Valve springs for 1974 750SF2

TeddyG

TeddyG

Hero member
Location
Portland Oregon
Greetings,

I need new valve springs for the above, and before I order from Wolfgang or DAM Classic Racing, can anyone tell me if there is a substitute/alternative manufacturer/bike model for these?
Thank you
 
I have bought valve springs that were so badly made and cut that the tapering end of the wire was obstructing the bores of the coils where the steel seat inserts at both ends, utter crap, the dealer said "just Dremmel off the offending bits" yeah right, once bitten etc etc.
CLEM
 
To follow up Marnix' comment, the OE factory springs truely seem to last indefinitely. Of course, the same cannot be claimed for many aftermarket springs. There are good and bad out there...

The stock springs will wear/settle, but after 40-odd years they mostly remain well within the factory service limits. Having said that, I'm pretty thrilled by Keiths' beehive springs! They allow a considerable weight saving if looking for a reliable hi-rev valve train, the top spring collar can easily be machined to save a couple more grams where it counts.

piet


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I am following the advice from the engine builder/machinist who is reboring the cylinders w/ new Ross pistons and seating the valves. He claims the spring tension should be stronger after measuring the old springs. The type he normally uses (I don't know what brand) are not fitting correctly. I'll mention the Beehive springs to him, and buy OEM as last resort.
 
Thank you all,
I can only say that this engine builder comes highly recommended from 2 local Laverda owners, along with a Norton and Ducati owner, but I will relay the above comments to him.
 
There are measurable specs for valve springs. If your spring doesn't meet those specs replace them while you're in there. Keiths springs sounds pretty good. So did Phil Todds at the time. BTW Laverda made a double valve spring kit for race application.
 
motoddrob said:
And what experience does your engineer have regarding 750 laverda spring tensions?
I did well over 200,000 kays on my SF2 with original springs. How many miles has your SF2 traveled?
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Similar here, Rob. Only fitted new ones when I went to a 5/C cam and SFC 7mm valves. If you plan on revvving your SF to over 8000 maybe new springs is good insurance ...
 
Vince said:
There are measurable specs for valve springs. If your spring doesn't meet those specs replace them while you're in there. Keiths springs sounds pretty good. So did Phil Todds at the time. BTW Laverda made a double valve spring kit for race application.
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The best answer to all of this would be if anyone can tell me what these specs are, since the machinist did measure them, and told me they are too weak. To all those who claim the springs last a lifetime- have you measured them and know these specs? Otherwise, how can you back up this claim? And just as the OEM diagram shows, mine have double springs, so what's w the "race kit" claim?
Again, I was merely asking for information about alternative valve springs before I order OEM.
 

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TeddyG said:
The best answer to all of this would be if anyone can tell me what these specs are, since the machinist did measure them, and told me they are too weak. To all those who claim the springs last a lifetime- have you measured them and know these specs? Otherwise, how can you back up this claim? And just as the OEM diagram shows, mine have double springs, so what's w the "race kit" claim?
Again, I was merely asking for information about alternative valve springs before I order OEM.
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Your looking at the wrong diagram, that’s where your going wrong!
 
TeddyG said:
To all those who claim the springs last a lifetime- have you measured them and know these specs?
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I have never seen spring loads quoted in any Laverda technical publication ever for any of the engines they designed
Only specs I have seen is on the triples where they quote 43mm overall length, there is also a measurement for the 500's as well but nothing for the twins that I have seen

TeddyG said:
mine have double springs, so what's w the "race kit" claim?
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comments made above are mixing up twins and triples, that is where the confusion comes in
Triples came out standard with single valve springs, twins have always had dual valve springs probably because of their heavier valves having 8mm Valve stems compared to 7mm for the triples and the Twins valves are a lot longer and larger

I have measured the spring loads on Laverda 500, 750 and triples, is part of building every engine I recondition
Asked this same spring load question over 20 years ago and no one could give me an answer so this is what I have worked out
On a 750 twin with their dual valve springs, closed is 80-85 lbs, open with 5C cams is 185-190 lbs

On a triple with new Valve springs because their springs do in fact require changing out unlike the 750 twins, closed is 52-58 lbs, open with 4C cams and 9.8mm lift is 150-160 lbs

Now don't ask me about the spring loads on the 1980 triple engines which is just an absolute joke, pull one of those engines down and if they still have their standard valve springs installed, measure installed height, transfer the spring to my Rimac 250 lb spring tester and at installed height the gauge does not even register, closed spring load is somewhere around 0-5 lbs, what an absolute joke

on my race engines I run PAC-Alloy dual valve springs and machine my own Titanium top and bottom Spring plates, with 10.0mm of lift, closed is 80lbs, open 190 lbs
So you can see from these figures that the twins have fairly reasonable spring load figures

Now if your engine builder is used to building say Harley engines or even Chevy small and big blocks then the spring load figures quoted above are going to appear to be rather anemic
Having worked on blown Chevy big block drag racing engines in a previous life where we were rebuilding cylinder heads every race meeting we were looking at 280-300 lbs closed and 650lbs open

so after all of the above, I totally agree with Marnix and Piet and others that the 750 twins do not need their valve springs changed out for OEM springs
If you do wish to install new Valve springs then buy the Beehive springs from Keith as they are a great upgrade

hope the above helps to clear up the confusion
 
Top post, Red. Statistics don't lie. I'd certainly look at Keith's beehive springs - they sound great.

I'd love to know how a 1980 triple can run with virtually no valve spring pressure on a closed valve??!! :eek: :eek: :eek:
 
Good info Red.
I'm assuming Teddy's bike has covered low miles as most US Laverdas are low miles when they come up for sale.
My experience and quite a few of the Oz owned 750s I know of have done 100s thousand kms in their lifetime with no problem with valve springs.
So why would a low mile 750 require new springs. The engineer, he may be a competent engineer that comes recommended but how much experience does he have with Laverdas. I have been bitten badly a couple of times after having recommended engineers work on my Laverdas.
A barrel being bored off centre on my 750 that seized the piston on it's first run. An inlet valve nipping up on my triple on it's first ride resulting in a hammered bucket and trashed cam lobe. And finally a trashed head on my triple that required a replacement head after spending 2000 fucking dollars on it. All respected engineers but little experience with Laverdas. Red is now the only guy I trust to work on my lav engines.
So how does your engineer determine what condition your valve springs are in? They are good at spending someone else's money.
The comments regarding 750 valve springs are coming from people who have along history riding and spannering these bikes.
I know who I'd be taking advice from.
 
Thank you for those specs Redax which I will pass onto the engine builder and I've contacted Summit Racing here to see if they have the Beehive springs. Exmoor- I attached the wrong file and corrected it. I am not an engine builder and can only assume this engine builder knows what he's talking about, but there's always the chance he could be wrong. And that's why I've posted my question, so thanks to all.
 
It's good to learn stuff, lots of hard won data there Red. My bet Keith had those springs custom-made. That Desmo comment I made was about the insanely soft springs in the 1980 heads, they just forget to fit the Desmo bits. That and the crank bearings did a lot of damage physically and reputationally, its a real head scratcher as to why they did it.
 
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