I'm not talking about beer cans. I've been reading about using either copper wire, gas-filled metal O-rings, V-section stainless steel rings, or actual piston rings in place of stock head gaskets for a better seal, provided that the cylinder's upper face has been machined with a narrow groove to accommodate. Has anyone used this kind of method?
I read this in the 2-stroke tuner's handbook.
hi temp rubber o-rings work too. i have the doppler high comp head and it uses a rubber o ring. i've already pulled the head once and it hasn't leaked a bit, it's pretty rad.
i machined a puch cylinder to accept a piece of copper wire soldered at the ends to make an 'o-ring.' worked fairly well, but i did a crap job of machining it and eventually the ring shifted and hit the piston. plus i ported the cylinder way too agressively and it barely ran on the low end... long story, failed experiment, but the gasket idea is sound. I'd say its still easier to go with copper sheet.
go to a hobby shop and get some copper sheet they have for hobbys. there is a rack at one in town near us that sells KS Metal brand of hobby metal they have sheets of copper 0,016 0.020 0.025 thick and you can get a couple of gaskets from each sheet. after you cut the gasket shape then anneal it with a torch and quench it in a bucket of water. anneal means basically softening up the surface so it can crush back to the original thickness and make the seal on the head.
i dont think it is worth machining and fabricating copper orings or v rings or gas filled rings for mopeds. a rubber oring would work good if you are racing n tearing down often.
it's one of those more exotic things to do even in racing. It's some good insurance if you are going super high compression- like up to 15:1. Machine the head and the cylinder. It won't have a chance to move.
im pretty sure high comp puch heads come with a rubber o ring and yeah i read this to in the book ure talking about
what would be really effective is a head and cylinder design like a garelli NOI. Not only does it center the head on the jug, it also provides for a smaller surface area of contact. Smaller surface area=more pressure= less leakage.
most effective is single casting where they machine the bore into a single casting so there is no head to bolt on. no joint no leak. most other small utility engines are made this way like chainsaws n blowers n larger trimmers.
With copper, don't you have to routinely anneal?
I bought a new 50cc puch high comp head and it didn't come with anything else but stickers (no rubber O-ring).
Rubber o-rings are exotic, but well worth the effort if you're running crazy high compression or revs.
There are no heads I know of for Puch that come standard with an o-ring.
Basicly, what you want is a head with a seperate chamber. Meaning that you can replace the combustion chamber as you like. These are not available ready made, and have to be machined.
The + about this, is that you can have a cylinder with a deck of, say, 2mm and you can make a drop in head with a rubber o-ring on the side. A drop in head gives you the ability to tinker with compression ratio and squish, while keeping the rest of the engine the same. Drop it down, get higher compression and lower squish. Take it up, get higher squish and lower compression. And you can alter the shape of the chamber pretty easily, all you have to do is have a new insert machined, instead of having a whole head modified again.
The downside is that these are a lot of extra variables to work with, and that those kinds of heads don't come cheap.
do they do that for aircooled too, the only heads i've seen like that are all watercooled for scooters. i've even seen some pocketbike heads that i've contemplated adapting, but it looks like a lot of work for nothing. i dont have the machining capabilities to do crazy curves and modify squish bands and such yet, so the whole thing is a moot point for me.
copper head gasket you only have to reanneal if you lift the head. just heat soak it with a torch n quench it into a bucket of water again then you are off to the races. you can do the same wif aluminum if you do the beer can gasket.
dont bother doing it to a steel shim gasket tho because you need way too much heat and there is too much risk of distorting it
I have only seen o ring type head gaskets on water cooled cylinders.
My aprilia runs o ring type gaskets on it's cylinderhead. I assume that this was don't to assure that the seal was perfect as there is water on the other side.
I don't see any negatives to machining a grove (or using the one already present on a puch high comp head. To accept a o-ring.
Another option is to just use a copper gasket vs an aluminum one. Since it is softer it will conform to the defects in the head much better than the aluminum ones that come with kits. You can get sheets in different thicknesses at the auto parts store.
Paz, are you talking about a certain stock puch high comp head? The new high comp head that I bought from treats doesn't have such a groove.
It's looking like copper is a popular choice so I'm definitely going to try that out, but I'm still left curious about the implementation of an O-ring.
The older aftermarket high comp heads looked just like the stock high comp heads (they have 2 rings with a grove in the center.
Sorry to state the obvious and slob method but some readers may need to be reminded that a very thin film of high temp RTV is very effective on heads that are not seriously warped.
you should NEVER use RTV anywhere near gas.
air cooled engines run hotter than water cooled, which might be a good reason for not using a rubber o-ring. teflon will take like 400 plus, but most rubbers used for o-rings only can take 350 at the most before they go to hell.
Why not?
dopper 50cc MBK AV10 moby high comp heads come with a groove and rubber o ring, it works phenominaly
How much should the ring be sticking out, relative to the groove, to ensure a seal? Half way? I would think that having a ring go all the way inside of a groove wouldn't do anything.
from the looks of it 1/2 to 1/3 is sticking out with rubber ring heads.
it depends on the material and size of the ring, if you go through the effort to do this, you should probably look up the data for the 0-ring and find out.
I would talk to a speed shop that does this to engines. Places that build competition Four wheeler, snowmobile, dirt bike, etc would have advice or just do it for you.
RTV all the way!
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