Akunar offset crank pins

[richban]

Stay away. The pins are hard, but very heavy. Looks like the half moon bearings can't handle the jandal. I have seen 2 fail on 2 different well built engines. Thats enough for me.

[hmurphy]

Speaking of them... I ordered a carb and a piston kit over 2 weeks ago and I emailed them about it. Took a few days to email back and the guy said he would ship it off within 48 hours last night. I paid extra for express mail too! Annoying!

[Kickaha]

Looks like the half moon bearings can't handle the jandal. I have seen 2 fail on 2 different well built engines. Thats enough for me.

Is it possible to source a better bearing?

So you'll look at relocating the crankpin instead? that's how we had it done when the limit was140cc

[richban]

Is it possible to source a better bearing?

So you'll look at relocating the crankpin instead? that's how we had it done when the limit was140cc

Not going to bother looking for a better bearing. I know split needle bearings are used in some outboards.

Yep relocating the standard pin. Works well. Should have done that in the first place.

[kel]

Rich, If Ive got this right you have lengthened the stroke? Im not questioning your engine development or power output to date but surely the greatest gain is in destroking the thing and running a longer rod? Power comes with revs, the FXR already pushes the limit for piston speed why would you increase its stroke and effectively reduces its rev potential? The CRF150R runs a bore to stroke ratio of 1.5:1, moto3 machine 1.65:1, point being by modern performance standards the FXR at 1.27:1 is already a long stroking motor. Im guessing you're aim is torque rather than all out power?

[richban]

Rich, If Ive got this right you have lengthened the stroke? Im not questioning your engine development or power output to date but surely the greatest gain is in destroking the thing and running a longer rod? Power comes with revs, the FXR already pushes the limit for piston speed why would you increase its stroke and effectively reduces its rev potential? The CRF150R runs a bore to stroke ratio of 1.5:1, moto3 machine 1.65:1, point being by modern performance standards the FXR at 1.27:1 is already a long stroking motor. Im guessing you're aim is torque rather than all out power?

Yep it was torgue we were after but also top end. Torque with the stroke and Top end with the cams / Cam timing. Don't forget you are also limited with the design of the head. The engines you mentioned have very big valves as standard the FXR by design is hampered in that area. The head on the bike now will flow 33hp with the carb. All we need to do develop it and try to get it up around the 27 28 mark. Any good a casting cylinder heads? Also with the stroke it is possible to get the capacity to exactly on the legal limit. As most pistons will only get you 2 156.

[koba]

Yep it was torgue we were after but also top end. Torque with the stroke and Top end with the cams / Cam timing. Don't forget you are also limited with the design of the head. The engines you mentioned have very big valves as standard the FXR by design is hampered in that area. The head on the bike now will flow 33hp with the carb. All we need to do develop it and try to get it up around the 27 28 mark. Any good a casting cylinder heads? Also with the stroke it is possible to get the capacity to exactly on the legal limit. As most pistons will only get you 2 156.

Old bikes with 2 valves, huge ports and odd combustion chamber shapes used that approach.
It seems alot of people shudder at their approach now but I've had a squirt on the track alongside an old Norton and it left my high tech Honda for dead. Seriously.
It really is all about working within the constraints of the standard engine design unless you do know someone who can cast a good head.
I know where to get good head but it's not going to help with horsepower.

[kel]

Any good a casting cylinder heads? .

Me? shit I have to pay someone to put fuel in the tank

[kel]

I've had a squirt on the track alongside an old Norton and it left my high tech Honda for dead. Seriously.

A CG125 is not high tech

[Grumph]

Do I gather that the offset pin uses a split needle roller race big end ?

If you're pushing things to the limit as far as RPM and piston speed goes, a split race is not good....don't care if some outboards use them - they don't see the rpm variation of a bike motor.

Have a look at the TKRJ on line catalogue - the rod kit specs quote pin od, rod id and bearing width - and the bearings are available separately.

[Yow Ling]

Do I gather that the offset pin uses a split needle roller race big end ?

If you're pushing things to the limit as far as RPM and piston speed goes, a split race is not good....don't care if some outboards use them - they don't see the rpm variation of a bike motor.

Have a look at the TKRJ on line catalogue - the rod kit specs quote pin od, rod id and bearing width - and the bearings are available separately.

But because the pin is offset you cant fit a full circle bearing

[Grumph]

Depends on the amount of offset....it is possible to pop the rollers out of the cage,slip the cage over the pin and reinsert rollers.