I just picked this up on Fleabay for a good price ( I thought at the time). I plan to turn it into a road racer but in a flat track style. I plan shorter ( maybe CB500F) forks and disc, a bit of work in the engine but keeping it to 250cc to stay in the 250 class, and some nice cosmetics. The more I look into it though, the worse it gets, but hey what's life without a challenge. The crank bearings are wrecked and they aren't available, the cam "bearings" are the same but at least it didn't smoke when I fired it up. It will be a long term project, but watch this space for updates. The engine is painted...badly. A trip to the soda blasters is coming up soon. The can bearings have seen better days. A Megacycle cam with needle rollers is the only solution.
I'd be very happy to hear solutions to the crankshaft problem. It seems the bearings are no longer available, what does everyone do to fix them?
I seem to remember reading some folks line bored the old bearings surfaces to accept a low profile ball type bearing... or just find another head.
Yeah, that's the camshaft bearings. I've got that under control, The crankshaft bearings are no longer available.
The crank bearings are available from CMSNL in Holland. Man, they're efficient. I have ordered several parts from them. Last time I put in an order on a Sunday ( Australian time) and they arrived on Friday. The big end was also shot: That was a bit of fun to fix. The parts are no longer available from anywhere I could find so... after hours searching the internet and various other catalogues, I found that a conrod from a KTM 520 and a crankpin from a XR400 Honda and a bearing from a catalogue would all fit together to make it work. The KTM conrod is 0.5mm longer, but I don't see that as a problem. After a lot of work with paint stripper, a wire brush and scotchbrite, the engine is looking OK. It's all together with a megacycle cam and a little bit of cleaning up in the ports, so hopefully it will go OK. Looking at the photo, I think I'd better tidy up that bench.
Quick update. I've managed to squeeze a CB350 twin leading shoe brake in there. The rim needs to be offset to get it in the middle. And the lug didn't match up so my friendly machinist made a plate to match them up. The swinging arm seems too wide. It has a 9.5 mm gap each side when the wheel is centred. I guess I'll have to get some spacers made up, or have I missed a couple of parts? That's how it came apart, the swinging arm was squeezed up tight when the axle was done up. It's a surprise it hadn't distorted. Did I mention the top fork yoke? There are a couple on ebay that I may bid on. I got a bit disheartened by all the hassles so I decided to cheer myself up by getting the spray cans out to make it pretty.
I've finished the paintwork. It's done with rattle cans and just when I finished the last clear coat a great big fly landed in it so I had to leave it to dry and rub it down again. I've found that to get a good finish I put the paint on too thick then pick the tank up and turn it upside down, and round and about to stop the runs, and keep it up until the paint's nearly dry. That's not too long a wait in the Australian summer Don't ask me why I chose those colours, I was going to to it red and silver, but just changed my mind. I know it's a little bit like Yamaha racing colours from the Kenny Roberts era, but hey, who cares?
What year is it? I have an old XL250 in the back shed I can take some photos and measurements for the back axle assembly if you want.
Thanks, but I just had a guy make a couple of spacers and the back axle is all sorted. I think it's 72 or 73. But the cylinder seems to be younger, it has the small fins on the cam chain side which I think makes it post '75?? The front brake is a bit of a hassle. The CB 350 brake I bought from the wreckers seems to be from two different models. When I tighten the axle, the brake plate locks up on the drum. I need to run a little spacer in the middle but that reduces the swept area of the brake shoes, so I might have to do a bit of machining on the back of the brake plate. I'm waiting for the top triple clamp to arrive then I can really get moving.
Pretty sure '72 was the only year without the fins on the camchain side of the cylinder. That's why my guess as to which year your bike is was '73-'75. In '76 the bike was redesigned a bit and the carburetor came straight back in the center of the head rather than off to the right side as yours does. The early bikes were known as side ports, the later ones, center ports.
Progress! I bought a top triple clamp from ebay, same model, three years younger and in great condition....didn't fit! They changed the fork offset between 73 and 76. One more thing to sort out and sap my funds. I got a local machine shop to bore it off centre and sleeve it down to fit. Anyway, it rolls now so I rolled it out of the garage to take a photo just to cheer myself up. I've ordered some mandrel bends so I can make the header which will be a bit of fun next week.
OK, I've joined a few bits of bent tube together with half an old expansion chamber that a mate gave me. It looks a bit like an exhaust, hopefully it might fit the bike. I'll check when I get home this afternoon. It will be getting some kind of silencing on the end . That's the next task.
CB 350 front brakes have a torque strap that connects to the fork leg . I believe your front brake to be from an earlier 305. I run a CB350 brake on the front of my Ducati Vintage racer.
I knew there was something amiss about it. The wrecker I bought it off said it was a CB350, but.... when my mate machined the little flange off to stop it binding he noticed a Yamaha symbol inside. It seems to be an early Yamaha brake plate and a CB350 hub! I'm waiting for the shoes to be re lined right now and hopefully it will all work soon.
