Hwan's BSA 250 Scrambler

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Hwan's BSA 250 Scrambler

Postby Andy Chaos » Tue Jan 28, 2014 9:15 pm

I have a 60 year old PE250 riding mate who is wanting to build a BSA 250 scrambler after getting his arse kicked by a trio of B50s and B44s.
He has come to me for my unlimited knowledge of BSAs, but the only experience I have of the little 250s is they tend to get stuck in the CCMs air filter.
So here we go with a few questions on his behalf
Which engine does he go for and which does he avoid.
Is there an OIF frame that can be used or is he best off with an oil tank.
What sort of HP can you reliably achieve on petrol.
Big end, shells or Rollers
Has anyone got any projects / engines / bits to sell to get him started because at 60 he's going to have to be quick.

Andy

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Re: BSA 250 Scrambler

Postby minetymenace » Tue Jan 28, 2014 9:22 pm

get the newest engine you can, pop it into an OIF and have fun. You can rev the nuts off them, cruise all day at 70mph, just keep the oil fresh and the tolerances tight as loss of oil pressure very quickly becomes and engine rebuild. Don't know about horse power but, it was only after the engine blew up that my bike club realised that my <12fs was a 250 not a 500 :thumb
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Re: BSA 250 Scrambler

Postby Ian Hingley » Tue Jan 28, 2014 10:38 pm

Andy Chaos wrote:... is they tend to get stuck in the CCMs air filter.


:thumb :laugh :laugh

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Re: BSA 250 Scrambler

Postby steve m » Wed Jan 29, 2014 6:55 am

Andy Chaos wrote: because at 60 he's going to have to be quick.


:roll: Aw Andy. :cry:
no hope for me then - i'm slow and over 60. :smile:

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Re: BSA 250 Scrambler

Postby Mark Cook » Wed Jan 29, 2014 10:10 am

Come see us Andy and have a chat.
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Re: BSA 250 Scrambler

Postby Andy Chaos » Wed Jan 29, 2014 8:52 pm

I have been planning top pop over to buy some bits for the CCM but the way it is here at the moment it might be Telford before we get to chat.

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Re: BSA 250 Scrambler

Postby Mr Mike » Thu Jan 30, 2014 4:05 am

Andy Chaos wrote:I have a 60 year old PE250 riding mate who is wanting to build a BSA 250 scrambler after getting his arse kicked by a trio of B50s and B44s.


Andy


Not sure what you mean Andy. Is your mate going down a class so he doesn't have to race these guys? Certainly he is not going to beat a B44 or B50 with a B25? Sixty is old to be riding hard. It is for rock hard skinny youngsters with no fear.

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Re: BSA 250 Scrambler

Postby steve m » Thu Jan 30, 2014 8:38 am

'fraid i've never seen a B25 beat a PE250, so what would be the point, if he wants a quicker bike to beat B50's and B44's, <201 :idea: let him ride your CCM....he is your mate. it beats bashing your heads against the wall :roll:
even in an "age" race (60+, whatever) over here you need a 650 Metisse or at least a 500 to be near the pointy end.
good perspective Mr Mike. :cool:

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Re: BSA 250 Scrambler

Postby Andy Chaos » Thu Jan 30, 2014 12:51 pm

steve m wrote:'fraid i've never seen a B25 beat a PE250, so what would be the point, if he wants a quicker bike to beat B50's and B44's, <201 :idea: let him ride your CCM....he is your mate.

steve

He's not that good a mate. <202 :roll:
The club we race with don't have a very good turn out of under 250cc British bikes and there is a specific class for them.

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Re: BSA 250 Scrambler

Postby hwan » Tue Feb 11, 2014 8:06 pm

Hello andrew, sorry about polluting this B44/50/CCM forum...

And he's no friend of mine - he's my cousin ...... <12fs
Mainly after riding your CCM is the reason i'm doing this (ceratinly not cos of Stu's XT250!), back to finding some answers on the TRIUMPH TR25 .....

They seem to have some bad press regarding the big-ends - is this a real problem or just piss poor rebuilds and maintainance - such as digging out the sludge trap, etc. ??????
Or do i start looking to persuade a B40 crank into it?
Any idea what the B40 crankpin diameter is ?

Regarding the rest of the engine it seems to be typical late british stuff which i am hoping will not cost and arm and leg to race, like the CCM - by sticking to 250cc rather than anything bigger.

