My new B50MX ...

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My new B50MX ...

Postby B50MX » Mon Feb 27, 2017 4:49 am

Hello everyone ...

I am 100% new to this forum! - first post. What a wonderful and well organized mine of information. I am hugely grateful to all those who have paved my way with information here, making (I hope) the resurrection of my newly acquired B50MX somewhat easier and less confusing. I am a long time two-stroke guy so the engine on my new B50MX has many strange and seemingly unnecessary parts that move in strange ways and do things that are totally inexplicable to my simple two-stroke brain ... I will need help!

The decision to take the plunge into a four-stroke MX bike has been a long time coming for me; I have for the last 6 years raced a 1973 Husqvarna CR400 - I also own some newer Japanese MX bikes but if truth be told I think I am a sucker for the pain, punishment and reward that comes from piloting old bikes. My ideal bike has vast amounts of unusable power, little to no suspension and even less performance in the braking department.

A few weeks ago I saw my first B50MX at a show in Florida, a truly beautiful bike that had been restored to the highest (and beyond) levels of perfection (and also as I discovered detailed here on this forum during its restoration) Anyhow, after I saw this bike I couldn't get it out of my mind and decided Id just have a wee-quick look on the internet's to 'just see' if there were any bikes for sale and 'how much' they might be ... (you see where I'm going here) So fast forward two weeks and I'm jumping in my friends 1988 Toyota truck to drive from NYC to deepest Pennsylvania to look at a 1973 B50MX that was described as being a 1-owner bike, stored since 1976 with hardly any use from new. The bike was more or less as described, the bike had been put away after it had seized, the motor pulled from the frame and the barrel removed for inspection ... And there it sat to this day. Luckily it had been stored indoors and had had liberal amounts of oil poured into it. The crank moved freely and nothing showed any signs of rust.
I am not sure if a total strip-down and rebuild will be the best path or if I can get away with just doing seals and a top end. Any and all thoughts welcome here ... (!?!?)

The bike is about as close to unused as any bike I've ever seen - it's wearing its original tires and unmarked original grips, it's just covered in a thick layer of dust. The tank is mercifully perfect. On careful inspection of the engine it's clear also that that the bottom end has never been apart. all the numbers match and it has a title to go with it that states it's a 'Triumph' - ha ha ha. (engine and frame are all stamped B50MX and it shows as being a March 73' build)

While there is much to be happy about I am missing a few things ... The dealer that sold the bike in 73' modified the bike to Enduro / Trails spec. They fitted the longer seat, headlight and different (plastic) fenders (or mud-guards) Due to this I am looking for the following parts: Correct side covers, Correct air-box, Short seat, Short muffler (silencer) I am keen to acquire NOS parts but if some of the repro stuff is very good Id go that way too.

I am also keen to get a general opinion on what modifications to make now before I do the build. I am aiming to return this bike to its stock appearance - with possibly a few small (and unseen) upgrades - such as electronic ignition (opinions welcome please)

I will post the few pictures I have (if I can figure it out)

Thank you all once again :)

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Re: My new B50MX ...

Postby B50MX » Mon Feb 27, 2017 4:56 am

B50MX.jpg

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Re: My new B50MX ...

Postby Barry Creary » Mon Feb 27, 2017 6:14 am

Try E&V engineering at the top of this forum Ed has supplied second hand parts to me and has been very helpful and also has new parts and he is on your side of the pond <135 &lt;069

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Re: My new B50MX ...

Postby koncretekid » Mon Feb 27, 2017 3:34 pm

Barry Creary wrote:Try E&V engineering at the top of this forum Ed has supplied second hand parts to me and has been very helpful and also has new parts and he is on your side of the pond <135 &lt;069


Yes, call Ed at E&V and he will give you the low-down. Ed is very approachable and seems to work about 10 hours per day and sometimes on weekends. He can supply you with everything from mild to full blown race bike. And if you get stuck, there will be a couple hundred advisors here on this forum. In fact, check out all the Tech Tips and get yourself a Rupert Ratio Unit Singles manual. Peter Quick at BSAunitsingles can supply one and just about any other part you need.

