Hwan's BSA 250 Scrambler

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Re: Hwan's BSA 250 Scrambler

Postby packw » Mon May 16, 2016 9:33 pm

I tried opening the Youtube video link but it was marked private. I haven't stumbled upon something unsavoury here, have I?

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Re: Hwan's BSA 250 Scrambler

Postby Andy Chaos » Tue May 17, 2016 6:39 am

No just me still learning.
I guess I need to un tick that little box that says private. :roll:
Don't get too excited it only about 10 secs long.
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Re: Hwan's BSA 250 Scrambler

Postby minetymenace » Tue May 17, 2016 8:00 am

Buxton in the sunshine! Must have been the semicentennial event.
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Re: Hwan's BSA 250 Scrambler

Postby hwan » Wed May 18, 2016 10:35 am

Yes the B25 is a 'shed' its a test bed continuously changing - this photo was last year and its changed a lot since then (still hasn't been painted).

Yes Buxton in sun - and boy was it hot - perhaps the reason for the 220DegC cylinder temps !

It seems that Matlock (next weekend) with be a mud-bath

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Fri May 20, 2016 8:08 pm

All ready for tomorrow - complete with clutch slip.

Anyway - twin plug + Wassel + 30mm MK2 Amal (running rich), makes for a much smoother engine so some sort of improvement.
Not had chance to sort the carb, but first guess is better than last years struggle, and i suspect that without clutch slip it will now lift the front wheel on the throttle!?
What a difference a better ignition curve makes.

Clutch is annoying as it looks like the plain plates have 'coined' as the new friction plates haven't made any difference, and winding the springs in as far as possible (now needing a full, as opposed to shorty lever, to get the effort down to a livable level) has made little difference.
Too late to do anything and AndyC's kind offer of the loan of an NEB clutch of his Bonneville bike has been graciously turned down - may get better and bed in (when has that ever happened?)
Or i may spend the day Marshalling - we shall see.

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Sun Jun 26, 2016 4:07 pm

Oh dear dear dear ......... :???:

Managed to transform a gutless but reliable bike, into something that is both lacking in power and unreliable ........

1st time out - fried the clutch before i realized the gearbox was upside down ......... (same as Norton but ...????)
Eventually coaxed it into life down a hill (wouldn't kick start cos of clutch) misfired like hell, but managed about 1.5hrs racing out of the 2 hours ........

2nd time out after 'sorting' the clutch ............. it wasn't sorted, HOWEVER also made an 'improvement' by going to an Amal MK2 carb as the above Kehein carb was not shutting off at end of the straight in 1st race - adding to the starting problem.
Once i coaxed it into life (down another hill, again) - it then proceeded to misfire like a b***h !! - then once i finally got it wide open, hit a rock which punctured the front tire (and ripped the sidewall ????) all in the first 1/2 mile or a 10mile lap!!!
Back to pit area - straight onto trailer and back out on KDX200 .... old faithful.

Then followed the farce over the last week of trying to get a damn clutch which would not slip ................... new everything later I'm only 99% certain I've succeeded - ho hum.
Anyway following another session with various carbs, its now on a 28mm Mk2 and starting fine - so replaced front inner tube and super-glued the tire rip - and ready for a test session or simply race the damn thing next weekend @ KING OF HILLS - Middlehills near Matlock (UK)
Hope cuz AndyC takes some tires with him in case its still running after the Saturday hill-climb ????????

I do seem to have made a bit of progress though, sorting the suspension - again this coming weekend will confirm.....

Now back to my new project - 1947 BSA C11 <218

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Re: Hwan's BSA 250 Scrambler

Postby HPbyStan » Sun Jun 26, 2016 4:50 pm

I had a '46 C11. Good luck with that, at least the B25 had potential.

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Sun Jun 26, 2016 6:11 pm

Oh there's absolutely no potential in the C11 - its something i had as a kid and have recently discovered that i enjoy and now have the patience to restore total crock's back to something like.

Its a 1947 'austerity' model (no chrome) which just about sums up the situation.

Wimbledon is about to start as well as Football (some European thing or other) and i need something which stops me from throwing something through the TV

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Re: Hwan's BSA 250 Scrambler

Postby minetymenace » Sun Jun 26, 2016 9:26 pm

:laugh :thumb
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Re: Hwan's BSA 250 Scrambler

Postby hwan » Tue Jul 05, 2016 9:15 am

Well the crock did 2 hours around a muddy field.

She is still running - but missing the brake side foot-rest and the g/change side is hanging off .......... i've a few extra bruises as well!

Carb is now a 28mm MK2 Amal - previous problem is either water in fuel (??) or too rich a pilot jet - she now has a 15 pilot jet, needs choke to start and is grumpy until warm, but carburet's fine.
Previously I've had to jet it rich low down to get rid of a flat spot - this has largely gone away now I'm running Wassel ignition.