Regarding PE vs TR25 - the PE will remain a damn sight faster, simply because the suspension will be easier to live with and race for 1-3 hours, thats another 'intresting' area for me. <12fs

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Re: BSA 250 Scrambler

Postby minetymenace » Tue Feb 11, 2014 8:57 pm

<135 to the forum hwan.

Would you update your profile and let us know roughly where in the world you are please?
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Re: BSA 250 Scrambler

Postby packw » Tue Feb 11, 2014 10:22 pm

At the Kendal Classic scramble meeting last year there was a frantically fast B25 that the rider said was pretty standard (including the plain big end) and reliable, so they can be made competitive.

At the same meeting I was also talking to the "mature" rider of a square barrel Cheney Victor. He'd just finished mid-field in the up-to-350cc class. When I suggested that his bike was 441cc , he replied indignantly that it was in fact 500cc.....and on methanol! "The only way he could keep up with the youngsters".

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Re: BSA 250 Scrambler

Postby midgie » Tue Feb 11, 2014 11:14 pm

re the quick b25, would that be andy camm by any chance?

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Re: BSA 250 Scrambler

Postby hwan » Wed Feb 12, 2014 7:41 pm

No idea how to update profile - but i'm one of the Donny Mob (Doncaster is due East of Sheffield for you southerners).
AndyChaos is very much the (CCM) rider and i'm the thinker - perhaps that should be OVER-thinker.

Yes we know all about Mr Cam, i do need to have a chat with him, as for capacity - whatever it takes to clean up the pits in the liner .............. when i get the piston out!
And Methanol - well, we race for 1hr and i do an enduro's which last 3hours at a time - i dread to think what size fuel tank i'll need on methanol.

The bottom end seems a little suspect.
Using the original pump i would like to think that the skew gear on the crank, has more starts to drive it faster for more flow - this is something Norton did with the twins (which made it relatively easy to fit a plain bearing into a norton single).
Perhaps Mr Cook would know if the skew gear on the B25/TR25's are different from roller big-end engines - if not then things get much more sensative to clearance/fit and this is why they seem to be a bit marginal.

I will fit a pressure switch/light to keep an eye on the pressure and find some better that white-metal bearings (as per this forum).

As for nitriding the crank - this will only work on certain specs of steel (i think EN9 or something) - mind you it gives a glass hard surface and massive smear resistance - did a NOURISH 920 crank and it was superb, a bit expensive as they charge by weight - and boy was it heavy!

My 650 TRiumph/Norton cranks had to be tufrided (a good but inferior process) as they were not an acceptable steel grade - stopped them from breaking across the journal - they broke acros the drive side-web instead!!!

AS it seems one option is fitting a B40 crank into the casing and as the crankpin is pressed into the flywheels, does anyone know the standard B40 crank pin diameter please?

Also, until i get this bloody piston out - can anyone give wrist-pin diameter and compression height for the standard TR25 piston, so i can start looking for something better to fit ???

much impressed by the tech stuff to be found on the forum - a gold mine! <12fs
Last edited by minetymenace on Thu Feb 13, 2014 1:02 pm, edited 1 time in total.
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Re: BSA 250 Scrambler

Postby Mark Cook » Wed Feb 12, 2014 7:58 pm

The B25 uses a higher capacity pump to maintain the pressure. The casting is machined deeper to take longer gears.
We do have roller bearing cranks for B25's
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Re: BSA 250 Scrambler

Postby hwan » Thu Feb 13, 2014 8:01 pm

Thanks 4 reply, it figures -
re roller crank, will see how i get on with existing, i'm not super comptetive, but i like to finish a race!

Just got cylinder off - lots of heat and everything looks re-useable, with new rings as they are of course stuck - more heat i think.

Split gearbox off and then emptied water out of crankcase ?
Considering everything else is bloody dust dry, the reason crank will not rotate is cos the mains are locked solid - due to water/rust :?: - more heat.

And as ever the big-end has gone.........
Will regrind as long as shells have not spun in the rod - if this is the case, then may start considering a roller crank, could be talking to you (Mr Cook) @ telford.

Hope pet crank grinder is still there, he was the only one who would put a radius on the wheel and not leave sharp corners after re-grinding journals - won't be running this crank 'slack' though (-20 thou or so) as the oil pump dosnt seem to have the capacity.