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Re: My new B50MX ...

Postby minetymenace » Mon Feb 27, 2017 6:07 pm

<135 to the Forum B50MX

Would you update your profile an let everyone know.......B!&&er me you must be the first person to join the forum without having to be prompted to fill in your locality!! Well done :grin:

Anyway, post lots of photos, don't forget the register etc etc...ask anything <135 <135 <135
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Re: My new B50MX ...

Postby B50MX » Mon Feb 27, 2017 11:38 pm

Barry Creary wrote:Try E&V engineering at the top of this forum Ed has supplied second hand parts to me and has been very helpful and also has new parts and he is on your side of the pond <135 &lt;069


I'm going to give them a call - Thank you ...

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Re: My new B50MX ...

Postby B50MX » Mon Feb 27, 2017 11:40 pm

koncretekid wrote:
Barry Creary wrote:Try E&V engineering at the top of this forum Ed has supplied second hand parts to me and has been very helpful and also has new parts and he is on your side of the pond <135 &lt;069


Yes, call Ed at E&V and he will give you the low-down. Ed is very approachable and seems to work about 10 hours per day and sometimes on weekends. He can supply you with everything from mild to full blown race bike. And if you get stuck, there will be a couple hundred advisors here on this forum. In fact, check out all the Tech Tips and get yourself a Rupert Ratio Unit Singles manual. Peter Quick at BSAunitsingles can supply one and just about any other part you need.

Tom


Thank you Tom ... (I am also Tom) I will be in touch with these guys. I am in the process of talking to people about the motor - which is my main concern at the moment. Waiting for a consensus of opinion as to if the motor needs to be fully pulled apart or just have the top end done ...

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Re: My new B50MX ...

Postby B50MX » Tue Feb 28, 2017 12:16 am

minetymenace wrote:<135 to the Forum B50MX

Would you update your profile an let everyone know.......B!&&er me you must be the first person to join the forum without having to be prompted to fill in your locality!! Well done :grin:

Anyway, post lots of photos, don't forget the register etc etc...ask anything <135 <135 <135


Thank you for the welcome! I will post lots of pictures as soon as I can get a chance ... Real work has well and truly b!&&er'd up my chances of spending any real time with the bike ... till then I have to be content with a bit of poking around on the internet, tracking down the parts I need etc. It seems like BSA's - and the B50 are well catered to for parts, I'm amazed at just how much NOS stuff seems to be knocking around ... WAY more then for my Husky or Greeves.

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Re: My new B50MX ...

Postby David S » Tue Feb 28, 2017 1:53 am

Try Peter Quick at BSA Unit Singles. I have bought many parts from him and he will have everything that you may need.

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Re: My new B50MX ...

Postby B50MX » Wed Mar 01, 2017 6:25 pm

David S wrote:Try Peter Quick at BSA Unit Singles. I have bought many parts from him and he will have everything that you may need.

David S


Thanks David, Just spoke to Peter ... Great guy. Very helpful and knows these bikes back-to-front and inside-out ...

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Re: My new B50MX ...

Postby David S » Sat Mar 04, 2017 3:35 am

Yes,Peter is a master of the unit singles.He runs a great parts shop.

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Re: My new B50MX ...

Postby B50MX » Mon Mar 06, 2017 8:56 pm

Here are some pictures of the bike in 'as dragged home' condition ...

The motor has gone to be built by Ricks UK cycles in White Plains New York. Tomorrow I hope I will get a call from Rick to let me know what the internals look like. In the mean time I can put an order in with Peter from Unit Singles to supply all the pretty bits this bike is missing ... I love the look of square number boards ... which I believe is not the popular choice. I like the slightly flat-track look this gives.

I want to build an original bike ... but am feeling quite tempted to build a set of alloy rimmed wheels to slip on. Might Ebay some hubs and build up a second set of rims.

The gas tank is perfect ... The Triumph stickers have come off and the original paint has come up well ... Just trying to get the rest of the sticker glue off.

