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Increasing the engine size of a B33

I see from the message board it is possible to increase the engine size on a B33, I have an idea that it involves fitting an M21 crank can anyone please help, thanks

Re: Increasing the engine size of a B33

Hi Ian..You have four basic options..Overbore the standard barrel only..do that and also fit a (substantially) modified M20 crank assembly..or do that and fit a less modified M21 crank assembly. The last is the biggest capacity choice but the engine is at the limit dimensionally in every respect..my own B33 is running with this set up but I regard the engine as 'experimental' at the moment having only completed a little over 1000 milres on it...and I have had it completely apart in that time to inspect aspects of it and to make adjustments to the set up. Alternatively you could fit the modified M20 crank assembly alone and leave the bore as it is. This provides a range of capacity options. For all options appropriate changes to cams, valve sizes, port sizes, compression ratios etc. etc. will also be required to one degree or another.
Your first decision is to decide what type of performance you want, a 'big banger' or a performance orientated engine..that will really dictate the format, details of the specification and the degree of modification you will have to do. The conrod type and barrel casting you currently have are also relevant when cosidering the possibilities.
These engines are extremely flexible specification wise and robust enough to take a lot of tuning whilst still retaining thier reliability...I have had good results at power increases considerably over 60% beyond standard...Ian

email (option): ian@wright52.plus.com

Re: Increasing the engine size of a B33

Hi Ian that all sounds great, what sort of mods are needed to an M21 crank? I would like some extra get up and go,not so much as a great speed increase although some extra would help but more to be able to pull an extra tooth on the gearing and to be better 2 up or am I asking to much? Thanks for your reply.

Re: Increasing the engine size of a B33

Hi Ian..what is the combination of parts you are considering?..Ian

email (option): ian@wright52.plus.com

Re: Increasing the engine size of a B33

Hi Ian I am starting with a clean sheet, it's something that I have been thinking about for some time. I know that I can stuff the engine with Goldie bits but that makes them tempramental, I would rather go the bigger banger route I think that would give me more torque. Any advice you can give me would be much appreciated.

Re: Increasing the engine size of a B33

Hi Ian..As I am sure you will appreciate tuning these engines is one of the things I do to earn a living. As such I won't post a detailed description of what can be done onto a public forum. Mail me off forum and we can continue the discussion...Ian

email (option): ian@wright52.plus.com

Re: Increasing the engine size of a B33

i didnt realise the touring cams were taller just a different profile ie a quicker lift

Re: Increasing the engine size of a B33

Hallo I own pre war M OHV bikes And they have a stroke 94 mm The later B31 or B33 have a 88 stroke I have make the flywheels from a M20 in a B33 So i have a B33 with a stroke 94 I resently has a M22 1938 special and i have use a flywheel from a B31 they are light and faster in RPM. I use special valves and GS spares like the touring cams. I let the flywheels special balansd at a specialist. it can be done. Greating Theo

email (option): indian@inter.nl.net

Re: Increasing the engine size of a B33

Hi Theo..That is the great thing about these engines...there are all sorts of combinations of standard and non standard parts and you can build an engine with exactly the characteristics you need. Also they are very strong...I have had a dyno tested figure of over 40BHP (at the engine) from a B33 with good reliability, when a standard engine produces 23BHP....Ian

email (option): ian@wright52.plus.com

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