Benelli 250 2c Big Bore Kit
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Thread: Benelli 250 2c Big Bore Kit

  1. #1
    Senior Member R Powell's Avatar
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    Richard Powell
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    Benelli 250 2c Big Bore Kit

    In the 1980's Speedscene in Huddersfield offered a full 250cc barrel and Piston kit for a 2c. This used Iron barrels bored out and 58mm Pistons. The 2c was sleeved down for the Italian market to 231cc and sold world wide at this capacity. I recently acquired 2 new 58mm Pistons from Italy and was going to get two iron barrels bored out to match these Pistons. However in mean time a set of aluminium barrels with Pistons and altered cyclinder heads came up on EBay Italy 🇮🇹 n the 58mm bore size.Attachment 24402 Attachment 24410 Attachment 24418
    The aluminium barrel has extra ports and enlarged inlet manifold aswell as the piston skirt being reduced to aid fuelling.
    when these are fitted I will report back on any power increase and top speed!
    The Benelliman
    1981 Benelli Sei 900
    1989 Benelli Sei 900
    1976 Benelli 125 Enduro
    1981 Benelli 250 2c
    1976 Benelli 250 Quattro
    1992 Ducati. 907 ie

  2. #2
    Senior Member
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    steve peace
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    Hi Richard
    I knew there was a big bore available but did not realize it was avaiable from Dudley. Can't be many around otherwise John South Racing would have loved one of these to compete with the Yams

  3. #3
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    Big bore kit

    Hi. I'd be interested in hearing how you get on. I would imagine that the bike may be a little difficult to ride on the road if it has a tune on it. I'm looking at taking my race bike out to a full 250cc and think I've worked out how to do it using an alternative piston, as I guess your set up is a one shot job, so get your jetting right. I should be making a start on it over the next few weeks so I'll report back once I've finished and given it a try.

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  5. #4
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    2c Race project

    I am interested in this post as i am in the process of starting a benelli 250 2c race project. I have two bikes one a '78 and the other '80. The 1980 one is pretty much complete road bike so i will be using the '78 one as the project. I have 2 complete engines one has ally barrels the other cast iron, i have had an experienced 2 stroke tuner look at them and although the cast iron ones would be best to bore out as no nikisil will be required he thought it would be more difficult to widen the inlet of the barrels as the stud pattern is narrower than the aluminium ones, he also suggested taking out to 250cc and to use some motorcross pistons he was pretty sure there would be some out there that would be suitable for the cast iron barrels but he was unsure whether the ally barrels could be bored out to take 125 pistons as there doesn't seem much material there or the skirt would be too thin. So whats the best solution? Cast iron barrels bored to 250cc with slightly larger inlets or ally barrels with standard pistons but with enlarged inlets and larger carbs (28-32 mm possibly?)
    He did mention a mass produced bigbore kit was available but thought it was extremely expensive and difficult too come by.
    If there is any one out there that races a 2c that could give me some info on tuning methods for the 2c that would be great and info on suitable expansion chambers too.
    i have read a few articles on what kind of power can be produced but they all seem to contradict each other, so i was hoping 40-45 bhp? i know its never going to break records but was hoping for something semi competitive, it will look the piece if nothing else.

    I currently race a vfr at tonfanau in wales and that is where i intend to race the finished project as they have good support for classic racing.

    Any advise greatly appreciated

    Rigsby

  6. #5
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    2C racer

    Quote Originally Posted by rigsby View Post
    I am interested in this post as i am in the process of starting a benelli 250 2c race project. I have two bikes one a '78 and the other '80. The 1980 one is pretty much complete road bike so i will be using the '78 one as the project. I have 2 complete engines one has ally barrels the other cast iron, i have had an experienced 2 stroke tuner look at them and although the cast iron ones would be best to bore out as no nikisil will be required he thought it would be more difficult to widen the inlet of the barrels as the stud pattern is narrower than the aluminium ones, he also suggested taking out to 250cc and to use some motorcross pistons he was pretty sure there would be some out there that would be suitable for the cast iron barrels but he was unsure whether the ally barrels could be bored out to take 125 pistons as there doesn't seem much material there or the skirt would be too thin. So whats the best solution? Cast iron barrels bored to 250cc with slightly larger inlets or ally barrels with standard pistons but with enlarged inlets and larger carbs (28-32 mm possibly?)
    He did mention a mass produced bigbore kit was available but thought it was extremely expensive and difficult too come by.
    If there is any one out there that races a 2c that could give me some info on tuning methods for the 2c that would be great and info on suitable expansion chambers too.
    i have read a few articles on what kind of power can be produced but they all seem to contradict each other, so i was hoping 40-45 bhp? i know its never going to break records but was hoping for something semi competitive, it will look the piece if nothing else.

    I currently race a vfr at tonfanau in wales and that is where i intend to race the finished project as they have good support for classic racing.

    Any advise greatly appreciated

    Rigsby
    Hi Rigsby. I love your idea of building a 2C racer. It's great to be different. I am currently campaigning a 2C with the CRMC. Currently it is the standard 56mm 231cc with a fair few mods and produces about 40bhp. Much lower than the RDs and X7s but it is about 20kg lighter so even at this early stage of development it is showing signs of being competitive. Going to 58mm for the full 250cc is not straightforward as the crown height of the piston is unusual and therefore hard to find alternative pistons. I was lucky enough to find some ASSO Pistons in the US. I also looked at the iron barrels as an option but figured that if I used them I would lose the 20kg advantage I have ;-) . I eventually had an iron liner inserted into a set of alloy barrels.

    Whatever you do you will end up with a bike that's brilliant to ride, handles like a dream and stops on a sixpence. The only problem you'll have is being tapped up in the paddock by folks wondering what you are riding. The other advantage is that it's eligible for 250 Aircooled with the CRMC and BHR will allow you to race in the Pre 73 Specials 250 class as well as Formula 3 BEARS. I'll be at the CRMC Race of the Year at Brands Hatch in October if you want to come along and have a chat. Meantime take a look at the bike...

    Benelli 250 2c Big Bore Kit-img_1431.jpgBenelli 250 2c Big Bore Kit-img_1408.jpg
    Kevin S likes this.

  7. #6
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    race 250 2c

    Thanks for prompt reply its great to find someone doing what i intend to do. He did comment on the weight of the cast iron barrels. He has experience with these engines and as i have a new set of asso standard pistons i will stick with the ally ones. He can still do the necessary porting/ head work and enlarge the inlets so that sounds the way to go then just have to pay the £130 for the nikisil(each barrel).
    What carbs are you using, venturi size etc?
    I have considered crmc but was unsure of the regs involved, at tonfanau i will be in a twin class up to 500cc so a mixed bag.
    Thanks for the heads up if i can visit to one of the crmc meetings i will and get some info.

    He is willing to start as soon as i have made my mind up, ill will post its progress.

    Thanks again

  8. #7
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    Hello Wezzo,
    I'm new here in the forum and have registered to ask you a question. Can you please send a photo showing your 2c from above?
    I rebuild a 250 2c to drive in Germany at the historic motorcycle championship and mountain races. I have finished the technique of the bike, I want to paint the fairing parts and the fuel tank, as with your bike, in the Italian tricolor. Surely your bike has the white stripe between the left green and the right red part in the middle of the longitudinal axis? Greetings from Germany by Zabaione

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