Drilling cylinder intake (Motobecane)

I just got this Mobylette in - the bike is in good shape, but the inside of the engine is solid solid rust. Luckily I had an extra engine laying around, but it's a 20mph one. The cylinder/piston off of the seized engine is in good condition, so I tried putting that on the 20mph engine with little luck.

It seems there's a slight cutaway on the 20mph cylinder for it to fit in the engine that the 30mph one doesn't have.

I figure instead of shaving that off - it would be easier to just open the intake port to the size of the 30 one. I've never done this before and would like a little help. I have a dremel tool, but which tool should I actually use for doing that? I was going to make some type of guide and tape it on there for while I drill - but any tips would be highly appreciated.

If anybody reading this has an extra 30mph cylinder/piston that they'd like to sell - I'd love to buy it too!

Thanks so much,

Beamer

Re: Drilling cylinder intake (Motobecane)

I modified a 25mph cylinder.

I had a 30mph, and a 25mph cylinder for a 50v, so I was able to compare the 2 before going at it with a dremel and grinding bit.

I have this engine as a back up now, so I have not tried it yet.

I would just go for it, the worst thing that happens is you mess up a 20mph cylinder - no big loss.

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