The head temperature seems high at around 195degC while racing, I'm still running my first guess at ignition timing, i suspect it needs a bit more advance, but i was loath do anything over the weekend as i was having enough trouble keeping the damn thing upright!
One for the dyno - now i can adjust it easily.

Ignition/charging system - the SIMPLE WIRING system previous published WORKS !!!!
Nothing else to say about it really - now I'm convinced its OK i may reduce the battery size right down - or may simply leave it on so it will take the warm-up current of the lambda sensor when i refit it.

As for the 320cc conversion ..... works well, giving that extra grunt when i'm knackered, come off the throttle and simply in survival/get to finish line - mode.
It's never leaked so little oil, so i guess crankcase pressure is under control ?? !!!!!!!

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Fri Jul 22, 2016 7:24 pm

Just been checking out my SCITSU rev counter for AndyChaos' Bonneville bike (long story) - i'm impressed/surprised just how the B25 revs offload - 10,000rpm minimum.....................!

Originally before the rebuild (with the exhaust guide going up/down with valve) it topped out at 8500rpm - now it actually sounds well in excess of 10K !!!!

once Andys B50 is something like and assuming B25 is still running after this weekends event, must get her on the Dyno..

Pity my extra revs/power dosnt compensate for my failing health.

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Re: Hwan's BSA 250 Scrambler

Postby sprinter » Fri Jul 22, 2016 8:51 pm

....sounds good !!!

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Fri Jan 27, 2017 7:16 pm

Back again.

After a relatively reliable season, it let its self down @ Vinduro in Sept 2016.
From the start it was smoking from the exhaust and poofing smoke out of the breather - bit of a surprise, but set off anyway .....
Luckily i buggered my thumb in a bog at the end of the 1st lap...

I say lucky, because now it comes to strip and rebuild the bike for 2017 - the oil tanks empty !!!!???
Yes a bit had wet-sumped into the engine over winter, but not all of it ...... so i have a problem?

Stripped the top end off her this afternoon - expecting to find broke rings or a damaged piston - but nada, zip, nothing????
Nothing worse than finding nothing obvious - it will require some serious looking at........

Engine is due to be stripped and a C15G crank fitting - the plain-bearing crank has given no bother at ago, but as this crank will not be used in another project, it may as well go in. It has a longer con-rod so as usual some more buggeration will be required.

Will stick with B25 cam as the MX cam will go in the other project, but as i will have more valve/piston clearnce i may as well try and get a bit more compression.

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Sat Jan 28, 2017 6:26 pm

Hmmm plot thickens -

I wondered if I'd blown the cam oil seal as it seemed that @ Vinduro, oil + vapor was being blown out of breather onto the exhaust.
But i cannot see anything like enough oil in the outer crankcase?

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Re: Hwan's BSA 250 Scrambler

Postby beat » Sat Jan 28, 2017 6:53 pm

guess it is simply the second manner of wetsumping.

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Re: Hwan's BSA 250 Scrambler

Postby HPbyStan » Sat Jan 28, 2017 6:59 pm

I push the cam bush out of the timing case, cut a new notch 180 degrees from the standard one and push the bush back in blocking that tiny stationary engine type timed breather which cures all the oil leaks in that area and put in a larger breather from one of any number of places on the engine that works better. The B25 properly set up can spin a lot of rpm and no stationary breather can cover the whole range imo. BTW, the standard B25 has a 2-1 rod ratio which is just over the ideal 1.9-1 ratio for a four stroke single of any displacement. I'm usually advocating for longer conrods as a lot of them are too short to make the engine as compact as possible. But one can for sure have a too long con rod as well. The real Gold Star had a too long rod ratio to begin with and BSA kept shortening it till they landed by dumb luck or on purpose at 1.9-1. Multi cylinder engines that turn "crazy" rpm, think F1 car engines, need like a 3-1 rod ratio but our BSAs sure don't.
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Re: Hwan's BSA 250 Scrambler

Postby hwan » Sun Jan 29, 2017 8:29 pm

I know what you are saying Stan, i used to run a reed-valve on the racing triumph twin and am a big believer in negative c/case pressures.
However, from the beginning this engine was super sanitary, with very minimal oil-leaks and blow-by?
Not usual for something I've revved the b******x off and run at crazy temperatures (+200C plug temp?).

Something has changed?

I was initially dismissive of BEATS comment, but i am wondering if something has cause oil to stay in the crank-case?
I'll strip the engine further, later this week, unfortunately i have too many projects and cash jobs on the go at the same time, so don't want to start stripping engine completely just yet, really i wanted to top end off, in case i had to start looking for XT pistons ......

