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Online hampshirebiker

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Re: billy's racer
« Reply #15 on: February 01, 2015, 09:56:00 AM »
It will be interesting to see what it gives on the dyno. You'll need about 20bhp to give 80mph & that's some 70% increase on standard. My guess would be about 15/17 bhp at 5,500 and 75mph.
Postal - Liphook Hants - But just into West Sussex.

Offline BillyF

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Re: billy's racer
« Reply #16 on: February 01, 2015, 10:46:06 AM »
hi ray
all i have done is opened up the drilling in the crankcase to the clack breather, opened up the holes as much as i can in the clack valve, soldered on a 10mm copper pipe taking a plastic pipe to the oil tank.
if you have ever examined the oil tank you would see that there is a small chamber at the top that feeds the oil tank breather, i cut off and welded up the breather pipe where it comes out of the bottom of the tank. drilled a 10mm hole in the top chamber, then you can just see inside the chamber and it has small holes drilled in its bottom, i enlarged them so as not to make a restriction then welded a stub to take a 10mm plastic hose that would be the breather to the atmosphere. i drilled another 10mm hole in the oil tank near the top (above the oil level) welded on an other stub to take the plastic pipe from the engine breather.
so the engine breathes through its one way breather into the oil tank, any oil being carried is separated in the oil tank and the air is vented to the atmosphere (well thats the theory anyway)
my thoughts on windage around the crank are if the scavenge pump is doing its job the crank case should empty, the only oil getting in to the main crank case is from the big end and leakage from the crank bush and over flow from the cam chest. with the smaller crank there should be less vacuum at the centre holding the oil in suspension. i havent fitted a windage scraper close to the flywheels because the bore and small end need some oil.
along with that the rings i have used should give very little blow past so the crank case pressure should be pulled below atmospheric
this is an on going project and i am just trying things to see what happens
(i have thoughts on an overhead cam jobby)
cheers bill

Offline BillyF

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Re: billy's racer
« Reply #17 on: February 01, 2015, 10:52:38 AM »
hi hampshire
you have to remember this bike is very light with the ability to get flat on the tank.
the maths is 12.8 mph per 1000 rpm
cheers bill

Online chaterlea25

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Re: billy's racer
« Reply #18 on: February 01, 2015, 08:35:09 PM »
Hi Billy,
THe BSA clak (disc) valve breather is very limited in its ability to work at revs  :(
It doesn't react fast enough
For high(er) revs BSA used a timed breather on the Gold Stars, A10's and the unit bikes
For the C engine I would use as large a bore breather tube as I could fit and then use a crankcase vent reed valve from either a Ducati or Japanese bike (XS 650)
A "Bunn" breather system would work well if you can get hold of one, a bit expensive tho!!

I dont think the dizzy will cope with 7k revs either  :(
It will cause high speed misfres and will be the limiting factor no matter what you do to the engine, too much backlash in the gears too  :(
I would fit  later C type outer timing cover, cam and electronic ignition, that would save some weight as well

As for what will explode first my 2 cents is on the crankpin ::) ::)

Good luck with the project, and keep us informed on your progress
John



Offline mistgreen

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Re: billy's racer
« Reply #19 on: February 01, 2015, 09:42:43 PM »
Unlike the steel flywheels in BSA's racers (Goldie etc) the C11's are cast iron.
The drive side shaft had a habit of coming loose in the flywheel as
it is only held in by press fit
Oz, but spend time in Dorset most years, love the place.

Offline Kiwi51C11

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Re: billy's racer
« Reply #20 on: February 02, 2015, 12:16:02 AM »
my intentions are to fit a brass stop valve in the feed, open up all the drillings, do away with the anti wet sumping bit,

Nice to see your having some fun with the C, but personally think you're asking for trouble fitting a brass stop valve.
Far to easy to overlook it and destroy your engine.
A bit of oil in the sump is hardly a drama.

Of course an iron motor would love being run on methanol  8)

Offline BillyF

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Re: billy's racer
« Reply #21 on: February 02, 2015, 11:05:04 AM »
hi chaterlea25
that xs 650 pcv looks perfect, do you know where i could buy one, i am in scotland.
my intention with the distributer was to remove the gubbings and make it a dummy and fit a system with advance curve and rev limiter once i work out what the engine needs inside the outer cover as there is no chain or dynamo it is already a dummy.
i dont want to put on a c11g casing because i want it try and keep it looking like a '48.
you are probably bang on with the crankpin.
cheers bill

Offline BillyF

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Re: billy's racer
« Reply #22 on: February 02, 2015, 11:17:10 AM »
hi mistgreen and kiwi
with the flywheel thing a pair of steel bands could be shrunk on to them as insurance.
if the outer nut is pulled up tight it should be pulling the shaft tight into the flywheel and stop it shuffling
i have big oil sticker stuck on the rev counter dial  in the hope.
but really the whole thing is just a fun project kidding myself i am building a racer
cheers bill

Online timsdad

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Re: billy's racer
« Reply #23 on: February 02, 2015, 11:20:40 AM »
The problem that crank case pressure causes on a tuned engine is that the oil in the sump will hang onto the flywheels so the scavenge pump at the bottom, even if doing its job very well, can't pick all this excess oil up because it's getting carried round and round. A vacuum, or very little pressure, prevents this so the oil can keep puddling down the bottom for the pump to return it all.

