Questions? Looking for parts? Parts for sale? or just for a chat,

The WD Motorcycle forum

WD Motorcycle forum
Start a New Topic 
Author
Comment
View Entire Thread
Re: 728cc sprinter/hill climber

Just someone with a good imagination

Ron posted this one a few days ago

email (option): horror@blueyonder.co.uk

Re: 728cc sprinter/hill climber


Ron posted this one a few days ago [/quote]

Oops sorry about that ,i know its been on here before, but some time back .

Re: 728cc sprinter/hill climber

['120mph now that's a fast M20']

'Estimated' is the key part of 'top speed with the right gearing is estimated at 120mph'... ...Ian

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

Re: 728cc sprinter/hill climber

Talking of SV sprinters - how you getting on with yours Ian ?

Knee-deep in instrumentation on the B25, following this weekends final MX, its going on the road (now I've found the NOVA docs) as a rolling test bed for cylinder head temp, Lambda sensor, another ignition (Wassell) system, Scitsu rev counter and my own LED rpm indication.

3HW has stagnated while doing other things, but hope to get it rolling for end of Nov. - currently being seduced into building a proper (vintage?) sprinter for next year - seems the Straight-Liner's are following the AMCA and giving a class down allowance for Side-Valves i.e. 500's run in the 350 class.............

FRED - is still racing the B/M21 side-valve (pix have been published) at the BUTTS MX (near Chesterfield) this coming Sunday ..... he's done the full Enduro/MX season on it + a 100 mile race and an 8hr team race.
We will be presenting him with a special trophy i think at this years AGM.

Re: 728cc sprinter/hill climber

Hi Nig, sorry to change the topic of this thread, but you don't list an e-mail address to contact you. I'm restoring a B25 at the moment and I'm sorting out sprockets. The original ones on the bike are ridiculously low geared with 15 gearbox and 52 rear, standard is 16 and 49. Most British bikes are well under geared and I usually up gear them without any problem. I want to up gear the bike for road use, I can only compare it to what I know as I haven't done a bike this small before. A Norton 16H with 13bhp has a ratio of 5.23 I was thinking of 19 gearbox and 47 rear for the B25. I've got a program I use that works out the ratios and speeds for the revs and this set up would be 54mph at 4000 revs with a ratio of 5.59 I'm sure a B25 has more HP that 13 although at higher revs. I've also found a website that will work it out for you http://b50.org/techindex.htm then click Advanced gearbox calc. in the left margin.

Do you think this is too high geared for this 250cc..?

This is what is says, I put 4000 revs as a mid way point.

Revs
4000

MPH
54.00147641831853


Crank
23
Clutch
52


Engine
19
Rear wheel
47


Gearbox ratio
5.592677345537758



Here you can check every gears speed (4000 revs)

MPH
Speed 1st
20.36419312744672

Speed 2nd
32.80254972517696

Speed 3rd
43.40788535061011

Speed 4th
54.00147641831853

Any input appreciated, thanks

email (option): horror@blueyonder.co.uk

Re: 728cc sprinter/hill climber

H

I've had to go the other direction, which involved a special 60T rear sprocket for my Bultaco rear-wheel + a higher 1st gear, so i could actually go somewhere other than straight up a vertical wall!!

She's going on the Dyno/Road in very near future, so i could suggest something more appropriate then.

Strange engine, pulls surprisgly well and currently reving to 9000rpm, but plagued by a mis-fire - seemingly cured by a 9Y extended nose plug at last meeting (the plug should be belting the piston/valve)???

Get me on

Is yours Oil In Frame - if so where is the damn frame number please???

Re: 728cc sprinter/hill climber

So these last two posts don't mean a thing to me??? Can someone please clarify what on earth you are both talking about. Ron

email (option): ronpier@talk21.com

Re: 728cc sprinter/hill climber

I realise you have a different use for your B25 Nig, I just wondered if you'd had any experience with road gearing for them.

I wish I knew what I was talking about too Ron :-)

email (option): horror@blueyonder.co.uk

Re: 728cc sprinter/hill climber

RON - very sorry and very off subject - BUT .....