Regarding rod:ratio, its more a case of the roller-bearing big end than anything - though them Ex Grass-track C15 engines certainly go well over here.
In addition the road-race fraternity seem to prefer the C15 engine - with a B25 Head and cylinder hacked to look like a C15 (!!??) - despite a B25 engine being eligible.
The guy we know who's building a R/Racer for the 2017 IOM is now going this route even though the class limit is pre 1970.

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Re: Hwan's BSA 250 Scrambler

Postby beat » Sun Jan 29, 2017 9:33 pm

hwan wrote: i am wondering if something has cause oil to stay in the crank-case?


this is what I am try to say.

first manner of wetsumping : oil leaks down trough pump WHILST ENGINE STANDING UNUSED.

second manner of wetsumping : oil get pumped IN to engine but NOT OUT OF ENGINE WHILST RUNNING because airlocked scavenge pump.

different reasons, - same consequences.

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Sun Mar 05, 2017 11:05 am

MYSTERY ?

On with rebuild for 2017 - last year ended in a lot of smoke and an empty oil tank ?

Engine now in bits and NOTHING OBVIOUS to cause the problem ;

The bore and ring pack are in excellent condition
There is no reason for wet-sumping due to oil not returning, as far as i can see?
There's no signs that oil could be somehow flooding down from the head ?

??????????
Anyway, on the positive side, the B40 crank has gone in ok (bit worried as the flywheel O/D is much greater than a B25 - have the B25 cases been machined same as the B44/50 ???) - a 6mm packer has been made to compensate for the longer con-rod.

Everything is looking well in the g/box, etc. just need to do something about the bloody clutch!

Plan - fit standard B25 cam - this time timed correctly (it was one tooth out :grin: ), remove 1.5mm compression plate to lift the CR (now i'm not messing with an MX cam), see how she goes with my Elextrex ignitor (leaving battery system on - just in case).

Then polish the turn that is the rolling chassis ..............

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Re: Hwan's BSA 250 Scrambler

Postby minetymenace » Sun Mar 05, 2017 12:23 pm

daughter's favorite expression:
You can't polish a turn( :???: ) but you can roll it in glitter.
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Re: Hwan's BSA 250 Scrambler

Postby hwan » Sun Mar 05, 2017 12:41 pm

An expression taught to me by an old secondary teacher - when he looked at the bunch of muppets i was supposed to teach MVT to....

I like the 'roll in glitter' - not heard that :grin:

And yes i should re-read what i done write.... :oops:

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Wed Mar 08, 2017 11:42 am

Shuffling forward .....
Thank god for a lathe and miller !

B40 crank in B25 cases - do go, however i have a 10mm gap between oilpump-drive thread and main-bearing ?
WP_20170305_18_09_51_Pro.jpg


Anyway - std B25 cam/followers fitted, but which timing mark to use?
Decided to go with Rubert and set the cam 'on the rock' which lined up with the 'I' mark as opposed to the 'V' mark ...now the cam case is bottled up i'm a bit worried, so will now have to use timing disc at see exactly what i have ...........

In the meantime, while test fitting cylinder an making up new push-rods - neither C15 or B25 are correct -

So, spacer made + new small-end + 'compression plate' annnnnnnd ... i now find the Cylinder retaining bolts are of course 1/4" too short ...................bollox!
Todays problem to solve
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Re: Hwan's BSA 250 Scrambler

Postby Mark Cook » Wed Mar 08, 2017 12:55 pm

Hope you checked if the crank is in the middle Nigel????
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Re: Hwan's BSA 250 Scrambler

Postby hwan » Wed Mar 08, 2017 7:43 pm

Yep - crank in middle - shimmed up to the Drive side, hence machining the spacer LESS THAN the main-bearing I/D - so this end of the crank can 'float' with expansion/contraction.
Usual crap BSA design as the d/s main-bearing isn't really retained but there is a substantial interference fit in the crank-case so .......

Managed to 'find' myself an extra 5mm of cylinder stud - by dropping a 1/4" ball-bearing into he bottom of the stud holes - at least these are 'fitted' properly with the bottom of the stud bottoming out before it runs out of thread - hence allowing this bodge.

Keeping it all BSA the B-B are from the back axle of a C11 which i converted to sealed (metric) bearings at Xmas :grin:

All going well until until final head fitting - it now hits the piston ??????

Tomorrows problem.

MARK - RE C15/B40 cam bearing - found i have a bunch of Oilite bearings with the correct I/D for the cam, after our conversation one of these will be machined to fit the worn hole :grin:
This engine can now be assembled and i can see what timing i get with an MX cam and C15 followers??

