Go to the OS website, I think they have that information in the rundown on each engine. If cranks are the same, they will have the same part number.
  Type at you later,
   Dan McEntee

Clowning round with a SF 46 CLONE , the 25 OD LA liner drops in .

The 40 SF has a DIFFERANT bore & stroke . SAME STROKE as a LA 46 .

46 SF bore 22 mm . - 46 LA bore 23 mm .

BUT if you use the SF 46 crank & get 51 cubes , youll have about  0.8 mm S.P.I. , & no guts with a muffler .
WHEREAS the SF 40 crank matches the LA Throw . Cant tell you if the 40 & 46 SF cylinder O.D.s match , however.

The SF 46 Case Bore IS LA 46 sized . If the SF 40 liners smaller O.D. , the LA liner aint gunna go in the 40 case .
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So Definately LA 46 Liner & SF 46 case & SF 40 Crank is a working proposition .

The Big End & Little End diameters match . Cant recall on the Rod Lengths . Think SF is longer & will be neccesary .

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RODS !

The FP & FSR 40 ( & FSR 45 & LA 46 ? ) Con Rods Are all the same .

The VF Rod is Longer by 1/2 m.m.

Im thinking the FS Rod is the 34.5 mm one, as per VF . But unsure on that .It IS the FSR / FP bush bore size match though . The VF Rod ISNT .

So theres a choice on ' factory ' rods , anyway .

BUT , With the ' Two Port ' Liner , a Wedge Chamber'd get you a 46 Ball race  ' Big art ' ish injun.

Was actually a Big Art SF 46 in classifieds here , a week back . Ive no idea what He did to them though . Similar to the FP youd guess  .

O.K. dug out this drivle last night . While reading Sherlock Holmes . the Hound of the Baskervilles .

The SF STROKE 40 & 46 are THE SAME .

HOWEVER , the FSR Cranks , T T $^ Cranks & SF Cranks will interchange .
 Bar latters bigger flywheel would need lessening for smaller FSR Case Bore .

So for the 18.4 m.m. " LA 46 Stroke " , Youll need to use a FSR ( or Clone ) SHAFT in the SF to get the LA 46 Bore / Stroke .

The BUGBEAR on the Overbore is the TOP LINER FLANGE . Often need NOTCHING to clear pitch circle diameter of head bolts ,

And the Obvious sub piston induction induced if you lengthen the stroke .
The Std. LA 46 piston appears only to have maybe 8 thou covering S P I ,
No Idea if the GARDNER set up is a longer piston .

THOUGH the SF Case & Rod get the Timing at 140 Ex compared to the LA's  148 or whatever .

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SO , a SF Rod & a FSR 40 Crank are likely prerequisets .

Pile of tables below , all relevant as the FSR 40 & FP 40 & 35 cylliners interchange .and heads . ( Anyone for a FSR 35 ! ? )

The FSR 45 , GP 44 , and to a extent , HP 40 Cylinders interchange . And Heads .

The SF & LA 46 liners interchange , to a degree , also with the VF . But Gudgeon & crankpin are larger on the VF
The VF Diameters match Como 51 & X 45 !  tho there rods the 34 not the 34.5 ! .

Whats happened is designing engines compact , the pistons cut to clear the crank at B D C , and therein lies the S P I conundrum whilst strokeing the stroke. or increasing it . The Bottom of the piston skirt is lifted . Often above the lower exhaust lip in the sleeve .

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T T Tirty six enine timing , top .

Bar bootom picture . all are Thunder tiger Spec sheets . The One Piece Case ' FSR ' ish ones .
The 40 & 46 crank'd drop in the SF . for what its worth .