A B25 is basically a 250 version of the B40 - which does have some WD relatives ... etc. etc.
I blame Ian and the rest of the BIG SV enthusiasts ...

HORROR - you have had a look at the B50 website and theres always Rupert Ratios book - many different ratios in there !!??

I'll have a think what gearing to try - i agree, most bikes will pull higher gearing - but, i suspect these little critters may actually go faster with more revs in top!

Don't forget - its TORQUE that matters, a gearbox is simply a torque multiplier - the B40/44/50's have superb mid-range torque, something the B25 is a little short of.

Re: 728cc sprinter/hill climber

Having re read the posts, I get the gist of it now About the gearing.

Yes I know what a B25 is Nige. I had a Starfire back in the mid 70's and have a hankering for another one. It felt like quite a big bike for a 250. Ron

email (option): ronpier@talk21.com

Re: 728cc sprinter/hill climber

RON, was'nt implying you did'nt know what a b25 was - just (jokingly)trying to tie it back to the WD values of this website.

Yes, a surprising little bike - with a poor reputation.
Really is classic, one new owner, the rest had no idea/money/etc. type of bike - not helped in the later years (1970 onwards) by poor manufacture/quality.

All based around the plain big-end bearing - lubricated by a marginal oil system designed for roller big-end + it needed to be revved to keep up with bigger or jap bikes and a weak conrod !
Expect any B25 you buy to need a bottom end rebuild - even if they tell you its had one !

So far, mine has had a sound thrashing over two years since i build the engine and so far has finished every race.
One more to go and its due to be taken out to 390cc for next year + a different cam.

Re: 728cc sprinter/hill climber

Nearest I've got to one of those now, is my WD C10. I'm looking for a genuine WD C11 if you see one

In the mean time, I'll wait for Horror to do a proper job on his Starfire before he sells it to me. Ron

email (option): ronpier@talk21.com

Re: 728cc sprinter/hill climber

Got a soft spot for a C11 or better a C10 ..... now must get to work on 3HW as its raining.

Re: 728cc sprinter/hill climber

Thanks Nig, I've got that book, I hadn't noticed anything about gear ratios, I'll have a look what it says :-) I realise the B25 might need the revs to get the HP, maybe a 17T or 18T gearbox sprocket would be better suited. Thanks for the input, I'll probably end up buying different ones until I get it right

I'll let you know when it's finished Ron, it's eating the money for a bike that won't be worth a fortune when it's done. You might have to wrestle Wendy if you want to buy it

email (option): horror@blueyonder.co.uk

Re: 728cc sprinter/hill climber

I'll wrestle Wendy again any time. ERon

email (option): ronpier@talk21.com

Re: 728cc sprinter/hill climber

looking at the original gearing for my 1968 TR250, this was 16 X 49 - pretty low.

Your 54mph @ 4000 rpm in 4th - equates to 81mph @ 6000rpm, my guess would be something like 80mph @ 7000 to 8000rpm would be more like.

As i say, i'm about to put my B25 onto a friends inertia dyno, mainly to get a base BHP but also to sort out my ignition/carb problems I've had all year.
I have the option on a 90x70 B44 motor for next year MX or Bonneville and need to get a handle on the b25 problems.

One thing about this type of dyno is that it can usefully predict road speeds for a given BHP

Re: 728cc sprinter/hill climber

looking at the original gearing for my 1968 TR250, this was 16 X 49 - pretty low.

Your 54mph @ 4000 rpm in 4th - equates to 81mph @ 6000rpm, my guess would be something like 80mph @ 7000 to 8000rpm would be more like.

As i say, i'm about to put my B25 onto a friends inertia dyno, mainly to get a base BHP but also to sort out my ignition/carb problems I've had all year.
I have the option on a 90x70 B44 motor for next year MX or Bonneville and need to get a handle on the b25 problems.

