I want to upgrade a cylinder for big bore 70 CC on my SR 50. My sr is from 2004 Piaggio carb model and it has 25,600 Km on the clock so thats approx 16,000 miles. And my question is do i have to change the crank if i upgrade cylinder to 70 CC? Because im worried if i will upgrade it then i will have to change the crank as well but on 50 is doing just fine. I'm worried mainly because of the mileage on my sr. I'm not gonna change the carb just leave the standard dellorto phva 17,5. I will just modify the carb a bit. Currently im running standard 50 cc piaggio cylinder, phva 17,5 carb 72 main jet, stage 6 sport pro variator with medium contra spring, stage 6 sport pro belt. laser exhaust. 55-60 mph on flat. And which one form cast kits is the best? Doppler s7r, Athena HP, Polini Sport, Italkit 70, Malossi Sport or Parmakit Sport? thanks for help
You should be fine with a sport kit, no probs crank wise. The most powerful sport (it's a high end sport really) is probably a S6 sport pro/Athena HP (they're identical).
But the key word in that reply above me was should. It's always a good idea to fit an uprated crank on any bike that's being tuned and especially one that's done quite a few miles. You may end up damaging quite a few parts if it all goes wrong and maybe even yourself if it happens when you are travelling at speed.
Yes indeed, I should have added that it's not a bad idea to upgrade the crank, even if not essential. I know better than most the damage that an exploding crank can cause.
Yeah but I read somewhere that, you dont need to replace the crank unless you want to have proper race engine.
I know that. I read that on this website http://www.scootnfast.com/. That guy is from America and his got quiet few useful informations on his website for the people who want to tune up their scooters.
This? ''A performance crank in most cases are not required. Many will say that a stock crank will not handle a 70cc kit. In most cases this usually isn't true. The only time you really "Need" a performance crank is when you are running a pretty extreme set up. What I mean is this, a stock 50cc cylinder usually runs around 7-8000rpm's and makes about 5hp. A standard 70cc kit will usually run around 8-10,000rpm's and make about 10hp. Your stock crank can usually deal with this increase in rev's and the higher torque. Now if you purchase a higher performance cylinder that is rated to run 12,000rpm's or higher and generates say 15hp or better, then yes, you should plan on purchasing a new crank with your cylinder. The stock crank simply won't hold up to this type of application.'' Yes, I agree with him. But, your crank has done a lot of miles and certainly won't be in tip top condition any more. The doubling of power from a 70 kit may well finish it off.
OK so as soon as I get some money I want to buy stage 6 street race cylinder kit, standard piaggio crank with race bearings, and rollers for my stage 6 sport pro vario. Everything will cost me around £190. I want to go for race crank but for now I do have only £200 quid to spend. BUT, on ped parts web site is a RMS racing crank. Is it any good? Because if is then maybe I will think about it.
A decent crank is maybe £20 more than a decent standard crank, a good investment. Also a good idea to get a water pump rebuild kit whilst your at it. If I was on a budget, I would get this: https://www.scooter-attack.com/shop...ce/MF3014002-Motoforce-Racing-Crankshaft.html
Totally pointless buying a standard crank and also pretty pointless fitting new main bearings and only fitting a standard crank. RMS is just a standard replacement crank. It's a pattern part. You will also have to pay someone to fit it as well? You don't seem to have factored this in. Can be anywhere from £100+ depending on who. I have a set of cases + crank and cylinder already built up for sale that would save you money and hassle on build costs but they may be a bit too advanced for you as they require an electric water pump and premix and are kickstart only.
I will fit everything my self. no worries. So terro, maybe if you have some spare parts in good condition for sale then I will buy something of ya? I just want my sr to drive like it should be. Thats all. If I will find out that is pointles to change anything in her. Then I will just get money for 125 with gears like aprilia sx or mx.
