To lighten crank or not to lighten crank

CLEMTOG said:
I have to comment on my learned friend Piets statement above


"Changing final drive ratios has nought to do with closer-spaced ratios in the box.  Final drive ratio dictates how fast you can go, gearbox ratios dictate how fast you get there."


This is correct Piet, in part, changing final drive ratios has nought to do with closer spaced ratios in the box, correct, inside the box nothing changes no matter what size front or rear final drive sprocket you use, but the lower that final drive ratio, the quicker you get to fifth gear, so the OVERALL ratios, from engine to rear tyre do get closer, if you gear your bike for a 100KMH top speed it will APPEAR to have very closely spaced ratios in the box, so for track, use changing sprockets can get you an advantage and a big disadvantage.

On my road bike (TOG) I have use 19/38 for a very long time, this is with a low comp, A11 cam engine, it suits me, I like it that way a lot, acceleration is a tad slower, and first gear "taller" as are all the others, but I don't use it in town, and Euro cruising is "relaxed" at around 80/90 MPH on occasions when Andrea came with me it was not exactly the best, but still OK
CLEM
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Clem,

The closer spaced ratios permit the next higher gear to engage a lot closer to the power band, revs don't fall off as much and acceleration is quicker.  So it does dictate how fast you get to wherever the engine can pull.  Closer spaced ratios will also have an effect with overall low gearing, although the benefit diminishes somewhat in that case.  But that isn't the point... we all want to ride faster than 100km/h, don't we.

The higher 1st gear also allows me to out-drag a lot of quite powerful "competitors" out of the former Bus Stop chicane at Spa.  I need to use 1st gear, but I can pull that to over 130km/h with my current 18/38 gearing.  Bikes with roadster boxes need to change at least one more time, most go through in 1st, as 2nd is too high for them to accelerate out of the corner quickly.  When they change up to 2nd, I blast by, still in 1st, and click into 2nd just before the others look for 3rd...

Alpine pass roads can be a bit of a bother with the tall 1st gear, but I usually manage with just a minimum of clutch slipping.  Usually swap the rear sprocket for a 39 or 40T for that sort of stuff anyway.

I wouldn't want to miss it.  Actually piecing together a closer-spaced box for the GTL. :D

piet
 
Right, can everyone shut up about close ratio gearboxes please, 'cos now I want one of them, I'll put it on the list along with the carbon fibre wheels.

FFF
 
Laverdalothar said:
I think he wanted to express a warning, that with a lightened crank, the danger of over-reving the engine is coming closer when f.e. missing a gear or so.

wonder why we all not just swap our beasts for something that has it all already...:

http://suchen.mobile.de/fahrzeuge/details.html?id=218326447&isSearchRequest=true&zipcode=&damageUnrepaired=NO_DAMAGE_UNREPAIRED&scopeId=MB&maxPrice=1000&makeModelVariant1.makeId=23600&makeModelVariant1.modelDescription=GSXR&pageNumber=1#

at least it's orange...  ::)
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Does that mean I can give your stuff to the scrap man next time he comes around?  :o :D

A rev limiter should prevent valves kissing the pistons, ignition should cut out long before things get dangerous.  I've messed up quite a few changes, mainly on the track bike with its LH gear change, despite the box being a lot slicker.  No damage so far...

piet
 
nick7 said:
Red,
Are you sure about the valve bending thing.Surely if a motor spins up so fast that ,in the case of our old engines, the heavy valves start bouncing as you hita10 k revs sooner than you thought, you will be experiencing fucked valves, bent if you are lucky, smashing their way through the Pistons to the gearbox if you are not. Have had that on a small Honda back in the day...entirely predictable, surely?if you are fitting hollow titanium valves over there with so per duper springs that can take it, let me know? :D
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I'll repeat what i posted earlier - as Red does them, they're a lot lighter than std - BUT still not a light crank in absolute terms.
As I said they're still heavier as an assembly - bare - than a Z1 or big Suzuki GS crank, neither of which are noted for being light....and both of which have the main masses concentrated closer to the centerline so have less rotational inertia.
The way the factory designed the crank means thet with the best will in the world you can't get them particularly light....I see quite a few lightened plain bearing jap bike cranks, some done well with knife edges and streamlined bobweights, some crudely. Now they're light....But matching that with a roller bearing crank ? hardly.
I'd endorse Red's cranks for road or track. And agree with him that if you tangle or break valves, you've got a quite different problem.
 
nick7 said:
Red,
Are you sure about the valve bending thing.Surely if a motor spins up so fast that ,in the case of our old engines, the heavy valves start bouncing as you hita10 k revs sooner than you thought, you will be experiencing fucked valves, bent if you are lucky, smashing their way through the Pistons to the gearbox if you are not. Have had that on a small Honda back in the day...entirely predictable, surely?if you are fitting hollow titanium valves over there with so per duper springs that can take it, let me know? :D
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have over a dozen machined cranks running around now Nick and the only person to bend any valves so far is Paul and that was due to a broken cam chain at 8,800 rpm, Turn 1, Eastern Creek, couple of weeks ago

no different to installing a Scat crank into a small block Chev and revving it to 10,000 rpm which is what we used to do with a blown small block running in Top Alcohol years ago
never had a valve issue in that engine, had a lot of block issues though


 
redax5 said:
no different to installing a Scat crank into a small block Chev and revving it to 10,000 rpm which is what we used to do with a blown small block running in Top Alcohol years ago
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Oh no, come on now. That's just talking dirty... Pure filth.
Have a care man, I'm at a difficult age.  ;)
 
redax5 said:
no different to installing a Scat crank into a small block Chev and revving it to 10,000 rpm which is what we used to do with a blown small block running in Top Alcohol years ago
never had a valve issue in that engine, had a lot of block issues though
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Now your talking them were the days.......still are for a lot gotta tell ya as can hear the thunder when the big boys are playing out at the creek from my joint... awesome sound

If you are bending valves gunna tell ya it aint down to a lightened crank more likely your valve timing is out or your springs have lost a lot of their tension ........amazing how ofter simple thing like valve spring tension gets overlooked. Not uncommon to see springs loose half their tension over time.



 
redax5 said:
been looking at Maxene as the pilot, she has a bike licence and weighs a lot less than us old farts
just need to get her some life insurance payable to me  :D
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I'm on a diet and I have lots of life insurance.....
 
Seems those MMC rods are intended for plain bearings. I'd guess it would be quite some effort to adapt the lubrication system of the Breganzies for using plain big end bearings.
 
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