This topic contains 33 reacties, has 6 deelnemers, and was last updated by swebass 5 years, 9 months geleden.
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Ritze, I looked in your post as you adviced. Thanks for the inspiration. I think I am sort of understanding what you did with the cylinder. You are probably right about practicing on a separate cylinder then the one I ride on currently.
Is 37€ a good deal for a complete cylinder kit, second hand in a top notch condition? In that case I might have a deal!
Cheers!
€37 for just a standard Piaggio cylinder sounds a bit pricey, but hey this can be because we talk about different countries. Over here in Holland there are a shitload of these spare cylinders to be found.
Anyway I’ve read the last posts about cylinder tuning. Most of the Piaggio cylinders have quit a strange port layout and blocking the exhaustport and transfers when piston is at bottom down center. So easier and more fulfilling is to raise your cylinder and mill the same or more from the top. I’ve build an engine with the purpose of only a cylinder to be tuned. The rest of the engine is original.
Setup is Piaggio kickcarters with 12/12 carburettor.
Since i only want to change the cylinder i raised it by an 1,5mm aluminum gasket and milled down the cylindertop by 2,5mm. Also grind the cylinderhead so there is more compression and less deck clearance.Furthermore i made 2 supporting transfers and 3 boosters in the cylinder all there to keep in mind the scavenging of the mixture. The exhaustport is only changed a bit so the whole portmap is symmetrical. In the proces it might be raised only by 1mm and the channel is flowed. Remember we raised the cylinder already by 1,5mm so exhaustduration and inletduration are already greater.
Since i don’t want to port the carters there are no changes made to the transfers and the 3 boosters are worked all over the cylinder wall. Results are quit good with a speed of around 55kmh with a Proma Citypower, but this setup really comes to live when a good expansion pipe is mounted. Easy 60+kmh.
Martino, My guess is that Sweden in general is a bit more pricey. I have been in Holland at least 15 times, and prices of every day items like food is at least 30-40% cheaper than in Sweden. Anyhow.
Thank you for your detailt post! It gives me the urge to start experimenting. I have some questions if you feel like you want to help me out.
- What do you mean by raising the cylinder? Is that done with aluminum base gaskets stacked on top of each other?
- If the pistion is covering some of the exit in it’s bottom position, wouldn’t it be possible to just remove the covering bit from the piston?
- Have you done any modification to the piston at all?
- Did you do any modification to the crankshaft, to modify the inlet timings?
- What do you mean by raising the exhaust port by 1 mm and flowing it?
- Last but not least, do you think it would have been any difference in performance if you had done the supporting channels from the bost ports and transfer ports in the carter instead if the cylinder?
Thanks in advance!
Wow Martino, nice cilinder. Damn good job on that thing 🙂
Looks insane goodAt topic starter, you wil have to read alot about 2stroke tuning, it’s very hard and it needs a good understanding about flow timings and compression. You gotta check out Graham Bell 2 stroke tuning 🙂
De budget beun tjoener: geen geld is te duur of het werkt nog niet
Link naar Mijn collectie / Projecten.This is a pdf off Graham bell 2 stroke tuning.
http://iheartstella.com/resources/manuals/tuning/Graham-Bell-Two-Stroke-Performance-Tuning.pdfRitze, Thanks for your input. You are right in that sense, one would need a lot of knowledge to get things right. I have allready planned to read a book or two on two stroke tuning, and Graham Bell is definitly on my to-read-list.
Zevenenergie, thanks a lot for the link! Now I do not need to buy it from Amazon.
Thnx zeven energie 🙂 couldn’t find it on my phone no more 🙂 @swebass have fun experimenting on the cilinders 🙂
De budget beun tjoener: geen geld is te duur of het werkt nog niet
Link naar Mijn collectie / Projecten.If you visit our country for a 16th time you can always come by and get some cheap original cylinders.
– For raising the cylinder i used indeed a thicker aluminum base gasket.
If you look closely you can see it on the first photo of this engine.– Yes you can also work your pistoncrown, but this will give you a bigger deckclearance and lower compression. Also not all pistons have this option, think about the piston with the L-shaped ring on top.
-No did not made any modification on the piston other then i replaced it for another brand(Meteor38,6) These are lighter as an oldtimer piston and have the L-shaped pistonring.
-As described, I’ve build this engine for the purpose of only a tuned cylinder which is plug and play. So no modifications at the crankshaft whatsoever.
– When working on the exhaustport to get a better shape logical there is material to be removed. In my case the port itself is raised or 1mm bigger towards the cylindertop. Also by flowing the channel everything is more smooth and in total a bit wider in diameter.
– Theoretically you can go a lot bigger when you use the carters for porting, but since the idea was to make a plug and play cylinder for original cases, I did not go there. I also think the difference in performance would be little to nothing.