On the positive side - all case threads seem very good, no rubbing/exploding damage, splines are all superb (even the alternator rotor center is tight!) and even the clutch taper is nigh perfect!

Noticed Cam gear is integral with the cams - will the B44/40/50 cam with seperate drive gear fit in the B25/TR25 ?????

Anyway - onward and upwards - will try and get the crank out this weekend.

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Re: BSA 250 Scrambler

Postby packw » Fri Feb 14, 2014 9:45 pm

Hi midgie,
re the quick b25, would that be andy camm by any chance?


That sounds about right. The bike was immaculate and painted dark metallic red with gold bits.

Bill.

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Re: BSA 250 Scrambler

Postby minetymenace » Fri Feb 14, 2014 9:50 pm

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Re: BSA 250 Scrambler

Postby midgie » Fri Feb 14, 2014 11:25 pm

packw wrote:Hi midgie,
re the quick b25, would that be andy camm by any chance?


That sounds about right. The bike was immaculate and painted dark metallic red with gold bits.

Bill.

I thought it had to be,there are only a few very quick b25 runners out there,simon cheney's being one and andy camms the other.both running on std shell bearing cranks regards midgie.

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Re: BSA 250 Scrambler

Postby HPbyStan » Sat Feb 15, 2014 8:39 pm

In an age of proper lubricants, I don't see why anyone would want a roller bearing crank in a B25.

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Re: BSA 250 Scrambler

Postby hwan » Sat Feb 15, 2014 8:49 pm

I hear what you say 'STAN' - but journal bearings rely on maintaining a film of lubricant between the surfaces.

If you do not have the lubricant flow, you cannot maintain film - flow being the problem, not so much pressure.
My racing mini engine ran nearly 1/2mm main bearing clearances, but it had an oil pump and oil gallerys able to maintain +40psi when hot.

Rolling element bearings actually prefer an oil mist for lubrication (and heat transfer), they can and do skid if fed to much oil under too much pressure.

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Re: BSA 250 Scrambler

Postby HPbyStan » Sat Feb 15, 2014 11:07 pm

Thank you, I understand the concept. <12fs
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Re: BSA 250 Scrambler

Postby Andy Chaos » Sun Feb 16, 2014 11:04 am

Whan seeing as your quite new to this forum why don't you ask Stan what he thinks about Castrol R as a proper lubricant. :shock: <216

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Re: BSA 250 Scrambler

Postby hwan » Mon Feb 17, 2014 7:14 pm

I'll keep out of the oil argument .......

Anyway having got over my dose of depression after reading 'Rupert ratio' book - seems i have a particularly early TR25 !
Knew i should have bought that '71 one from USA!

Anyway i understand i need a cast-iron oil pump + a better con-rod - 1970 onwards, then carefully assemble everything, use a particularly good lub. and bingo - i can start worrying about the gearbox!

I think i'll start patching the PE chaincase and sort its clutch - i'm not certain when this idea will get off the ground !?

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Re: BSA 250 Scrambler

Postby bossy » Mon Feb 17, 2014 7:37 pm

Remember that the 'Rod design is only half of the issue. The post '71 Rods may have been fine when new but they are at least 42 years old now. Fitting any Rod with an unknown history is asking for trouble. New ones are £185 from Thunder Engineering, surely a worthwhile investment for any B25. My bar hopper Barracuda got one and that will probably never go north of 6000 rpm.

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Re: BSA 250 Scrambler

Postby hwan » Wed Feb 19, 2014 7:25 pm

hmmm getting lots of 'advice' both verbal and written, trying to pick my way though it all.......

So shes getting a new/better rod.
Sourced a nice new solid skirt NOS piston
Sorted a good reborer and crank grinder.

An i correct in thinking i need the best/latest pump for the b25 - preferably a Cast Iron bodied one, if i can find one ?
Can a A50/65 pump be made to fit - its a very similar mounting/drive arrangement ?

Also, what are the merits of drilling out oilways and blanking off the sludge trap some USA 'tuners' are recommending?

RE the sludge trap - a truely bizzar arrangement?
Fitted at an elbow on the way to the B.E. - this smacks more of cost saving than anything based on engineering - why not drill straight from the main shaft to the crankpin and place the sludge trap the other side of the big end - so you actully centrifuge out the particles, instead of sort of store, mix them and then feef the resulting sludge to the shell bearings ???
Surely there was enough metal/web-strength for this drilling ?

