Hello Everyone
Thanks for the response Bikedoctor.
Sometimes what seems like a good / neat idea backfires, like standing at scrutineering (tech.inspection) trying to explain that the chassis is a "breather catch tank" and definately has enough capicity for the rules is not much fun !
Unfortunately in UK classic / vintage racing there's not realy a place for CB72 / 77's, there used to be a pre 63 group but that was a long time ago now. I think thats why most of the race intrest is in the US and Australia etc. Here the 250's are in with the two strokes, Suzuki T20,Yamaha TD1's etc. and the 305/350's are in with the 350K's, short stroke 7R,s etc. Even with a good rider on board (ie.not me) they are not competitive. So I only race them because I like them and I have a Drixton type 350K for the real competition stuff (and would you belive that goes even better with a faster rider as well).
Gordon
SAFOJ
Racebike Only Thread.
Well everyone, Had a disastrous week end at Phillip Island. I was sick for 3 days throwing up at differenr times. Levi did a big end on the 500 in second practice and that was that bike out. We then entered the 350 to run in the 500 class as well as the 350 class. In qualifying Levi qualified pole for the 350 P3 class and qualified 2nd pole on the 350 for the 500 P3 class. Unfortunately during qualifying the clutch had a bit of a moment and the outer clutch basket disintegrated into 26+ pieces (that has never happened before). Probably does not like spinning so fast. Will be making billet baskets now out of 7075 alloy T6. All the best Jerry
Jerry,
Sorry to hear that news. I had been watching times and results and couldn't work out what happened to Levi. Sorry to hear about the mechanicals and sickness, but hopefully everyone is OK now. I ran a big end a few years ago but that was a stock CB77 conrod with 10 pairs of rollers. No probs after I changed to race kit big ends with 20 individual rollers. BTW, I did find a few big end cages with cracks in the "corners" and found that stock rollers are often very square at the tends, so I rounded them all off slightly to reduce the probability of failure. Also found that replacement cages (when we could get them were sometimes too square and that's an issue for crack propagation. But I doubt any of the above is an issue on your motors. What's the next race meeting for the team? Teazer, I run Honda 450 bottom end suitably modified in the 500 with Cappalini single roller billet cages. Crank was 3 meetings old. We do however run the 500 up to 12500. Anyway one step at a time. Have to make the billet clutches first and already have a spare crank to drop in. The Barry Sheene will be the next outing I would think. Jerry
Jerry, 12,500 sounds high for that crank arrangement. I wonder if the loads are too high or the roller surface speeds. Do you know what the design specs on that bearing are for load or rotational speed?
You may have to think about a plain big end bearing design change or smaller rollers. I don't know how large those are, so I'm just speculating here. Teazer, The 350 we run as high as 13500. It is a matter of settling down to a sensible maintenance program on my part. Going through my book work it is working out that crank assys. should be rebuilt after 7 outings (2 day race meetings) and then rebuilt. After that it is a bin job for the whole crank. Sounds tough but that is racing if you want to be at the pointy end. Jerry
My first thought was that's a lot of revs for a 54mm stroke and then I realized you are probably using a 50mm or so crank which does reduce crank loads a little.
Are those 350 cranks using single roller cages too? 7 outings. Ouch. That's about 7 by say 4km * say 8 laps * say 3 races=700 Kms. That's a little low but sounds about the number one should expect from such as hi performance. My math is probably a touch generous and that's probably closer to 500 km/crank. Are you using Ti rods and super light sliver plated cages or stock type rods with Aluminum cages? Plastic cage might be a possibility for lightness if the pin temps stayed low enough. BTW did you change to rotary oil pumps on those motors or just gear the stock pump differently?
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