BonKunU

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I dont want to sound like a know it all as I dont but that was a little contradictory. You say dont upgrade the crank but then say to polish it and get it checked for straightness and balanced. Conrods, checked for straightness and wear but where do they actually wear as the big end has a bearing shell that takes the wear and the small end has a press fitted gudgeon pin... The engine that I have as a replacement is a '94 model I think but is pretty well identical to the '96 apart from different jetting as mine was sold in Australia and the replacement motor in Canada. It also had quite a few kilometers on it but seems to be in far better condition than the original motor. The valves are still warn badly to the point that it wont start as was my own original motor. Seems they all had very soft metal that should have been run with lead to make them last. Guess Yamaha forgot to consider this when they were put in an unleaded engine. Hopefully the new ones are much harder. Still wanting some more info on benefits of doing any possible work on the crank and rods. Preferable from well informed people.

History I bought the bike in approx 2000 as my first big bike after only eve having a 1981 gsx250. It was a big step up and a big learning curve. It took a few hits too in the process, mostly low speed slides. Had one front end hit after I ran up the back of a stationary vehicle which gave me an excuse to buy some brand spanking new forks for it as the original ones had started leaking pretty badly anyway. I had spent a year in Japan earlier on so had contacts there that were able to send me a set cheaper than I could have rebuilt the originals. After a few years I started to become quite proficient on it at fast cornering and wheelies but all the thrashing around left it starting to drop out of gears and then eventually changing gears by itself as I would be on the power around a corner at speed. Very nerve racking!!!! I decided that it was time for the big rebuild and what was going to be a 6 month job has stretched out to 3 years. It now has a 2001 R6 tail grafted on to it after much fabrication and welding work. It helps being a welder by trade!! The R6 tail now bolts on as it does on an R6. The subframe assembly was shortened approx 50mm to make everything fit correctly but I think it looks pretty sweet. The Engine is taking a little longer to sort out. I bought all new bearings, seals and everything from the US for it after coming across a second bike while living in Canada. My engine upon dis assembly was a bit of mess and was very close to spinning a big end and spitting me off and the gearbox is going to need all new syncros and probably forks. I have pulled the crank from the newly found engine and it seems to be fine and so now I have all new bearings that suit this crank and case. The head was completely rebuilt with new valves as the originals were warn down to a knife edge and were no longer sealing making it a complete mongrel to start. At 65,000km Im not surprised really though! It had a hard life! I spent hours upon hours cleaning ports after lots of research into the job and will have it all sent off to check my work before closing the engine. Arias 856 Pistons have arrived and the cylinders all prepped for the upgraded capacity. This was quite a process as the Kit does not specify what sleeves to use. After quite a bit of research into different options Ive found the Thunderace 1000cc (75mm I think) cylinders were the best for the job. Only the latter years though from memory. There was a few mm different over the course of production. So sleeves removed from a set of 1000cc cylinders and fitted to my 750 cylinders with the little cup cut outs and all. Machined to 77mm to suit the new pistons and all ready to go. Next thing to sort out is the Crank, Rods and gearbox and I can look at putting it back together!!! Maybe someone can let me know how I can upload pics and I will...

Do warn emultion tubes cause that stuttering, like it just wont rev randomly? Mine used to do that quite a bit before I stripped it down.

Already got the new sleeves, pistons, bearings etc all ready to go together. Just dont know what options I have for upgrading conrods and cranks. Never had any experience with getting it done. Whats going to be the best option???

Ok, I have a Crankshaft upgrade query. Im in the process of installing a an ARIAS 856 big bore kit into my '96 YZF750R. I have all the piston side of things sorted now but Im a little worried about the extra power being put through the crank and rods. When I pulled the engine down it was already about to spin a big end and that was with stock ponies. I have sourced another engine to install the upgraded pistons/cylinders which has good bearing surfaces but still Im wondering if I should send the crank away to be cleaned up in some way. Nitrided again? polished? balanced? lightened? Rods also, should I get these polished and balanced and nitrided and all that or what? What do you think? Im pretty hard on engines. lotsa revs and plenty of wheelies which may have been the reason for nearly spinning the big end through lack of oil pick up. Should I mod the pick up somehow too???

I can vouch for the thunder race pots being able to be bolted straight down onto the 750. I am in the process of installing an ARIAS 856 Piston kit in my 750 for some more grunt. I toyed with all the different possibilities and found this the most acceptable as the engine from the outside is all stock. Nobody can tell theres anything different until I blow them off in a drag. I bough the thunder race pots to steal the cylinders out of. The actual cylinders are about 10mm taller than the 750 but all can be mixed and matched. Only problem would be the combustion chambers wouldnt match perfectly if using a 750 head on 1000 barrels. Anyway, I have pulled the sleeves from the 1000 and had the 750 sleeves removed and replaced with the 1000 sleeves. They were then machined out to suit the 856 pistons. This is where Im at now. Waiting for more time and money to rebuild the rest of the case. New bearings and seals ready to be installed. Cant wait to get it all back on the road. Also has a 2001 R6 tail grafted onto the back end and its all done to look factory. Looks very much like an R7 now. It helps being a welder by trade. Had to remove the rear alloy subframe from the spars and fabricate new brackets to suit the R6 bolt on subframe. Also the R6 subframe needed to be shortened by approx 5cm to make everything look right. Looks really trick now though!! Vaughan