Finally, go on then, for cuz Andy, i'll ask the question - what oil for this engine ....... R or a mineral oil ?

Been impressed on quality of technical info on this forum - keep it up.

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Re: BSA 250 Scrambler

Postby minetymenace » Wed Feb 19, 2014 7:36 pm

hwan wrote:what oil for this engine ....... R or a mineral oil ?


Oh no, stock up your supplies of tinned food and bottled water, it is time to retreat to the bunker.

Sludge trap works BTW.
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Re: BSA 250 Scrambler

Postby HPbyStan » Wed Feb 19, 2014 7:43 pm

"R or mineral oil"
Come on, it's 2014, the answer is non of the above.

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Re: BSA 250 Scrambler

Postby Mark Cook » Wed Feb 19, 2014 8:04 pm

I'm going mineral on my road bike, no problems with R even in the cold. Just horrible to keep clean where it weeps :cry:
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Re: BSA 250 Scrambler

Postby beat » Wed Feb 19, 2014 8:43 pm

HPbyStan wrote: non of the above.
HPbyStan wrote:"R or mineral oil"
minetymenace wrote:Oh no

all wrong guys !
BSA's running with Mineral ore R ore Sunflowers ore Oliveoil, - what ever is your choice.
only one thing you have to make shure:

do not mixing it up in the engine :!: :!: :!: :!: :!:

so, at the end, you can clearly telling us wich juice was braking the bearings ore bigend, ore sizing the piston :!:

hi Ian Hingley,
can you say exactly the mixture that giving you a reason for a good look in to your engine last time :?: :?:
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Re: BSA 250 Scrambler

Postby Mark Cook » Wed Feb 19, 2014 8:47 pm

You gear Beat is 2 Module and I have a cutter now :ban
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Re: BSA 250 Scrambler

Postby beat » Wed Feb 19, 2014 9:06 pm

hi mark,
good news !!!

what abouth bringing the gear here to me with your " R " lubbet IHR so we can go for a nice little ride together to the Ligurian Coast this Springtime ?
I will help you to wipe the " R " tears on your engine to make a nice pictures of it on the mediterranian sea :!:
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Re: BSA 250 Scrambler

Postby hwan » Sat Feb 22, 2014 7:12 pm

nitromors (or however its spelt) is the thing to remove baked on R - doesnt damage the ali either. <12fs

I presume non of the above means Synthetic ?

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Re: BSA 250 Scrambler

Postby Ian Hingley » Sat Feb 22, 2014 11:08 pm

Stan Swears Synthetic! :thumb
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Re: BSA 250 Scrambler

Postby hwan » Tue Mar 18, 2014 9:12 pm

Trundling on with this project;
Plumbed for the shell bearing option, got an R&R rod, decent shells, CI pump, NOS solid-skirt piston, etc. and starting on rebuild.
Bearing in mind i don't want a mega revving, alki burning, sprinter - as our main events consist of 2x1 hour stints - minimum, per meeting.

QUESTION #1 - FOR THOSE WITH EXPERIENCE OF THE B25 - wot cam ?

QUESTION #2 - do you always have to machine metal of the inside of the flywheels to fit the R&R rod ?

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Re: BSA 250 Scrambler

Postby hwan » Wed Mar 02, 2016 9:49 pm

Thought I'd resurrect this thread, seeing as its 2 years since i asked the question and then basically answered it myself in the ensuing 2 years of Enduro'ing the B25!

So - after being 'raced' as a std B25 with various carbs to try and sort out an ignition (electrex - good but not for B25) curve problem - she is no in ever smaller bits.

The Oil-galleries and Crank were given the full E&V treatment + Vandervall T100 bearings, late CI oil-pump and, ..................... its knackered !
At least the crank is ok and only new shells needed.

Plan is new Glacier shells + later type outer-casing so i can measure oil pressure when build - race it with an idiot light/pressure switch and sometime mid season measure pressure again to monitor what happening.

Piston will be 0.25 o/s Y*maha xt250 at 75mm - biggest i can fit without needing to open up the crankcase mouth.

Head has been twin plugged and fitted with a very nice S&W nitride coated SS valve from an A65 - with the bigger bore at least its not shrouded by cylinder wall. Although the throat has been opened up, the port hasn't - for now, this will be work in progress when ai get the flow-bench working/calibrated.

