Crankshaft compatability? 2T crank 3T block

[styler]

**example** *pin height is into the oil ring I think*
AGAIN all theory

yeah thats 5mm off the bottom area and thinner ring lands = 5mm of the top area
so theres your 10mm, if they are forged it would be great but still those are quite thin ring lands in my opinion for reliability and may crack easily but hey it seems to work...
you would still need to modify the skirts if they are too long but dont qoute me on that as im not 100% sure just going off what i last remember when i looked.

it would be an expensive build as its all custom forged and not as reliable as i would have
it but it would go pretty damn well if built right...

[styler]

3T crank 78mm : 2T crank 70mm
rod: 4.850" std

According to BRD I can get 5.400" rods 14mm longer to suit the 3T crank(modified) and pistons.
So I guessed seeing as the 2T crank has 8mm less throw, with the 14mm longer rods I could push the pin height of the 3T piston up 14mm anyways and get away with a much higher rod stroke ratio..

the 2t crank has 4mm less throw, remember it throws both ways, up and down.
a crank with a bigger stroke is the same extra length on both on the upwards and
downwards stroke, ie at the top and the bottom...

anyway (78-70mm) stroke / 2 = 4mm throw

[Radar]

So using the 5.400"rod with a custom piston to suit a 10mm longer rod instead of a 14mm rod everything should land dead flat with nothing poking out the block and I'll be able to use the 2T crank with 3T rods and pistons.
All sounds good..

[Radar]

the 2t crank has 4mm less throw, remember it throws both ways, up and down.
a crank with a bigger stroke is the same extra length on both on the upwards and
downwards stroke, ie at the top and the bottom...

anyway (78-70mm) stroke / 2 = 4mm throw

Indeed always forget about the other way, cheers for clearing that up

[Radar]

One more question, to clear things up 100%.
If the difference between a 2T piston and a 3T piston is 4mm pin height, could you run a custom 4mm longer rod on the 2T crank and use a STD forged 3T piston?
(Std rod: 4.850" + .157")

[styler]

One more question, to clear things up 100%.
If the difference between a 2T piston and a 3T piston is 4mm pin height,
could you run a custom 4mm longer rod on the 2T crank and use a STD forged 3T piston?
(Std rod: 4.850" + .157")

yes you could in theroy, as those dimensions stated are compatiable,
there is one more dimension to check that you left out though which is
bottom of piston skirt to crank counterweight clearance, seeing since your
piston is 4mm lower, if it was standard the skirt would also be lower by 4mm,
and the bottom of the skirt could hit the crank counterweight when the whole
engine is rotating...

now im not sure on how much clearance there is but its not a lot,
a couple of mm? maybe more? its something to check though...

but you could shorten the skirt or buy custom short skirt pistons to suit
as the skirt is quite long although just remember the shorter the skirt the
more the piston rocks in the bore and this is not desirable but you might be
able shorten it to a degree that still only has a small effect?

otherwise you could cut down and re shape the crank counterweights
to suit, which would lighten it at the same time, just make sure you
get it balanced afterwards obviously. im not sure if this would affect
strength/balance/counterbalanceof rotating parts/harmonics etc etc but
its probably possible to some degree?

[WDE_BDY]

I doubt skirt clearance would be an issue with that combo, pin height is 4mm higher in the piston but the rod is 4mm longer to compensate and you have a shorter throw on the crank.

Callum

[Radar]

Sensational, cheers heaps fellas for the help.. Very much appreciated
Now onto the hunt for a good engine builder in Adelaide