Cylinder head designs for the 80cc / 66cc 2-stroke Chinese bicycle engine

[Deleted member 12676]

Furry, with sandpaper and glass you can plane down a stock head to give good compression, and if you aren't overstressing the engine like Fabian does then its cooling ability will be good enough.

 

[FurryOnTheInside]

Thanks jaguar; but with a slant head HT kit and the unavailability of replacement straight heads I'd be looking to reduce compression, AFAIK. From what I've read here on MBc it appears I can simply run thicker/two head gaskets; but I can see the slant head's combustion chamber looks totally different to all the others. I am just wondering if there is scope to mess around with that and make it a bit better.
I'd really like to build for more extreme use than it will ever see, and bolt-on fins do sound good and pretty impossible to damage the engine by trying it out. I wish I could remember who to give credit to for that idea.

 

[Deleted member 12676]

I notice you don't state what the psi is so you are totally running on assumptions.
You know what happens when you ass-u-me.
Step one: get a compression tester
Step two: go from there

 

[FurryOnTheInside]

Yes, based on the video that Fabian posted where he said that the HT slant head is a high compression head compared to the other HT heads and most of the after-market billet heads that he has tried. I will buy a compression tester of course, and use it before doing anything to modify the head.. no point in omitting that step when compression testers are only £15 on Amazon.

I was only asking about whether the head will break if it is reshaped a bit, and whether some reshaping would help with such a weird shaped combustion chamber.

 

[Deleted member 12676]

when you dremel away at the dome, do not dremel the top but rather the sides, more so at the lower section.
there is plenty of aluminum there so you don't have to worry about weakening it.
If you don't dremel to reduce too-high compression you are guaranteed a weakened/warped head because of the extra high temperature which will be the result.

 

[Fabian]

Furry, with sandpaper and glass you can plane down a stock head

You might find that a lot of sandpaper is needed.

if you aren't over stressing the engine like Fabian does

It's not just the engine that takes a good beating, but the bakes as well, not to mention the drive train.
If only SickBikeParts would make a conversion kit to mount a 10 inch, twin disk front bake system on front suspension forks with I.S. mounts.

 

[Fabian]

you are guaranteed a weakened/warped head because of the extra high temperature which will be the result.

or you just get a well designed billet head that's designed to work properly and get the job done!

 

[Deleted member 22467]

I have a cast angled plug head with the combustion area of the standard low compression straight plug heads on my bike. Angled plug heads aren't high compression by nature, just the one you had was high compression by design.

 

[Fabian]

Thanks for making me aware of the low compression angled spark plug cylinder head, because every angled spark plug cylinder head that i've seen are of the shallow dish (high compression) design.

 

[FurryOnTheInside]

I have a cast angled plug head with the combustion area of the standard low compression straight plug heads on my bike. Angled plug heads aren't high compression by nature, just the one you had was high compression by design.

PHEW! Thanks for that info, Butre. I hope this is the norm and the slant heads that Fabian has seen are the exception. I really didn't like the idea of having to mess around with that!