -5
Or could I just re-use the gasket I have installed now ? it has only been on it for about 100 km.
|
|
|
|
Post by KSR Moto on May 30, 2018 17:13:51 GMT -5
Could I use a high heat resistent paper gaasket? Or does it have to be alu? If so what thickness should I use? ( paper gasket) the easiest way would be, if I just could use the stock gasket and open it up a little. Would this be advisable I think that there is some type of copper spray which you can use but i have never seen it before, at least not where I live Paper gasket is too weak! |
|
|
|
Post by KSR Moto on May 30, 2018 17:15:24 GMT -5
Or could I just re-use the gasket I have installed now ? it has only been on it for about 100 km. I dont see why not if you have a gasket that came with 47mm bore use that with old head(39mm head) |
|
|
|
Post by GrumpyUnk on May 31, 2018 10:37:15 GMT -5
I think the sheet metal head gaskets have a wrinkle/stamping that raises a ridge. The ridge gets compressed when the gasket is installed and torqued. If you feel you can place the gasket in the exact same position as it was originally installed, it might work fine. Or not. I think I would have another gasket on order if I re-used a head gasket. That being said, I don't think it would hurt anything to try it. Worst case, it leaks, and you lose compression. If bad enough, you won't be able to start the engine. If it does leak, you may erode some of the head/cylinder surface if it is leaking and you continue to use it.
The last one I took apart had leakage, as shown in the posted images. Gas 'shadow' radiated outwards from the cylinder, leaving black marks / deposits in a 'fan' pattern. Pretty sure the gasket was blown, and there was erosion on the head. How long? Dunno. But it was unstartable when I obtained it.
tom
If you are going to use a 39mm gasket on a 44/47mm bore, place the gasket on the head, and see where it will seal, uncut. Do the same on the cyllinder. Realize mentally that those two 'circles' will be the sealing point. If they are outside the cylinder diameter, they should work. If inside the cylinder walls, they won't.
tom
|
|
|
|
Post by magoconnor on May 31, 2018 18:30:58 GMT -5
Have you tried re-using a head gasket?
|
|
|
|
Post by GrumpyUnk on Jun 4, 2018 9:20:52 GMT -5
mag:Have you tried re-using a head gasket?
Not on one of these, never on a car/truck engine, but several on lawn mower engines. A stamped steel gasket becomes flattened when torqued to spec. I don't know if it will seal if re-used.
I suspect it may be more prone to leaking if re-used. In a pinch, I would try to re-use one, but would also try to get it aligned to the exact same spot it previously held. When re-using flathead gaskets, I moved the head around until I could feel the indentations 'fit' back to where they had been prior to disassembly. So far, so good, and it's been several years.
If I was going to re-use a head gasket, it would make sense to me to add some 'filler' that would allow better conformance between the two surfaces. I think I would really consider using some spray paint on both sides of the head. There is/was a compound called "Copper Coat" (kopper koat) that was smeared on gaskets to make them more likely to seal. It came in a can with a 'dauber' dipped in the product. You stirred it with the dauber, then got a glop and spread it on the gasket surfaces. I think it had finely ground copper mixed with whatever formed the 'goo' part. I assume(yeah.) that the copper could 'fill in' some of the defects in the cylinder head and block sealing surfaces. I think aluminum paint may have similar properties, but it may be something else used to provide the color other than powdered aluminum. On that note, I think a head gasket could be re-used if it was coated, lightly, and after installation, time for the paint to solidify was allowed before use. IOW, let it dry overnight before trying to start the engine. It might do the job adequately.
tom
|
|
|
|
Post by benji on Jun 4, 2018 10:01:50 GMT -5
Copper coat still exists as a spray paint like product. I use it alot, especially on heads and cylinders.
|
|