I think even the timed breathers have a certain amount of overlap at top and bottom centres so the usual way on old bikes is to just fit an additional breather pipe higher up on the engine somewhere, with a simple one-way valve in it, and carry it straight to the back via a catch-bottle so the piston pushes the pressure out of this pipe on the way down and can't suck anything back in when it goes up again, therefore creating a sort of vacuum effect inside the cases.

Ray
Just a motorcyclist.

Online chaterlea25

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Re: billy's racer
« Reply #24 on: February 02, 2015, 10:21:00 PM »
HI Billy,
Heres a link to the XS breather valve https://www.mikesxs.net/product/15-0677.html

Quote
you are probably bang on with the crankpin.
LOL!!
The life of the pin depends largely on it having the correct fit in the flywheels,
The shoulder on the pin needs to butt against the flywheel at the same time the nut is fully tight
The holes in the flywheels enlarge when the pin has been changed a few times  :( :(
Making new steel flywheels with a press fit crankpin would be the ultimate solution

Thats a neat solution to fit the electronic pickup inside the dynamo drive case  8)

Cheers
John

Offline Kiwi51C11

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Re: billy's racer
« Reply #25 on: February 04, 2015, 12:53:24 AM »
but really the whole thing is just a fun project kidding myself i am building a racer
I hope you are planning to add a little castor oil to the fuel! in the absence of running the motor actually using castor, adding a bit to the fuel gives it that pukka racer smell  :P as well as giving a bit of useful upper cylinder lube.

With an engine on castor and methanol its not uncommon for people to deliberately inhale the fumes or comment on the lovely smell  8)

Offline BSAc11g

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Re: billy's racer
« Reply #26 on: February 04, 2015, 11:26:52 AM »
The problem that crank case pressure causes on a tuned engine is that the oil in the sump will hang onto the flywheels so the scavenge pump at the bottom, even if doing its job very well, can't pick all this excess oil up because it's getting carried round and round. A vacuum, or very little pressure, prevents this so the oil can keep puddling down the bottom for the pump to return it all.

I think even the timed breathers have a certain amount of overlap at top and bottom centres so the usual way on old bikes is to just fit an additional breather pipe higher up on the engine somewhere, with a simple one-way valve in it, and carry it straight to the back via a catch-bottle so the piston pushes the pressure out of this pipe on the way down and can't suck anything back in when it goes up again, therefore creating a sort of vacuum effect inside the cases.

Ray

When Rex was doing the research for the Bunn, he found that negative crankcase pressure was a bit of a myth at anything much over idle speeds. Further more air has mass and there fore momentum and mass inertia both of which has to allowed for.
As the piston descends it does not simply pump air out but sets up a compression wave which will bounce around quite a lot inside the cases.
The comprression wave travels at a fixed speed but the piston does not.
Add to that the geometry of the cases where an upright cylinder will suffer from the compression wave reflecting off the crankcase floor while inclined cylinder suffer less from this phenomia.
The upshot of all the work was to realise that a flow through system actually works a lot better and consumes far less energy.
On some racers it could account for nearly a full Hp.
While times breathers are head & shoulders above flapper valves at higher speeds they still end up being totally out of phase over several rev ranges so when the vent opens there will be a negative wave node on the other side & it will suck air in insted of blowing fume out.
just like an exhaust a breathers efficiency will radically increase if there is a tuned outlet pipe.
All PCV valves will have resonant frequencies so you need to pick one that will not resonate withing your operating revs which is why he used the exotic material for his valve which is where about 1/2 the cost is.
So there is a lot more in it than one might think but at the very least you need a pair of PCV valves, one letting air in and another letting gasses out.
Bike Beesa
Trevor

Online timsdad

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Re: billy's racer
« Reply #27 on: February 04, 2015, 03:15:40 PM »
It's sort of what I meant, Trevor, but maybe a bit over-simplified for a C11!

On low-revving old Triumph twins a cheap one-way valve fitted in place of the timing plug behind the barrel base, to let the pressure out, seems to do the job. No doubt it can be greatly improved but seemed to work for me.

I read a while ago that this is a major problem on big V8 engines because the crank can carry a good gallon or so of oil round clinging to it once the things get on the boil. That's two tanks full for a BSA!

Ray
Just a motorcyclist.

Offline Kiwi51C11

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Re: billy's racer
« Reply #28 on: February 04, 2015, 07:15:21 PM »
Billy,
 Ignoring the breathers for the moment, I think you're missing a couple of key elements in your "look" for the bike that you should consider:
  • putting a vent on the front brake to let the rain in
  • rearsetting the footrests so its less comfortable
  • taking off the kick start (weight) so you can do the le mans type starts at the shops
What sort of tacho have you got fitted and whatcha think it'll rev to... :-X


Online hampshirebiker

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Re: billy's racer
« Reply #29 on: February 04, 2015, 07:54:50 PM »
Look mate, just because your lot thrashed Pakistan there's no need to get clever.  ;D
Postal - Liphook Hants - But just into West Sussex.