I am most happy that all the 'trail-enduro' clutter is off the bike ...
Attachments
Light.jpg
Grips.jpg
Electrics.jpg
front wheel.jpg
Frame.jpg
Wheel.jpg
Elec panel.jpg
Tank.jpg
Triumph.jpg
Ready for build.jpg

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Re: My new B50MX ...

Postby beat » Mon Mar 06, 2017 9:03 pm

:thumb :thumb

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Re: My new B50MX ...

Postby B50MX » Mon Mar 06, 2017 9:05 pm

If you open the photos they rotate into the correct axis*

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Re: My new B50MX ...

Postby B50MX » Mon Mar 06, 2017 9:18 pm

The motor was taken apart in 1976 and has sat like that ever since ... Allegedly a very low hours bike. We will see whats what soon ... :uhu
Attachments
Engine.jpg
Bottom end.jpg
Numbers.jpg
Head.jpg

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Re: My new B50MX ...

Postby midgie » Mon Mar 06, 2017 9:29 pm

dont forget the 'active ingredient' the mx cam. the 73 b50mx was fitted with the standard road cam as standard, don't leave that standard rod in there, your exciting project deserves a carrillo to ensure the safety of those crankcases. I'm sure the bike will be a great success and give much pleasure.

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Re: My new B50MX ...

Postby B50MX » Mon Mar 06, 2017 9:46 pm

midgie wrote:dont forget the 'active ingredient' the mx cam. the 73 b50mx was fitted with the standard road cam as standard, don't leave that standard rod in there, your exciting project deserves a carrillo to ensure the safety of those crankcases. I'm sure the bike will be a great success and give much pleasure.


Midgie ... Ok, so school me; the 73's didn't have an MX cam! - is this a good or bad thing? and why would they remove it for 73? Regarding the Carrilo rod, do I need that for MX? MX is not going to be quite as high in the RPM range as Track or maybe even road ... Please give me your thoughts on this. I am very interested to learn more!

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Re: My new B50MX ...

Postby midgie » Mon Mar 06, 2017 10:39 pm

in my opinion its a bad thing, as the mx cam is superb. I use them even in my road bikes and they idle, give great all round performance. the carrillo rod is a must have as the standard rod is a known weak link, and when it fails always breaks just below the small end eye. taking at the very least your hard to find and expensive crankcases with it. I think for 73 bsa tried to soften up the bike for the American (their only market) hence the road cam and the compression reducing plate you can see fitted under the barrel. also for 73 came capacitor discharge ignition as opposed to the 71/72 mx model energy transfer ignition. for 73 also came a 21" front wheel, side stand, engine bash plate and polished fork sliders and wheel hubs, and 2 gallon fuel tank, and twin silencers which most customers quickly binned!

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Re: My new B50MX ...

Postby midgie » Mon Mar 06, 2017 10:48 pm

midgie wrote:in my opinion its a bad thing, as the mx cam is superb. I use them even in my road bikes and they idle, give great all round performance. the carrillo rod is a must have as the standard rod is a known weak link, and when it fails always breaks just below the small end eye. taking at the very least your hard to find and expensive crankcases with it. I think for 73 bsa tried to soften up the bike for the American (their only market) hence the road cam and the compression reducing plate you can see fitted under the barrel. also for 73 came capacitor discharge ignition as opposed to the 71/72 mx model energy transfer ignition. for 73 also came a 21" front wheel, side stand, engine bash plate and polished fork sliders and wheel hubs, and 2 gallon fuel tank, and twin silencers which most customers quickly binned!

I have not listed all the changes for 73 as at this time of night, I might be sending our readers to sleep!

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Re: My new B50MX ...

Postby stew79 » Mon Mar 06, 2017 11:45 pm

midge, what is this "capacitor discharge ignition" you keep going on about ? or are you still just taking the piss ?
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Re: My new B50MX ...

