Pistons for Laverda SF2 advice wanted

Jens

Jens

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Hi all,

I need a set of pistons for a SF2 engine and now I am checking what suits best.

What I have and what is fixed for that engine: Standard motor with standard crank. Bore will be 82mm. 36mm carbs. Standard head or slightly modified head with C5/C6 like cams. It will be ambitiously used on racetracks but for fun.

First thing I am not sure about: The weight of the pistons.

An Asso piston with pin weights about 440gr a Mondial piston about 390gr as far as I know. I did read of much more lighter pistons.

Does anyone have experience, which weight works best in high revs? Without modifying crank. Perhaps a very light piston would be counterproductive in that setup regarding performance and vibrations?

Second thing: The compression ratio should be about 10:1. What is available? Which pistons are in stock in the world now? Any suggestions?

cheers, Jens
 
Second thing: The compression ratio should be about 10:1. What is available? Which pistons are in stock in the world now? Any suggestions?
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Hi Jens Not sure which pistons you could choose - but if fitting a set and modifying the head anyway - it is best to do a proper  CR check with measured fluid - head can be skimmed to get (almost) as much CR as you want - Regards - Phil
 
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Hi Phil,

I will definitely do it. Many thanks for the advice (thumbup)

Jens
 
Hi Jens,
We fitted a set of Ross Racing Pistons 880cc size and they weighed 349 grams, had them internally machined and profiled to suit the crown
To me the lighter the piston the better as that is a big slab of weight to have to stop and turn around twice every revolution especially at high RPM

Triple engine I am building at the moment has pistons that weigh in at 248 grams

Have to order some of those 880cc pistons soon if you wish to get some, send an email

Red
 
i put ross pistons in my sf2, straight from Wolfgang - he reckons the compression is approaching 9.5-10:1 with these and stock head setup no shaving etc. the bike runs fine with them in, though to be honest i think the difference between the stock pistons and the ross pistons power wise is negligible 

though i bet some of Reds 880 ones would make a noticeable difference, though image the  barrel would need to be relined?
 
I had Ross make up 89mm (880) pistons for my project SF(Q) and with undercrown profiling they are as per Red's (did you use the Job no they created for me, Red?), 350g (total with gudgeon, circlips and rings 441g).

They were based on a dome pattern from Wolfgang's 1974 SFC replica Ross pistons, with a wider swish, but I believe with the larger bore they will tend to be a higher than for an 80-82mm bore ... and a little too high (for road use). I'm yet to burette the head and check the comp ratio, but I may need to machine down the dome a tad (which looks to still have quite thick metal left), so they may come down a few grams yet. I wouldn't go over 10.25:1 (measured) for road use, and you'd need to modify the advance curve if you up the comp ratio.

They are heavier than Mondials because they are forged. The lighter the better tho. Going big bore is loads more work and even more expense than a simple rebore - my bike#2 will remain std (ie no oversize sleeving, machining head spigots and fitting dowels, overboring cases, barrels and buying very expensive head gaskets).
 
buying very expensive head gaskets
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For one-offs we used to remove the flame ring from the original gasket - snip round with nail scissors and fit some larger flame rings from Guzzi gaskets - did find a car head gasket that was even more economical - but can't remember what it was off. - Regards - Phil
 
Hi all,
When I built my Monty engine with 78mm Ross pistons (thanks Red) I used Wiesco wrist/gudgeon pins that had an internal taper and were a lot lighter than Ross pins.
The overall weight of 78mm Ross piston plus Wiesco pin was less than standard 72mm pistons and pins.

Material Type:  Steel
Inside Diameter:  15.00mm
Outside Diameter:  20.00mm
Length:  55.50mm
Weight - Nominal:  55.61g
Wall Type:  Taper
Coating:  None
Product code (I think?) is S423

Andy
 
after your replies and trying to empathise with an engine :) I will follow this path:

- the weight of piston and pin can be choosen as low as possible or available

- will contact Wolfgang and the other suspects regarding what 82mm pistons are available

I will also use the tapered pins.

Red, I will give you a note by mail regarding the big bore pistons.  :D

Thanks - Red, Phil, Mike and Andy - your help is worth a fortune for me  :)

if there are more ideas, don't hesistate,

Jens
 
phil37 said:
Hi Jens Not sure which pistons you could choose - but if fitting a set and modifying the head anyway - it is best to do a proper  CR check with measured fluid - head can be skimmed to get (almost) as much CR as you want - Regards - Phil
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just a word of warning not to overdoe this, please. We had a "Specialist" in Germany called Klaus Nieland. He offered "high compression 1220 Race engine modification" - and skimmed down the barrels by several milimeters (!!!!) to compensate for the wrong piston hights... Timing was off, compression was as low as 6,5:1 or so still and you could not adjust the chain anymore... :o

so - just a word of warning to recognise the "(almost)" in Phil's advise, please...  ;) (and also that he only talked about the head, not the barrels...!)
 
phil37 said:
  For the sake of a few CC's - why not use the 81mm pistons that are readily available? - regards - Phil
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to be honest, I do not know which sizes of pistons are waiting on the shelves right now. My thought was, there could be a batch of 82mm pistons be produced in the last time. You are right, if they do not exist, it might not be worth the few CCs.

just a word of warning not to overdoe this, please. We had a "Specialist" in Germany called Klaus Nieland.
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I am sure I will not replicate Klaus Nielands faults. Will do my own ones  :D  Lothar, I will take your warning seriously.

Cheers, Jens

 
Laverdalothar said:
just a word of warning not to overdoe this, please. We had a "Specialist" in Germany called Klaus Nieland. He offered "high compression 1220 Race engine modification" - and skimmed down the barrels by several milimeters (!!!!) to compensate for the wrong piston hights... Timing was off, compression was as low as 6,5:1 or so still and you could not adjust the chain anymore... :o

so - just a word of warning to recognise the "(almost)" in Phil's advise, please...  ;) (and also that he only talked about the head, not the barrels...!)
Click to expand...

you just ruined my day :'(
 
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