What? Are you mad?
I was talking with Harry Barlow today and he showed me his new 61mm crank. Hmmm. Nothing new in 61mm cranks, is there? Well, this one is different, because the diameter of the crank webs is 99mm, rather than 96mm. This give more meat around the big-end pin, but does require the crankcase to be bored out (through the mag-flange hole).
I thought the extra machine work an extravagance, but as Harry was quick to point out, if you are fitting a 60+mm crank, you will be chasing out the back of the crankcase for clearance for the big-end at BDC anyway. Given that machining out the crankcase is a relatively easy task (especially if you have a bl00dy great mill), it isn't that extravagant afterall.
The crank webs are CDC machined. Very tidy. The manufacturer says this improves tolerances over cast webs. I wonder if it aids balance of the crank?
The cranks retail at a shade under £300, with a full choice of con-rods.
So what will bigger webs do to your flywheel weight?
99mm crank
whats cdc?
Its in bits scooter club: www.facebook.com/groups/132415046859320
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sean brady scooters
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the downside is...maybe that crankcases will be approx 1.5/1.8 mm thinner all around (allowing for clearance)...and maybe weaker...
however ,primary comp ratio will be reduced slightly (which is a good thing)and the extra mass in the webs would sustain even lighter flywheels...
however ,primary comp ratio will be reduced slightly (which is a good thing)and the extra mass in the webs would sustain even lighter flywheels...
Sean Brady Scooters - 01765 690 698
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Knowledge
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Yes Sean. On that point, I have always considered that the closer the mass is carried to the centre of the crank, the better. It has got to be an improvement over carrying the mass on the end of a shaft (like a flywheel). The extra mass on Barlow's webs is, in my opinion, in the best place.sean brady scooters wrote:....and the extra mass in the webs would sustain even lighter flywheels...
I guess someone has thought of this before (I know The Cooler ran big webs when built by Big Webster), but the idea of altering the crank mouth to suit a bigger web on a road bike seems both radical and sensible at the same time.
Now how can I get some time on the mill at work, without being caught?
Martin
Any updates on the HB barrel that you posted about a while ago Martin ?
The extra width on the original cooler crank was a result of several different things....... the need to fit a reliable crank capable of withstanding forces that until then had been twisting traditional lambretta cranks, the need to fit a reliable motorcycle based ignition (and therefore matching flywheel boss and therefore crank taper) and the desire to fit an external (i.e. chain side) driveside seal. Now running a 64mm crank, the additional machining is needed anyway to mill back all the alloy welded crankcase reinforcemment.Knowledge wrote:Yes Sean. On that point, I have always considered that the closer the mass is carried to the centre of the crank, the better. It has got to be an improvement over carrying the mass on the end of a shaft (like a flywheel). The extra mass on Barlow's webs is, in my opinion, in the best place.sean brady scooters wrote:....and the extra mass in the webs would sustain even lighter flywheels...
I guess someone has thought of this before (I know The Cooler ran big webs when built by Big Webster), but the idea of altering the crank mouth to suit a bigger web on a road bike seems both radical and sensible at the same time.
Now how can I get some time on the mill at work, without being caught?
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sean brady scooters
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sorry chaps but i,m a bit confused...
knowledge refered to extra diameter of webs only...and soulad is now refering to extra width/thickness of webs...and both refering to this cooler crank...so please explain further and to please clarify.
knowledge refered to extra diameter of webs only...and soulad is now refering to extra width/thickness of webs...and both refering to this cooler crank...so please explain further and to please clarify.
Sean Brady Scooters - 01765 690 698
Sorry Sean, didn't mean to confuse ... the cooler crank (a motorcycle derivative) is not to be confused with HB's new crank.
I was just pointing out that the Cooler crank was chosen for many other reasons than simply extra meat around the big end pin. It is approx 50% wider than a standard lammy crank BUT does however require extensive crankcase welding and machining.
That said all the additional benefits Martin has rightly outlined with Hb's crank can only be a good thing for Lambretta owners ... BUT if it was my engine I would think about getting some relatively cheap additional ally welding done. Theres no point in improving the reliability of one engine component at the expense of another?
I was just pointing out that the Cooler crank was chosen for many other reasons than simply extra meat around the big end pin. It is approx 50% wider than a standard lammy crank BUT does however require extensive crankcase welding and machining.
That said all the additional benefits Martin has rightly outlined with Hb's crank can only be a good thing for Lambretta owners ... BUT if it was my engine I would think about getting some relatively cheap additional ally welding done. Theres no point in improving the reliability of one engine component at the expense of another?