Postby B50MX » Mon Mar 06, 2017 11:54 pm

midgie wrote:
midgie wrote:in my opinion its a bad thing, as the mx cam is superb. I use them even in my road bikes and they idle, give great all round performance. the carrillo rod is a must have as the standard rod is a known weak link, and when it fails always breaks just below the small end eye. taking at the very least your hard to find and expensive crankcases with it. I think for 73 bsa tried to soften up the bike for the American (their only market) hence the road cam and the compression reducing plate you can see fitted under the barrel. also for 73 came capacitor discharge ignition as opposed to the 71/72 mx model energy transfer ignition. for 73 also came a 21" front wheel, side stand, engine bash plate and polished fork sliders and wheel hubs, and 2 gallon fuel tank, and twin silencers which most customers quickly binned!

I have not listed all the changes for 73 as at this time of night, I might be sending our readers to sleep!


You don't have to worry about sending me to sleep ... So essentially I ended up with the least desirable year; bloated tank, side-stand, and shiny bits! AND huge twin pipes. I will be going with a smaller pipe. I wont toss the old mega-phones in the bin but I am not surprised that many did ... Interestingly my other bikes (Husqvarna's) have 'Bing' carbs on them and I've heard people refer to Bing's being named after the sound they make make when you toss those in the bin ... (personally I have nothing against my Bings) ... I digress though.

So, back to business, My B50mx motor build should include an: MX Cam, Regular base gasket, Carrillo Rod, Boyer Ignition setup (or similar)

I am fitting Falcon Shocks to the back and running modern MX tires. Anything else?

Just to go back to those huge twin pipes, I can just imagine those brummies at BSA being like "oh just stick those HUGE twin pipes on and make the forks shiny ... The yanks will LOVE it" I have heard many stories about things the people at Jaguar 'thought' would work in the US market ... Not working etc etc ... and we all know what happened to the British automotive industry.

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Re: My new B50MX ...

Postby Michael Moore » Tue Mar 07, 2017 12:46 am

Tom, I suspect that those giant mufflers with spark arrestors (IIRC) were put on because most of the bikes being sold were not being raced. The TR5MX I'm putting up for sale was converted to street trim (the purchaser wanted a B50SS but none were to be had) straight from the showroom floor and has zero dirt miles on it.

The B50MX I raced in 1988 was built in Sept 1971 and came to me with a T tank instead of the slim MX tank, but then it had probably been through a few hands in the intervening 15+ years. In stock trim with 932 AMAL the engine was just fine for my Novice 500 Sportsman needs and I could almost always be first, or among the first, to the first corner after the start.

If you need a cam then get one, but if your (probably milder) cam is OK then ride it like that until you find the power lacking. I don't know how much less power a 930, compression plate and T cam makes, but it seems like with the BSA you make up ground by maintaining traction, not showy wheel spin/rooster tails. Dick Mann seems to suggest a standard throttle, not a quick turn, so you can more easily dial in the throttle "just enough" earlier in the corner. I think he also recommends not putting a giant rear tire on as it may make the handling a bit worse.

If you can get/make a set of moved-back foot pegs (Triumph TR5T, Dick Mann Specialties) I found that to make a significant improvement because the standard pegs are too far forward for me to easily stand instead of sitting. I'd put that high on the list of recommended chassis modifications.

It seemed like every time I fell down the stock forks were either twisted in the clamps or bent. I changed to some Marzocchis in Betor clamps and that stopped being an issue (but I kept falling down).

The wheels are heavy, and the rear wheel seems very heavy. I used a conical Y*maha front wheel, but it always felt like the rear wheel was slamming into every bump it met.

If you intend to race the bike I'd suggest a wheel/fork swap, and put the stock stuff aside for when you want to return the bike to stock.

The MX tank looks cool, but if you are going to slide up and sit on the back of the tank the T tank is probably going to be much more comfortable!

I didn't get along well with the ET ignition so I put a standard 120w full circle stator in and a RITA electronic ignition and was much happier.

