Modern Vespa

I understand it's all about obstruction. The spinning crank and turbulent mixture get in the way. If the charge enters via reed between the piston and crank turbulence, more gets in. Just up down turbulence and less tornado style turbulence. At higher rpm this makes all the difference.

Cheers Jack. That does sound logical. I wonder why more cylinders are not made like this? I guess it's more expensive.

Because you need someway to lubricate the bearings 😀

What constitutes an error in cutting it?

Cheerws

I wonder this too. Pinasco made a direct induction 225 cylinder but was the usual reliability.
For small frames just about all the high power kits have direct induction and that's because getting high power and ride ability without direct induction is very difficult. Even dirt bikes with fuel injection have direct induction. Easiest way to get the job done.

The VR and BFA cases for the LF are dangerous enough and the inlet is further forward. I think if there were SF style kits for the LF they would be selling even more rebuild spares.

I always understood that with direct intake you're limited by the size of the cylinder, whereas rotary allows induction into the entire crankcase. Like they say, there's no replacement for displacement.

Yeah when I started to think about that is when I realised the gas flow is not directly into the cylinder. It goes into the cylinder, pushed into the crankcase and back up into the cylinder. I imagine that for every direct intake cylinder they would have to supply a manifold (or is that singlefold?) as there is no factory option to fall back on. Then usually reeds, carb connection etc. Does make it more expensive. That makes sense. The easy intake into the cylinder becomes a much more complicated proposition when it comes to getting a big reed into a (relatively) small cylinder. The M1L-60 below for example! If you put too much pressure on the cutting tool from inside the port as it gets to the nicasil, there is a small danger of delaminating at the edge. Also of accidentally scarring the surface when you're not controlling the tool closely enough. If you give the ports a bit of a chamfer I've found it's not a big problem. If you do leave a sharp edge the rings can catch it, especially when it's very hot at the top of the exhaust port.

So, perhaps remove the lining first... 🤔

Let's say I am porting from the inside of the cylinder, high speed on the tool with light pressure on the coating wins the race?

Tool of choice for "editing" nicasil, a carbide burr or belt grinder?

As said de laminating is the biggest issue but chipping comes a close second.
Taking your time helps but taking too long gives more time to make mistakes.
Need a full suite of porting tools. Nothing too new or corse helps.

Re lining a cylinder in the UK is over £250 now. Meaning any serious chip means it's junk.

I can point you towards a place.in the UK that will replace with a chrome-moly lining Jack221

I've found that it's harder to mess it up in reality than you are probably thinking, but I understand your concerns.

Both of those tools will work. The little sanding drums or tapers are very useful as well. If at all possible, see if you can find someone with an old cylinder you can practice on. A motorcycle shop that does dirt bikes perhaps.
But if you start by matching the case transfers to the cylinder, you'll already have some good practice in before moving on to the nicasil.

If you're working on an exhaust port you are more or less forced to work through the port from outside, as you really need a right-angle dremel/grinder to work from inside. If you were 'just' doing what's shown in the photos, there's good access and you shouldn't need anything highly specialised to do it I think.

Not sure what you mean by removing the lining?

I've ported cylinders in my moped racing days, but none were aluminium, so there was no nicasil to be worried about. What I meant by removing the lining first is, if there's a risk of delaminating when porting from the outside in, then there would be no risk of there's no lining at the location where material is being cut off.

Purely hypothetically... let's say I'm adding a direct transfer port to the cylinder. Like the one on a Quattrini m244. Not touching anything else, just that.

I'd start from the inside of the cylinder, using a small 10mm belt sander. The idea is to sand down the spot where the new port will go, effectively removing the nicasil lining in that area. Ideally about 1mm wider than the port itself, to give me a some breathing space, which will later be chamfered.

Once that's done, I'd switch to the outside of the cylinder and use a milling cutter to hog the aluminium out from the outside, just enough to open up a proper window. Hypothetically.

I feel like you don't need to do that, but this guy reckons it's a good idea.

I used to watch him in the early days but it dragged a bit too much for me.

Same here, I gave up a while ago. Hopefully he didn't have too much whiskey prior to explaining this. 😁

Certain view in this topic: Crankcase volume (Post 2746333)
had me wondering.

In the photo are visible the "direct" a.k.a. reed valve port (in blue) and regular a.k.a. rotary valve port (in green). Are they really that close, or am I looking at the wrong thing? Perhaps I'm thinking about this thing all wrong... 🤔

Here's the Q 172 on an LML case -

Thanks for that. Ok, that looks more like I envisioned it. My LML is older, so it does not have a factory reed valve, so in my mind, it appears even slightly further apart.

Ok, not insane then. 🥳