Been busy these last couple weeks doing all sorts of things like raking leaves ,riding motorcycles ,painting my neighbors house ,riding motorcycles,going to car shows,working on my wagon and finally I got down to business with my motor build for my friend John .Back in August at the Vintage Japanese Motorcycle Show & Swap Meet he bought this 1965 Yamaha Big Bear Scrambler .It needs a total restoration and I am rebuilding the motor for him. Brought the motor home in my truck and the bike went home with John to Tennessee .Well,the other day I finally got down to business on it.
The motor is stuck, We got it to spin using the rear wheel so this told me the kick shaft gears are broken and I need to split the case. The other day I did this job and split the case then removed the crankshaft and transmission .At first it looked good just the broken kick start stuff needed to be replaced so I dug out the later version of them which are stronger and interchange with the earlier ones and got that mess fixed.
As you can see the replacement gears are stronger with less teeth that are thicker .This was a common problem and this is how Yamaha corrected it at serial number 26060 according to the factory parts manual . So,all was going well and yesterday I cleaned the crankshaft ,the engine cases and then started on the piston assemblies when I saw a real problem. One of the wrist pins had a very worn spot where the small end bearing rides and it was also tapered to one side.This tells me there is a serious problem with a connecting rod being slightly bent. I looked at the crank and after staring at it forever I could just make out a very slight bend on the left side con rod.It was barley detectable but that's all it takes so I started to think of a solution.
I had a cup of coffee and decided to dig out another motor with a good crank and use it for the parts I need. Got it on the bench and apart before dinner .
This motor was originally going to be used in the bike I built for my friend Tony back in 2007 but I ended up using a 305cc for that bike so it sat on the shelf since then collecting dust. I'm glad I finally found a good use for it.Lucky for me I have a couple more and I don't really need that many spares now as my days of building these are nearing an end. So,after a nice dinner with my wife I went downstairs into the basement and cleaned the crankshaft . Checked it all out and lubricated it so it spins really smoothly and called it a day .
The case is all cleaned and ready to go , the crank problem has been solved, it's a beautiful day and going to warm up to about 50 F later on so you know what I'm going to do, RIDE ! Later on after my ride I'll clean up both transmissions and compare them .I'll use the better one if there is a better one.From first glance they both look real good. Well,it's almost 10:30 in the AM and starting to warm up some so time for me to put on the leathers and hit the road . It's nice being retired .
That was back in the Fall .Did some stuff over the winter on the motor like digging out the parts I am going to use and going over the parts to be bought by John new that we are going to need. I really got going on it in April. This is when I began to build it. It never goes easy but rather more like a battle .This one was no different.It went together and came apart numerous times . I had three different transmissions in it before I finally had it the way I wanted . Finally in mid June I had the bottom end completed and now I'm in the final stages of doing the top end components.The actual assembly will be done at the show in August .It's easier to install it in the frame without all the external stuff like clutch,generator ,cylinders and so on. So,today I'm dealing with the carbs .I did the clutch rebuild the other day and in the top end the two cylinders are just about ready for paint and the heads are all cleaned and polished .Here are some photos of where it's at now
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