Don't worry about making your bike more powerful, make it reliable, easy starting, light and well-suspended. Once you've done all that, if you need more power you can add it in. Most of us don't need more hp, we need less weight/more strength/more riding time/some actual skill. :)

FWIW, I've got a long Carrillo rod/JE piston, NEB 3 speed and PES clutch to go into my engine when it is finally resurrected. I had the 932 AMAL set up with a hard-chrome Mikuni slide, and I plan to run the 932 and the MX cam (if it is in good shape). The stock MX puts out plenty of power and it is very well mannered while it does it.

Here's a page for the BSA from a period open-class MX shoot-out in which all the bikes were dynoed

http://www.eurospares.com/graphics/engi ... omsq4a.jpg

You can read the rest of the article by changing the number in the URL, or just go to the root of that folder and click on the links.

cheers,
Michael

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Re: My new B50MX ...

Postby midgie » Tue Mar 07, 2017 8:12 am

stew79 wrote:midge, what is this "capacitor discharge ignition" you keep going on about ? or are you still just taking the piss ?
stew

no mate, not taking the piss, that's what these bikes came with from the factory, a capacitor, zener diode, coil. condenser, and rectifier, alternator.

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Re: My new B50MX ...

Postby stew79 » Tue Mar 07, 2017 1:07 pm

midgie, just because the word "capacitor" is in there it dosent make it a "cdi". its "mdi" or normal points, condenser (capacitor?) generator ignition. cdi is quite a separate type of ignition that bsa did experiment with on the b50 speed way project. no wonder i couldn't find any any reference to it any were!
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Re: My new B50MX ...

Postby koncretekid » Tue Mar 07, 2017 1:50 pm

Michael,
Thanks for that link. Before I knew about the LSR site or this site, I communicated regularly with Michael for ideas and inspiration in the early part of my build. I visited your site often (probably every day) for tips on building my own jig and frame as well as many other ideas. I never could get all the way thru your site because there is just so much good information there for anyone building their own bike. Thanks again.
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Re: My new B50MX ...

Postby minetymenace » Tue Mar 07, 2017 2:13 pm

stew79 wrote:just because the word "capacitor" is in there it dosent make it a "cdi". its "mdi"


Semantics gentlemen, if BSA (and I don't mean Boy Scouts of America) called it "cdi" then it will be known as "cdi" by BSA enthusiasts (and I don't mean Boarding Schools Association). If you are an electronics engineer and are used to the vocabulary prevalent in that trade it may mean something else to you (probably not the Career Development Institute).

So as to keep things BSA (and I don't mean the British Stammering Association) if "cdi" is mentioned on this site we are talking about the thing BSA (and I don't mean the Building Society Association) called "cdi" (and I don't mean Centre for Defence Information), unless otherwise stated.

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Re: My new B50MX ...

Postby B50MX » Tue Mar 07, 2017 8:53 pm

Michael Moore wrote:Tom, I suspect that those giant mufflers with spark arrestors (IIRC) were put on because most of the bikes being sold were not being raced. The TR5MX I'm putting up for sale was converted to street trim (the purchaser wanted a B50SS but none were to be had) straight from the showroom floor and has zero dirt miles on it.

The B50MX I raced in 1988 was built in Sept 1971 and came to me with a T tank instead of the slim MX tank, but then it had probably been through a few hands in the intervening 15+ years. In stock trim with 932 AMAL the engine was just fine for my Novice 500 Sportsman needs and I could almost always be first, or among the first, to the first corner after the start.

If you need a cam then get one, but if your (probably milder) cam is OK then ride it like that until you find the power lacking. I don't know how much less power a 930, compression plate and T cam makes, but it seems like with the BSA you make up ground by maintaining traction, not showy wheel spin/rooster tails. Dick Mann seems to suggest a standard throttle, not a quick turn, so you can more easily dial in the throttle "just enough" earlier in the corner. I think he also recommends not putting a giant rear tire on as it may make the handling a bit worse.

If you can get/make a set of moved-back foot pegs (Triumph TR5T, Dick Mann Specialties) I found that to make a significant improvement because the standard pegs are too far forward for me to easily stand instead of sitting. I'd put that high on the list of recommended chassis modifications.

