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Rick Parkington
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Posted: Mon Jun 16th, 2008 10:06 am |
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Excellent!
R
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sportspecial
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| Joined: | Fri Feb 29th, 2008 |
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Posted: Mon Jun 16th, 2008 07:25 pm |
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In the u.s.a., there probably are the greatest side-valve tuners of all time. Years of racing Harleys, Indians and flathead fords developed them to the highest levels.
There are still thousands of non-vintage and classic side-valve racers in the united states right now! These are go-kart racers, who's sport is dominated by Briggs and Stratton lawn-mower engines running on alcohol.
Just now they are talking of switching over to the newer OHV Briggs engines, but it has not happened yet!
Anyway to get power out of a side valve you have to know what kind of racing you will do with it. This is important because as you know the higher you raise the compression in the engine the more you cut off it's breathing.
So if top end speed and power is more important then put porting and flow first, if acceleration is more important as for sprinting or short-tracks, then you have to play with higher compression ratios and cam profiles and porting optimized for lower rpms.
The potent side-valve Harley Davidson WR and KR models had engines in which hardly one part would interchange with it's common street look-a-like, despite class C racing in the u.s.a. supposedly being a series based on common road models.
The Harley racing side-valves had their valves tipped at an angle towards the bore to give the fuel a straighter shot at their backside, and to get the valves closer to the bore so they could have the highest compression for a certain amount of flow, makes sense right?
Also the racing Harleys had cases and timing covers machined so all shafts ran on ball bearings instead of plain bushings the street engines had on the cam shafts.
A good friend of mine won a road race championship with an alcohol burning side-valve kart and he let me take it for a spin one day, it was fast enough to be scary unless you had lots of space to run it.
The carts run alcohol because their engine cases are aluminum and so fragile that if they get too hot their reliability is lost, and the alchohol keeps them cool, my buddies kart forming ice on the intake manifold and part of the block where the intake port was.
Alcohol is a nice alternative fuel these days and would be a great way to end cooling worries on an old side-valve motorcycle too. Also it is easy to rejet old Amals for it as long as you know about it's corrosive problems.
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Rick Parkington
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Posted: Mon Jun 16th, 2008 07:41 pm |
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Interesting; ove rhere karting was - and I guess still is - dominated by to strokes. It's certainly true that to a large extent Britain abandoned the side valve in the early twenties as any kind of performance engine.
R
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sportspecial
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Posted: Mon Jun 16th, 2008 10:06 pm |
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They race two-stroke and ohv karts in the united states too, but the side-valve karts make up half of the karting scene. It is supposed to save the karters money having a production based engine, but you know how that goes. If you go to Briggs and Strattons website they still sell a ready to race version of their side valve engine, but they also sell racing versions of the ohv model which is in the process of taking over.
The sidevalve engines will not run as cleanly in rototillers and lawnmowers as the ohv models, so it is now uneconomical for Briggs to make sidevalves only for the kart racers.
I guess that will be the end of another golden era in racing then, when the last briggs engined kart shuts it's engine off.
There is already vintage kart racing in the u.s.a. though so I am sure they will add a class for the sidevalve briggs motors. In the sixties and early seventies special-made two-strokes dominated kart racing in the u.s.a., but that is expensive so they started the lawnmower engine class, so they actually went backwards here.
I am sure it would be interesting to talk with top sidevalve kart engine builders and pump them for information that might be applied to old motorcycles. Next time I am at my buddies machine shop I will ask him about the special needs his sidevalve kart engines had in contrast to the ohv engines he builds for dirt-track automobiles.
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Rick Parkington
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Posted: Mon Jun 16th, 2008 10:42 pm |
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Yes hopefully the Briggs and Stratton will be racing for some time to come. I think Villiers Kart engines were stilll in use long after production had ceased.
R
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