One thing about this type of dyno is that it can usefully predict road speeds for a given BHP

Re: 728cc sprinter/hill climber

Ron Pier
I'll wrestle Wendy again any time. ERon


She said she pinned you down easy

Ok thanks Nig, I'll work out an equivalent gear ratio then.

email (option): horror@blueyonder.co.uk

Re: 728cc sprinter/hill climber

Just finished last MX/H&H of season - a toughy.
B25 trundled round as ever - FYI now has a flat-slide 30mm OKO carb on it for a change (?)
Yes its pulling 8000rpnm in all gears ............. (fitted Scitsu for practise) and definately comes on cam/exhaust about 3-4000rpm when loaded up.

Various people commented how well it went, turns out its the only actual 250 out there, with many out to 72mm bore (+40 Triumph piston) and a few out to 76mm (T140 piston) - all but one on dope !

Contact me by email if you want a chat.

Re: 728cc sprinter/hill climber

Well done Nig, please send me your email address, mine is below, thanks

email (option): horror@blueyonder.co.uk

Re: 728cc sprinter/hill climber

To stay off topic for a little while longer. As I remember it, the 'Starfire' I had in the 70's was a B25....I think? And the 'Barracuda' I believe was the American version. But I have heard mention of the Barracuda as a C25. Was there a difference in the engines? Ron

email (option): ronpier@talk21.com

Re: 728cc sprinter/hill climber

Between C25, D25 or TR25W (triumph) not much general difference, but many many detail changes, including the use of UN/UNC threads, etc.....
Which makes buying one a lottery as most engines by now have been stripped and rebuilt using whatever is at hand - often metric !
Add crap 'pattern' parts and ..............

It was commented upon that my B25 has basically raced for 2 years without it being rebuild

I did point out that it was a 250 originally and no surprise that B44/B50's shred their gearbox, clutch and damn near everything else !!!!
The CCM has a 3 speed gearbox in it to allow for wider/stronger gears and even then it does 3-4 races to a gearbox lay shaft & n/bearing basically cos there's not enough metal to fit anything bigger !!!!

I originally built the B25 as a bit of a joke, the CCM was starting to get away from me due to a shoulder injury and i was just recovering from a knee op.
But it seems to have weedled its way into my heart, its now my preferred weapon for Enduros or H&H/MX with twiddly bits.
Hence its growth towards 326c for next year .

Re: 728cc sprinter/hill climber

You've just got to watch you don't do the same thing as the B44/B50's and start breaking gears. It sounds like the 250cc is being reliable as it is, it's a tricky one, more power without breaking things..!

Did you up-grade the oil pump? I've read in Rupert Ratio's book that the later pump can be fitted to the earlier engine with a bit of machining. I'm going to see if SRM or someone does a better pump for my 1970 bike.

email (option): horror@blueyonder.co.uk

Re: 728cc sprinter/hill climber

Torque my friend is the killer - that lovely feeling we enjoy when you wide open big single - and that sinking feeling as it skips gears, as the teeth fall off!

The bottom end has been re-built as per E-V's article on B50 forum, the con-rod is a billet jobby, bought cheap as it was one of a pair for a Daytona.
The rod is a problem area, a trident or later daytona rod will fit, but depending one the year of the crank (mines 1969) you may need to machine the inside of the (removable) flywheels for clearance.
You also need better quality shell bearings, mine are NOS early triumph twin - lead/iridium types - the standard ones are soft and crush out of tolerance when revved.

Re oil-pump - yes mine is one the three bolt cast-iron jobbies, ended up bidding and winning (on Ebay) three pumps which where on at same time - priced from £70 down to £21 !!!
I waited a few weeks until none where listed and sold two of them for more than what i bought the 3 for - tee hee.
Make sure you get the higher output pump, not all CI/3-bolt pumps have a higher output - i think they are marked VC or something, i was able to strip and check which was which.

In my cases, i didn't need to do any grinding of the crankcases - 1970 cases shouldn't need machining either.

One thing i have picked up and will be fitting is a 1970 onward inner-case (cam side) - this has provision for an oil-pressure switch, i'm fitting a 20psi from some car or other connected to a warning light.

Make sure you fit a new crankshaft end oil-seal, that the end of he crank isn't bell'ed and that is is smooth and well lub'ed when you fit the inner case.

Re: 728cc sprinter/hill climber

HORROR - email me again please, managed to delete your email rather than passing to my PC for viewing ......

Nieuwe pagina 1