It seemed like every time I fell down the stock forks were either twisted in the clamps or bent. I changed to some Marzocchis in Betor clamps and that stopped being an issue (but I kept falling down).

The wheels are heavy, and the rear wheel seems very heavy. I used a conical Y*maha front wheel, but it always felt like the rear wheel was slamming into every bump it met.

If you intend to race the bike I'd suggest a wheel/fork swap, and put the stock stuff aside for when you want to return the bike to stock.

The MX tank looks cool, but if you are going to slide up and sit on the back of the tank the T tank is probably going to be much more comfortable!

I didn't get along well with the ET ignition so I put a standard 120w full circle stator in and a RITA electronic ignition and was much happier.

Don't worry about making your bike more powerful, make it reliable, easy starting, light and well-suspended. Once you've done all that, if you need more power you can add it in. Most of us don't need more hp, we need less weight/more strength/more riding time/some actual skill. :)

FWIW, I've got a long Carrillo rod/JE piston, NEB 3 speed and PES clutch to go into my engine when it is finally resurrected. I had the 932 AMAL set up with a hard-chrome Mikuni slide, and I plan to run the 932 and the MX cam (if it is in good shape). The stock MX puts out plenty of power and it is very well mannered while it does it.

Here's a page for the BSA from a period open-class MX shoot-out in which all the bikes were dynoed

http://www.eurospares.com/graphics/engi ... omsq4a.jpg

You can read the rest of the article by changing the number in the URL, or just go to the root of that folder and click on the links.

cheers,
Michael


Hi Michael,

Thank you so much for your thoughts . I am totally new to the world of B50mx's and value this chance to learn from others who have been around these bikes for a long while.
I know that when I compare the B50 side-by-side to my 73' Husqvarna CR400 the B50 looks antiquated (geometry & engineering) generally it's my Husky that looks old, but not in this case. To your point regarding power, I think it's generally accepted that these old big-bores were not short of power but short of suspension, brakes and handling ... My Husky which I've raced for over 6 years, delivers way more power than I need; the overall performance is held back by a lack of suspension and my lack of skill - what however I lack in skill I make up for with noise and roost :cool:

Regarding the the position of the foot pegs, I will take a look at them and see if something cant be 'cobbled' together to try out a more rearward location, I'll give that a go for sure. Finally - I think I am tempted to add a Carrillo Rod as it cant hurt? - I have the motor apart so it's the best time to do it. I don't like the idea of the OEM rod exploding my cases.

Regards

Tom

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Re: My new B50MX ...

Postby Michael Moore » Tue Mar 07, 2017 11:35 pm

Tom, I don't have a photo of the DMS footpegs that came on my B50MX. They used the existing peg/engine (maybe center stand too) mounts to put the pegs roughly outside of the k/s spindle. The right peg used the mounting points below and to the front, and I the left used below and to the rear.

I made some rear pegs for a local guy, it was my usual "let me underestimate the time and complexity of this project by at least a factor of 4" projects. I'm pretty sure that since at that time I either still had my bike or it was fresh in my mind that I used the same mounting points as the DMS parts. Also keep in mind that I was going for a big safety margin as I didn't want to kill anyone with a peg failure or break a case if the peg was pushed into it. DM's pegs were probably both easier to make, lighter and a better design.

left peg:
Image

Image

right peg (not trimmed of excess yet):
Image

If you are a good weldor perhaps you can cut the stock pegs apart and move them back. Maybe cutting the peg loose from the vertical stem and them swapping the stems left for right before welding the other side's peg back on would work. Or if you've got access to a mill make new peg mounts and save those stock pegs for a future restoration. The two-point mounting does add some peace of mind for me. On my singles page there are some photos of how DM mounted things on his B50 frames which might give you some other ideas.

E&V has the standard and long length Carrillos and pistons/pushrods/spacers on their website. I had Ed do the rod install/cylinder bore (with fresh sleeve) for the parts I'd gotten from Stan Millard. Stan touts the long rod, I figured "why not?" because I was going to put in a rod no matter what and the JE piston is probably better than a NOS piston.

cheers,
Michael


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