roberto Posted October 8, 2006 Report Share Posted October 8, 2006 Hi maybe some out there can help. I am rebuilding a Cota 350, which has basically the same engine as a 349. I had the crank rebuilt and the rod used is not a Montesa original rod but a Metrkit rod which is aprox 1 mm thicker in the rod width, the base and top being the same as the Montesa rod. I recentered the crank using some of the different guaged spacers, and got everything lined up with an even distanve between crank halfs and the rod centered in the middle of the crank cases. Everything seemed ok until I put the piston and cylinder on and there is a noise as I turn the engine over. From what I can see, the connecting rod is shifted to one side as the engine turns and rubbing slightly against the crankshaft halfs as it come around. There isn't a lot of room on the lower ened since the rod is thicker. I used the same small end bushings and didn't expect this to take place, it seem that the piston and bore is slightly off center and moves the rod over after a couple revolutions....any tips, help?? Quote Link to comment Share on other sites More sharing options...
woody Posted October 8, 2006 Report Share Posted October 8, 2006 It's not the same as an Ossa is it, where you have to centre the crank in the crankcases by tapping on the appropriate end of the crankshaft with a hide mallett. If the crank is too far to one side this may cause the rod to touch the crank itself. Just a guess as I've never had a 350 Mont apart but I've had the same problem on an Ossa. I had a 350 Montesa back in 1985/6. All red with a slimmer tank than the 349. It was brought out to capitalise on Gorgot's win in the SSDT on the prototype 330, the production version of which was running late. So they modified the 349 into the 350 until the 330 came out (I think that's right anyway...) Whatever, I loved it. Fantastic motor, pulled really well, loads of torque and grip. Awful clutch though. Wish I still had it now. Wonder where it is. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted October 8, 2006 Report Share Posted October 8, 2006 It is possible that there is runout at the primary drive gear which causes a noise as the crank rotates (primary drive meshing having no clearance at one point). Easily diagnosed by trying it without the clutch fitted. Quote Link to comment Share on other sites More sharing options...
roberto Posted October 13, 2006 Author Report Share Posted October 13, 2006 Hi, thanks for the advice. This bike is driving me a little crazy. New connecting rod, piston, rebored, all new bearings, I recentered the crank with the shims...I don Quote Link to comment Share on other sites More sharing options...
vintagecota Posted October 13, 2006 Report Share Posted October 13, 2006 You say you centered the conrod with shims... Do you mean the shims under the main bearings? You don't mean you shimmed between the conrod and the crank weights, do you? The conrod floats around on the crankpin and centers itself while running. The thrust washers on the small end are important to this end as well. On the clutch, originally they came with little spring clips installed around the outside of the clutch between the basket and the plates that act as noise reducers by pulling the plates against the basket so they don't rattle. Don't use them, they can fall off and get lunched in the works. You end up with a little rattle from the clutch until you pull the lever, then it stops. Without actually hearing the noise...<G>... I think I'd run it gently for a while to see if the interfering parts clearance themselves. Frequent oil changes will reveal metal shavings if this is happening. Of course if the noise suddenly gets worse, shut it off immediately and prepare for a teardown. Hope this helps... VintageCota Quote Link to comment Share on other sites More sharing options...
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