Cam - hmmmm, lot of unhelpful info out there - i cannot be convinced that the same cam is good for a B44MX/B50 and a B25.
The overlap values of the MX cam is out there on its own when compared with comparative motors.
All being said - i'm fitting the MX cam, timed as per Cooky/PES and lets see how it is......?
Cannot help but think that with a big inlet valve and a small engine - something like a 4Valve cam or something similar ... we shall see.

So, the above is the plan, to be implimented this month as my entry has gone off for the first race of the season in April :ban

A high 1st gear is to be fitted, with the std box if i lower the 4th gear (an even bigger sprocket!!) 1st becomes unusable - be interesting to see how it will be on the twiddly bits.

Ignition, initially will be Elextrex - on side or center plug and see how she is.
Eventually will copy Cuz AndyChaos 'self-gen' ignition system and fit the Wassel i have - with twin coil/plug.

Carb .... god knows, i'll let the engine tell me - anything from a 28/30mm MK2 Amal, 28/30/33 Keihen or a 30/32/34 Mikuni ...................

After seeing the cam and b.e. wear, i think is will be trying a different oil than the synthetic currently used .........

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Re: BSA 250 Scrambler

Postby HPbyStan » Wed Mar 02, 2016 10:23 pm

If your B25 engine is '69 or earlier, getting with lathejack on this forum for his oil pressure relief valve should be a must imo. Read the thread on "In search of reliable B25 oil pressure". After putting an oil pressure gauge on my latest '68 B25 engine, I won't even start the darn thing up again till his valve gets here. <1011

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Re: BSA 250 Scrambler

Postby hwan » Thu Mar 03, 2016 11:56 am

HP - been reading 'lathejack' thread with interest - hence fitting a 71/72 outer-casing with piston type relief valve.

I've found a 20 psi pressure switch which i intend fitting - if that lights up at anything above tick-over, then i head for the pits ........
Once warm, i wouldn't expect the relief valve would be operating - i'd be damn surprised if it was !!!!???

One thing i was surprised by was a small 1cm square seizure mark on the (std) piston on the forward thrust face ...
Insufficient oiling?
Over scavenging of return oil ?
S**t oil ?

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Re: BSA 250 Scrambler

Postby lathejack » Fri Mar 04, 2016 12:27 am

Hwan.

Were the T100 Vandervell shells you used just White Metal? I had thought all shells specified for the T100 were the higher grade stuff, I must make sure I get some Glacier shells as well then.

When you said you were fitting a 71/72 outer casing with the piston type relief valve, did you mean the inner timing cover? The relief valves are fitted to the main crankcase half, just the pressure switch is fitted to the inner timing cover. B25 & T25 crankcases and inner timing covers from 1970 onwards have the piston type valve and pressure switch fitting.

Although the pressure relief valves remain closed once the hot oil pressure drops below the valves operating pressure, they then do have to form a reliable seal to maintain whatever pressure is there. But that useless ball type valve on my motor just wouldn't do its job, leading to just about zero pressure at idle speed, slowly rising to around 15 - 20 psi max.

Have you had a pressure gauge fitted before? If so, I just wondered if it showed the ball type relief valve was playing up like mine.

Now, I must get my own relief valves finished over the weekend, I think somebody wants one and they've waited long enough!

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Joined: Tue Feb 11, 2014 7:53 pm
Location: Doncaster, UK
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Re: BSA 250 Scrambler

Postby hwan » Fri Mar 04, 2016 7:01 pm

The Vandervell shells are copper backed types - now it stripped and cleaned - no copper showing all dark grey but a definite wear line.

Yes meant inner timing cover and no, not run a pressure gauge YET - may cause me to worry unnecessarily if fitted - hence idiot light.

I suspect main problem with lack of oil pressure is con-rod to crank-web clearance - this should be 0.005" in my case its 0.016" - so seizure shouldn't have due to LACK OF OIL ?.
Also probable reason for strange wear on the shell - its unworn down the center - which aligns with the crank-pin oil-way. And evenly worn on both sides up to the edge of the shell.
Allows rod to rock - but gives no up/down play .......

I am using an R&R rod which seems to have been machined a bit narrow across the bearing journal - a standard b25 rod on the same crank/journal shows about 0.005" clearance.

Its going to get rebuilt as is, as it does a season racing (about 20-30 hours running) - will use Vandervells which i have now found (good old triumph twins) and send back the glaciers i've on order and get 0.030" undersize for my spare crank.


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