40HP Crank in 1300-1600 case

sander288 "Bolt-on Master"

1,404 posts · joined Aug 2008 · 27 Sep 2010, 11:35 am

#804397

I currently have a 1300 motor (69x77) might need to change to 1200 for historic racing (64x77), just wanted to know what was involed in the swap of cranks.

I'm on the look for a 40HP crank at the moment, and I wanted to know what was involved in putting the new crank in.

Will the rods needs to be changed?
Pistons?

Will the Comp ratio be affected?

Can I use after market barrels and pistons that are for 1600 based motors with this crank? (87-94mm bore)

It would be interesting to find out,

Cheers

Shaun

BMW R65 LS
1967 1300 Deluxe
Swing-axles FTW ❗

1500S Custom Title Time!

1,418 posts · joined Mar 2005 · 27 Sep 2010, 3:33 pm

#804424

I would think you'd have to machine the base of the 1300 cylinders shorter by 2.5mm otherwise CR will be mighty low. Rods and pistons should still fit with the 2.5mm shorter cyls.

DH

dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 · 27 Sep 2010, 4:25 pm

#804432

rods use the same bearings,
but the rod is wider at the big end and uses a smaller gudgeon pin.(20mm instead or your 22mm).
the rods use a bolt only, as opposed to the 1300's bolt and nut.
easiest to use the the 1300 case and cylinders(shortened).
i think their length may be shorter too(??)

1200 stuff should be thoroughly checked for size and crack tested!

westi wrote:That's mad Alan.