Grinstead_77G, on 13 February 2012 - 07:19 PM, said:
That Carrillo rod, with a smaller piston wrist pin, has to be matched up with the correct CP piston and pin and a Carrillo lower end rod bearing... I've also heard of a few folks running a Suzuki lower rod needle bearing. (Honda doesn't sell their lower rod bearing as a separate part, making cranks rebuilds a challenge). They claim an improvement in reliability over the stock rod setup. I also understand that when using the Suzuki bearing, the cage needs to be machined (narrowed) a bit to fit. Seems like a lot of work to me, but any small improvement in crank durability is probably worth the effort and may have been a response to some problems with the 2010 cranks.
As far as the effects of longer rod lengths, a longer rod length will put less side load on the piston wrist pin and reduce piston "rocking" loads when the piston is at mid stroke when the crank is at 90 degrees to the cylinder center line. Piston skits today are almost non-existent, so any reduction in side loads on the piston is a good thing. An additional 2 mm on the Carrillo rod would also raise compression unless the matching CP piston has the wrist pin positioned higher to compensate.
Does anyone know if the stock piston dome to wrist pin centerline is the same for 2004-09 as the 2010-2012s?
I'd really like to run an 82 mm Wiseco piston vs the Athena piston, but don't want to buy one just to measure it.
We tried the long rod setup back in our 85CC days, under the assumption - more intake volume would create a greater intake charge. I think this was more theory in the tuners mind than anything. We never saw any kind of a performance increase with the 85's. If anything it probably created more problems than the advantages it was supposed to have.
The KTM 250F lower rod bearing is the same size the Honda but I do not think the KTM uses side thrust washers so the washers still need to be sourced from somewhere.