72cc cylinder kit please help

[madassbore]

hi
i have recently purchased a 72cc cylinder kit for my sachs madass and fitted it to my madass, but there is a problem the piston doesnt seem to be right for my cylinder hit because i took apart the cylinder and i could see dents been made in the actual piston from the tapets(i think there called that). Could someone please help me if i need a new cylinder head or piston.
Thanks any help would be much appreciated.

[veeeffarr]

Not a mech by any sense of the word but surely it'd be striking the valves?

[madassbore]

what do u mean ?

[veeeffarr]

https://www.uefap.com/images/engine.gif

I thought the 'tappets' were like rockers above the valve, so presumably the piston would be hitting the valves.

[veeeffarr]

Sorry I'm only really trying to help because no one else is on here...

Is the piston longer than the old one? that's the only reason I can think of it striking the valves, although I'm pretty sure there's other reasons.

I thought usually you bored out the cylinder (made it wider) rather than fitting a longer piston.

Meh, dunno.

[madassbore]

yeah thats what i meant sorry i didnt no the names , so do you know how to stop this would i need a new piston? or cylinder head ?

[veeeffarr]

[madassbore]

its not new engine time cas i changed it back to 50cc cylinder and piston and it worked again

[Misc]

I don't know much about bikes but when i got a 70cc kit for my scooter, i also needed a bigger piston.

[cagiva gezzer]

https://www.1977mopeds.com/images/models/sachs/madass/1.jpg

It's a four stroke.

Did you set up the valve timing right? If its based on a honda C50/90 engine you should have cam chain in there.

You need to set the timing marks on the top and bottom end up together, otherwise the valves will contact the head.

If they've already done this i'd pull them out and make sure they're not bent.
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"because one stroke isnt enough and four strokes waste two"

[edd]

Toby R your pic is of a pushrod engine, these have the camshaft at the bottom end and pusrods to operate the valves. Nearly all bike engines are overhead cam, which means that the camshafts are in the head.

Madassbore id suspect you have probably bent your valves if you havent timed it up properly after installing the big bore kit. This is not good. You will need to replace these valves with new ones, and time your engine up properly.
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Bluespark Automotive - Diesel Tuning for Performance and Economy

[veeeffarr]

Ah well I tried