Here's one for you MARK - modifying the cam/gearbox cover so you can access the cam without stripping the gearbox - like a normal engine !!!?
I reckon you could machine the cover to expose the cam and fit another cover over the cam/oil pump area - then you can make some progress sorting a decent cam for Road-racing, etc.
I'll ponder this tomorrow :ban

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Thu Mar 09, 2017 6:28 pm

Grind of a day -

installed piston correct way round (?) now there's piston head clearance of less than 0.010" using solder method - sod messing, so 1.5mm compression plate fitted from last build, didn't bother to measure resulting CR.

Now cylinder studs are definitely to short !
Thank you Mr Cook for helping me out with the standard B44 cylinder stud's - very easy to machine, BSA obviously bought metal for easy of machining than strength ....?
Ended up with 3/8" UNF cylinder nuts, thought i was using a 3/8" cycle thread to use Triumph 12 point cylinder base nuts - but no....... :(

A happy hour or so buggering about making new push-rods and discovered the rocker-box I'm using has a hole in to for a decompressor - lucky i spotted it and bodged a bolt into it to seal it (wheres that oil coming from ????)

I now have the engine bottled up - need to measure valve timing and decide on clutch and fit Electrex ignition.

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Sat Mar 11, 2017 8:09 pm

I had hoped that being a b40 rod, i could use the original Y*maha xt250 g/pin - as i thought it was 19mm .....
But no - its 20mm - makes things a bit tricky machining 0.5mm thick 'top-hat' adapters that thin!

So had to fit a 5/8" small end into the rod and use the original 5/8" to 20mm top-hats;
WP_20170309_10_46_37_Pro.jpg
not that much of problem because i have my eye on using this engine in the 250 sprinter, while the C15/B40/B25 engine is finished - the 'std' small-end will allow me to fit the C15 piston/B25 cylinder to a true 250 (as opposed to a 330!).

Down to Cookys (again) today and purchased a new Clutch basket - the theory goes that a knackered/grooved up basket can cause clutch slip problems ?
In addition i'm 'etching' the plain clutch plate in phosphoric acid - i use this stuff to remove rust, but have also discovered that if you leave steel in 40% solution for long enough, it comes out looking like its been sand blasted :lol:
Don't know if any of the above will cure my perennial clutch slip, but we live in hope!

There's always the C15/Jawa clutch arrangement - or fit something like an RD250/350/400 clutch assembly ....... (Uncle Ron is using a K*wasak* KH250 clutch assembly grafted onto a C15 clutch sprocket).

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Sun Mar 19, 2017 8:18 pm

Back together and running.

Fitted Electrex ignition (again) and as i turned engine over to get to oil around it, with a loose s/plug - it fired up!!!!
Whatever faults there many be regarding B25 advance curve (see later) it certainly produces a good spark.

Oil return now is PRODIGIOUS - all the work to give good oil flow to the standard Plain-brg big end is apparent with the roller-crank now fitted.

Back to single spark-plug, the old 'off idle' flat spot has returned, its early days and the timings not set i'm hoping to overcome it (????).
Plan is to give it load more advance and see where its goes - i may take the rear road-race wheel/tire from the C15, fit it to the B25 and see what it produces on the dyno and try and see what happens when you change between side and center s/plug.

Setting valve timing via Rupert method has produced an Inlet opening value of 34deg BTDC @ 1mm valve lift - substantially retarded from its previous timing.

Vibration is MUCH reduced with the heavier std B40 flywheels, compared with the std B25 flywheels :smile:
The C15 crank in the sprint project, has been heavily machined and are lighter than the B40, but is still heavier than the B25...........
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Re: Hwan's BSA 250 Scrambler

Postby Andy Chaos » Mon Mar 20, 2017 10:25 am

Had to google PRODIGIOUS : :?:
As for vibration i didn't think it had a PRODIGIOUS amount before the new crank and what about the PRODIGIOUS amount of smoke has that been cured. ;-)

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Re: Hwan's BSA 250 Scrambler

Postby hwan » Mon Mar 20, 2017 11:30 am

It had oodles of vibration on the B25 crank - rebalancing it after i fitted the big rod and then rebalancing it again after i fitted the Xt250 piston (to BSA values) - did f***-**l to reduce it.

Luckily it never was held at full throttle for long, other than the day i MOT'd it - one blast down the A19 was enough to convince me it needed much higher gearing and not to use it as a long distance tourer!

As for the PRODIGIOUS Lamont of smoke & empty oil tank (as i say, it was lucky i stuffed it into the bog and buggered up my thumb!) - that seems to have been 'cured' (???) for now - a longer run will tell.

Just been refitting the Bultaco re-wheel - the rear tire is like new ...................... which says something about the distance it went last year :???:


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