Martino, thank you for writing such infornative answers. I wish I had a mill to use to mill down the cylinder head and the cylinder top. But sadly I don’t.
- I know there are ways to flatten the cylinder top using sandpaper on a flat surface, but I do not know if that is adviced at all?
- For doing the ports, did you use a drill, a dremel and files? Or did you have any other valuable tools that you could recomend?
I will hopefully have a cylinder to work with on monday.
Thanks in advance!
Actually i did the removal of material from the top of the cylinder with just a flat glass surface and some sanding paper. Although this can take for ages. This method really takes a while, but this will ensure a flat surface.
I’ll advise you to use some good machinery though.The ports are first made by drilling some holes of where roughly they need to be. Then worked with a Dremeltool to get the right form and last is used a file. When all of this is done is sandblasted the cylinder so you can see more clearly where it need more finishing.
I’m curious to know how your cylindertuning will go forward? Not to forget you started this topic to find your right pulley size.
Martino, thanks again for good answers!
That at least give hope when it comes to sanding down the cylinder head since I will not get my hands on a mill any time soon. Tho I read in the Graham Bell book that it is not adviced to mill the cylinderhead if your spark plug is not centered in the cylinder top, and my sparkplug is offset to the center. Any thoughts?
I know, this forum thread went a other direction, for the better in my opinion. I will keep you posted about my progress anyhow. Next week I am working a lot, but the week after that I am free, so then I know I will have time to work on this project for sure. If I remember to take pictures during the progress, I might even do a new thread for this project with some text, if it is of any value for this forum, and if it is okay if I “copy” your design?
Thanks again!
Also, where did you get those thick base gaskets? Did you craft them yourself or did you bought them somewhere?
I read Graham Bell again and realised I misunderstood the concept of a offset sparkplug totally, so forget what I said about that. But these two quote kinda confuces me a bit, especially the last part:
“Reducing the squish clearance is not easy, you can’t just machine 1mm, or
whatever, off the head as the compression ratio would end up many numbers too high.”“After the clay thickness is measured you can work out how far the head must be
machined to give the desired squish clearance. As mentioned previously, the combustion
chamber must also be machined deeper into the head to keep the compression ratio at
an acceptable level. If you wish to keep the compression ratio the same as standard, the
combustion chamber will have to be machined twice as deep as the amount skimmed
off to reduce the squish clearance, assuming a 50% squish band. Therefore if 0.9mm is
removed, the combustion chamber will have to be made 1.8mm deeper.”Any thoughts from you guys?
I think this can be best explained using an image, so I made this one using the numbers in your Grahem quote above. In case you got any questions about this image don’t hesitate to ask.
Note that I’m not an expert at this and this is simply my interpretation. If anyone thinks I’m wrong about it, please say so.Edit:
You can probably see why Graham says “Reducing the squish clearance is not easy”. Removing 0.9 mm isn’t that hard. The tricky part will be to deepen your combustion chamber, especially when you have an offset combustion chamber. So far the only one I’ve seen who has deepend his combustion chamber was zevenenergie (and his combustion chamber was centered ).I think a much better practice will be to raise your stock cylinder with a thick base gasket and mill the top of the cylinder untill the piston actually gets to the top of your cylinder. The squish is already at 0.8 mm – 1 mm with a stock cylinderhead, asuming the piston gets to the top. Atleast this was the case with my 50cc Athena.
However, if you do choose to deepen your combustion chamber, you probably also want to raise your sparkplug with the same distance using some washers.
Welkom op ons forum!
Breng een bezoekje aan mijn Ciao project.AA-T, This was the answer I was looking for! Thank you for spending so much effort on the answer. I was also thinking that raising the cylinder and milling a bit of the top might be the better option in this case. I am going to measure how many mm’s the piston is covering the bottom of the exhaust port and then raise the cylinder accordingly with a home made aluminum gasket. At least if we are talking 3 mm, otherwise a few standars gaskets on top of each other might work?
Somehow you also managed to answer my question about raising the spark plug, I was wondering about it but forgot to ask!
As you say, it might be tricky to deepen the combustion chamber in my case, since my top is of the offset spark plug type. I guess I could win 2-5% extra power in the low-mid by increasing the compression, at least if one would trust Mr Graham on this:
“Two Stroke Performance Tuning
Heat is the enemy of two-stroke engines and stretching the compression ratio to
give a 10% power increase will possibly result in a 3% power rise at the most; the rest
will be lost in heat energy and pumping losses. However, at lower engine speeds the
cylinder will not be completely filled with fuel/air mixture and the power may jump by
5-6% because there is not such a heat loss. This is, in fact, the real benefit of raising the
compression ratio, not to increase maximum power but to pick up mid-range power
and possibly widen the power band.”I wonder if it is really worth the trouble trying to grind out and deepen the combustion chamber?
Thanks once again for a good answer!
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