[alfa] Re: single-row timing chains

[Joe Elliott <jee@xxxxxxxxxxxxxx>]

At 7:33 PM +0000 11/8/04, alfa-digest wrote:
> I want to be careful with my words, but I would bet my left ... that 
> their is no 5 - 10 HP gain by going to a single-row chain on an Alfa 
> engine.  That is impossible.  I am not buying it at all. 
> As a mechanical engineer in my previous career at Ford, and from a 
> practical perspective, that is just not possible.  I have an 8HP 
> riding mower that can carry me around my yard, cut 10" grass, etc. 
> or a 8 HP snowblower that can throw 24inches of snow twenty feet... 
> there is no way it takes this much power to bend and mesh an 
> additional row on a chain in the Alfa engine.
>
> I don't mean to offend anyone, I am just not even close to buying 
> that argument.  Whatever dyno test was done was not done properly or 
> was "goal seeking" (for those familiar with the Excel function...).
I wouldn't be so sure.  For sure, flinging the mass of that second 
row of chain around at engine speed requires a not-insignificant 
amount of power (although I'd have guessed maybe 2-3hp, I'm too lazy 
to do the math).  Then there's the friction between the various metal 
parts, as well as friction with the oil.  If you go to smaller 
pulleys, then you're saving rotating mass as well, which doesn't 
necessarily take any power to drive at constant speed, but does 
require power to accelerate from one speed to another, right?  Keep 
in mind that however silly you think timing belts are, lower mass and 
lower friction compared to chains was a major motivation for their 
widespread use in engine designs of the '70s and '80s.  Certainly 
halving those losses in a traditional chain must be worth something. 
(Perhaps that's why your lawnmower and snowblower likely have 
sidevalve engines--giving up that much power to drive the valvetrain 
isn't worth it in a small, crude engine that might not gain a whole 
lot from an OHC design.)

However, I wouldn't say that there's *no* loss in reliability.  Even 
if a modern single-row chain is just as strong in various tests as a 
double-row chain from 30 years ago, two rows is going to offer some 
redundancy in the event of certain failures.

Joe Elliott
'82 GTV-6 (toothed rubber belt, and no complaints)
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