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Engine basics => Engine set up tips => Topic started by: Motorman on November 29, 2019, 01:56:04 PM
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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
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Do the 40 SF and the 46 SF have different strokes/cranks?
I want to put an LA46 piston/sleeve in the SF ball bearing case. The 40's are cheaper and easier to find but I want to end up with a 46 displacement.
Thanks,
Motorman 8)
I will check my parts but I know they made 2 different cranks, 1 RC and one Control line, lower timing
Randy
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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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Where itll be a machine room job , is the head . Banding the SF head would be the easiest fix , for the + 1 m.m. Bore .
https://stunthanger.com/smf/engine-set-up-tips/os-40-fp-set-up-q%27s/
From Dave Adamisin ( The WEDGE Chamber Head set up )
The combustion chamber is too shallow too. Try a short reach plug. and don't go beyond about .010 head clearence if you can. Don't load it up with a lot of oil. Oil lowers the octane of the fuel and causes detonation which can lead to heat. My nephews engines have never been run on more than 18% pure ucon. fp's hate castor.......... We also use an assymetric combustion chamber which runs a cleaner four cycle. We use venturi dia's from .281 to .312 depending on the power required with St needles. Props have been easy: 11x6 Power Prop (no longer available) to very special: 10.5x5.25 Eather three blades. Uni-flo tanks with muffler pressure.
Will throw pics Of the Head / Chamber , & use a meauring stick . Then you can do one for ME , too. VD~ S?P
One could always Heliarc the Piston lower edge, & use the long stroke crank . But youve got to draw a line somewhere .
Some VF parts may interchange too .
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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 . :P >:(
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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 .
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Just might know someone , with one of these FSR 40 Cranks , if you know anyone with a 6001 Enya 45 ! . ;D S?P
Std FSR 40 RC timing specs , middle picture .
" Big Art " FP 40 Head . Other pitchers in the re invigoreated FP 40 Fred .
the bore & stroke came out barely ? ledgable in so pics . so solly . but you can see - displacement - bore - stroke . From Left .
the SF STROKE are THE SAME . 46 top 40 lower . bore Varies obviously .
Let us know if the 40 case is 25 mm bore ( same as 46 case ) if you get there .
And if the bolt pattern on the head of 40 & 46 SF match ( they DONT on the FSR 40 to FSR 45 )