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Author Topic: rb cranks info needed  (Read 720 times)

dynoryder

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rb cranks info needed
« on: March 07, 2010, 09:33:40 PM »
can a rb30 crank be used in a rb26

and if not is it posible to use six bolt mains on a rb30 block or are they to weak

rrcredline

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rb cranks info needed
« Reply #1 on: March 16, 2010, 11:52:43 AM »
Quote from: dynoryder;491307
can a rb30 crank be used in a rb26

and if not is it posible to use six bolt mains on a rb30 block or are they to weak


No I would think not. RB30 longer stroke I thought so will push the pistons above the block level.

Nigel

live4liners

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rb cranks info needed
« Reply #2 on: March 17, 2010, 12:15:54 AM »
yes but then youd shorten the con rods, and it should fit fine.  havnt tried it personally. but its the same as using 25 crank in a 20 to get 2.2 engine and a 26 crank to get 2.3 ltr engine..i think :D
i think the problem then would also be whether or not the piston would bottom out?

the stroke of rb30 is 86 mm from memory. and stroke of rb26 is more like 76mm. thats 5mm either side of mid crank. so youll have to shorten your conrod appx 5mm. that may not be entirely neccessary, depending on if you want to increase or decrease your compression ratio and provided it still doesnt fowl with valves. then because youve had to make sure its not going to fowl at the top, its going to travel 5mm lower with the crank change, and 5mm lower because of conrod change. so youd need an extra 10mm at the bottom of the cylinder. if you say the piston is 60mm high or so, the cylinder needs to be around 151mm long? unsure about my maths abilities at midnight :) so then if it is too short. u could look at new pistons with shorter sides (are they sleeves i forget?) or look at resleeving your cylinders.

id be looking at machining costs if i was going to modify the crank case for 6bolts. esp if u have a 26 which is probably stronger, not neccessarily though.
im not so sure im posting such a quick reply :)